Relationships Between Soil Conditions and Earthquake Ground Motions in Mexico City in the Earthquake of Sept

PB8S-17a991

REPORT NO. UCB/EERC-87/15 EARTHQUAKE ENGINEERING RESEARCH CENTER OCTOBER 1987

RELATIONSHIPS BETWEEN SOIL CONDITIONS AND EARTHQUAKE GROUND MOTIONS IN MEXICO CITY IN THE EARTHQUAKE OF SEPT. 19, 1985

H. BOLTON SEED MIGUEl P. ROMO JOSEPH SUN A. JAIME J. LYSMER

A report on research sponsored by the National Science Foundation

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See back of report for up to date listing of EERC reports. ~~".!~Lll. :so Recipient's Acceaslon No, HI~F'O,RT DOCUMENTATION \1, REPORT NO. I~ PAGE NSFjENG~87040 P8iJ - /19 99/ 04.. Tltl. end Subtltl. 5. Report Date Relationships between Soil Conditions and Earthquake Ground October 1987 Moti ons in r'1ex ico City in the Earthquake of Sept. 19, 1985 6- .- 7. Author(s) 8. Performlne Oreanlzatlon Rept, No. H.B. Seed, i~. P. Romo, J. Sun, A. Jaime and J. Lysmer " UCBjEERC -87/15 9, Perforrnlnll: Organization Name end Address 10. Project/Task/Work Unit No. Earthquake Engineering Research Center University of California 11. Contract(C) or Grant(G) No. 1301 South 46th Street (C) California 94804 Richmond, (G) ECE86-11066

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16. Abstract (Limit: 200 words)

One of the most dramatic aspects of the earthquake effects in Me:-: ico City in t he earthquake of September 19, 1985 was the enormous differences in intensities of shaking and associated building damage in different parts of the city. It is the purpose of this report to describe the soil conditions in Me:·: ico Ci ty l present the results of spec iaJ studies rnade since the earthquake to e~plore in detail the soil conditions at the sites of strong-motion recording stations and at other sites of interest in and near the city, and to present the results of some analytical studies of the extent to which the observed differences in shaking intensities can be predicted usiqg simple analyses of ground response incorporating measured properties of the shear wave velocities of the soils. The stL\dy is part of cooperative investigation of these and other aspects of ground response in the Mexico City earthquake of September 19, 1985 being undertaken by investigators at the National University of Mexico and the University of California at Berkeley.

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EARTHQUAKE ENGINEERING RESEARCH CENTER

RELATIONSHIPS BETWEEN SOIL CONDITIONS AND

EARTHQUAKE GROUND MOTIONS IN MEXICO CITY

IN THE EARTHQUAKE OF SEPT. 19,- 1985

H. Bolton Seed Miguel P. Romo Joseph Sun A. Jaime J. Lysmer

Report No. UCB/EERC-87/15

October 1987

A report on research sponsored by the National Science Foundation

College of Engineering University of California Berkeley, California

Table of Contents Page No. 1. Introduction 1

2. Ground Motions in the Sept. 19, 1985 Earthquake 7

3. Ground Motions on Rock and Hard Soil at UNAM 17

4. Detailed Studies of Soil Conditions at Recording Stations 24

5. Dynamic Properties of Mexico City Clay 36

6. Relationship Between Soil Conditions and Ground Motion Records 38

7. Analytical Studies of Ground Motions Based on Soil Properties Determined from Ground Motion Records 46

8. Analytical Studies of Ground Motions Based on Measured Values of Shear Wave Velocity 53

9. Use of Scaled Records of Outcrop Motions in Analyses of Ground Response 86

10. Predictions of Ground Motions at Sites of Special Interest 97

11. Conclusions 107

References 112

1. Introduction

One of the most dramatic aspects of the earthquake effects in Mexico

City in the earthquake of September 19, 1985 was the enormous differences

in intensities of shaking and associated building damage in different parts

of the city. In the south-west part of the city ground motions were moder

ate and building damage was minor. However in the north-west part of the

city, catastrophic damages occurred and a record of the earthquake motions

near the southern end of this heavy damage area showed a very high inten

sity of shaking. Similar patterns of building damage intensities have been

observed in previous earthquakes and the differences attributed to the dif

ferences in sail conditions in different parts of the city. In the 1985

earthquake these differences seem to be somewhat mare accentuated than in

other earthquakes in the past 40 years, and the availability of recordings

of ground motions in different parts of the city makes it possible to

explore, in greater detail than heretofore, the relationships between sail

conditions and intensities of shaking.

It is the purpose of this report to describe the sail conditions in

Mexico City, present the results of special studies made since the earth

quake to explore in detail the soil conditions at the sites of strong motion recording stations and at ather sites of interest in and near the

city, and to present the results of some analytical studies of the extent

to which the observed differences in shaking intensities can be predicted using simple analyses of ground response incorporating measured properties

of the shear wave velocities of the soils.

The study is part of cooperative investigation of these and other

aspects of ground response in the Mexico City earthquake of September 19,

1985 being undertaken by investigators at the National University of Mexico and the University of California, Berkeley.

Soil Conditions in Mexico City

The soil conditions in Mexico City have been the subject of many investigations in the past 50 years and before the earthquake of

September 19, 1985 they were already reasonably well-established. The city is located on the edge of an old lake bed; thus while the western part of the city is underlain by rock and hard soil deposits, the eastern part of the city is located on soft clay deposits filling the former lake bed. An east-west profile showing this variation in soil conditions (after

Zeevaert, 1972) is shown in Fig. 1-1. Between the hard formations in the west and the deep clay deposits in the east, there is a "transition zone" where the soils have generally stiff characteristics but may also involve some limited depths of soft clay.

In the lake bed area, the soft clay deposits which have shear wave velocities ranging from about 40 to 90 m/sec, are underlain by very stiff and hard formations (the hard layer) with shear wave velocities of the order of 500 m/sec or greater; thus there is a very marked change in wave velocity at this boundary and this facilitates considerably the analyses of wave propagation effects in the Mexico City clays. Contours showing the approximate depths of soils (mostly involving a surface layer of sand fill and an underlying deep layer of soft clay with interbedded layers of sand and silt) which overly the hard layer are shown in Fig. 1-2 (modified after

Resendiz et al., 1970).

It is important to recognize that the clay beds extend considerably to the north and south of the main part of Mexico City. The city itself is

Downtown Mexico City I

o I 10 Lacustrine volcanic silty clay 20 Sand and gravel 30

2km 40

Horizontal scale 50

60m Vertical scale

Fig. 1-1 EAST-WEST SOIL PROFILE - BASIN OF VALLEY OF MEXICO (after Zeevaert, 1972)

eCAO eCAF

~ .... ~"fIIQO .... .I -' ... I

cotos, en m

___ -Heavy damage zone a Locations of strong-motion .. occelerOgro.phS fig. 1-2 PLAN Of MEX1CO CITY SHOWING OEPTHS Of SOIL AND LOCATIONS OF INSTRUMENT STATIONS

located on the edge of the former Texcoco Lake which extends about 35 kms to the north. This lake was separated by a ridge of hills across the southern part of the city, from a second lake, the Xochimilco-Chalco Lake as shown in Fig. 1-3. Both of the lake beds are now essentially filled with clay deposits, but the clays have somewhat different characteristics, the Xochimilco-Chalco Lake clays being somewhat stiffer and stronger than the Texcoco Lake clays.

Damage surveys show that virtually all the structures which collapsed or suffered major damage in the earthquake of September 19, 1985 lie within the zone bounded by the chain-dot line in Fig. 1-2. The soil depth con tours in Fig. 1-2 indicate that within this zone, the depth to the hard layer typically ranges from about 26 to 44 meters. On the shallow soil deposits to the west and south, and on the deeper clay deposits to the east and north, damage was relatively minor. Surveys show that the major damage in the heavy damage area occurred to structures with story heights ranging from about 6 to 18 stories.

, I • TXC ,-, I \ , I,/" ,-_.I 1 ..._ " " ...... ~- I -",I, I " \. "\ , " I TEXCOCO I TRANSITION \.) I LAKE I, I, .TXL \ \ \ '&Air \ MEXICO ~port \ , CITY T:"I I .CAO I I eCAF .'I I I , ·.v .",-...... , ,,-----...... \, i \/ , ..r\o~ '... {HILLS I ,/ \ ,I ...'s\, " I • CU""'\ "'-"""Q~" ./ HILLS I , ~" --"" , I ~--- <.... _- " \ ...... ------".", ,I c.. XOCHIMILCO- CHALCO ,, LAKE eTLD \ \ eTLB I HILLS \ \ ...... , ...... __ .. ~ ..--- " ,,

Fig. 1-3 LAKE DEPOSITS NEAR MEXICO CITY AND LOCATIONS OF RECORDING STATIONS

2. Ground Motions in the Sept. 19, 1985 Earthquake

Strong motion records of the earthquake of Sept. 19, 1985 were obtained at a number of sites in and around Mexico City including:

1. Three sites located on the rock and stiff soil area at the

University of Mexico (UNAM).

2. One site on the rock and stiff soil area at Tacubaya (T).

3. One site located on the transition zone at Viveros (V).

4. One site (the SCT Building site) on the clay deposits near the

southern boundary of the heavy damage area; the depth of soils

overlying the hard formations at this site is about 37 m.

Acceleration response spectra for the two components of motion at

this site are shown in Fig. 2-1.

5. Two sites about 0.5 km apart on the deeper clay deposits in the

Central Market area; at one site (CAF) the soil depth was about

45 m and at the other site (CAD) the soil depth was about 56 m.

Acceleration response spectra for the motions recorded at each of

these sites are shown in Figs. 2-2 and 2-3.

6. Two sites about 3 kms apart to the south of the city on the clay

deposits formed in the Xochimilco-Chalco Lake. At one of these

sites (TLD) the depth of soil was about 65 m and at the other site

(TLB) the depth to the hard layer was about 105 m. Acceleration

response spectra for the motions recorded at these sites are shown

in Figs. 2-4 and 2-5.

7. Two sites on the Texcoco Lake clay deposits to the north or east

of Mexico City, designated TXC and TXL in Fig. 1-3. No detailed

1.0 ,.. I,. ,I II ,I ,I E-W Component 0.9 ,,I, ,I N-S Component , I , I , I , I , I 0.8 , I , ~~ ,, ,, ,: \,... _... ,,\, 01 0.7 , ' I, 'I - I ' c , 'I , I 0 , I , I - 0.6 I I -l-' , I , I 0 , I L I I , I (l) I I 0.5 I I - , I (l) / ' u ,I ', I I u 0.4 , I « ., 'I " I ,,' l - r" I ' 0 ,, .,\ / ', L 0.3 ... ' " \ -l-' I , "" \ ' ...... -' "" U '" ,,'~, , I ,'\ ~" .. ...,' " .... _~ (l) I ...... 0.. 0.2 ,I ' _ ... , A. ""'" (J) ~~~ ~~ ... _--- ... '~~ ~~ 0.1 '~, ~ '------, 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 2-1 ACCELERATION RESPONSE SPECTRA FOR GROUND MOTIONS RECORDED AT SeT SITE (X)

1.0

0.9 E-W Component N-S Component 0.8

01 0.7 c- 0 0.6 -+--' 0 L ill - 0.5 ill U ,,~ ..... , \ u , \ « 0.4 ,, \ , , \ ,, "\ - , \ , \ 0 , \ , \ L 0.3 '--_...... " -+--' U \ , ill \\ '" 0... 0.2 ...... (.f) " " " 0.1 "-'-'",,-,-

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

\0 Fig. 2-2 ACCELERATION RESPONSE SPECTRA FOR GROUND MOTIONS RECORDED AT CAF SITE

1.0 ---.-.- E-W 0.9 Component L N-S Component I 0.8

(J) 0.7

~ c 0 .-...... 0.6 0 L Q) - 0.5 Q) u «u 0.4 ,."",.-- ...... , - , 0 I , I , L 0.3 ,~' ,, ...... , .... -_ ... , .... " , ,, u , ,-_ .... --- Q) , ,, , ,, ,, 0... 0.2 /, ,-' I , , ,, -- ,, U1 '-'' , ~~ , ~, " 0.1 I J~ " .r--...... ~ '.

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

~ Fig. 2-3 ACCELERATION RESPONSE SPECTRA FOR GROUND MOTIONS RECORDED AT CAO SITE o

1.0

0.9 E-W Component N-S Component 0.8

(J) 0.7 c- 0 0.6 +J 0 L. -Q) 0.5 Q) 0 «0 0.4 - 0 L. 0.3 +J ... -... , 0 " .... , '_ ...... " ' , "'~',, Q) \ \ , \ .' \ , \ -' '. ", ,,-' \ , \ \ , \ 0.. 0.2 I I \ , \ (f) \~, \ , , ..----_/------0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

~ Fig. 2-4 ACCELERATION RESPONSE SPECTRA FOR GROUND MOTIONS RECORDED AT TLD SITE ~

1.0

0.9 E-W Component N-S Component 0.8

(J) 0.7 c ~ 0 0.6 -I-' 0 L -Q) 0.5 Q) u «u 0.4 - 0 L 0.3 -I-' """ ... U Q) "" ...~ D... 0.2 (f) I~'-"'\ ,-' ... ----_ ...... --, ...... ' 0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period) seconds

I-' Fig. 2-5 ACCELERATION RESPONSE SPECTRA FOR GROUND MOTIONS RECORDED AT TLB SITE N

information is available concerning the soil conditions at these

sites.

The locations of all these recording sites are shown in Figs. 1-2 and 1-3.

The records of the earthquake motions obtained at the various sites indicate that:

1. Motions recorded at the University sites and at Tacubaya on the

rock and hard soil deposits had generally similar characteristics

with peak ground accelerations of the order of 0.04 g, peak spec

tral accelerations (5% damping) of about 0.11 g, and a predominant

period of about 2 seconds.

2. There was a major amplification of the motions by the soft clay

deposits underlying the SCT and Central Market sites. At the SCT

site, where the soil conditions are more closely comparable to

those in the heavy damage area to the north, the peak ground

acceleration was about 0.17 g and the peak spectral acceleration

for 5% damping was about 1.0 g at a period of about 2 seconds.

3. There were significant differences in the ground motions recorded

at the SCT building site and at the Central Market sites, with the

Central Market sites showing lower peak accelerations and maximum

spectral amplifications at higher periods than at the SCT site.

Thus at the CAO site, where the depth of soil was about 56 m, the

peak ground acceleration was about 0.09 g, and the peak spectral

acceleration (5% damping) was about 0.35 g at a period of about

3.5 seconds.

A comparison of representative average spectra for the SCT Building site, the Central Market site (CAO) and for sites in the rock and stiff soil zones is shown in Fig. 2-6. It is readily apparent from this comparison

0.9 5% Damping

0.8

0.7 SCT Site (depth to hord layer, D::: 37m) 0- I c 0 0.6 -....0 Q) Q) (.) 0.5 (.) 0.3

0.2

0.1

0 a 2 3 4 5 Period - seconds

Fig. 2-6 AVERAGE ACCELERATION RESPONSE SPECTRA FOR MOTIONS RECORDED ON DIFFERENT SOIL CONDITIONS

why damage was negligible in the rock and stiff soil zones but very severe

in the central part of the city underlain by clay layers with depths rang

ing between about 30 to 45 m.

It is interesting to note that one day after the main shock, the city was subjected to a major aftershock of Magnitude 7.5. Ground motions were

recorded at some of the same stations in the aftershock; the motions were

somewhat lower in intensity during the aftershock, as evidenced by the com

parison between the response spectra for main shock and aftershock motions

at the CAO site shown in Fig. 2-7. It is noteworthy that the forms of the

response spectra at this site were remarkably similar for the two events,

although the spectral peaks occurred at slightly lower periods in the

aftershock, suggesting that the strains induced during the September 19

event were high enough to produce some small non-linear effects in the

ground response (Romo and Seed, 1986).

0.5,------, 5% Damping

0' I c 0.4 o Main Shock -...o (Sept. 19)

0.1

OL-__.L.-__-'--__-'--__-'--__--L-__--'-__...... I o 2 3 4 5 6 7 Period - seconds

Fig. 2-7 AVERAGE RESPONSE SPECTRA AT CAO SITE FOR MAIN SHOCK AND STRONGEST AFTERSHOCK

3. Ground Motions on Rock and Hard Soil at UNAM

Of particular interest in studying the effects of local soil condi tions on the ground motions throughout the city are the characteristics of the motions recorded on the rock and hard soil formations at the 3 stations located at the National University of Mexico. A shear wave velocity pro file for one site in this area is shown in Fig. 3-1. At this site there is a layer of fractured lava about 12 m deep overlying soft rock with a shear wave velocity ranging from 450 to 600 m/sec at depths between 12 and 21 m.

However the depth of the lava cover varies and outcrops of soft rock are readily apparent in the area. It is believed that the conditions in this area are thus reasonably representative of the "hard layer" which underlies the clay deposits throughout Mexico City.

In all, six horizontal components of motion were obtained at the three recording stations at UNAM. The response spectra for these six components are shown in Fig. 3-2. While the motions show some variations, they have some general characteristics in common, most showing spectral peaks at periods of the order of 0.9 second and about 2 seconds. The mean spectral shape for the six records is shown in Fig. 3-3, together with the upper and lower bounds of the spectral values determined from the six records. The mean value can presumably be considered to provide a good general charac terization of the motions developed on the hard layer in the University area and at any similar outcropping of the hard layer in the Mexico City area.

For ground response analysis purposes it is necessary to select a ground motion record which can be considered representative of the motions on the hard foundation. Fig. 3-4 shows a comparison of the average

Shear Wave Velocity, ft/s

0 250 500 750 1000 1250 0 I I I I I 0

- 25 10 f- to 450 m/s - 50

~ to 600 m/s at C.L. -21 m 20 ------75

30 f- - 100 0 C1> '"tJ E r+- - 125 ::r t- ~ ..c- 40 -+-' -to. 0- r+- ID 0 - 150 50 ~ - 175

60 f- - 200

- 225 70 f-

- 250 80 I I I o 100 200 300 400 Shear Wave Velocity, m/s

Fig. 3-1 SHEAR WAVE VELOCITY PROFILE AT UNAM SITE

0.20

0.18

0.16

O'l 0.14 c- 0 ~ 0 0.12 L- V V u 0.10 «u 0.08 0 L- +J u V 0.06 n.. en 0.04

0.02

0.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 3-2 ACCELERATION RESPONSE SPECTRA FOR GROUND MOTIONS RECORDED AT UNAM SITES t-' 1.0

0.20

0.18

0.16

(J"l 0.14 c ,(\, 0 ,I +i ,'\ . \ 0.12 .\ . . 0 f" , I,, "- , , '. ., Q) , 0 '} I I· \... \ Q) I '. , u 0.10 :···D:\ u ,0 o' \, ...... , <{ '. • 0 _ ", , ' "'- , 0.08 , 0 . " , "- . " ... +J • : "1-...... u . . "", Q) 0.06 ", 0- ,, (f) , " 0.04 . ''':,-..... -~- '"" 0 -'''', -.,~-~-__ - ""l." '. "''1- 0 0.02 "._-'~,~---~--,-,~~~~

0.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

Fig. 3-3 UPPER AND LOWER BOUNDS AND AVERAGE SPECTRA FOR MOTIONS RECORDED AT N UNAM SITES o

0.20

0.18 ------Average UNAM Spectrum

0.16 -- CUMV-NS ,Component (1985) O'l 0.14 c- 0 4J 0 0.12 "- Q) Q) u 0.10 u

0.02

0.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

Fig. 3-4 COMPARISON OF AVERAGE SPECTRUM FOR MOTIONS RECORDED AT UNAM SITES WITH SPECTRUM FOR N-S COMPONENT OF MOTIONS RECORDED AT CUMV SITE ....N

response spectra for the six UNAM records with the response spectrum for one of the components (N-S) of the motion recorded at the CUMV site at

UNAM. It may be seen that this NS component has spectral characteristics very close to the average for all components and thus provides a reasonable representation of the average motions on the hard-rock formation in the

Mexico City area.

This record has a peak ground acceleration of 0.038 g and it has spec tral peaks at about 0.9 seconds and 2.1 seconds. The full acceleration and velocity time histories of the motion are shown in Fig. 3-5.

0.04

01. 0.02 c 0 +J 0 0.00 I- QJ QJ u -0.02 «u -0.04 0 10 20 30 40 50 60 Time, seconds

20 u QJ en "- 10 E u 0 >. +J .-U 0 -10 QJ > -20 0 10 20 30 40 50 60 Time, seconds

Fig. 3-5 ACCELERATION AND VELOCITY TIME HISTORIES FOR N-S COMPONENT OF MOTIONS N RECORDED AT CUMV SITE W

4. Detailed Studies of Soil Conditions at Recording Stations

The characteristics of the Mexico City clay and other soils at the

recording stations in and around Mexico City were determined using a vari

ety of techniques including:

1. Boring and sampling procedures.

2. Measurements of penetration resistance using CPT procedures.

3. Laboratory tests (resonant column and cyclic triaxial tests) on

good quality undisturbed samples.

4. Evaluation of average shear wave velocities of the soils from the

earthquake records for each station. For this purpose the clay at

any given site was considered to be uniform with depth and the

average stiffness was determined from the natural frequency of the

site evaluated directly from the Fourier spectrum of the recorded

motions. It was recognized that this procedure would not normally

be available for other sites but it was considered to provide

probably the best estimate of average shear wave velocities of the

soils of any of the techniques available.

5. Direct measurements in boreholes of the shear wave velocity pro

file of the soil deposits using down-hole techniques and P-S sus

pension logging techniques.

These studies led to the following determinations of the soil conditions at the various sites.

(1) SCT Site

The subsoil conditions at the SCT site consist of a compact 4 m thick

layer of mixed sand, silt and clay, followed by a 27 m thick clay layer with interbedded seams of silty sand, volcanic glass, fly ash, sands and

silts; the water content in the clayey materials ranges from about 100% to

450% and the undrained shear strength varies from 0.25 to 0.8 kg/cm2 .

Underlying this layer there is a very compact, lightly cemented 3 m thick stratum of sandy silt, followed by a 4 m thick layer of very stiff clay overlying the so-called hard layer; the hard layer consists of deep deposits of a very hard and stiff layer (more than 100 SPT blows/ft) of cemented silty sand which is usually considered as the base of the soil profile.

Based on the natural period of the site, the average shear wave veloc ity of the clay layer was determined to be about 75 m/sec leading to a determination of the soil profile for the site as shown in Fig. 4-1.

The results of direct measurements of the shear wave velocities of the various soil layers are shown in Fig. 4-2, and an interpreted representa tive shear wave velocity profile, based on these results is shown in Fig.

4-3. It may be seen that the measured shear wave velocities in the clay are somewhat lower than the average value determined from the natural period of the site for the motions recorded in the 1985 earthquake.

(2) CAD Site

The subsoil conditions at the CAD site consist of a layer of silty sand 5 m deep followed by a 37 m thick layer of clay with interbedded seams of silty sand, fly ash, volcanic glass and silts; the water content in the clayey soils varies from about 150 to 500 percent, and the undrained shear strength from about 0.2 to 0.6 kg/cm2 . Underneath this clay layer are a series of intercalated strata of sandy silts and silty clays about 10 m in thickness, followed by a 4 m thick layer of stiff clay which overlies the deep hard deposits.

SCT Site CAF Site CAD Site

Om ------Om ------Om ------4m Sand 70 m/s Sand 64 m/s Silty sand 60 m/s 5m ------5m --.:..------

Fig. 4-1 SOIL PROFILES AT SCT, CAF AND CAO SITES BASED ON BORINGS AND FREQUENCY CHARACTERISTICS OF N RECORDED GROUND MOTIONS C]\

Uelocl~~ (m/~ec) 20 50 10e 2ee see le00 2ee0 I I III, I I IIIIII T - -- 1 ~l+ ~ ----- ~-- I't 5 l- - - I: J..-" , -~ • Ie ~ +' ~ +1 qc • .. "'=-lI- r I: IS r - ~+ ~ ::::::> ~ • 20 ~ t( ~ vp 25 J Vs ~ - r"\ r E '\.J ~ I! ~ .I:. 30 -t.I Q.. II ~ 1 • a ~ I· · + 35 I• - '\ 1++ ~ L..; 40 , I -- ) . r. t ++1 45 - :::. .r - C •I ~ ,. • 50 I • Suspension P-S logging I 55 ------Downhole wave velocit" measurements I - I

I I I I I I,,I I I II t I I I I 2 5 10 20 50 lee 200 qc (kg/cm2)

Fig. 4-2 MEASURED SHEAR WAVE VELOCITIES AT SCT SITE

Shear Wove Velocity, ftjs Shear Wove Velocity, ftjs Shear Wave Velocity, ft/s

a 250 500 750 1000 1250 o 250 500 750 1000 1250 0 250 500 750 1000 1250 a a o I I I I 0 a 0

=:J 25 25 25 - 10 10 l- 10

50 50 50 20 I- 20 L..- 20 75 - 75 75

30 I- 30 100 - 100 30 100 0 0 0 CD CD CD "0 "0 "0 E ..... E

225 s 225 70 I- - 70 I -i 250 - 250 250 I I I I I I ] I I I 80 I 80 0 100 200 300 400 a 100 200 .300 400 0 100 200 300 400r Shear Wave Velocity, m/s Shear Wave Velocity, m/s Shear Wove Velocity, m/s

SCT Site CAD Site CAF Site

N 00 Fig. 4-3 INTERPRETED SHEAR WAVE VELOCITY PROFILES AT SCT, CAD AND CAF SITES

Based on the natural period of the site, the average shear wave veloc

ity of the clay was estimated to be about 60 m/sec, leading to a determina

tion of a representative soil profile as shown in Fig. 4-1.

The results of direct measurements of the shear wave velocities of the various soil layers are shown in Fig. 4-4, and an interpreted representa

tive shear wave velocity profile, based on these results, is shown in Fig.

4-3.

(3) CAF Site

The CAF site is located about 0.8 km south of the CAD site. The upper

15 m of the soil profiles at the two sites are very similar but the clay

layer at the CAF site seems to be slightly stiffer and about 11 m less in

thickness. Thus the hard layer is encountered at a depth of about 45 m at

the CAF site.

Based on the natural period of the site, the average shear wave veloc

ity of the clay was estimated to be about 64 m/sec and the soil profile to

have the general characteristics shown in Fig. 4-1.

The results of direct shear wave velocity measurements at the site us

ing downhole techniques and P-S logging techniques are shown in Fig. 4-5,

and an interpreted representative shear wave velocity profile based on

these results is shown in Fig. 4-3.

(4) TLB Site

The soil conditions at the TLB site consist of a layer of sand fill

about 5 m thick underlain by a thick layer of clay, containing seams of

sand and silt, which extends to a depth of about 105 m, where the hard

layer is encountered.

30 Uetocl~~ (m/&ec)

~ r;..B__.;;;;r-_,....-~;;;;.-,~~te;;-;.e~---.;2;;;..;;e;..;;;e_or-~....y..;;.,r-T'"-rT,;;..;-__r--.-., I 1<><> 5 ~f .1<><>

t e J----=~.-.:;:::=_-+----t__------+__-I.--<>-____t 1<><> I <> <> t5 ....J <> r <> <> I <> • • <> 20 t------~,-----<.-----_t_------++--+-...... -___1 1 • <><> • <> I <> <> 1 <> • <> 1 <> • <> v • <> s • 1<> .L • <> "E.. 35 ·1<> I) • <> o ·1<> • <> • 1<> 401------12:!~~::==1-----1_:_t~1• <> • <> t~

45 ----- ~• <> <>+ ~• • <> <> <> <> <> 55 <> <> <> <> <> 60 t------+------~----_t_--+_--_t • Values of v based on Suspension P-S Logging S Values of vs based on Down-hole 65 Velocity Measurements

2 5 10 20 5e tee 2ee qc (kg/cm2)

Fig. 4-4 MEASURED SHEAR WAVE VELOCITIES AT CAO SITE

Ueloci~y (m/&ec) 1ee 2ee

1e~---~-~ -=----r-~--~~_r- L •• I 15 •I • ·• r- Vp 213 ~-----i~'--=-'--I---+------+--t---;• •

.L -0+-·1 +'a.. 25 • II • o • 3e~------=~~;~~~~~~q~c~==~~~-=-·-1 • 35 •• 48L~--=±5~~==--J·~-J • Suspension P-S logging -,• 45 --Downhole wave velocity measurements f

213 513 tee 2ee qc (kg/cm2)

Fig. 4-5 MEASURED SHEAR WAVE VELOCITIES AT CAF SITE

The results of direct measurements of the shear wave velocities of the various soil layers using P-S logging techniques are shown in Fig. 4-6, and

an interpreted representative soil profile, based on these results, is

shown in Fig. 4-7.

(5) TLD Site

The soil conditions at the TLD site are generally similar to those at

the TLB site but the depth of the clay layer is substantially smaller. The hard layer in this case is reached at a depth of about 65 m.

The results of direct measurements of the shear wave velocities of the

soil deposits are shown in Fig. 4-8, and an interpreted representative soil profile, based on these results, is shown in Fig. 4-7.

(m/eec) ~ ;;.B__..:;;;2r-B_-r-"""'T""..;;,;;...,...... ,r-T'"n-__-,-_~_r-50r0_r_r_r'T"BrB-B--2-BT"0-0___.

IBL----=~~~e======---__t_--_1

2t:l t----~~~~::;:======---__t---_l

.L 3t:l l------=:::::.,~::+------_+_----__; +' 0... III Q 35

4t:l l------.l~------_+_.----___t

5t:l 1------8It------+------i • Suspens i on P-S 1oggi ng

Fig. 4-6 MEASURED SHEAR WAVE VELOCITIES AT TLB SITE

Shear Wave Velocity, ftls Shear Wave Velocity, ftls

0 250 500 750 1000 1250 0 250 500 750 1000 1250 III II I ,: ~ p 25 ] r T-f 25 l-I 50 1 50 I 20 t- 20 ~ 75 30 f- j" 30 100 100 0 0 C1l C1l "0 "0 E ro- E ,... 125 :T 125 :T ~ .c 40 +' +' -. 0- ,... 0- ro- aJ ~t Q) 150 - ISO 0 0 50 50 l 175 60 f- I 60 ]'" 200 fa I to 480 m/s Depth of soil 105 m 225 -f 225 70 f- I Measurement terminated 70 at C.L. -80 m j 250 -f 250 80 I ,I I I 80 I I I I 0 100 200 300 400 0 100 200 300 400 Shear Wave Velocity, mls Shear Wave Velocity, mls

TLB Site TLD Site

Fig. 4-7 INTERPRETED SHEAR WAVE VELOCITY PROFILES AT TLB AND TLD SITES w .j::-

35 Uelocit~ (m/&ec) gr-B 2T''B-__r_---,.-5..,..B""'"T'"""T"""'!....,l,B-0--2-Br-0-.,.-~-50T"B__r_.,...,....,..1 B..,..0_B__2,BB_B----,

~------I 5 :1 ~I t 0 l-----~oc:=====:::;::==t==L--_-----L---.-:·~--J

30 J------4IF-~H_------!+------t

r\ E • "oJ •• .L 35 • +'c... • II • Cl • 40 ~------_=E:::::i===~.....-----l+---+-::----1 ¢ ¢ ¢ ~ 45 ¢ ¢ ¢ ¢ ¢ 50 t------+-r-~--ll:------f+----+-----t ¢ ¢

--, ¢ ¢ 55 1 g I g ¢ 60 t------,--+-I---~--=------_+_-+-~-----I ¢ 1 ¢ • Suspension P-S logging t 65 --Downhole wave velocity t measurements 1

70 t------:-~------&-:----+_--!.----;

Fig. 4-8 MEASURED SHEAR WAVE VELOCITIES AT TLD SITE

5. Dynamic Properties of Mexico City Clay

The dynamic properties of Mexico City clay have been the subject of several studies, notably by Leon, Jaime and Rabago (1974) and again by Romo and Jaime as part of an on-going investigation following the earthquake of

September 19, 1985.

The results of both of these studies provide generally similar results of the form shown in Fig. 5-1. Compared with other clays Mexico City clay shows only a small reduction in shear modulus over a large range of strains, the shear modulus reducing by only about 10% even at strains as high as 0.15%. At strains above this level, however, there is a marked reduction in shear modulus.

Similarly the damping ratio of Mexico City clay is relatively low at strains up to about 0.15% and shows marked increases at strain levels above this value.

20,---...,...----..,------r-----r-----,---~--. o~ I o ~- 10t------+--4------4---+----_+~~~--_+-~ 0' .-c: 0. E o o 0 ~~--.L...-----I~---&...----a~---..L..-----I"-----""------' 10-3 10-2 10-1 10

)( ~ 1.01-----t~~~~::__-+ Range of experimental values ~ for Mexico City Clay (!) en 0.9t------+--+------+----::!~~--_+-_l_---_+-~ ::s ::s 'Co ~ 0.8 t------;---+---~-_+_-~h-_+_-f__--__I-__1 'o Q) enJ:. 'C 0.7t------+--4------4---+-----\,/9k--_l_---_+----4 Q) N o E a 0.6t------t--+-----t----t------t--vt+----_+--I Z

10-2 10-1 10 Shear Strain - percent

Fig. 5-1 STRAIN-DEPENDENT SHEAR MODULI AND DAMPING RATIOS FOR MEXICO CITY CLAY (after Leon et al., 1974 and Ramo and Jaime, 1986)

6. Relationship Between Soil Conditions and Ground Motion Records

The establishment of soil profiles, both in terms of soil types and

shear wave velocities at six of the major recording stations in Mexico City

(UNAM, SCT, CAF, CAD, TLB and TLD) makes it possible to prepare plots show

ing the relationship between ground motion characteristics and local soil

conditions at these sites. Thus Figs. 6-1 to 6-6 present plots showing in

the upper part of the figure the average response spectrum for the motions

recorded at each of the six sites and in the lower part of each figure a

shear wave velocity profile for the soil conditions at the site.

It is very clear that the UNAM site is very different from the other

sites but for the remaining five sites it is necessary to examine the soil

profiles in detail to be able to determine the changes in depth and stiff

ness of the soils which led to the marked variations in ground surface motions at the five sites. This is particularly well-illustrated by a com

parison of the soil conditions underlying the SCT and CAF sites, which are

shown together in Fig. 6-7. From an engineering point of view these sites might be considered to be very similar with regard to the depths and stiff

nesses of the underlying soils, but as shown in the upper part of the fig

ure, the minor differences in soil conditions were apparently sufficient to

cause significant differences in the response spectra of the ground surface motions.

It was to permit the development of procedures for anticipating these

differences that ground response analyses were performed for the five sites

underlain by clay soils. The results of these analyses are described in

the following sections of this report.

1.0

0.9

0.8

01 0.7 t: o :;:; 0.8 c L. Q) "ii 0.5 u u < 0.4 "0 L. ...u 0.3 4) a. Ul 0.2

0.1

0.0 0.0 0.:5 1.0 1.:5 2.0 2.:5 3.0 3.5 4.0 4.5 5.0 Period. seconds

Shear Wave Velocity. ft/s

a 250 500 750 1000 1250 o I I I I I 0

- 25 10 f- to 450 mI. - 50 20 l- to 600 m/s at C.L -21 m - 75

I- 30 - 100 0 E ....CD - 125 :T .r:. 40 f- " ....a. 4) .... 0 - 150 - 50 f- - 175

80 I- - 200

70 I- - 225

- 250 80 I I , o 100 200 300 Shear Wave Velocity. m/s

Fig. 6-1 AVERAGE ACCELERATION SPECTRUM FOR RECORDED MOTIONS AND INTERPRETED SHEAR WAVE VELOCITY PROFILE FOR UNAM SITE

1.0

0.9

0.8

C' 0.7 c o :o:i 0.8 E Cl 1) 0.5 o o < 0.4 ~ ti 0.3 a.Cl en 0.2

0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

Shear Wave Velocity. ft/s

0 250 SOO 750 1000 1250 0 0 ~ I I I I - 25 10 ~ - 50 20 - ...... - 75

30 ~ - 100 0 III E I ~,... I - 125 ::r .£ 40 ~ to 550 m/s ..a. ,... Q) 150 - 0 - 50 - - 175

80 ~ - 200

225 70 - -

- 250 I I I 80 0 100 200 300 400 Shear Wave Velocity. m/s

Fig. 6-2 AVERAGE ACCELERATION SPECTRUM FOR RECORDED MOTIONS AND INTERPRETED SHEAR WAVE VELOCITY PROFILE FOR SCT SITE

1.0

0.9

0.8

gI 0.7 C o ~ 0.8 ~ G ""ii O~ o o < 0.4 f ti 0.3 G 0- (I) 0.2

0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Shear Wave Velocity, ftls

0 250 500 750 1000 1250 0 0

25 10

20 75

30 100 0 C1I "Q E 125 M":r 40 to 400 m/s .c: -. .. M" 0- aI 150 Cl 50 175

60 200

225 70

250 80 0 100 200 300 400 Shear Wave Velocity, m/s

Fig. 6-3 AVERAGE ACCELERATION SPECTRUM FOR RECORDED MOTIONS AND INTERPRETED SHEAR WAVE VELOCITY PROFILE FOR CAF SITE

1.0 o.g

0.8

C' 0.7 c ~ 0.8 ~ I) "ii 0.5 u u 4( 0.4 E o 0.3 a.G) (f) 0.2

0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Shear Wave Velocity, ft/s

o 250 500 750 1000 1250 o -r o ~ I I I - 25 10 '- - 50 20 I- L-- - 75

30 '- - 100 0 CD E "tI,... 125 40 - :J'" or;.., - a. ,... Ql 150 - 0 - 50 '- - 175 to 400 m/s 60 I- - 200

70 I- - 225

- 250 80 I I I o 100 200 300 Shear Wave Velocity, m/s

Fig. 6-4 AVERAGE ACCELERATION SPECTRUM FOR RECORDED MOTIONS AND INTERPRETED SHEAR WAVE VELOCITY PROFILE FOR CAO SITE

1.0

0.9

0.8

0' 0.7 c o 'Z 0.6 o c... "ii 0.5 u o < 0.4 0... ..u 0.3 a. (J)" 0.2

0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Shear Wave Velocity, ft/s

0 250 500 750 1000 1250 0 0 ;J I I I I - 25 10 I-

- 50

20 I- - 75

'-- 30 ~ - 100 0 1II E 'tJ - 125 ?" £ 40 "'" - ....a. aCIl - 150 - 50 '"" - - 175

60 f- - 200

Depth of :soil 105 m - 225 70 - lAeo:surement terminoted ot C.L -80 m - 250 80 I , I 0 100 200 300 400 Shear Wave Velocity, m/s

Fig. 6-5 AVERAGE ACCELERATION SPECTRUM FOR RECORDED MOTIONS AND INTERPRETED SHEAR WAVE VELOCITY PROFILE FOR TLB SITE

1.0

0.9

0.8

Cl 0.7 c o :;; 0.6 ~ III Q) O.S t.l t.l < 0.4 ...."0.. t.l 0.3 III 0. Ul 0.2

0.1

0.0 0.0 0.5 1.0 1.:5 2.0 2.S 3.0 3.:5 4.0 4.:5 5.0 Period, saco.ods

Shear Wove Velocity, ft/s

0 250 500 750 1000 1250 0 J I I T I 0 25 10 >- -

- 50 20 I- - 75

30 I- - 100 0 III E "0 125 .... 40 - :iT .....s::. - 0. III .... 150 - C - 50 I- - 175

60 I- - 200 to 480 m/_

70 I- - 225

, - 250 110 I I 0 100 200 300 400 Shear Wove Velocity, m/s

Fig. 6-6 AVERAGE ACCELERATION SPECTRUM FOR RECORDED MOTIONS AND INTERPRETED SHEAR WAVE VELOCITY PROFILE FOR TLD SITE

1.0

0.9

0.8 seT

Ol 0.7 c :1S 0.6 o 'v Qj 0.5 o u 4: 004 o '- U 0.3 v a. " (/) 0.2 """"'"

""',., , .

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

Shear Wove Velocity, ft/s 0 200 .wO 600 BOO 1000 1200 0 0

5 20

10 -- SCT (39 m) 40 __ CAF (43 m) 15

60 20 0 CD E "C,... BO?" ..c: 25 ....a. ,... Q) - 0 --; 30 100

35 ---I 120 .w 140 45

160 50 0 100 200 300 400 Shear Wave Velocity, m/s

Fig. 6-7 COMPARISON OF AVERAGE ACCELERATION SPECTRA FOR RECORDED MOTIONS AND INTERPRETED SHEAR WAVE VELOCITY PROFILES FOR SCT AND CAF SITES

7. Analytical Studies of Ground Motions in Mexico City Based on

Soil Properties Determined from Earthquake Records

Because of the fact that the heavy damage zone in Mexico City is

located in the area of the lake-bed deposits mainly to the north of the SCT

Building site, it is desirable to develop procedures for evaluating the

characteristics of the earthquake ground motions in those parts of the city where no records were obtained but which are never-the-less of major inter est for damage evaluation purposes. To this end it is first necessary to demonstrate that any analysis procedure which may be used for this purpose

is capable of predicting the main characteristics of the motions at those

sites where recordings were made. Analyses of ground response using wave propagation procedures seem to provide the most logical choice of a suit able method for these purposes.

Such analyses for the sites in Mexico City are made possible by:

1. The existence of information such as that presented in the preced

ing pages which provides detailed information concerning the soil

conditions above the hard layer at the recording stations.

2. The availability of information, such as that shown in Fig. 5-1,

concerning the dynamic properties of the clay and other generally

applicable information for the sandy formations in the soil

deposits.

3. The fact that the clay deposits in Mexico City are very thin com

pared with their lateral extent so that in most cases, the dynamic

response of the deposit at any given site can be evaluated using

one-dimensional wave propagation theory.

4. The fact that previous studies (Herrera and Rosenblueth, 1965;

Seed and Idriss, 1969) have shown that one-dimensional ground

response analyses using vertical wave propagation, as illustrated

in Fig.7-1, can provide values of ground surface motions in good

agreement with values recorded in previous earthquakes, and that

most of the amplification of motions takes place in the soil

deposits overlying the hard layer.

5. The availability of the records at UNAM to provide good general

information on the characteristics of the motions developed on the

hard layer in the 1985 earthquakes.

Thus, assuming that the motions developed on the hard formations are reasonably represented by the N-S component of the record obtained at the

CUMV station at UNAM (see Fig. 3-4) and that for preliminary analysis pur poses the soil properties at the recording stations are reasonably well represented by the wave velocities deduced from the observed natural fre quencies of the various sites (see Fig. 4-1), it is possible to make analy ses of the ground motions likely to develop at the ground surface in areas underlain by clay deposits using one-dimensional wave propagation theory, as incorporated in computer programs such as SHAKE (Schnabel et al., 1972).

Because of the low intensity of the motions developed in the hard layer in the 1985 earthquake, the response does not involve any large non-linear effects and thus equivalent linear methods are likely to be sufficiently accurate for the conditions involved.

On this basis, analyses were made for the following conditions:

Time ·Secon :;00, -It--_.,;::0 ;;20"-- -'l30

i II ~ !---t+--++-~i----H·-IL--I'--~-----41--1

o Surface Motion fill Y·71pcl G.6.1.10·psf

50 Cia, Y·78pc' G·Z.I.IO'psl

100 Sill Y '86pc' G.3·Z-1O, psI CIo, Y ·86pc' lSa G'3 2 "0 ps' Cia, Y·109po' G'66 -to' psf

S,II, ,and Y 'l09pcl G'66 '10' psI

soo S,", cia, Y'"0pcl G.4.'.10' psI and land

1130 o"""'''''lml VII\Y/AYIA Boll. Motl()l'l

Time·Second'

Ln:t 2£

Fig. 7-1 ANALYSIS OF SOIL RESPONSE AT SITE IN ALAMEDA PARK, MEXICO CITY (after Seed and Idriss, 1969)

Shear Wave Unit Weight Site Depth Velocity of Clay Soil Profile of Soil

SCT 38 m 75 mlsec As shown in Fig. 4-1 1.2 t/m3 CAF 45 m 64 mlsec As shown in Fig. 4-1 1.2 t/m3 CAO 56 m 60 mlsec As shown in Fig. 4-1 1.2 t/m3

Using these characteristics, in conjunction with the strain-dependent values of soil properties shown in Fig. 5-1, and an iterative procedure to determine strain compatible properties for use in equivalent linear analyses, computations of the ground surface motions were made for the SCT, CAF and CAO sites.

The results of these studies are shown in Figs. 7-2, 7-3, and 7-4, where the acceleration response spectra for the computed motions are compared with the average spectra for the recorded motions. It may be seen that there is a very good degree of agreement between the spectra for the computed and recorded motions, indicating that the analytical procedures and the soil characteristics determined from earthquake records provide a good basis for predicting motions for the Mexico City environment (Ramo and

Seed, 1986).

1.0

0.9 Computed spectrum 0.8

O'l , - 0.7 ,, c ,, 0 ~ .. c 0.6 \ ~ Average spectrum for ... \~ 'recorded motions (l) , Q) , u 0.5 u \\.. <{ \\. 0.4 \ ...c '\,\ ~u Q) 0.3 \\, a. ,, CIl , 0.2 "\"" '. '.'. 0.1 .••.••.•......

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

SCT Site

Qm ------4m Sand 70 m/s _

Clay 75 m/s

31m Sandy Silt 110 m/s 34m Clay 110 m/s 38m

Hard layer 900 m/s

Fig. 7-2 ANALYSIS OF GROUND RESPONSE AT SCT SITE BASED ON SOIL PROFILE DETERMINED BY BORINGS AND FREQUENCY CHARACTERISTICS OF RECORDED MOTIONS

1.0

0.9

0.8

Ol 0.7 c: 0 :;:; a 0.6 Average spectrum for L..

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

CAF Site Om ------Sand 64 m/s 5m ------

Clay 64 m/s

31m Sandy silt & 100 m/s silty clay 41m stiff clay 100 m/s 45m

Hard Loyer 900 m/a

Fig. 7-3 ANALYSIS OF GROUND RESPONSE AT CAF SITE BASED ON SOIL PROFILE DETERMINED BY BORINGS AND FREQUENCY CHARACTERISTICS OF RECORDED MOTIONS

1.0

0.9

0.8 0\ 0.7 c- 0 :;i 0 0.6 L. V Average spectrum for V recorded motions ~ 0 0.5 «0 0.4 Computed spectrum ~ a L. .... ,,------_.~-- 0 0.3 ...... ,"... Va. (f) """'" 0.2 ". ""'" 0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

CAO Site Om ------_ Silty sand

Clay 60 m/s

Fig. 7-4 ANALYSIS OF GROUND RESPONSE AT CAO SITE BASED ON SOIL PROFILE DETERMINED BY BORINGS AND FREQUENCY CHARACTERISTICS OF RECORDED MOTIONS

8. Analytical Studies of Ground Motions in Mexico City Based on

Measured Values of Shear Wave Velocity of Soils

In the preceding section of this report, analyses of ground motions in

Mexico City were based on values of shear wave velocity for the clay deposits estimated from the frequency characteristics of the earthquake ground motion records. Thus there is good reason to expect that such values, incorporated in a reasonable method of analyses, would provide good evaluations of ground response effects at the various sites of interest.

In other conditions, such records of ground motions from which soil properties can be determined may not be available and it is therefore nec essary to determine the shear wave velocities of different soil layers by direct measurement. There are a number of in-situ techniques available for accomplishing this including cross-hole measurements, downhole measure ments, up-hole measurements, P-S suspension logging, etc. and in some cases representative values of shear wave velocity can be determined by labora tory tests on good-quality undisturbed samples.

It is generally recognized, however, that in-situ tests provide the most reliable results because they are not significantly influenced by sam ple disturbance and, in the present study, direct measurements of shear wave velocities were made at four sites (SCT, CAF, CAD, and TLD) using downhole shear wave velocity measurements and P-S suspension logging meth ods (Ohya et al., 1986). At a fifth site (TLB) shear wave velocities were determined by P-S wave logging only. The results of these tests have already been presented in Section 4 of this report.

It will be noted that there are some differences between the values measured at each site by the two measurement techniques used in this study

and that the direct measurements indicate somewhat lower values for shear wave velocities in Mexico City clay than the average values determined from the ground motion records. There are a number of technical reasons why some small errors may exist in the direct measurement of shear wave veloci ties:

1. For the P-S suspension logging method, the sides of the bore holes

were not cased and irregularities in the sides of the holes would

tend to lower the measured values below the time values.

2. Although casing was used in the downhole velocity measurements the

sensing device may not have been tight against the walls of the

hole, thus leading to a lowering of apparent wave velocity values.

3. In some cases the values of shear wave velocity measured in the

field tests were lower than the values determined by resonant col

umn tests on undisturbed samples. Since even extremely small

levels of sample disturbance can cause major reductions in shear

moduli and shear wave velocities for clay soils, this result is

difficult to understand unless the field values were too low for

some reason.

Because of these possible errors in the measured values of shear wave velocity it was considered desirable to allow for these uncertainties by allowing some variations in the soil property data used in the analytical studies of ground response. At the same time it was recognized that errors might also result from the use of a single ground motion record to repre sent the hard-layer motions in Mexico City. It is apparent from the data shown in Fig. 3-3 for motions recorded at the three UNAM sites that some deviations may occur from the average spectrum, no matter how closely a single earthquake record may represent this motion.

Accordingly in making the ground response analyses for the five clay

sites in Mexico City it was considered desirable to consider the probabil

ity of errors both in the input motions and in the soil properties used in

the analyses by adopting the following probabilistic procedure:

1. Using the best representative hard-layer record (i.e. the N-S com

ponent of the motions recorded at the CUMV site at UNAM) as the

mean value for ground motion characteristics and then considering

other motions which might deviate from this mean value by differ

ences in amplitude of ±20% or by differences in predominant period

of +10%.

2. Using the interpreted shear wave velocity profiles shown in Figs.

4-3 and 4-7 as mean values and then considering that actual shear

wave velocities might deviate from these values by ±10%. This is

a rather small allowance for possible errors. It could well be

argued that since any errors in field shear wave velocity measure

ments are likely to lead to values which are too low, it would be

more appropriate to vary the soil properties by amounts ranging

from 0 to +20% or more, but the value adopted was ±10% never-the

less.

Allowing for these variations from the mean values of intensity and predom

inant period in the hard-layer motions and from the representative mean values of shear wave velocity in the soil profiles requires the conduct of

27 separate analyses using the ground response analysis program SHAKE.

Although the time required is not excessive, it may be desirable in the future to write a probabilistic version of the SHAKE program or use some other similar program such as PLUSH (Romo et al., 1980) which can consider such variations in analysis parameters more expeditiously.

The results of probabilistic analyses of the ground surface motions at the five recording stations located on clay deposits in Mexico City (SCT,

CAF, CAD, TLB and TLD) are presented in Figures 8-1 to 8-20. For each site plots are presented to show:

1. The soil profile used for the analyses of ground response together

with the upper and lower bounds of the spectra for the computed

motions and the average spectrum for all the computed motions at

the site.

2. A comparison of the upper and lower bounds of the spectra for the

computed motions for the site and the average spectrum for the

motions recorded at that site.

3. A comparison for each site of the average spectrum for the com

puted motions and the average spectrum for the motions recorded at

that site.

4. A comparison of the 75-percentile response spectrum for the com

puted motions at each site and the average spectrum for the

motions recorded at that site.

Thus such results are shown:

(a) For the SCT site in Figures 8-1 to 8-4.

(b) For the CAF site in Figures 8-5 to 8-8.

(d) For the TLD site in Figures 8-13 to 8-16.

(e) For the TLB site in Figures 8-17 to 8-20.

It may be seen that the spectral characteristics of the ground motions determined by the analytical studies are in reasonably good agreement with the average spectra for the recorded motions at most of the recording stations. To evaluate the degree of agreement, assessments were made of

1.0

0.9 '. / Computed upper bound l\ ,, . , ..I II 0.8 ,••",,I ,, '.. : ~, 0\ 0.7 i \ Average of computed c : \ spectra 0 ;' \ :;:J 0.6 0 :I ". L.. , OJ ,, 1Il 0.5 u :' u : Computed lower bound « ,,: 0.4 ,, a L.. ;\ l'/ \\ ...., ~... u 0.3 .' ~ ,~'" \ 1Il : a. ,.... .:'\J' to,,_.,,'" U1 ! ~, \" 0.2 , '" ---.-' '...... , ", 0.1 ...... _------"----.. 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

seT Om Sand 100 m/:l 6m

Clay 56 m/:l

20m

Cloy 79 m/:l 30m Clay 300 m/:l 36m Clay 39m 160 m/:l

Hord loyer 550 m/s

Fig. 8-1 RESULTS OF GROUND RESPONSE ANALYSES FOR SCT SITE BASED ON SHEAR WAVE VELOCITIES INTERPRETED FROM FIELD MEASUREMENTS --ACCELERATION RESPONSE SPECTRA FOR COMPUTED MOTIONS

1.0

0.9 ~ Computed upper bound 0.8

0\ 0.7 ,.--Average for recorded ~ motions c 0 :.;:; 0.6 0 L. Q) Q) 0.5 u u <{ 0.4 -0 , Computed lower bound \ L. \ \ \ (J 0.3 \ \ Q) \ \ \ a. \ \ \ C/) 0.2 \ \\"'.' 0.1 ------0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 8-2 COMPARISON OF RESPONSE SPECTRA DETERMINED BY GROUND RESPONSE ANALYSES V1 BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE SPECTRUM FOR 00 RECORDED MOTIONS AT seT SITE

1.0

0.9 for recorded motions ,_ rAverage 0.8 , , , \ , \ , \ CJ'l , \ 0.7 , \ - :I \'. r---Average of computed spectra c , \ I \ 0 , \ ~ , \ 0.6 I \ 0 , \ I \ lo- , \ Q) , \ , \ \ Q) , \ 0.5 ,J \ , u , ,, \ u I \ , \ , \ , \

Fig. 8-3 COMPARISON OF AVERAGE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE V1 ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE 1.0 SPECTRUM FOR RECORDED MOTIONS AT SCT SITE

1.0

0.9 Average for recorded motions 0.8

,,,'"'\ r , \ ,, \ (J'\ 0.7 , .\ , \ c- ,,I \.. 0 ,, . , .\ ; Computed 75-percentile :;J 0.6 , , .. spectrum a , .\ L- , \ Q) ,, Q) 0.5 • (J (J « 0.4 -a L- a 0.3 Q) a. U1 0.2

0.1 "~

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 8-4 COMPARISON OF 75-PERCENTILE SPECTRUM DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMETNS WITH AVERAGE SPECTRUM ""o FOR RECORDED MOTIONS AT SCT SITE

1.0 -.------,

0.9

0.8

01 0.7 c: Computed upper bound o :;:; 0.6 o Average of computed spectra '- Q) Qj 0.5 u Computed lower bound u <{ 0.4 o '- U 0.3 Q) a. (f) 0.2

0.1

0.0 -t---,----.----,----.----,----.----r-----,----y----; 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

CAF Om Sand 100 m/s 5m Clay 54 m/s 11m

Clay 41 m/s 22m Cloy 80 m/s 29m

Cloy 135 m/s 37m Cloy 230 m/s 43m

Hard Loyer 400 m/s

Fig. 8-5 RESULTS OF GROUND RESPONSE ANALYSES FOR CAF SITE BASED ON SHEAR WAVE VELOCITIES INTERPRETED FROM FIELD MEASUREMENTS--ACCELERATION RESPONSE SPECTRA FOR COMPUTED MOTI ONS

1.0

0.9

0.8

Ol 0.7 Computed upper bound c- a :+J 0.6 a lower bound L.. Q) Q) 0.5 I Average for recorded motions u u <: 0.4 -a L.. (J 0.3 , Q) ,, 0- '''''' (f) 0.2 " ....' ..,...... 0.1 ""-- ...... _-----

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 8-6 COMPARISON OF RESPONSE SPECTRA DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE SPECTRUM FOR '"N RECORDED MOTIONS AT CAF SITE

1.0

0.9

0.8

0" 0.7 c- 0 .-...... , 06. 0 I- (l) Average for recorded (l) 0.5 motions • () () spectra

Fig. 8-7 COMPARISON OF AVERAGE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE 0\ SPECTRUM FOR RECORDED MOTIONS AT CAF SITE W

1.0

0.9

0.8

O'l 0.7 c- 0 .-...... 06. c "- Average for recorded Q) motions Q) 0.5 u u 75-percentile ~ 0.4 c "- U 0.3 Q) c.. en 0.2 ,,-,,

~~" "...... -- 0.1 ~~ .,-- --- --..

0.0 0.0 0.5 1.51.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds Fig. 8-8 COMPARISON OF 75-PERCENTILE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH 0\ AVERAGE SPECTRUM FOR RECORDED MOTIONS AT CAF SITE +:'-

1.0

0.9

0.8

0\ 0.7 c o :;:i 0.6 o Computed upper bound L- a> a> 0.5 Average of computed spectra o o « 0.4 Computed lower bound o L- ," V 0.3 '''-'" ,,"', ,,' """ a> '.. ' ".. '... a. i\"\··\ "\. l/) 0.2 /\1 ,~ ,..,,' ...... _- ...... ~ ..... 0.1 .' "-::\. ..._--- ~~~::: ..---_." _-- , __.. __.._. ..' _-_.---_ _.._------_------_._-----_. 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

CAD Om Sand 100 m/s 7m

Clay 40 m/s

22m

Cloy 70 m/s

40m

Cloy 180 m/s

S8m ------

Hard loyer 400 m/s

Fig. 8-9 RESULTS OF GROUND RESPONSE ANALYSES FOR CAO SITE BASED ON SHEAR WAVE VELOCITIES INTERPRETED FROM FIELD MEASUREMENTS--ACCELERATION RESPONSE SPECTRA FOR COMPUTED MOTIONS

1.0

0.9

0.8

Ol 0.7. c- 0 ~ 0.6 0 L. Q) Q) 0.5 u u \Average for recorded -< 0.4 \ motions - 0 L. ,,"~~----~-----, () 0.3 , / '" ''''',, Q) ,, a. " ,, (f) 0.2 " ,, "'''' 0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 8-10 COMPARISON OF RESPONSE SPECTRA DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE SPECTRUM FOR 0\ RECORDED MOTIONS AT CAO SITE 0\

1.0

0.9

0.8

Ol 0.7 c- 0 :;i 0.6 0 L.. Q) Q) 0.5 0 Average ~AVerage for 0 speclra of cam",Uled \ malians recorded « 0.4 -0 L.. ",.. -..... ", ----_ ... ----- U 0.3 ,'-,\ , \ " , Q) ,, , " ," , , \ " , , \ ,, a. , \ , , \ , (J') 0.2 , \ ,, ," \, ,, \ , \ , '" 0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.54.0 5.0 Period, seconds

Fig. 8-11 COMPARISON OF AVERAGE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE (j\ SPECTRUM FOR RECORDED MOTIONS AT CAO SITE -.....J

1.0

0.9

0.8

Ol 0.7 c- 0 -;:i 0.6 0 I.- Q) Q3 0.5 u ~Average for recorded u Computed 75-percentile ""motion. « 0.4 spectrum \. -0 l.- , ...... -...... t) 0.3 ,," ._---~~--- ... , ,, , , Q) ,, " " ,, a. , ,, (f) 0.2 , / ', ,"" ,'\~ ~" ,, ----...... --''-- ''''... 0.1 ... _--_.- "'"

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 8-12 COMPARISON OF 75-PERCENTILE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH 0' AVERAGE RESPONSE SPECTRUM FOR RECORDED MOTIONS AT CAO SITE 00

1.0

0.9

0.8

0\ 0.7 c: Computed upper 0 bound +J 0.6 0 \...

TLD Om ------__ Sand 80 m/s Sm ------__

Clay 72 m/s

36m ------_ Cloy 100 m/s 43m ------__

Clay 150 m/s

S5m ------_

Hard layer 480 m/s

Fig. 8-13 RESULTS OF GROUND RESPONSE ANALYSES FOR TLD SITE BASED ON SHEAR WAVE VELOCITIES INTERPRETED FROM FIELD MEASUREMENTS--ACCELERATION RESPONSE SPECTRA FOR COMPUTED MOTIONS

1.0

0.9

0.8

0' 0.7 c~ ;-Computed upper 0 :;:; 0.6 / bound 0 Average for recorded L motions j Q.) ,. Q.) 0.5 u u j Computed lower ~ 0.4 bound 0 L (J 0.3 Q.) 0- if) 0.2

0.1

0.0 0.0 0.5 1.51.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 8-14 COMPARISON OF RESPONSE SPECTRA DETERMINED BY GROUND RESPONSE ANALYSES "-.J BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE SPECTRUM FOR o RECORDED MOTIONS AT TLD SITE

1.0

0.9

0.8

Ol 0.7 c- 0 :;:; 0.6 0 L Q) for recorded motions Q) 0.5 /verage u u 4: 0.4 Average of computed spectra -0 ,...... " L ,I " ... ~ '. I \ U 0.3 I \ I , Q) a. en 0.2 \} /\~ '"-----~,,, ~--~" '\ . ", ".- "" \ / "-_. . . 0.1 ' '...._------._--..._---

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

Fig. 8-15 COMPARISON OF AVERAGE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE ...... ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE ...... SPECTRUM FOR RECORDED MOTIONS AT TLD SITE

1.0

0.9

0.8

Ol 0.7 cA 0 :f:j 0.6 0 L- a> Average for recorded Computed 75-percentile (i) 0.5 spectrum---. CJ CJ motion'i, « 0.4 0 ,, ., L- ,, -., t) 0.3 ,, '' a> \ a. " ' ...... ,.... --- .. (/) 0.2 ..... _- "", " ...... -...... , " ...... , .. ~"""" ..,------, '" 0.1 ...... _--

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

Fig. 8-16 COMPARISON OF 75-PERCENTILE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH '-J AVERAGE SPECTRUM FOR RECORDED MOTIONS AT TLD SITE N

73 1.0

0.9

0.8 Computed upper bound

Ol 0.7 Average of computed c spectra 0 :oJ 0.6 0 "~ ,~ L- ,I' I, V ,, ". V 0.5 ,, Computed lower bound u ,, «u ,, 0.4 ,, 0 , L- , -oJ ,"'\,\ I u 0.3 ,- \J \" V ,, " ...' Q. ,., (f) , 0.2 \ , ,,,'\",' ,,,,.,,, ,, \ _ ... -..., I -,I'" , 0.1 ,-" ...... _-, ...... _-- ...... ----' ..._-----', ...... _-- ... _------0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds TLB Om _

Cloy 55 m/s

28m ------__

Cloy 90 m/s

50m _

Cloy 110 m/s

80m _

Cloy 150 m/s

Hard layer

Fig. 8-17 RESULTS OF GROUND RESPONSE ANALYSES FOR TLB SITE BASED ON SHEAR WAVE VELOCITIES INTERPRETED FROM FIELD MEASUREMENTS--ACCELERATION RESPONSE SPECTRA FOR COMPUTED MOTIONS

1.0

0.9

0.8 Computed upper bound

0' 0.7 . recorded c 0 :;:; 0.6 0 L.. Q) Q) 0.5 lower bound u u « 0.4 - 0 L.. U 0.3 Q) 0.. (f) 0.2

0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 8-18 COMPARISON OF RESPONSE SPECTRA DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE SPECTRUM FOR RECORDED MOTIONS AT TLB SITE .,..'-J

1.0

0.9

0.8

0'1 0.7 - Average for recorded c motions 0 ...;J 0.6 0 ", '- I, Q) I \' / Average of computed Q) 0.5 I \ spectra u ,,,, u ,,,, « 0.4 , \ ...... -0 ," ,,'" ...... '- , "'''''''''''''''' , ...',, \. t) 0.3 I~ '-_ ...----' " Q) , .. 0.. " , __ , 11f ...... , ..... (f) 0.2

0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 8-19 COMPARISON OF AVERAGE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE SPECTRUM

FOR RECORDED MOTIONS AT TLB SITE '-l VI

1.0

0.9

0.8

01 0.7 ~ Average for recorded c motions 0 :+J 0.6 0 I~\ I- , / Q.) ,, ,, Q.) 0.5 I \ ...-- Computed 75-percentile u - , u , <: 0.4 - " ..... 0 " .... I- , "\ \ \ (J 0.3 \ Q.) \ a.. \ \.... _..---,,- (f) 0.2 .._---,--'

0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

Fig. 8-20 COMPARISON OF 75-PERCENTILE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE ANALYSES BASED ON SHEAR WAVE VELOCITY MEASUREMENTS WITH AVERAGE RESPONSE SPECTRUM FOR RECORDED MOTIONS AT TLB SITE -....J 0"

1. Whether the average spectrum for the recorded motions falls within

the upper and lower bounds of those for the computed motions

(bearing in mind that the ranges of parameters incorporated in the

analyses were quite small, e.g. Vs = ±10%, etc.). 2. The degree of agreement between the average spectra for the

recorded and computed motions. and 3. The degree of agreement between the average spectrum for the

recorded motions and the 75 percentile spectrum for the computed

motions. This comparison was made in recognition of the fact that

the measured values of shear wave velocities are probably lower

than the true values and the use of these values tends to lead to

unreasonably low values of computed motions for the Mexico City

sites. Allowance for this bias in the data could be made either

by making the analyses using values of shear wave velocity which

vary by -0 and +20% from the measured values or alternatively,

allowing variations of +10% from the measured values and then

adopting a higher than 50 percentile value of the computed motion

spectrum for predictive purposes. The latter option was used in

this case and the spectral level selected was the 75 percentile

value for each site.

The comparative results for each of the five sites included in the study are summarized in Table 8-1. On balance it may be concluded that in most cases the average spectra for the recorded motions lie within the bounds of those corresponding to the computed motions and that the agreement between the average spectra for the recorded motions and the 75 percentile spectra for the computed motions ranges from Fair to Very Good, with the overall assessment being rated as Good.

Table 8-1

Site SCT CAF CAO TLD TLB

Average recorded spectrum Mainly within upper and lower Yes Yes up to Mainly Mainly bounds of computed spectra T = 3.5 sec

Degree of agreement between Fairly Fairly Fair Fair Fair average recorded and Good Good average computed spectra

Degree of agreement between Very Very Fairly Fair Good average recorded spectrum and Good Good Good 75-percentile computed spectrum

It would appear from these results that if allowance is made for pos

sible deviations from the best average deterministic study results and

ground response problems are considered on a probabilistic basis, they can

provide very useful data for assessing the influence of local soil condi

tions on the general form of the earthquake motions likely to develop at

sites underlain by clays, similar to the conditions existing in the old

lake-bed area of Mexico City.

This need to consider possible deviations from measured properties is

especially important in view of the sensitivity of the analytical results

of ground response analyses to small changes in soil conditions, either in

depth of soil or in stiffness of soil, under conditions such as those

existing in Mexico City. This has already been illustrated in Section 6,

where the small differences in soil conditions between the SCT and the CAF

sites were shown to be associated with a very significant change in the

response spectra of the motions recorded at these sites. It is also appar

ent from the very large differences in upper and lower bounds for the spec

tra for the computed motions, shown in Figs. 8-1, 8-5, 8-9, 8-13, and 8-17,

resulting from comparatively small variations in either soil properties or

the level of base excitation used in the analyses.

It can be further illustrated by the analytical results determined for

the SCT site. Fig. 8-21 shows the soil profile interpreted from the

results of the shear wave velocity measurements at the SCT site, together with a modified profile in which the shear wave velocity of the clay, in

the depth range from 10 to 20 m below the ground surface, was considered to

be reduced by 15 m/sec below the original interpreted values. This change

in velocity profile is well within the accuracy of interpretation of the

shear wave velocity data. The upper part of Fig. 8-21 shows the response

80 1.0

0.9

0.8

(]I 0.7 c- 0 :;:; 0.6 a L Q) Q) 0.5 (J (J -eX: 0.4 a L ~ u 0.3 Q) 0- U') 1 ---....--...... ,'-' 0.2 " ...... -... ,i'/ "'\., ,- --...... - -, 0.1 "---...... _--,,--' --- " ...... _----- ...... -... _- ...... - 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Shear Wave Velocity, ft/s o 200 400 600 BOO 1000 1200 o I" I I I" I I 0

5 ~ ~ - 20

10 f- j- -- Interpreted Profile I I I - 40 · _•••••--. Modified Profile 15 f- I ·I • ·I - 60 I 20 f- ·.- '-- E l- - .!: 25 ~ -. a. ~ Q) a 30 t- - 100

35 t- - 120 r to 550 m/s 40 t- - 140 45 ~

I I I - 160 50 o 100 200 300 400 Shear Wave Velocity, m/s

Fig. 8-21 EFFECT OF MINOR CHANGE IN SHEAR WAVE VELOCITY PROFILE AT SCT SITE ON ACCELERATION RESPONSE SPECTRUM FOR COMPUTED MOTIONS

spectra for the computed motions at the ground surface for the two pro files, using the same excitation in the hard layer for both analyses. It may be seen that this very small change in shear wave velocity over a very limited depth leads to a very significant change in the spectra for the computed motions at the ground surface.

Thus both observationally and analytically, small changes in soil characteristics, at least in Mexico City, can have a major effect on the characteristics of the ground surface motions, making it very difficult to anticipate the precise character of the motions likely to develop at any given site and emphasizing (a) that even "good" agreement between observed and computed motion characteristics is a significant achievement in ground motion prediction in the Mexico City environment; and (b) the importance of considering the possible effects of errors or variations in soil properties or base motion characteristics, through the use of probabilistic studies, in any attempt to study site effects in areas of such high sensitivity.

Despite these difficulties, however, ground response analyses can help significantly to anticipate the effects of local soil conditions on ground surface motions. This is well-illustrated by a comparison of the response spectra shown in Figs. 8-22 and 8-23. Fig. 8-22 shows the average response spectra for the motions recorded at four very different sites: UNAM, SCT,

CAF and CAO. Fig. 8-23 shows the 75-percentile spectra for the computed motions at the same sites, based on the measured shear wave velocities of the soils and assuming that the UNAM motion was developed at an outcropping of the hard layer. There is considerable similarity in these two sets of results indicating the potential usefulness of ground response analyses in anticipating the nature of earthquake motions. For further comparison Fig.

8-24 shows the spectra for the same four sites based on ground response

1.0

0.9

0.8 seT

01 0.7

~ c 0 :;::; 0.6 a I- Q) Q) 0.5 () () <{ 0.4 -a l- t) 0.3 Q) 0... U1 0.2

0.1 ------0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

FIG. 8-22 COMPARISON OF AVERAGE SPECTRA FOR RECORDED MOTIONS AT UNAM! SCT! CAF AND CAO SIrES 00 tv

1.0

0.9

0.8

0'1 0.7 seT c~ 0 :;:; 0.6 0 L... Q) Q) 0.5 () () « 0.4 -0 L... U 0.3 Q) 0. U1 0.2 ""...... " --, -----, 0.1 ""-~~---~--~-~-~- 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

00 Fig. 8-23 COMPARISON OF 75-PERCENTILE SPECTRA FOR COMPUTED MOTIONS AT UNAM, SCT, w CAF AND CAO SITES--ANALYSES BASED ON MEASURED SHEAR WAVE VELOCITIES

1.0 seT 0.9

0.8

(J1. 0.7 c 0 :;:; 0.6 0 I- Q) Q) 0.5 u u « 0.4 -0 l- t> 0.3 Q) CL (f) 0.2

0.1

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 8-24 COMPARISON OF SPECTRA FOR COMPUTED MOTIONS AT UNAM, SCT, CAF AND CAO SITES--ANALYSES BASED ON SHEAR WAVE VELOCITIES INFERRED FROM FREQUENCY CHARACTERISTICS OF RECORDED MOTIONS 00 .J::-

analyses incorporating soil properties determined from earthquake records

(Figs. 7-2 to 7-4). These analytical results are in even better accord with the spectra for the recorded motions indicating that whereever possi ble, it is desirable to refine direct measurements of shear wave velocities with data that may be obtained from actual earthquake records.

9. Use of Scaled Records of Outcrop Motions in Analyses

of Ground Response

In the analyses of ground response in Mexico City described in previ

ous sections of this report, motions at the SCT, CAF, CAO, TLD and TLB

sites were computed on the basis of the known motions in the hard layer at

the UNAM sites. In many cases where estimates of site effects are

required, however, the specific details of the hard layer or rock outcrop motions will not be known and the motion can be described only in general

terms, say by specific values of such parameters as peak ground accelera

tion, peak ground velocity, predominant period of motions, general form of

response spectrum and duration of shaking. However in order to make a

deterministic analysis of ground response a complete time-history of hard

layer or rock outcrop motions is required.

In such cases the only means available to obtain the required time

history of hard layer or rock motions are

1. To generate a totally artificial earthquake motion having the gen

eral characteristics required;

or 2. To take some existing record of earthquake motions and modify it,

by appropriate scaling of either or both the acceleration and time

scales to make it conform to the prescribed characteristics.

Both procedures are used, but perhaps the scaling procedure is used more

frequently since it is easier to accomplish and the results will necessar

ily have the irregularities associated with a real earthquake record, since

they are derived from a real earthquake record.

In order to investigate how the use of this procedure might affect the

results of ground motion studies for a city such as Mexico City, analyses

were made to determine the ground motions which might be expected at the

SCT site using a scaled accelerogram from the available set or records from past events. Desirably such a record would be generated by a magnitude 8 earthquake, would be recorded on rock or hard soil at a distance of about

300 kms from the source, would have predominant periods of about 0.9 and

2.0 seconds and would have a peak ground acceleration of about 0.038 g.

Not surprisingly, such a record does not exist and it is necessary to select some record which comes reasonably close to the desired requirements and then scale the record to meet the requirements more closely.

In the United States, the largest magnitude earthquake for which records are available is the 1952 Kern County (California) earthquake which has a magnitude of 7.6. Several records are available, but one of the more distant is that obtained at a Pasadena station where the record has the following characteristics:

Peak acceleration: 0.057 g

Predominant periods: 0.65 and 0.82 seconds

By multiplying the acceleration scale of this earthquake motion by 0.52 and the time scale by a factor of 2.5, the characteristics are changed to:

Peak acceleration: 0.030 g

Predominant periods: 1.6 and 2.0 seconds which meets the desired characteristics quite well. After scaling in this way, the time-history of accelerations has the form shown in Fig. 9-1 and the acceleration response spectrum shown in Fig. 9-2. It may be seen from

Fig. 9-2 that the acceleration response spectrum of the scaled record is in reasonably close agreement with the average of the motions recorded at the

UNAM sites.

0.04

0'1 c~ 0.02 0 +:i 0s.... Q.) 0.00 Q.) u «u -0.02

-0.04 0 10 20 30 40 50 60 Time, seconds

20 u Q.) en ...... 10 E u 0 Z' .-u 0 -10 Q.) > -20 0 10 20 30 40 50 60 Time, seconds

00 Fig. 9-1 TIME HISTORIES OF ACCELERATION AND VELOCITY FOR SCALED ACCELEROGRAM OF 00 PASADENA RECORD OF KERN COUNTY (CALIFORNIA) EARTHQUAKE OF 1952

0.20

0.18 ------Average UNAM Spectrum (1985)

0.16 -- Modified Pasadena (1952) C1l 0.14 c- 0 :.;::; 0 0.12 L Q) Q) ,., 0.10 oJ I u I " I u I I « l".JI ,,\I ... _, ,I 0.08 ,, 0 I L ,I 4-J u I','" I Q) 0.06 I ,I 0.. f\, U1 ,,I 0.04

0.02 "',._------

0.00 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Period, seconds

00 Fig. 9-2 COMPARISON OF ACCELERATION RESPONSE SPECTRUM FOR SCALED PASADENA RECORD \0 AND AVERAGE SPECTRUM FOR UNAM RECORDS (1985)

Thus the scaled record of the Pasadena recording of the Kern County earthquake was used to compute the ground surface motions at the SCT site, using the soil profile determined by the shear wave velocity measurements and shown in Fig. 9-3. As in the previous studies, soil properties and hard layer outcrop motions were allowed to vary as follows

Shear wave velocities: +10%

Hard layer accelerations: +20%

Predominant period of outcrop motion: +10%

The results of the analyses are presented in Figs. 9-3 to 9-6. Fig. 9-3

shows the soil profile used in the analyses and the upper and lower bounds of the spectra for the computed motions. The average spectrum from the 27

analyses performed is also shown in this Figure. Figure 9-4 shows the

upper and lower bound spectra for the computed motions, together with the

average spectrum for the recorded motions. In general the average spectrum

for the recorded motions falls within the range of the spectra for the com

puted motions, albeit near the upper bound of the range.

Fig. 9-5 compares the average spectrum for the recorded motions with

the average spectrum for the computed motions at the SCT site and Fig. 9-6

compares the average spectrum for the recorded motions with the 75

percentile spectrum for the computed motions. As in the case of the

preceding analyses described in Section 8, the 75-percentile spectrum for

the computed motions is in good agreement with the average spectrum for

the recorded motions.

Finally, Fig. 9-7 compares the 75-percentile spectra of the motions

computed for the SCT site using both the CUMV-NS component of the motions

recorded at UNAM in the 1985 earthquake and the modified Pasadena record of

the Taft earthquake as hard-layer outcrop motions. It may be seen that

1.0

0.9 i\ r Comput,d uppe, bound 0.8 ,-..,' '.., ...., ,, . Ol , .. 0.7 , . . · ., --Average of computed c · , spectra 0 · ., :;:; 0.6 ! " {) : L. .I Q) .: Q) 0.5 u :. u /,1 Computed lower bound , , « 0.4 , /'" .\ {) \ .....L. u 0.3 Q) / a...... " \ (f) 0.2 ...... ' " "\ \." .. " ......

0.1 ,.' --'" •...... _---- - _.. --_ .....---".' ....•....._ -. __._-_ _ __ . 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

seT am Sand 100 milS 6m

Clay 56 milS

20m

Clay 79 milS 30m Clay 300 milS 36m Clay 39m '60 milS

Hard layer 550 milS

Fig. 9-3 RESULTS OF GROUND RESPONSE ANALYSES FOR SCT SITE USING SCALED PASADENA RECORD AS HARD LAYER OUTCROP MOTI ON

1.0

0.9 rcomputed upper bound

0.8

(]I 0.7 I Average for recorded motions c- 0 :;:i 0.6 0 I.- (1) (1) 0.5 u I Computed lower u bound « 0.4 - 0 l.- t) 0.3 (1) Cl. U1 0.2

0.1 ·····~----I ...... _--. __..._---.._-- 0.0 0.0 0.5 1.51.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

\0 Fig. 9-4 COMPARISON OF RESPONSE SPECTRA DETERMINED BY GROUND RESPONSE ANALYSES N USING SCALED PASADENA RECORD AS HARD LAYER OUTCROP MOTION WITH AVERAGE SPECTRUM FOR RECORDED MOTIONS AT SCT SITE

1.0

0.9 for recorded motions " / --Average 0.8 ,, ,, ,,, \ C1l 0.7 , \'\ , \ . , \ Average of computed spectra , \ c , \ I \ 0 I \ , \ :;:; 0.6 , \ 0 , \ , \ '- , \ Q) , \ ,, \, Q) 0.5 , ,, u ,, , u ,,, ',, , \ « 0.4 ,, ', , \ , \ , \ o ,, ,, '- , \ , \ t) 0.3 Q) ,"','".' \ , 0.. / .-..,--_.. \ \ / \ ,_ ' . \ (f) 0.2 .. . ", ' \ , ._.. " '''''' ...... , ...... 0.1 " --,--.-. 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 9-5 COMPARISON OF AVERAGE RESPONSE SPECTRUM DETERMINED BY GROUND RESPONSE \0 ANALYSES USING SCALED PASADENA RECORD AS HARD LAYER OUTCROP MOTION W WITH AVERAGE SPECTRUM FOR RECORDED MOTIONS AT SCT SITE

1.0

0.9 Average for recorded motions

0.8 /;~ Computed 75-percentile ,, ,, / spectrum , \ , \ , \ 0'1 0.7 , \ , \ ,, c- , o ,, :;:; 0.6 , o , I- ,, Q) ,, Q) 0.5 , ,, \ , u , \ u , '\, ,, ,, « 0.4 ,, ,, \ , o ,, I- \ \ , \ U 0.3 \ \ Q) \ \ "" \ c. ;'" ...... __ ...... -- \ (f) \ \ , 0.2 ,,".' ,, " " ---'" " " ',,\ 0.1 -.. _-- .. _---- 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 9-6 COMPARISON OF 75-PERCENTILE SPECTRUM DETERMINED BY GROUND RESPONSE 1.0 ANALYSES USING SCALED PASADENA RECORD AS HARD LAYER OUTCROP MOTION .po. WITH AVERAGE SPECTRUM FOR RECORDED MOTIONS AT SCT SITE

1.0 Computed 75-percentile spectrum 0.9 using GUMV-NS record (1985) Computed 75-percentile spectrum 0.8 using modified Pasadena record (1952)

0'1 0.7 - A c r, 0 --,, :;:; 0.6 ,, 0 , L. • Q) ••, Q) 0.5 •, u ••, u \ ..

0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period. seconds

Fig. 9-7 COMPARISON OF 75-PERCENTILE SPECTRA DETERMINED BY GROUND RESPONSE \D ANALYSES USING SCALED PASADENA RECORD AND N-S COMPONENT OF CUMV RECORD \Jl AS HARD LAYER OUTCROP MOTIONS

there is little difference in these spectra whether the CUMV-NS record or the modified Pasadena record is used as the control motion for the analy sis.

This result would seem to demonstrate that good evaluations of soil effects on ground response can be made even when the rock or hard layer motions must be represented by scaled records from other earthquakes, pro vided the scaling results in an accelerogram which reasonably represents

both in acceleration level and frequency content, the characteristics of the anticipated rock outcrop motions.

10. Predictions of Ground Motions at Sites of Special Interest

The ultimate goal of the field investigations and analyses performed in this study is the development of an ability to predict, with some level of confidence, the nature of the ground motions which are likely to have occurred at critical sites or in critical zones of Mexico City where major damage occurred but where no instrumental records were obtained. Typical examples are presented below.

CUP] Site

One such site for example is the CUPJ site, near the location of much of the very heavy damage and building collapses during the September 19,

1985 earthquake (see Fig. 10-1). Clearly a first step in making an evalua tion of the ground motions which led to the collapse of this building is a determination of the soil conditions at this particular site. The results of a soil exploration program showed that the soil conditions at this site consist of a 4 m thick layer of sand, underlain by about 26 m of clay con taining thin seams of silt and fine sand, followed by a 9 m thick layer of sand and stiffer clay, followed by the hard layer. The variation of mea sured shear wave velocities with depth is shown in Fig. 10-2, and an inter preted profile of the site conditions based on all of this data is shown in

Fig. 10-3.

It is immediately apparent from the results presented that this soil profile at the CUPJ site, shown in Fig. 10-3, is very similar to that for the SCT site. A comparison of the interpreted soil profiles is shown in

Fig. 10-4. In view of the very close similarity in the soil conditions it would be reasonable to conclude by observation that the earthquake motions at these two sites would also be closely alike.

...... -...... ' -,~- . cotos• en rn

_. _ .Hea'l'1 damage zone • LOCO lions of strong-molion acce\erogra.phS fig. 10-1 PLAN Of MEXICO CI1Y SHOWING LOCA110NS Of INS1RUMENl S1Al10NS ANO CUPJ SllE

LJeloci'ly (m/aec) ~B 2B 5B 'BB 2BB 5BB IBBB-, 2BBB 5 I J ·L 'B , ) '5

.~ ,...., 25 E ~ 'J ..c. ~ -+' a.. II 33 a r . t 35

40 ...------+------f--~--__+--__,I__~• • r :1 45 · :,I 50 t------+------1Jt------+---+--iL.--~• • Suspension P-S logging I :1 •I --Downhole wave velocity easurements • 55 •I 1 2B 50 'BB 200 qc (kg/cm2)

Fig. 10-2 MEASURED SHEAR WAVE VELOCITIES AT CUPJ SITE

100

CUPJ Om Sand 120 mls 4m

Cloy with seams of silt and sand 50 mls

18m

Clay with seams of silt & sand 78 mls

30m Silty sand & Stiff Cloy 125 mls 39m

Hard layer 500 mls

Fig. 10-3 INTERPRETED SOIL PROFILE AT CUPJ SITE BASED ON SOIL BORINGS AND SHEAR WAVE VELOCITY MEASUREMENTS

Fig. 10-4 COMPARISON OF INTERPRETED SOIL PROFILES AT SCT AND CUPJ SITES

~ o ~

102

To confirm this observation, a series of ground response analyses were made for the conditions at the CUPJ site following the same procedures as those used for the SCT site. The basic profile used for analyses is that shown in Fig. 10-3, but allowance was made for variations in soil proper ties and hard-layer excitation as follows

Shear wave velocities: Varied by ±10%

Amplitude of hard layer motions: Varied by ±20%

Predominant period of hard layer motions: Varied by ±10%

The results of these analyses are shown in Figs. 10-5. Fig. 10-5 shows the upper and lower bounds of the spectra determined from the computed surface motions, emphasizing again the wide range of computed motions which may result from small changes in soil characteristics and input motions for such soil conditions. Fig. 10-6 shows the 75-percentile spectrum for the set of computed motions and a comparison of this spectrum with that com puted for the SCT site and the average of the recorded motions at the SCT site. The similarities in these results leaves little doubt that the motions at the CUPJ site were likely to have been very similar to those at the SCT site in the September 19, 1985 earthquake.

Heavy Damage Area

An area of major interest in the earthquake of Sept. 19, 1985 is the very heavy damage area shown in Fig. 1-2. It is not possible to explore in detail the soil conditions at all building locations in this area but suf ficient studies have been made to indicate that the clay deposits are generally similar to those at the SCT site but they vary considerably in depth to the hard layer with such depths ranging from about 24 to 44 m.

1.0

,I·", ,I. 0.9 I, ,II, i \~ Computed upper bound 0.8 ,I•, ,,: I., ,, ,, 0'. 0.7 : ~ II 'I c I I I I 0 I I Mean computed spectrum ~ I ' 0.6 I ' 0 ,, '' "- ,, '' Q) ,, Q3 0.5 ,, u , u ,", " / 4: : ",' , I Computed lower bound 0.4 ,V 1 \ l :. l -0 I I ' , I ' ' \ "- I • ' , I ' ' , t) 0.3 I ' I , 1\' \" ,, Q) ,, ...,,,",. r r""'\ ... ,, ..' " a. J (f) r 0.2 I ",--'_ ',..-,__ ---r \ ' -_..-,,' --~,,,-" ,. ----, '. .,., " , ,,, . -..--. ._--,.' '..--..' ... .." .. '.'--- -- 0.1 ------"- -...... ------~~~~~~~~~~~~~~~~:::: 0.0 0.0 0.5 1.51.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Period I seconds

Fig. 10-5 RESULTS OF GROUND RESPONSE ANALYSES FOR CUPJ SITE BASED ON SHEAR t WAVE VELOCITIES INTERPRETED FROM FIELD MEASUREMENTS--ACCELERATION o RESPONSE SPECTRA FOR COMPUTED MOTIONS w

1.0 Computed 75-percentile 0.9 spectrum at SCT

0.8 Computed 75-percentile spectrum at CUPJ

0"1 0.7

~ c 0 :;::; 0.6 Average for recorded 0 L.. motions at SCT Q) Q) 0.5 u u « 0.4 -0 L.. 1J 0.3 Q) 0- (/) 0.2

0.1

0.0 0.0 0.5 1.51.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Period, seconds

Fig. 10-6 COMPARISON OF 75-PERCENTILE SPECTRA FOR COMPUTED MOTIONS AT SCT AND CUPJ SITES WITH AVERAGE SPECTRUM FOR RECORDED MOTIONS AT SCT SITE ...... o +'-

105

In order to explore the probable nature of the ground motions in this large area, a series of ground response analyses were performed using the soil properties deduced from the earthquake motions and shown in Fig. 4-1.

These properties have already been shown to lead to response spectra in good agreement with the recorded motions at the SCT site when they are incorporated in a ground response analyses using the UNAM average motion as a control motion.

Thus to explore the possible variation in motions throughout the heavy damage area, a series of analyses were made using the soil profile shown in

Fig. 4-1, using the N-S component of motions recorded at the UNAM-CUMV site as outcrop excitation, but varying the depth to the hard layer; analyses were made for hard layer depths ranging from 25 to 45 m.

The results of these analyses are shown in Fig. 10-7. It may be seen that because of the different depths of clay in the area, ground motions are likely to have varied significantly in different locations, though they are generally quite high throughout the entire zone. Based on these results a representative average spectrum for the entire zone has been indicated in Fig. 10-6. This average spectrum might be appropriate in efforts to relate the overall damage in this zone to the nature of the motions producing it and could be considered useful for such generalized studies. For particular building locations, however, it is clear that more site-specific motions should be used in damage evaluations.

1.0 . ,1\, ,, ,, ,,,I Computed for different 0.9 ,, depths to hard layer II ,I ,I , I I , Spectra for recorded 0.8 ,,I I I , motions at SCT site I " ,,I ' :, ''-_ ...... \ O'l 0.7 I ' I ' Representative Average ~ I \ c \, for Heavy Damage Area o ,, +-' 0.6 ,, o ,, L , Q) , I, Q) 0.5 ,, o , \, o ,, « 0.4 ,, ,, o ,, L ., o 0.3 Q) 0- ", .... -... , (f) 0.2 ", " " '" .... _- ... - ... 0.1 " " " " ~=.:=.-.,,:::::: 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.54.0 5.0 Period, seconds

Fig. 10-7 COMPUTED SPECTRA FOR HEAVY DAMAGE AREA FOR SOIL DEPTHS RANGING FROM 25 TO 45M. AND EVALUATION OF REPRESENTATIVE AVERAGE SPECTRUM FOR HEAVY t-' DAMAGE AREA o 0"

107

11. Conclusions

On the basis of the data and analyses presented in the previous sec tions of this report, it appears reasonable to draw the following conclu sions:

1. The characteristics of earthquake ground motions varied widely in

Mexico City in the Sept. 19, 1985 earthquake with marked differences in

motions occurring

(a) in different zones of the city such as the hard and rock-like

areas, the transition zone, and the area of the old lakebed

underlain by deep clay deposits.

and (b) in the lakebed area itself where markedly different motions

were recorded at sites underlain by different depths of clay.

2. The characteristics of the ground motions recorded at sites underlain

by clay showed generally similar frequency characteristics in the main

shock and in the aftershock, indicating that these characteristics were

controlled mainly by the local soil conditions rather than the source

characteristics of the earthquake (see Fig. 2-7).

3. The records of ground motions recorded at different locations of the

city underlain by Mexico City clay show that the characteristics of the

motions were very sensitive to small changes in the shear wave veloci

ties of the clay. Thus although the soil conditions at the SCT and CAF

sites appeared to be generally similar, the motions recorded at these

sites had quite different frequency characteristics (see Fig. 6-7).

4. The ground surface motions computed by ground response analyses using

the same control motion on a hard layer outcrop also indicate that a

108

small change in shear wave velocity of the clay in the soil profile

will have a significant influence on the frequency characteristics of

the motions (see Fig. 8-21).

5. The dynamic stiffness of the clay in Mexico City can be determined by

means of borings (to establish the general soil profile) and the use of

recorded motions to determine the characteristic site period and the

average shear wave velocity of the clay in the soil profile. The use

of soil properties determined in this way in ground response analyses

in which the average recorded motions on the hard layer in the UNAM

area are used as control motions provides good predictions of the ef

fect of local soil conditions on the characteristics of the motions

recorded at the SCT, CAO and CAF sites in Mexico City.

6. The characteristics of the clay at the SCT, CAO, CAF, TLB and TLD sites

have also been determined by in-situ downhole shear wave velocity mea

surements and by P-S Suspension Logging procedures. The values of

shear wave velocity determined by these procedures are slightly lower

than the values interpreted from the frequency characteristics of the

ground motion records, probably because small errors associated with

the in-situ wave velocity measurement procedures tend to lead to some

what lower values than the actual wave velocities.

7. To allow for the uncertainties in (a) the accuracy of shear wave veloc

ity measurements and (b) the characteristics of the control motions on

the hard layer outcrop, which must be used in predicting ground

response by wave propagation theory, in cases where the results are

very sensitive to small changes in these parameters, as in Mexico City,

it is desirable to use a probabilistic approach to ground response pre

diction. Thus in computing the effects of local soil conditions on

109

ground response in Mexico City it was considered desirable to allow for

possible uncertainties in these parameters as follows:

Possible uncertainty (error) in shear wave velocity: ±10%

Possible uncertainty in hard layer motion amplitude: ±20%

Possible uncertainty in predominant period of hard layer motion: ±10%

8. Using the probabilistic approach outlined above to compute the effects

of local soil conditions on ground motion characteristics, it was found

that:

(a) in most cases the average spectra for the recorded motions at

the SCT, CAO, CAF, TLB and TLD sites in Mexico City lie

within the bounds of the spectra computed by ground response

analyses.

and (b) the agreement between the average spectra for the recorded

motions at each of the five sites located on the lake-bed

clay deposits (SCT, CAO, CAF, TLB, TLD) and the 7S-percentile

spectra for motions computed by the probabilistic ground

response analyses described above, ranged from Fair to Very

Good, with the overall assessment being rated as Good (see

Table 8-1).

9. On the basis of the results of the ground motion studies, it would

appear that if allowance is made for possible small deviations from

the best average deterministic ground response analysis parameters,

and ground response is considered on a probabilistic basis, ground

response analyses can provide very useful data for assessing the

influence of local soil conditions on the characteristics of the

ground motions likely to develop at sites underlain by clays, similar

110

to the conditions existing in the old lake-bed area of Mexico City

where motions vary widely depending on the depth and stiffness of the

clay deposits.

10. Even in cases where a record of motions in a hard layer is not avail

ablet good predictions of the effects of local soil conditions on ground motions characteristics can be made provided a hypothetical

motion or scaled earthquake record having appropriate frequency char

acteristics is used for the control motion in ground response analyses

(see Fig. 9-7).

11. Because of the generally good results obtained in using ground

response analyses for the five sites at which motions and soil char

acteristics are known in Mexico CitYt the same procedures can be

expected to provide a good basis for predicting motions at sites where

motions were not recorded in the September 19 t 1985 earthquake. Typi

cal examples are the CUPJ site (Fig. 10-5) and the heavy damage area

(Fig. 10-6). Also it can be expected that these procedures may pro

vide a good basis for predicting ground motions at sites in the lake

bed zone due to other earthquake sources and source mechanisms.

III

Acknowledgements

The studies described in this report were sponsored jointly by the

U.S. National Science Foundation and by CONACYT (the Consejo Nacional de

Ciencia y Tecnologia) of Mexico. The authors gratefully acknowledge this support which made the investigation possible.

Grateful appreciation is also expressed to Mr. Satoru Ohya, Vice

Chairman of Oyo Corporation for technical support and for providing equip ment for field measurements of wave velocities, and to Mr. Takashi Kanemori of Oyo and Dr. Efrain Ovando of the Institute of Engineering, UNAM, for their diligence and interest in performing the wave velocity tests and the data interpretation.

112

References

Herrera, 1. and Rosenblueth, E., "Response Spectra on Stratified Soil," Proceedings, III World Conference on Earthquake Engineering, New Zealand, Vol. I, pp. 44-60, 1965.

Leon, J. L., Jaime, A. and Rabago A., "Dynamic Properties of Soils- Preliminary Study," Institute of Engineering, UNAM, 1974 (in Spanish).

Ohya, S., (1986) "In-Situ P and S Wave Velocity Measurement," Proceedings of Specialty Conference on Use of In-Situ Tests in Geotechnical Engineering, Geotechnical Special Publication No.6, American Society of Civil Engineers, 1986.

Resendiz, D., Springall, G., Rodriquez, J. M. and Esquivel, R., "Recent Information About Subsoil Characteristics and Foundation Engineering Practice in Mexico City," V Reunion Nactional de Mecanica de Suelos, Mexico, D.F., November, 1970 (in Spanish).

Romo, M. P., Chen, J. H., Lysmer, J. and Seed, H. B., "PLUSH: A Computer Program for Probabilistic Finite Element Analysis of Seismic Soil-Structure Interaction," Report No. UCB/EERC-77/01, University of California, Berkeley, September, 1980.

Romo, M. P. and Jaime, A., "Dynamic Characteristics of Some Clays of the Mexico Valley and Seismic Response of the Ground," Technical Report, DDF, April, 1986 (in Spanish).

Romo, Miguel P. and Seed, H. Bolton, "Analytical Modelling of Dynamic Soil Response in the Mexico Earthquake of Sept. 19, 1985," Procs., An IntI. Conf. on the 1985 Mexico Earthquake, Factors Involved and Lessons Learned, Sept. 19-21, 1986, Mexico City.

Schnabel, P. B., Lysmer, J. and Seed, H. B., "SHAKE: A Computer Program for Earthquake Response Analysis of Horizontally Layered Sites," Report No. EERC/72-12, University of California, Berkeley, December, 1972.

Seed, H. B. and Idriss, 1. M., "The Influence of Soil Conditions on Ground Motions During Earthquakes," Journal of the Soil Mechanics and Foundations Engineering Division, ASCE, Vol. 94, No. SMl, pp. 93-137, January, 1969.

Zeevaert, Leonardo, "Foundation Engineering for Difficult Subsoil Conditions," Van Nostrand Reinhold Company, 1971.

113

EARTHQUAKE ENGINEERING Rl<:SEARCH CENTER REPORT SERIES

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UCB/EERC-lW/O I "Earlh,!uake Response of Connete Gravity Dams Induding Hydrodynamic and roundation Interaction EHects," by Chopra, A.K., Chakrabarti, P. and Gupta, S., January 191W, (AD-A087297)AIO. U CB/EER C-RO/O 2 "Rocking Response of Rigid Blocks to Earthquakes," by Yim, C.S., Chopra, A.K. and Penzien, J., January 1980, (PBSO 1M 002)A04. UCB/EERC-lW/03 "Optimum Inelastic Design of Scism iC'-Resistant Reinforced Concrete Frame Structures," by Zagajeski, S.W. and Berteru, V.V., January 1980, (PBllO 164 635)A06. UCB/EERC-IW/04 "Elrects of Amount and Arrangement uf Wall-Panel Reinforcement on Hysteretic Behavior of Reinforced Concrete Walls," by Iliya, R. and Berteru, V. V., rehruary 19S0, (PBlll 122 525)A09. U CB/EER C-lW/05 "Shaking Tahle Research on Connetc Dam Models," by Niwa, A. and Clough, R.W., September 19S0, (PB81 122 3(8)A06. U CB/EER C-XO/Ol> "The Design of Steel Energy-Absorbing Restrainers and their Incorporation into Nuclear Power Plants for Enhanced Safety (Vol lal: Piping with Energy Absorbing Rc'Strainers: Parameter Study on Small Systems," by Powell, G.H., Oughourlian, C. and Simons, J., June 1980. UCB/EERC-SO/07 "Inclasti<: Torsional Response of Strudures Subjected to Earthquake Ground Motions," by Yamazaki, Y., April 1980, (PB81 122 327)A08. U CB/EER C-lW/08 "Study of X-Braced Steel Frame Stru<:tures under Earthquake Simulation," by Ghanaat, Y., April 19S0, (pB81 122 335)AII. UCB/EERC-lW/09 "Hybrid Modelling of Soil-Structu re Interaction." by Gupta, S., Lin, l'.W. and Penzien, 1., May 19S0, (PBSI 122 319)A07. UCB/EERC-IW/IO "Ueneral Apl'li<:ability of a Nunlinear Mudel of a One Story Steel Frame," by Sveinsson, B.I. and McNiven, H.D., May 1980, (PB81 124 877)A06. UCB/EERC-IWIII "A Green-Function Method fur Wave Interaction with a Submerged Body," by Kioka, W., April 19S0, (PB8 I 122 2(9)A07. UCB/EERC-IWII2 "Hydrodynamic Pressure and Addnl Mass for Axisymmetric Bodies.," by Nilrat, F., May 19S0, (PBSI 122343)AOS. U CB/EER C-RO/ 13 "Treatment of Non-Linear Drag Forces Acting on Offshore Platforms," hy Dao, B.V. and Penzien, J., May 1980. (PBlll 153 413)A07. U CB/EERC-IW/14 "2D Plane/Axisymmetric Solid Element (Type 3-Elastic ur Elastic-Perfectly Plastic) for the ANSR-I1 Program," by Mondkar, D.P. and Powell, G.H., July IYllO, (PBSI 122350)A03. U CB/EERC-80115 "A Response Spectrum Method for Random Vibrations," by Der Kiureghian, A., June 1981, (PBSI 122 301)A03. U CB/EER C-801l1> "Cydic Inelastic Buckling of Tuhular Steel Braces," by Zayas, V.A., Popov, E.P. and Martin, S.A., June 1981, (PB81 124 885)A 10. UCB/EERC-80/17 "Dynamic Response of Simple Arch Dams Including Hydrodynamic Interaction," by Porter, C.S. and Chopra, A.K., July 19SI, (PB81 1240(0)AI3. UCB/EERC-IW/18 "Experimental Testing of a Frictiun Damped Aseismic Base Isolation System with Fail-Safe Characteristics," by Kelly, 1.M., Beucke, K.E. and Skinner, M.S., July IYllO, (PBSI 148595)A04. U CB/EERC-SO/19 ''The Design of Steel Emergy-Absorbing Restrainers and their Incorporation into Nuclear Power Plants for Enhanced Safety (Vol.l B): Stochastic Seismic Analyses of N uelear Power Plant Structures and Piping Systems Subjected to Multiple Supported Excitations," by Lee, M.e. and Penzien, 1., June 19S0, (PBS2 201 S72)AOS. U CB/EERC-80/20 "The Design of Steel Energy-Absurbing Restrainers and their Incorporation into Nuclear Power Plants for Enhanced Safety (Vol 1<:): Numerical Methud for Dynamic Substructure Analysis," by Dickens, 1.M. and Wilson, E.L., June 19l10. U CB/EERC-lW/21 "The Design of Steel Energy-Absorbing Restrainers and their Incorporation into Nuclear Power Plants for Enhanced Safety (Vol 2): Development and Testing of Restraints for Nuclear Piping Systems," by Kelly, J.M. and Skinner, M.S., Junc 1980. UCB/EERC-80/22 "3D Solid Element (Type 4-Elastic or Elastic-Perfectly-Plastic) for the ANSR-II Program," by Mondkar, D.P. and Powell,G.II., July 1980, (PBSI 123 242)A03. U CB/EERC-llO/23 "Uap-Frictiun Element (Type 5) for lloe Ansr-II Pr.>gram," by Mondkar, D.P. and Powell, G.H., July 19S0, (PBSI 122 285)A03.

114

UCB/EERC-80/24 "U-Bar Restraint Element (Type 11) for the ANSI{·II Program," by Oughourlian, C. and Powell, G.H., July 1980, (PB81 122 293)AO~. UCBjEERC-1W/25 "Testing of a Natural Rubber Base Isolation Sysll:m by an Explosively Simulated Earthquake," by Kelly, J.M., August 1980, (PB81 20 I 360)A04. U CB/EERC-80/26 "Input Identification from Structural Vibrational Re'ponse," by Hu, Y., August 1980, (PBS I 152 308)A05. UCB/EERC-80/27 "Cyclic Inelastic Behavior of Steel Offshore Structures," by Zayas, V.A., Mahin, S.A. and Popov, E.P., August 1980, (PH81 196 ISO)AI5. U CB/EERC-80/2S "Shaking Table Testing of a Reinforced Concrete Frame with Biaxial Response," by Oliva, M.G., October 1980, (PB81 154 ~04)A10. U CB/EERC-ll/29 "Dynamic Properties of a Twelve-Story Prefabricated Panel Building," by Bouwkamp, J.G., Kollegger, J.P. and Stephen, R.M., October 1980, (PB82 DR 777)A07. UCB/EERC-80/~O "Dynamic Properties of an Eight-Story Prefabricated Panel Building," by Bouwkamp, J.G., Kollegger, J.P. and Stephen, R.M., October 1980, (PBSI 20(313)A05. UCB/EERC-SO/31 "Predictive Dynamic Response of Panel Type Slructures under Earth,!uakes," by Kollegger, J.P. and Bouwkamp, J.G., October 1'180, (PB81 152 316)A04. U CB/EER C-80/~2 "The Design of Steel Energy-Absorbing Restrainers and their Incorporation into Nuclear Power Plants for Enhanced Safety (Vol ~): Testing of Commercial Steels in Low-Cycle Torsional Fatique," by Spanner, P., Parker, E.R., Jongewaard, E. and Dory, M., 1980. UCB/EERC-1I0/33 "The Design of Steel Energy-Absorbing Restrainers .lnd their Incorporation into Nuclear Power Plants for Enhanced Safety (Vol 4): Shaking Table Tests of Piping Systems with Energy-Absorbing Restrainers," by Stiemer, S.F. and Godden, W.G., September 1980, (pBIL! 201 880)A05. UCB/EERC-lW/34 "The Design of Steel Energy-Absorbing Re.strainers and their Incorporation into Nuclear Power Plants for Enhanced Safety (Vol 5): Summary Report," by Spencer, P., 1980.

UCB/EERC-80/~5 "Experimental Testing of an Energy-Absorbing Bas<: Isolation System," by Kelly, J.M., Skinner, M.S. and Beucke, K.B., October 1980, (PB81 154 (72)A04. U CB/EERC-S0/36 "Simulating and Analyzing Artiticial Non-Stationary Earth Ground Motions," by Nau, RoF., Oliver, R.M. and Pister, K.S., October 1'180, (PB81 153 397)A04o U CB/EERC-SO/37 "Earth,!uake Engineering at Berkeley. 1'180," by , :-;':ptember 1980, (PB8 I 205 674)A09. U CB/EERC·80/3S "Inelastic Seismic Analysis of Large Panel Buildings," by Schricker, V. and Powell, G.B., September 1980, (PB81 154 338)A 13. UCB/EERC-80/39 "Dynamic Response of Emhankment, Concrete-Gavity and Arch Dams Including Hydrodynamic Interation," by Hall, 1.1'. and Chopra, A.K., October 1980, (pB81 152 324)AII. UCB/EERC-SO/40 "Inelastic Buckling of Steel Struts under Cyclic Luad Reversa!.," by Black, R.G. , Wenger, W.A. and Popov, E.P., October 1980, (PB81 154312)A08. UCB/EERC-SO/41 "Influence of Site Characteristics on Buildings Damage during the October 3,1974 Lima Earthquake," by Repetto, P., /\rango, I. and Seed, H.B., September 1980, (PR81 16\ 739)A05. UCB/EERC-80/42 "Evaluation of a Shaking Table Test Program on Response Behavior of a Two Story Reinforced Concrete Frame," by Blondet, J.M., Clough, R.W. and Mahin, S.A., December 1980, (PB82 196 544)AII. UCB/EERC-811/43 "Modelling of Soil-Structure Interaction by Finite and Infinite Elements," by Medina, F., December 1980, (PB81 229 270)A04.

UCB/EERC-SI/O\ "Control uf Seismic Response of Piping Systems and Other Structures by Base Isolation," by Kelly, J.M., January 1981, (PBS I 200 735)A05. UCB/EERC-81/02 "OPTNSR- An Interactive Software System for Optimal Design of Statically and Dynamically Loaded Structures with Nonlinear Response," by Bhalli, M.A., Ciampi, V. and Pister, K.S., January 1981, (pB81 218 851)A09. UCB/EERC-X 1/03 "Analysis of Local Variations in I'ree Field Seismic Ground Motions," by Chen, I.-C., Lysmer, J. and Seed, H.B., January 19SI, (AD-A09950S )AlJ. UCB/EERC-SI/04 "Inelastic Structural Modeling of Braced Offshore Platforms for Seismic Loading. ," by Zayas, V.A., Shing, P.-S.B., Mahin, S.A. and Popov, EoP., January 1981, (PBS2 138 777)A07. UCB/EERC-81/05 "Dynamic Response of Light Equipment in Structures," by Der Kiureghian, A., Sackman, J.L. and Nour-Omid, B., April 1981, (pBS I 218 497)A04. UCB/EERC-81/06 "Preliminary Experimental Investigation of a Broad Base Liquid Storage Tank," by Bouwkamp, J.G., Kollegger, J.P. and Stephen, R.M., May 19SI, (PBS2 140 385)A(U. UCS/EERC-SI/07 "The Seismi" Resistant Design of Reinforced Concrete Coupled Structural Walls," by Aklan, A.E. and Bertero, V.V., June 19S\, (PB82 113 358)AII. UCB/EERC-SI/OS "Unassigned," by Unassigned, 1981.

115

UCB/EERC-81/09 "Experimental Behavior of a Spatial Piping System with Steel Energy Absorbers Subjected to a Simulated Differential Seismic Input," by Slielller, S.F., Godden, W.G. and Kelly, J.M., July 1981, (PB82 201 898)A04. UCB/EERC-8I/10 "Evaluation of Seismic Design Provisions for Mast.nry in the United States," by Sveinsson, 8.1., Mayes, R.L. and McNiven, H.D., August 1981, (PBX2 166075)A08. UCB/EER C-81 /II "Two-Dimensional Hybrid Modelling of Soil-Strudure Interaction," by Tzong, T .-J., Gupta, S. and Penzien, J., August 1981, (PE82 142 118)A04. U CB/EERC-81 /12 "Studies on Effects of Inlills in Seislll ic Resistant R/C Construction," by Brokken, S. and Bertero, V.V., October 1981, (PBS2 166 190)A09. UCB/EERC-81/13 "Linear Models to Predict the Nonlinear Seismic Behavior of a One-Story Steel Frame," by Valdimarsson, H., Shah, A.H. and MeNiven, H.D., September 1981, (PB82 138 793)A07. UCB/EERC-8I/14 "TLUSH: A Computer Proh'fam for Ihe Three-Dimensional Dynamic Analysis of Earth Dams," by Kagawa, T., Mejia, L.1I., Seed, H.B. and Lysmer, 1., September 1981, (PB82 139 940)A06. UCB/EERC-81/IS "Three Dimensional Dynamic Response Analysis of Earth Dams," by Mejia, L.H. and Seed, H.B., September 1981, (PRS2 137 274)AI2. UCB/EERC-81/16 "Experimental Study of Lead and Elastomeric Dampers for Base Isolation Systems," by Kelly, J.M. and Hodder, S.B., October 19SI, (PB82 166 182)A05. UCB/EERC-81/i7 "The Influence of Ba"" Isolatiotl on the Seismic Response of Light Secondary Equipment," by Kelly, 1.M., April 1981, (PRIl2 255 266)A04. U CB/EERC-SI /l 8 "Studies on Evaluation of Shaking Table Response Analysis Procedures," by Blondet, J. Marcial, N ovem ber 1981, (PB82 197 278)AIO. UCB/EERC-81/19 "DI'LIGHT.STRUCT: A Computer-Aided Design l:nvironmeutfor Stru.:tural Engineering. ," by Balling, R.J., Pis ter, K.S. and Polak, E., December IlJXI, (PB82 21S 496)A07. UCB/EERC-81/20 "Optimal Design of Seismic-Resistant Planar Steel Frames," by Balling, R.J., Ciampi, V. and Pister, K.S., December 1981, (PBIl2 220 179)A07.

U CB/EERC-1l2/0 I "Dynam ic Behavior of Ground for Scism ic Analysis of Lifeline Systems," by Sato, T. and Der Kiureghian, A., Janu ary 1%2,

116

UCB/EERC-1l2/16 "The Behavior of Submerged Mullip'e Bodie, ill Earthquakes," by Liao, W.-G., September 1982, (PB83 158 709)A07. U CB/EERC-1l2/17 "Elfects of Concrete Types and Luading Conditiuns un Local Bond-Slip Relationships," by Cowell, A.D., Popov, E.P. and Bertero, V.V., September 1982, (PB83 153 577)A04. UCB/EERC-82/18 "Mechanical Behavior of Shear Wall Vertical Boundary Members: An Experimental Investigation," by Wagner. M.T. and Bertero, V.V., October 1982, (PHS3 159 764)A05. UCB/EERC-1l2/19 "Experimental Studies of Multi-suppurt Sei"nic Loading on Piping Systems," by Kelly, J.M. and Cowell, A.D., N Ovem ber 1982. UCB/EERC-82/20 "Generalized Plastic Hinge Concepts for 3D Beam-Column Elements," by Chen, P. F.-S. and Powell, G.H., N ovember 1982, (PB83 247 981)A13. UCB/EERC-82/21 "ANSR-ll: General Computer Program for Nonlinear Structural Analysis," by Oughourlian, C.V. and Powell, G .H., November 1982, (PB83 251 330)A12. UCB/EERC-82!22 "Solution Strategies for Statically Loaded Nonlinear Structures," by Simons, I.W. and PowelI, G.H., November 1982. (PBIl3 197 970)A06. UCBtEERC-1l2!23 "Analytical Muuel of Deformed ~ar Anchorages under Generalized Excitations," by Ciampi, V., Eligehausen, R., Bertero, V.V. and Popov, E.P., Nuvember 1982. (1'1383 169 532)A06. UCB/EERC-82124 "A Mathematical Model for the Respunse of Masonry Walls to Dynamic Excitations," by Sucuoglu. H., Mengi, Y. and McNiven. H.D., November 191<2, (pR83 169 OII)A07. UCB/EERC-82!25 "Earthquake Response Considerations of Broad Liquid Storage Tanks," by Cambra, F.I., November 1982, (PB83 251 215)A09. UCB/EERC-82/26 "Computational Models for Cyclic Plasticity, Rate Dependence and Creep," by Mosaddad, B. and Powell, G.I-I., Nuvember 1982, (PB83 245 829)A08. UCB/EERe-1l2!27 "Inelastic Analysis of Piping and Tubular Structures," by Mahasuverachai, M. and Powell, a.H., November 1982, (PB83 249 987)A07.

UCB/EERC.1U/O I "The Economic Feasibility of Seism ic Rehabilitation of Buildings by Base Isolation," by Kelly, J.M., January 1983. (Pil1l3 197 988)A05. UCB/EERC·8J/02 "Seismic Moment Connectiuns fur Mum~nt-Resisting Steel Frames.," by Popov, E.P., January 1983, (PB83 195 412)A04. UCB/EERC-83/03 "Design of Links and Beam-tn-Column Connections for Eccentrically Braced Steel Frames," by Popov, E.P. and Malley, J.O., January 1983, (pRfn 194 811)A04. UCB/EERC-8J/04 "Numerical Techniques for the Evaluation of Soil-Structure Interaction Effects in the Time Domain," by Bayo, E. and Wilson, E.L., February 1983, (PBS3 245 605)A09. UCB/EERC-83/05 "A Transducer for Measuring the Internal Forces in the Columns of a Frame-Wall Reinforced Concrete Structure," by Sause, R_ and Bertero, V.V., May 1983. (PB84 119 494)A06. UCB/EERC-ll:I/06 "Dynamic Interactions Between J-'loating lee and Offshore Structures," by Croteau, 1'., May 1983, (pB84 119 486)AI6. UCB/EERC-83/07 "Dynamic Analysis of Multiply Tuned and Arbitrarily Supported Secondary Systems. ," by Igusa, T. and Der Kiureghian, A., July 1983, (PB84 118 272)AII. UCB/EERC-83/08 "A Laboratory Study of Submerged Multi-body Systems in Earthquakes," by Ansari, a.R., June 1983, (pB83 261 842)AI7. U CB/EERC·83/09 "Effects of Transient Foundation U pliti on Earth<.juake Response of Structures," by Yim, C.-S. and Chopra, A.K., Ju ne 1983, (PB83 261 396)A07. UCB/EERC-83/10 "Optimal Design of Friction-Braced Frames under Seismic Loading," by Austin, M.A. and Pister, K.S., June 1983, (PB84 t 19 288)A06. UCB/EERe-83/ll "Shaking Tahlc Study of Singlc-Story Masonry Houses: Dynamic Performance under Three Component Seismic Input and Recommendations," by Manos, a.c., Clough, R.W. and Mayes, R.L., luly 1983, (UCB/EERC-83/II)A08. UCB/EERC-ll.'/12 "Experimental Error Propagation in l'seudodynamic -Testing," by Shiing, P.B. and Mahin, S.A., lune 1983, (1'884 119 270)A09. U CB!EERC·83/13 "Experimental and Analytical Predictions of the Mechanical Characteristics of a liS-scale Model of a 7-story R/C hame-Wall Building Structure," by Aktan, A.E., Bertero, V.V., Chowdhury, A.A. and Nagashima, 1'., June 1983, (pB84 119 2I3)A07. UCB/EERC-83/14 "Shaking Table Tcsts of Large-Panel Precast Connete Building System Assemblages," by Oliva, M.a. and Clough, R.W., June 1983, (PB86 110 210/AS)AII. UCB/EERC-8.1/15 "Sei.,mic Behavior of Active Beam Links in Eccentrically Braced Frames," by Hjelmstad, K.D. and Popov, E.P., July 1983, (pB1l4 119 676)A09.

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UCB/EERC-8~/I6 "System Identification of Structures with Joint Rotation," by Dimsdale, J.S., July 1983, (PB84 192 210)A06.

UCB/EERC-8~/17 "Construction of Inelastic Response Spectra for Single-Degree-of-Freedom Systems," by Mahin, S. and Lin, 1., June 1983, (PB84 208 834)A05. UCB/EERC-83/18 "Interactive Computer Analysis Mclhods for Predicting the Inelastic Cyclic Behaviour of Structural Sections," by Kaba, S. and Mahin, S., July 1983, (pB84 192 OI2)A06. UCB/EERC-83/19 "Ell'ects of Bond Deterioration on Hysteretic Behavior of Reinforced Concrete Joints," by Filippou, F.C., Popov, E.P. and Bertero, V.V., August 1983, (PB84 192 020)AIO. U CB/EER C-83/20 "Analytical and Experimental Correlation of Large-Panel Precast Building System Performance," by Oliva, M.G., Clough, R.W., Velkov, M. and Gavrilovic, P., November 1983. UCB/EERC-83/21 "Mechanical Characteristics of Materials Used in a 1/5 Scale Model of a 7-Story Reinforced Concrete Test Struc ture," by Bertero, V.V., Aktan, A.E., Harris, H.G. and Chowdhury, A.A., Odober 1983, (pB84 193 697)A05. UCB/EERC-83/22 "Hybrid Modelling of Soil-Structure Interaction in Layered Media," by Twng, T.-J. and Penzien, J., October 1983, (PB84 192 178)A08. UCB/EERC-83/23 "Local Bond Stress-Slip Relationships of Deformed Bars under Generalized Excitations," by Eligehausen, R., Popov, B.P. and Bertero, V.V., October 191n, (PR84 192 848)A09. U CB/EERC-83/24 "Design Considerations for Shear Lmks in Eccentrically Braced Frames," by Malley, J.O. and Popov, E.P., November 1983, (PB84 ]92 186)A07.

UCB/EERC-84/0 I "Pseudodynamic Test Method for Seismic Performance Evaluation: Theory and Implementation," by Shing, P.-S. B. and Mahin, S.A., January 1984, (PBK4 190 644)A08. U CB/EERC-84/02 "Dynamic Response Behavior of Kiang Hong Dian Dam," by Clough, R.W., Chang, K.-T., Chen, H.-Q. and Stephen, R.M., April 1984, (PB84 209 402)A08. UCB/EERC-84/0~ "Refined Modelling of Reinforced Concrete Columns for Seismic Analysis," by Kaba, S.A. and Mahin, S.A., April 1984, (PB84 234 384)A06. U CB/EERC-84/04 "A New Floor Response Spe<:trum Method for S~ismic Analysis of Multiply Supported Secondary Systems," by Asfura, A. and Der Kiureghian, A., June 1984, (Pll84 239 417)A06. UCB/EERC-84/0S "Earthquake Simulation Tests and Associated Studies of a 1/5th-scale Model of a 7-Story R/C Frame-Wall Test Structure," by Bertero, V.V., Aktan, A.E., Charney, F.A. and Sause, R., June 1984, (PB84 239 409)A09. U CB/EERC-84/06 "R/C Structural Walls: Seismic Design for Shear," hy Aktan, A.E. and Bertero, V.V., 1984. U CB/EERC-84/07 "Behavior of Interior and Exterior f'lat-Plate Conuections subjected to Inelastic Load Reversals," by Zee, ILL. and Moehle, J.P., August 1984, (PB86 117 629/ASjA07. UCB/EERC-84/08 "Experimental Study of the Scismic Behavior of a Two-Story Flat-Plate Structure. ," by Moehle, J.P. and Diebold, 1.W., August IY84, (PB86 122 553/ASjAJ2. U CB/EERC-84/09 "Phenomenological Modeling of Sleel Braces under Cyclic Loading," by Ikeda, K., Mahin, S.A. and Dermitzakis, S.N., May IY84, (PB86 132 198/AS)A08. U CB/EERC-84/I0 "Earthquake Analysis and Response of Concrete Gravity Dams," by Fenves, G. and Chopra, A.K., August 1984, (PUSS 193 902/AS)AI J. UCB/EERC-84/11 "EAGD-84: A Computer Program for Earthquake Analysis of Concrete Gravity Dams," by Fenves, G. and Chopra, A.K., August 1984, (PB8S 1Y3 6] 3/AS)A05. U CB/EERC-84/12 "A Relined Physical Theory Model for Predicting the Seismic Behavior of Braced Steel Frames," by Ikeda, K. and Mahin, SA, July 1984, (PB8S 11)1 4S0/AS)A09. UCB/EERC-84/1 ~ "Earthquake Engineering Research at Berkeley - 1984," by, August 1984, (PB85 197 341/AS)AIO. UCB/EERC-i14/14 "Modu]i and Damping Factors for Dynamic Analyses of Cohesionless Soils," by Seed, H.B., Wong, R.T., Idriss, I.M. and Tokimatsu, K., September 1984, (pB85 191 4t.8/AS)A04. U CBtEERC-84/1 5 "The Influence of SPT Procedures in Soil Liquefaction Resistance Evaluations," by Seed, H.B., Tokimatsu, K., Harder, L.F. and Chung, R.M., October 1984, (PBSS [91 732/AS)A04. UCB/EERC-84/16 "Simplified Procedures for the Evaluation of SeUkments in Sands Due to Earthquake Shaking," by Tokimatsu, K. and Seed, H.B., October 1984, (PB85 197 887/AS)A03. UCB/EERC-84/17 "Evaluation of Energy Absorption Characteristics of Bridges under Seismic Conditions," by Imbsen, R.A. and Pen zien, J., November 1984, U CB/EERC-84/18 "Structure-Foundation Interactions under Dynamic Loads," by Liu, W.D. and Penzien, 1., November 1984, (PB87 124889/ASjAII. UCB/EERC-84/19 "Seismic Modelling of Deep Foundations," by Chen, C.-H. and Penzien, J., November 1984, (PB87 124 798/AS)A07. U CB/EERC-84/20 "Dynamic Response Behavior of Quan Shui Dam," by Clough, R.W., Chang, K.-T., Chen, H.-Q., Stephen, R.M., Ghanaat, Y. and Qi, J.·H., November 1984, (PB86 I 15 I77/AS)A07.

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U CB/EERC-85/0 I "Simplified Methods of Analysis for Earthquake Resistant Design of Buildings," by Cruz, E.F. and Chopra, A.K., February 1985, (PB86 112299/AS)A 12. UCB/EERC-85/02 "Estimation of Seismic Wave Coherency and Rupture Velocity using the SMART I Strong-Motion Array Record ings," by Abrahamson, N.A., March 1985, (PB86 214 343)A07. U CB/EERC-llS/03 "Dynamic Properties of a Thirty Story Condominium Tower Building," by Stephen, R.M., Wilson, E.L. and Stander, N., April 1985, (PB86 11896S/AS)A06. UCB/EERC-IIS/04 "Development of Substrueturing Techniques for On-Line Computer Controlled Seismic Performance Testing," by Dermitzakis, S. and Mahin, S., February 1985, (PB86 132941/AS)A08. UCB/EERC-85/05 "A Simple Model for Reinforcing Bar Anchorages under Cyclic Excitations:' by Filippou, F.C., March 1985, (PB86 112919/AS)A05. UCB/EERC-1l5/06 "Racking Behavior of Wood-framed Gypsum Panels under Dynamic Load:' by Oliva, M.G., June 1985. U CB/EERC-85/07 "Earthquake Analysis and Response of Concrete Arch Dams," by Fok, K.-L. and Chupra, A.K., June 1985, (PB86 139672/AS)AIO. U CB/EERC-IIS/01l "Ellect of Inelastic Behavior on the Analysis and Design of Earthquake Resistant Structures," by Lin, J.P. and Mahin, S.A., June 1985, (PB86 135340/AS}A08. U CB/EER C-S5/09 "E

UCBtEERC-1I6/01 "A Study of Seismically Resistant Eccentrically Braced Steel Frame Systems," by Kasai, K. and Popov, E.P., January )<)86, (PBS7 124 178/AS)AI4. U CB/EERC-1I0/02 "Design Problems in Soil Liquefaction," by Seed, H.B., l'ebruary 1986, (PBS7 124 186/AS)A03. UCB/EERC-86/03 "Implications of Recent Earthquakes and Research on Earthquake-Resistant Design and Construction of Buildings," by Rertero, V.V., March 1986, (PB87 124 194/AS)A05. UCB/EER C-86/04 "The Use of Load Dependent Vectors for Dynamic and Earthquake Analyses:' by Leger, P., Wilson, E.L. and Clough, R.W., March 1986, (PB87 124 202/AS)AIl. UCB/EERC-1l6/0S "Two Beam-To-Column Web Cunnedions," by Tsai, K.-C. and Popov, E.P., April 1986, (PB87 124 301/AS)A04. UCB/EERC-86/06 "Determination of Penetration Resistance for Cuarse-Grained Soils using the Becker Hammer Drill," by Harder, L.r. and Seed, H.B., May 19110, (PHII7 124 21O/AS)A07. UCB/EERC-86/07 "A Mathematical Model for Prediding the Nonlinear Response of Unrein forced Masonry Walls to In-Plane Earth quake Excitations:' by Mengi, Y. and McNiven, H.D., May 1986, (PB87 124 780/AS)A06. UCB/EERC-86/08 "The 19 September 1985 Mexico Earthquake: Building Behavior:' by Bertero, V.V., July 1986. UCB/EERC-86/09 "EACD-3D: A Computer Program for Three-Dimensional Earthquake Analysis of Concrete Dams," by Fok, K.-L., Hall, J.F. and Chopra, A.K., July IY1I6, (PB87 124 228/AS)A08. UCB/EERC-86/10 "Earthquake Simulation Tests and Associated Studies of a 0.3-Scale Model of a Six-Story Concentrically Braced Steel Structure:' by U ang, C.-M. and Hertero, V.V., December 1986, (PBS7 I 63564/AS)A17. UCB/EERC-lIo/l1 "Mechanical Characteristics of Base Isolalion Bearings for a Bridge Deck Model Test," by Kelly, J.M., Buckle, I.G. and Koh, C.-G., 1987. UCB/EERC-86/12 "Modelling of Dynamic Response of Elastomeric Isolation Bearings:' by Koh, C.-G. and Kelly, J.M., 1987.

U CB/EERC-1I7/0 1 "The FPS Earlhquake Resisting System: Experimental Report," by Zayas, V.A., Low, S.S. and Mahin, S.A., June 1'J87. UCB/EERC-1I7/02 "Earthqu ake Sim ulator Tests and Associated Stud ies of a 0.3-Scale Model of a Six-Story Eccentrically Braced Steel Structure," by Whittaker, A" Uang, C.M. and Benero, V,V., July 1987.

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UCB/EERC-87/03 "A Displacement Control and Uplift Restraint Device for Base-Isolated Structures," by Kelly, J.M., Griffith, M.C. and Aiken, LG., April 1987. UCB/EERC-87/04 "Earthquake Simulator Testing of a Combined Sliding Bearing and Rubber Bearing Isolation System," by Kelly, 1.M. and Chalhoub, M.S., 1987. UCB/EERC-l;7f05 "Three-Dimensional Inelastic Analysis of Reinforced Concrete Frame-Wall Structures," by Moazzami, S. and Ber tero, V.V., May 1987. U CB/EERC-87/06 "Experiments on Eccentrically Braced Frames With Composite Floors," by Rieles, 1. and Popov, E., June 1987. U CBIEERC-87/07 "Dynamic Analysis of Seism ically Resistant Eccenlrically Braced Frames," by Rieles, 1. and Popov, E., June 1987. U CB/EERC-87/08 "U ndrained Cyclic Triaxial Testing of Gravels - The Effect of Membrane Compliance, " by Evans, M.D. and Seed, H.B.. July 1987. U CB/EERC-87/09 "Hybrid Solution Techniques For Generalized Pseudo-Dynamic Testing," by Thewalt, C. and Mahin, S. A., July 1987. UCB/EERC-87/10 "Investigation of Ultimate Behavior of AISC Group 4 and 5 Heavy Steel Rolled-Section Splices with Full and Par tial Penetration BUll Welds," by Bruneau, M. and Mahin, S.A., July 1987. UCB/EERC-87/11 "Residual Strength of Sand From Dam Failures in the Chilean Earthquake of March 3, 1985," by De Alba, P., Seed, H. B., Retamal, E. and Seed, R. B., September 1987. UCB/EERC-87/12 "Inelastic Response of Structures With Mass And/Or Stiffness Eccentricities In Plan Subjected to Earthquake Excita tion," by Bruneau, M., September 1987. UCB/EERC-87/13 "CSTRUCT: An Interactive Computer Environment For the Design and Analysis of Earthquake Resislant Steel Structures," by Austin, M.A., Mahin. S.A. and Pister, K.S., September 1987. VCB/EERC-87/14 "Experimental Study of Reinforced Concrete ColuJllns Subjected to Multi-Axial Loading," by Low, S.S. and Moehle, 1.1'., September 1987. UCB/EERC-87/15 "Relationships Between Soil Conditions and Earth'plake Ground Motions in Mexico City in the Earthquake of Sept. /9, 1985," by Seed, H.B., Romo, M.P., Sun, J., and Jaime, A., October 1987.