Geotechnical Earthquake Hazards of the Umbria and Marche Regions (Italy)

Geotechnical earthquake hazards of the Umbria and Marche regions (Italy)

M. Maugeri, P. Capilleri &M. R, Massimo Department of Civil and Environmental Engineering, Universip of Catania, Italy

Abstract

The seismic sequence which occurred in the 1997-1998 Umbria and Marche Regions (Central Italy), though characterised by quite moderate magnitudes, caused significant damage to buildings and the failure of many slopes. Such an event gave once more evidence of the need to zone all the seismic areas in relation to the seismic site amplification, landslide and liquefaction phenomena. As far as the 1997-1998 earthquake sequence is concerned, an explanation of extensive darnage occurring in spite of moderate magnitude seismic events can be detached in terms of geotechnical characteristics of the soil involved. The high vulnerability o~many masonry buildings and the cumulative effect due to the long earthquake repetition also play an important role. The aim of this work is the evaluation of site-dependent response spectra in terms of acceleration, velocity and displacement by means of the analysis of about 150 accelerometric records. The site dependent response spectra, are than compared with those provided by the new draft version of EC8 (2000), which considers se$en subsoil classes instead of three classes as the older one (EC8 1994).

1 Introduction

The Umbria-Marche earthquake sequence started on 26 September 1997 with a shock of ML equal to 5.5 and it was followed by a stronger earthquake characterised by ML 5.8, which occurred 9 hours later. The last significant shocks took place in October with magnitude ranging between ML=5 and ML=6 (Marcellini et al., 2001). In spite of the moderate magnitude values achieved, the two shocks caused significant damage to building , Moreover, the damage was also caused by site amplification, as shown by accelerometer time histories © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

586 RiskAnal~sisIII

Figure 1: Location of the accelerometric station recorded in different types of soil (Capilleri et. al., 2001, Carrubba &Maugeri 2001). The dynamic sequence occurred in the Regions of Umbria and Marche were recorded by more than 30 stations (Fig. 1) of the Servizio Sismico Nazionale (S.S.N., 1999) located in this area. The akailable records regarding this earthquake sequence are subdivided in four different groups, according to subsoil class given by EC8 (2000). Thus, the acceleration records are grouped according to the local soil conditions summarised in tables 1,2,3 and 4. The site-dependent response spectra in terms of acceleration are obtained by means of the analysis of about 150 accelerometric records, The result obtained are normalised with respect to the peak ground acceleration recorded in situ and then compared with the response spectra given by the new version of EC8 (2000). Site- dependent response spectra in terms of velocity and displacement an evaluated. This work is the prosecution of a similar work perfomed considering the previous version of EC8 (EC8 1994), which considered only three soil classes ( Carrubba & Maugeri, 2001).

2 The Eurocode 8 prescription about response elastic spectra

The European Standard Code EC8 (2000) deals with the design and the construction of buildings and civil engineering works in seismic regions. © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

RiskAnalysisIII 587 Table 1: Registration on Soil A

I I

I Digitale I ASSISI STALLONE 03/09/1997 220731 0,01 0,04 56,32 1 Digitale I ASS 1S1 STALLONE 07/09/1997 232807 0,02 0,01 43,52 10/09/1997 6,46,58 0,00 0,00 24,32 iN 1 26/09/1997 0,33,24 0,03 0,03 9,34 2610911997 0,33,25 0,03 0,03 28,67 ELUCO 2610911997 0.33.23 0,05 0,04 28,09 BBIO (PIANA) 26/09/1997 0.33,10 0,03 0,03 75,51 Digitale I ASSISI STALLONE 26109/1997 0,33,44 0,16 0,11 25,6 Analogico MONTE FIEG ;N1 26/09/1997 9,40,38 0,03 0,03 28,75 AnaIogico CASCIA 26 f0911997 9.40.36 0$02 0,02 29,05 Analogico GUBBIO 26/09/1997 9.40,40 0,09 0,07 28,95 Digitale GUEBBIO (PIANA) 26/09/1997 9.40,22 0,10 0,09 106,2 Analogico PIETRALUNC2A 26/09/1997 9.40,58 0,07 0,04 28,55 Analogico CAGLI 2610911997 9.40,46 0,02 0,02 25,44 Digitale ASSISI STALLCONE 2610911997 9.40,58 0,12 0,19 29,44 Analogico GUBBIO O6I1OI1997 23.25.09 0,04 0,03 33,01 Analogico MONTE FIEGiNI ! 06/10/1997 I 23.2 5.05 0,02 0,01 18,78 An,lnm;,-o PAS------CIA I 06/10/1997 I 23.25,08 0,02 0,02 21,75 Digitale GUPBBIO (PIANA) 06/10/1997 2324.52 0,06 0,07 72,95 Digitale ASSISI STALLONE J 06/10/1997 I 23,25,20 0,19 0,10 34,56 Digitale GUBBIO (PIAhYA) I 14/10/1997 ] 15.2 3,19 0,01 0,02 72,95 Analogico NORCIA I 14I1OI1997 I 15.23,17 0,14 0,10 39,13 Analogico SPOLIITO MONTEBLUCO ] 114I1OII997 15.23,18 0,05 0,03 39,33 I Analogico CASCIA 14I1OII997 15.23,18 0,06 0,05 35399 Analogico MONTE FIEGiN 1 14/lo/1997 15,23,22 0,02 0,o1 28,05 Digitale ASSISI STALLCONE 14/10/1997 15,23,43 0,03 0,01 32 Digitale ANNIFO 14/10/1997 15,23,03 0,07 0,06 38 I Digitale I CESI MONTE 14/10/1997 15,23,01 0,1o 0,18 36

Table 2: Registration on Soil B I .$.’ X.*.. 8....<+, .;:~,.:...... $ :y *;+;$ .*.:.::.%&.,.$K~. ..\.\. w.. ..,;,..$$!:..%:.:+$~.. ,,,..,. + ‘ye.*y.:~~*“ ‘:$g~$)$~:f.;p:$~fy:$ .w.i.:::>,. .,\ ~‘+ : ‘+ ,:;: . * ~ ~ .-z W $ ~ Instrumentation type Locality Date d t(s) -j R g $ 4 Arralogico NOCERA UMBRA 03/09/1997 220731 0,16 0,31 26,99 Analogico NOCERA UMBRA 07/09/1997 232807 0,07 0,06 22,93 .halogico NOCERA UMBRA 26/09/1997 0.33.13 0,28 0,61 28,88 Analogico FORCA CANAPINE 26/09/1997 0.33,28 0,07 0,07 28,19 halogico NOCERA UMBRA 26/09/1997 9.40.30 0,51 0,56 41,33 halogico FORCA CANAPINE 26109/1997 9.40.53 0,03 0,03 28,51 Analogico PEGLIO 26109/1997 9.40.54 0,07 0,06 29,74 Armlogico PENNABILLI 26/0911997 9.41.02 0,02 0,02 28,93 halogico NOCERA UMBRA 06/10/1997 23.24,57 0,31 0,53 37,2 Analogico FORCA CANAPINE 06/10/1997 23.25.08 0,04 0,04 19,21 Digitale NOCERA UMBRA 2 06/10/1997 23.24.53 0,26 0,43 28,99 Analogico NOCERA UMBRA I4I1OI1997 15.23.20 0,14 0,13 32,79 Analogico FORCA CANAPINE 14/10/1997 15.23.22 0,07 0,08 28,4 Digitale NOCERA UMBRA 2 14/10/1997 15.23.16 0,11 0,11 25,99 © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

588 Risk Analysis III Table 3: Registration on Soil C

1 997 I 0.33.17 0,06 0,04 46,33 ,24 0,05 0,05 28,5 26/09/1997 9,40,33 0,08 0,08 50,51 Analogico MATELICA 26/09/1 997 9,40.34 0,11 0,12 29,04 Analogico SENIGALLIA 26/09/1 997 9.40.57 0,04 0,05 27,01 Analogico BEVAGNA 06/1 0/1 997 23.25.01 0,05 0,04 28,94 Analogico NORCIA I 06/1 0/1 997 I 23,225.06 0,02 0,03 28,01 t Analogico MATELICA I 14/10/1997 I 15,23,26 I 0~32 0,03 27,33 Analo gico I BEVAGNA I 14/10/1997 I 15.23,20 I 0,04 0,05 4037,

Table 4: Registration on Soil D

L Analogico COLFIORITO 03/09/1997 220731 0,07 0,12 12,99 Analogico COLFIORITO 07/09/1997 232807 0,07 0,07 24347 Andogico COLFIORITO 10/09/1997 6.46.58 0>03 0,05 8,75 halogico COLFIORITO 26109/1997 0,33.16 0,47 0,35 44,44 Analogico CASTELNLIOVO (ASSISI) 2610911997 0.33.18 0,07 0,10 47,18 Analogico LEONESSA 26/09/1997 0.33.25 0,03 0,03 28,75 1 Digitale I BORGOOTTOMILA 26/0911997 0.33.19 0,01 0,01 78,07 I Analogico COLFIORITO 2610911997 9.40.30 0,32 * Analogico CASTELNUOVO (ASSISI) 26/09/1997 9,40).31 0,11 0,17 55,32 Analogico LEONESSA 2610911997 9.40.40 0,02 ~ Digitale BORGO OTTOMILA 26/09/1997 9.41.36 0,01 0,01 78,07 Analogico COLFIORITO 06/10/1997 23.24.56 0,11 0,14 28,25 Analogico N. UMBRA (SALMATA) 06/10/1997 23.24.57 0,19 0,15 37,35 Analogico CASTELNUOVO (ASSISI) 06/10/1997 23,24,59 0,08 0,11 28,78 Aclalogico LEONESSA 06/10/1997 23.25.20 0,02 0,03 28,92 Digitale N.UMBRA(BISCONTTM) 06/10/1997 23.24.53 0,38 0,27 25,59 Analogico LEONESSA 14/10/1997 15.23.31 0,05 0,04 28,92 Analogico N, UMBRA (SALMATA) 14/10/1997 15,23,22 0,03 0,02 29,85 Andogico CASTELNUOVO (ASSISI) 14/10/1997 15.23.23 0,03 0,06 29,76 Analogico COLFIORITO 14/10/1997 15.23.16 0,07 0,09 41,87 Digitale N UMBRA(BCSCONTN) 14/10/1997 15,23.16 0,06 0,04 21,75 Digitale BORGOOITOMILA 14/10/1997 15,23,01 0,01 0,01 97,27 © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

Risk Analysis III 589 Table 5: Soil stratigrafic profile given by EC8 (2000) and EC8 (1994)

IA1 RmkmcUwmck.like @c#c4 Gnmltcm irdi+a MM 5 mofwakamluid a! ,FE,wk I*

-. —.. I I

I % C.=PU! dlwdatk d),, dm>dwdqa mmycdwio,l POla ID, UXILLMM d= A.EmS,

The European Code EC8 provides normalised elastic response spectra, according to specific soil conditions. The old version of EC8 (1994) distinguishes three different spectra in order take into account different soil conditions, A,recent draft version of EC8 (2000) introduces significant changes in the subsoil classification for the deftition of the design earthquake. Subsoils are grouped into seven different classes (A, B, C, D, E, S1and S2), In Table 5 the description of stratigraphic profiles for the different subsoil classes given by the EC8 (2000) draft and by the old version of EC8 ( 1994) is reported. The equations that define the elastic response spectrum S,(T) reported in EC8 (2000), are listed below: r 1 ‘e(T)=ags11+:(254‘1) TB

-- (3)

59(I Risk Analysis III where:

Se(T) is the ordinate of the elastic response spectrum, T is the fundamental vibration period of a linear single degree of freedom system; s is the soil parameter % is the design ground acceleration for the reference return period; T~Tc are the initial and final abscissas of limits of the spectrum plateau; T~ is the value defining the beginning of the constant displacement response range of the spectrum, ?l is the, damping correction factor with reference value q = 1 fox 5% viscous damping:

~= 10 >0,55 (5) U5+; )

The values of S, T~, Tc and T~ reported in EC8 (2000) in relation to the subsoil classes are summarised in table 6, The elastic displacement response spectrum SD, (T), can be obtained by direct transformation of the elastic response spectrum S,(T), using the following expression:

2 sDe(T) = se(T H; (6) For vibration periods greater than T~, (Tab,6) the ordinates of the elastic displacement response spectrum are obtained according to the following relationships: rf \ 7 TE

SDe(T) = dg = (),Osa#TCTD (8)

The values periods TE and TF which define the shape of the displacement spectra (EC8 2000) are listed in table 6.

3 Analysis

The accelerometric records of the 1997-1998 Umbria–Marhe seismic sequence given by the Servizio Sismico Nazionale (S.S,N., 1999) are fustly grouped on the base of the geological features of the recording site, following the guidelines of EC8 (2000), so the subsoil classes A, B, C and D mentioned in EC8 are considered. The main features of these records are summarised in tables 1,2,3 and © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

Risk Analysis III 591 Table 6: Parameter describing the elastic response spectra given by EC8 (2000)

4 for the different subsoil classes A, B, C and D. No subsoil class E, S1 and Sz (EC 8, 2000) conditions are found on the investigated sites, The selected time-histories are analysed to obtain the elastic response spectra for each subsoil classes in terms of acceleration velocity and displacement. The acceleration spectra are normalised dividing the ordinate values by the maximum ground acceleration achieved in the corresponding records, in order to homogenise all the results. Of example fig.2 shows the all considered normalised elastic response spectra in terms of acceleration for subsoil class A (tab. 1), For each subsoil class the mean spectrum is evaluated by means of the statistical analysis of the normalised ones. Figure 3 shows the normalised average elastic response spectra in terms of acceleration for subsoil class A, considering the damping ratios equal to 2°/0, 5% and 10O/O. Figure 4 shows the comparison between the normalised elastic average response spectra of subsoil classes A, B, C and D for fixed damping ratio 5°/0.

I I

O,cm 0,50 1,C.3 1,50 2,C0 2,50 3,CQ

T[s] Figure 2: All normalised response spectra for subsoil class A © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

592 Risk Analysis III ,,,, ~_.._ —— ..—._—— —— ‘-”-l

4,50 Average Spectra for ~ = 29’o 4,00 * !1 + 3,50 Ill \ / Average Spectra for ~ =5% ~ 3,00 N

3 + 2,50 IT a _ ~_ Average Spectra for ~ = 10% * 2,00 fl.

1,50

1,00

0,50

0,004 I 0,00 0,50 1,00 1,50 2,00 2,50 3,00 T [s] Figure 3:Norrnalised average elastic response spectra in terms of acceleration fo~ subsoil class A, considering the damping ratios of 2°/0,5°/0and 10O/O.

Average Spectra Soil C m Average Spectra Soil D

,!:: 0,50- —

,’,::.:,:>!$,!$>!!,i!.,.l..:.:,:,,,,,,:,:,:,:,.

0,00 0,50 1,00 1,50 2,00 2,50 3,00 T[s]

Figure 4:Normalised average elastic response spectra in terms of acceleration for different subsoil class considering the damping ratio of 5Y0. © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

Risk Analysis III s%

h, — Sml B EC8(1994) WI , J It&-x I

I a,cm 1 0,04 0,,0 w ,>0 ml 2>0 w

T l.) ,,03- ‘AVWW SW4NIII S.)1 C ,,,0. —s.{1 c BC8 (2DW)

l,m — soil c ec8 (1594) 1 \

2$0- I \ jzm.

,,50.

Qso -

3,m — Sal D EC8(20W)

—Sml CBC8( 1984)

1,54

O,ca O,m 0,% l,WJ l,EO 2,03 2,50 3,ca

T [s1

Figure 5: Comparison between normalised average elastic response spectra in terms of acceleration, for different subsoil class, considering the structural damping ratio of 5%, and the elastic response spectra given by EC8 (2000) © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

59zl Risk Analysis III

0’30r

0,25

0,20

0,15

0,10

0,05

0,00 0,00 0,50 1,00 1,50 2,00 2,50 3,00

T[s] Figure 6: Normalised average elastic response spectra in terms of velocity for different subsoil class considering the structural damping ratio of 59’.,

Some important differences can be observed not only in terms of maximum normalised spectral acceleration SalAmax, which varies fkom 2,5 for subsoil classes C and D to 3,3 for subsoil class A, but also in terms of critical period vdlues. For all the subsoil classes a critical period value of about 0,20 can be observed; nevertheless for subsoil class C also the critical period value of 0,55 s can be observed. The comparison between the evaluated response spectra in terms of acceleration and those given by the new and old EC8 (EC8 1994; 2000) for subsoils A and B, while they are considerably less severe than those given by EC8 (2000) and slightly more severe than those given by EC8 (1994) for subsoils C and D, Figure 6 show the normalised response spectra in terms of velocity for all the define subsoil classes. The most severe response in terms of velocity is reached for subsoil C for period less than about 1 sec and for subsoil D for period greater than about 1sec. Finally, the comparison between the evaluated normalised response spectra in terms of displacement and those given by EC8 (2000)is show in fig.7, The evaluated displacement response spectra are generally less severe than those given by EC8 (2000), a part from for the cases of subsoils A, B and C for period greater of about 2.5 sec. © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

RiskAnalysis111 595

0,08- ~~~ . . . . — EnsPlamna %!1 A

0,07- — %,1 A EC8 (21XJO) — %1 B EC8 (20W j n ,,.

lx--’- 1

0,0 0,5 1,0 1,5 2,0 2,5 3,0 T [S]

0,, , -—- -—... -..-... —--. — .. —.--—- ..-.. —.- ..-.-... . --—- ‘DisPlmemenl S.!1 B

‘EC8 (2000 )SO, ] B 0,,0, —EC8 (2000 )s.$1 c

0,0, //

0,0, 0,0, ,,,0 ),00 ,,,0 ,,,, ,,50 3,,0 T 1.1 ,,!2, -- . . . . . ‘D, @.canwn, Sol C

0,)0

I 0,08,

0,06-

O,M

0,02-

0,00

0,00 0,50 1,00 1,50 2,00 2,50 3,00

T [s] Figure 7: Comparison between normalised average elastic response spectra in terms of displacement, for different subsoil class, considering the structural damping ratio of 5%, and the elastic response spectra given by EC8 (2000) © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Risk Analysis III, CA Brebbia (Editor). ISBN 1-85312-915-1

596 Risk Analysis III

4 Conclusion

Many horizontal acceleration records were collected during the recent Italian Umbro-Marche earthquake, happened in the September –October 1997. Site conditions are known in detail for all the recording station sites, so allowing a classification of the records into four groups (Soil A, Soil B, Soil C and Soil D), Elastic response spectra in terms of acceleration, velocity and displacement are evaluated for each subsoil class and different damping ratio. The comparison of the results with the EC8 (2000) and EC8 (1994) has shows that the Umbro-Marche earthquake sequence gives (Fig.6) elastic acceleration spectra for soils A and B which are slightly more severe than those given by EC8 (1994; 2000). The elastic acceleration response spectra for soil C and D are considerably less severe than those given by EC8 (2000), but slightly more severe than those given by the old EC8 (1994). Finally as far as the response spectra in terms of displacement are concerned, the evaluated ones generally less severe than those given by EC8 (2000), a part from for the cases of subsoils A, B and C for period greater of about 2,5 see,

References

[1] Capilleri P,, Massimino M. R,, Maugeri M,. The ground motion grade-3 microzonation of Sellano, Italian Geotechnical Journal, Italian Geotechnical Journal XXXV, n.4 -October-December 2001, pp.97-l 11.

[2] Carrubba P., & Maugeri. M.,(2001) Site dependent spectra for the Umbro- Marchigiano Earthquake (Italy) of September –October 1997, Fourth International Conference on recent Advances in Geotechnical Earthquake Engineering, San Diego, California, March 26-31,2001.

[3] Eurocode 8, (1994), Design of structures for earthquake resistance, Official version the Italian language of the experimental European Code ENV 1998-1- 2, October 1994.

[4] Eurocode 8, (drafl 2000), Design of structures for earthquake resistance, ?fficial version the English language of the experimental European Code ENV ENV 1998-1-2, May 2000.

[5] Marcellini A., Daminelli R., Tento A., Franceschina G.,Pagani M., “The Umbria- Marche Microzonation Project: outline of the project and the example of Fabriano result”, Italian Geotechnical Journal XXXV, n.2 –April -June 2001, pp.28-35.

[6] S.S.N, (1999), Registrazioni accelerometriche del terremoto Umbro- Marchigiano del Settembre-Ottobre 1997, Servizio Sismico Nazionale, Roma, (Italy),