U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY

BOREHOLE VELOCITY MEASUREMENTS AT FIVE SITES THAT RECORDED THE CAPE MENDOCINO, CALIFORNIA EARTHQUAKE OF 25 APRIL, 1992

by

James F. Gibbs1, John C. Tinsley1, and David M. Boore1

S Velocity (m/sec) 0 500 1000 1500 0

20

40 CRW

(m) RIO FFS

Depth 60

80 RVM

LFS

100

U.S. Geological Survey Open-File Report OF 02 -203

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

1Menlo Park, CA 94025 U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY

BOREHOLE VELOCITY MEASUREMENTS AT FIVE SITES THAT RECORDED THE CAPE MENDOCINO, CALIFORNIA EARTHQUAKE OF 25 APRIL, 1992

by

James F. Gibbs1, John C. Tinsley1, and David M. Boore1

U.S. Geological Survey Open-File Report OF 02 -203

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

1Menlo Park, CA 94025 TABLE OF CONTENTS Page Introduction...... 1 P - and S-WaveTravel-TimeData...... 1 RegionalMap...... 2 Summary Velocity Profiles ...... 6 Acknowledgments...... 8 References...... 8 Appendix A–Detailed Results: College of the Redwoods ...... 9 Fortuna Fire Station ...... 16 Loleta Fire Station ...... 23 Redwood Village Mall ...... 30 RioDell...... 37 Appendix B–Poisson’s Ratios: College of the Redwoods ...... 44 Fortuna Fire Station ...... 45 Loleta Fire Station ...... 46 Redwood Village Mall ...... 47 RioDell...... 48

i BOREHOLE VELOCITY MEASUREMENTS AT FIVE SITES THAT RECORDED THE CAPE MENDOCINO, CALIFORNIA EARTHQUAKE OF 25 APRIL, 1992 by James F. Gibbs, John C. Tinsley, and David M. Boore INTRODUCTION The U.S. Geological Survey (USGS), as part of an ongoing program to aquire seismic velocity and geologic data at locations that recorded strong-ground motion during earthquakes, has investigated five sites in the Fortuna, California region (Figure 1). We selected drill sites at strong-motion stations that recorded high accelerations (Table 1) from the Cape Mendocino earthquake (M 7.0) of 25 April 1992 (Oppenheimer et al., 1993). The boreholes were drilled to a nominal depth of 95 meters (310 ft.) and cased with schedule 80 pvc-casing grouted in place at each location. S-wave and P-wave data were acquired at each site using a surface source and a borehole three-component geophone. This report contains the velocity models interpreted from the borehole data and gives reference to locations and peak accelerations at the selected strong-motion stations.

P - AND S-WAVE TRAVEL-TIME DATA Shear waves were generated at the ground surface by an air-powered horizontal ram (Liu et al., 1988) striking an anvil at either end of an aluminum channel 2.3 m long. The ram was driven first in one direction and then in the other to generate pulses of opposite polarity. A switch attached to the shear source triggered the recorder and established the reference for the timing of arrivals. P -waves were generated by striking a steel plate with a sledge hammer. The recorder was triggered by a switch attached to the handle of the sledge hammer. P - and S-wave sources were offset from the borehole (same horizontal distance but different locations) to minimize the effect of waves traveling down the grout surrounding the casing. The source offset was 4 meters except at Rio Dell where available space limited the offset to 3.5 meters. These offsets are shown in the data tables. Downhole measurements were made at 2.5 m intervals (starting at 2 meters depth) with a three-component geophone clamped to the casing by an electrically-activated lever arm. A second three-component geophone was placed on the surface 5 to 10 m from the shear source for recording an on-scale reference trace (useful for amplitude studies and timing verification). The data were recorded on diskettes using a 12-channel recording system.

VELOCITY PROFILES The procedure for determining velocities is summarized in Figure 2. Because the orientation of the downhole geophone could not be controlled when moving from one depth to the next, the azimuth of the horizontal geophones relative to the source was unknown and changed with depth. To minimize the effects of those changes, the horizontal components were rotated to the direction that maximized the integral square amplitude within a time interval containing the shear wave (Boatwright et al., 1986). P - and S-wave first-arrival times were determined from the time series displayed at each depth on a 20-inch computer screen. The P -wave arrival-time was obtained from the vertical trace, and the S-wave

1 CRW Pacific Ocean 40o40’ LFS

RVM FFS Ferndale

40o30’ RIO

(degrees) Projection of rupture surface

Eel River Latitude

Petrolia 40o20’ 0 10 km

-124o20’ -124o10’ -124o Longitude (degrees)

Figure 1. Regional map showing the locations of boreholes (triangles) included in this report. LFS and RIO are in the towns of Loleta and Rio Dell, respectively, and RVM and FFS are in the town of Fortuna. Locations of river and coastline are approximate. The projection of the fault rupture for the 1992 Cape Mendocino mainshock (shaded) corresponds to model B of Murray et al. (1996).

2 Table 1. Site names, station codes, coordinates using North American Datum of 1927 (NAD27) and 1983 (NAD83), and peak horizontal accelerations.

Station Name StaCode Lat:NAD27 Long:NAD27 Lat:NAD83 Long:NAD83 pga (cm/s2) College of the Redwoods CRW 40.69913 -124.20045 40.69898 -124.20162 171 Fortuna Fire Station FFS 40.58969 -124.14630 40.58954 -124.14746 349 Loleta Fire Station LFS 40.64438 -124.21976 40.64423 -124.22093 252 Redwood Village Mall (Fortuna) RVM 40.58472 -124.14538 40.58457 -124.14654 114 Rio Dell RIO 40.50334 -124.09913 40.50320 -124.10029 539

3 Figure 2. Flow-chart outlining the data processing and steps in the interpretation.

4 arrival-times were obtained from the average of the rotated horizontal traces for ram strikes in opposite directions. The arrivals were timed to the nearest millisecond, probably a realistic precision for clear arrivals uncontaminated by noise. A trial set of layer boundaries was chosen for the S-wave model, based on the lithologic descriptions and geophysical logs. The travel-time data were fit in a least-squares sense by a model made up of constant velocity layers, taking into account refraction across the interfaces between layers. The travel times were weighted by the inverse of an assigned normalized variance. A normalized standard deviation of 1 was assigned to the clear arrivals and values up to 5 were assigned to the others. The residuals were examined, and layer boundaries were added, if necessary, to reduce large residuals or to remove systematic trends in the residuals. This was an iterative process conducted by the team of authors of this report. The process continued until the team was satisfied that the interfaces were consistent with the borehole seismic data as well as available geological and geophysical logs. The P -wave travel time data were analyzed initially with the set of layer boundaries finally determined for the S-wave data. Layer boundaries were then added if needed to fit the data and deleted if not needed. Commonly, an additional layer boundary corresponding to the top of the zone of water saturation was needed to fit the P -wave data. Some of the dynamic Poisson’s ratios σ, calculated with initial velocity models, resulted in ratios that were out of the accepted range of values (0.0–0.5). To obtain a value in the acceptable range we made minor adjustments to the velocities using one or more of the following procedures: repicking shallow arrivals (usually P arrivals because small changes in P travel-times have greater effect on σ), adding a shallow layer, and/or adjusting layer thickness to ensure that Poisson’s ratio was in the range 0.0–0.5. In most cases the small changes were made in the P-wave velocities at shallow depths (for more details see, Gibbs et al., 2000). Overall, the changes in velocity required to produce acceptable values of σ were small and were only in a few layers. SUMMARY VELOCITY PROFILES Figures 3 and 4 show the S- and P -wave velocity profiles determined from the borehole measurements at the five sites. The velocity profiles are plotted at the same scale for ease of comparison. DESCRIPTION OF APPENDICES Appendix A contains for each site: a location map, S- and P -wave time-series records, a time-depth plot, velocity profiles with a generalized geologic log, and tables giving arrival times and velocity values. The upper and lower bounds on the velocity plots show approximate 68 percent confidence limits. The bounds are not symmetrical because they are based on the inverse velocities in the layers. Appendix B contains tables of P- and S-wave velocity models and the Poisson’s ratios obtained from those models.

5 S-WAVE 0

20 ) 40 CRW m ( RIO FFS h t p

e 60 D

80 RVM

LFS

100 0 500 1000 1500 Velocity (m/s)

Figure 3. S-wave velocity models from all five boreholes (see Figure 1, Table 1) shown on the same figure for comparison.

6 P-WAVE 0

FFS

20 RIO

LFS

) 40 m ( h t p

e 60 D

CRW RVM 80

100 0 500 1000 1500 2000 2500 3000 Velocity (m/s)

Figure 4. S-wave velocity models from all five boreholes (see Figure 1, Table 1) shown on the same figure for comparison.

7 ACKNOWLEDGMENTS We could not have completed these studies without the assistance of many individuals who helped us to gain access to the sites, assisted with utilities clearances and granted permission to conduct the studies. We thank Tom Fumal for his careful review of the manuscript.

REFERENCES

Boatwright, J., R. Porcella, T. Fumal, and H.-P. Liu (1986). Direct estimates of shear wave amplification from a borehole near Coalinga, California, Earthquake Notes 57, 8.

Gibbs, J.F., J.C. Tinsley, D.M. Boore, and W.B. Joyner (2000). Borehole velocity measurements and geological conditions at thirteen sites in the Los Angeles, California region, U.S. Geol. Surv. Open-File Rept. 00-470, 118p.

Liu, H.-P., R.E. Warrick, R.E. Westerlund, J.B. Fletcher, and G.L. Maxwell (1988). An air-powered impulsive shear-wave source with repeatable signals, Bull. Seism. Soc. Am. 78, 355–369.

Oppenheimer, D., G. Beroza, G. Carver, L. Dengler, J. Eaton, L. Gee, F. Gonzalez, A. Jayko, W. H. Li, M. Lisowski, M. Magee, G. Marshall, M. Murray, R. McPherson, B. Romanowicz, K. Satake, R. Simpson, P. Somerville, R. Stein, and D. Valentine (1993). The Cape Mendocino, California, earthquakes of April 1992: Subduction at the triple junction, Science 261, 433–438. Murray, M.H., G.A. Marshall, M. Lisowski, and R.S. Stein (1996). The 1992 M = 7 Cape Mendocino, California, earthquake: Coseismic deformation at the south end of the Cascadia megathrust, J. Geophys. Res. 101, 17,707–17,725.

8 APPENDIX—A Detailed Results Figure A-1. Site location map for the borehole at College of the Redwoods. The accelerograph is located approximately 30 meters from the borehole.

9 S-WAVE Time (sec) Time (sec) 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 50

5 55

10 60

15 65

) 20 70 m (

h 25 t 75 p

e 30

D 80 35 85 40 90 45 95 50 100 College of the Redwoods

G:\FORTUNA\REDWOODS\R11_45.GRAG:\FORTUNA\REDWOODS\R05_45.GRA G:\FORTUNA\REDWOODS\R05_90.GRAG:\FORTUNA\REDWOODS\R11_90.GRA G:\FORTUNA\REDWOODS\R11.DTG:\FORTUNA\REDWOODS\R05.DT G:\FORTUNA\REDWOODS\R05.DTG:\FORTUNA\REDWOODS\R11.DT Dec 28, 2001 12:23:0312:24:22 pm Dec 27, 2001 11:36:49 1:33:43 pm am

Figure A-2. Horizontal component record section (from impacts in opposite directions) superimposed for identification of S-wave onset. Approximate S-wave time picks are indicated by the hatch marks.

10 P-WAVE Time (sec) Time (sec) 0 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 0 50

5 55

10 60

15 65

) 20 70 m (

h 25 t 75 p

e 30

D 80 35 85 40 90 45 95 50 100 College of the Redwoods

G:\FORTUNA\REDWOODS\VERT\VERT_45.GRA G:\FORTUNA\REDWOODS\VERT\VERT_90.GRA G:\FORTUNA\REDWOODS\VERT\004.DT G:\FORTUNA\REDWOODS\VERT\004.DT Dec 3, 2001 3:33:07 pm Dec 3, 2001 3:34:55 pm

Figure A-3. Vertical component record section. Approximate P-wave arrivals are indicated by the dots.

11 Time (sec) 0 0.05 0.1 0.15 0.2 0.25 0.3 0

20 ) s

r 40 e t e m (

h P S t p

e 60 D

80

100 College of the Redwoods

Figure A-4. Time-depth graph of P-wave and S-wave picks. Line segments are straightline interpolations of model predictions at the observation depths. The times for zero depth, not shown, are given by the horizontal offset (hoffset) divided by the velocity in the uppermost layer (see accompanying tables of velocities for specific values).

12 College of the Redwoods (CRW1) S Velocity (m/sec) P Velocity (m/sec)

0 200 400 600 Age Lithology 0 500 1000 1500 2000 2500

0 Fill: Yellowish brown silt and clay; tr0. v.f. sand. 240 m/s Hookton Fm. of Ogle (1953). Chiefly dark 348 m/s 369 yellowish brown sand and gravelly sand, with 559 10 interbeds of gravel, sandy silt, and1 s0ilty clay. Franciscan source (greenstone, red chert). 281 20 20 Clayey interbeds below 55 ft are dark green- ish gray, sl. sticky, sl. plastic, non-carbonate. 48-120 ft: Very fine sand and silt with clayey silt 30 interbeds. Sands are non-sticky, n3o0n-plastic and moderately sorted. Clayey interbeds are sl. sticky, sl. plastic and sl. effervescent. Sand 40 % decreases below 105 ft. 110-12400 ft = poss. 0 0 trace of Little Salmon Fault? (LSF). 355 Pleistocene 516 120-130 ft: Mainly silty clay of uncertain facies 20 interbedded with brown and yellow sand beds.

50 Hookton Fm. (Ogle, 1953) 130-150 ft: Greenish gray 10GY4/510 clay & silty clay; 10 40 common black peat masses 135-140 ft. Probable 1 520 Humboldt Bay mud overthrust (?) by LSF.

13 150-180 ft: Silty clay containing sctd. bivalves, 60 60 389 20 wood, and masses of peat and re6ed0 fragments; foraminifers noted in tip of Pitcher barrel sample. 80

70 30 100 70 225-250 ft: Mainly fine silty sand interval, with few thin clayey silt and silty clay interbeds.

120 Depth (meters) 245-250 ft: Abundant peat, marsh plant remains. 80 40 80 463 140 Possible low-stand deposit? 250-312 ft: Stiff to v. stiff silty clay and clayey silt. Sticky, plastic, sl. effervescent as disseminated

Depth (meters) 160 90 50 carbonate. Bivalves and oyster fra9g0ments in return. 513 Common peat masses noted in return. 180 13 100 60 200 100

220 deposits Humboldt Bay

70 Pleistocene and Holocene 240

260 80 280

90 300

320

Total drilled depth = 312 ft 100

M--Depth--Ft

Figure A-5. S- and P-wave velocity profiles with dashed lines representing one standard deviation. 14 15 Figure A-6. Site location map for the borehole at Fortuna Fire Station. The accelerograph is located approximately 35 meters from the borehole.

16 S-WAVE Time (sec) Time (sec) 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 50

5 55

10 60

15 65

) 20 70 m (

h 25 t 75 p

e 30

D 80 35 85 40 90 45 95 50 100 Fortuna Fire Station

G:\FORTUNA\FFS2\R11_45.GRAG:\FORTUNA\FFS2\R05_45.GRA G:\FORTUNA\FFS2\R05_90.GRAG:\FORTUNA\FFS2\R11_90.GRA G:\FORTUNA\FFS2\R11.DTG:\FORTUNA\FFS2\R05.DT G:\FORTUNA\FFS2\R05.DTG:\FORTUNA\FFS2\R11.DT NovDec 13,4, 2001 2001 8:55:58 10:13:08 am am DecNov 4,13, 2001 2001 8:54:26 10:13:08 am am

Figure A-7. Horizontal component record section (from impacts in opposite directions) superimposed for identification of S-wave onset. Approximate S-wave time picks are indicated by the hatch marks.

17 P-WAVE Time (sec) Time (sec) 0 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 0 50

5 55

10 60

15 65

) 20 70 m (

h 25 t 75 p

e 30

D 80 35 85 40 90 45 95 50 100 Fortuna Fire Station

G:\FORTUNA\FFS\VERT\FFSV_45.GRA G:\FORTUNA\FFS\VERT\FFSV_90.GRA G:\FORTUNA\FFS\VERT\FFS_V.DT G:\FORTUNA\FFS\VERT\FFS_V.DT Dec 4, 2001 8:59:28 am Dec 4, 2001 8:57:31 am

Figure A-8. Vertical component record section. Approximate P-wave arrivals are indicated by the dots.

18 Time (sec) 0 0.05 0.1 0.15 0.2 0

20 ) s

r 40 e t e m (

h P S t p

e 60 D

80

100 Fortuna Fire Station

Figure A-9. Time-depth graph of P-wave and S-wave picks. Line segments are straightline interpolations of model predictions at the observation depths. For the depth intervals 37–44.5 m and 72–87 m arrival times were difficult to pick and were downweighted in fitting the model. The times for zero depth, not shown, are given by the horizontal offset (hoffset) divided by the velocity in the uppermost layer (see accompanying tables of velocities for specific values).

19 Fortuna Fire Station S Velocity (m/sec) P Velocity (m/sec) 0 500 1000 Age Lithology 0 1000 2000 3000 0 0 0-17 ft: 5Y3/2 dk olive gray to10YR4/6 dk yellowish brown silt (ML) and lean silty clay (CL); sl. stiff; sl. s4ti2ck1y ,m /s sl. plastic, no CO 10 3; few org. smears, no pet1ro0l. odors. Holo.

Alluvium 17-46 ft: 10YR4/4 yellowish brown med-cse sand and gravelly sand; sl. dense, poor sorting, loose; takes fluid. 46-64 ft: 5G5/1 greenish gray sandy clay (CLS) and lean 20 silty clay (CL-ML); stiff, sticky, plastic, no C2O0 172 m/s 3 o r fossils . 2381 346 0 0 64-134 ft: 5Y5/4 olive to 2.5Y4/4 olive brown sand (SW) 30 and gravel (GW) w/ rare interbedded 3si0lt (ML) and clay. 20 V. dense, poorly sorted, mostly non-sticky. Franciscan 439 provenance indicated by greenstone, red chert, minor 40 10 serpentinite and graywacke; sorting im4p0roves in basal 40 10 ft of interval. 60 134-146 ft: 5GY4/1 dark greenish gray clayey silt and silt (ML); sticky, plastic, no CO 50 20 50 80

60 30 100 60 120 3 or fossils; UCS >4 T/sq.ft. 20 829 146-192 ft: %Y4/4 olive sand (SP) and gravelly sand 40 192-246 ft: N/4 to 5GY4/1 gray - dk. greenish lean gray 70 140 (SWG); quiet-drilling intervals are 3-6 inches thi7ck0 and silty calraey e aitnhde rc lsaaynedy osril ts; ilvty. sstaifnf,d s li.n stetircbkeyd, ss.l. plastic, no CO 160 50 80 80 180 epth (meters) Pleistocene Depth (meters) 60 200 D 90 90 220 3 or obvious fossils; USC >4.5 T/sq.ft. Scattered 20 70 Hookton Fm. (?) of Ogle (1953) bursts of wood and bark fragments; fines slake in water. 100 240 100

246-285 ft: 10YR4/3 brown coarse lithic sand and 730 260 285-316 ft: 5Y5/3 olive silt (ML) and lean silty clay (CL); 1749 80 gravelly sand and gravel with few silt interbeds (SW, dark siltstone chips and common wood fragments; GW); v. dense, poorly sorted, non-sticky, non-plastic, 280 fines are stiff, sl. sticky, sl. plastic, no CO no CO 90 300

3; Franciscan clast source. 100# pulldown @ 280 ft. 320

Total drilled depth = 316 ft 3 .

100

M--Depth--Ft

Figure A-10. S- and P-wave velocity profiles with lithology. Dashed lines represent plus and minus one standard deviation of velocities. 21 22 Figure A-1. Site location map for the borehole at Loleta Fire Station. The accelerograph is located approximately 15 meters from the borehole.

23 S-WAVE Time (sec) Time (sec) 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 50

5 55

10 60

15 65

) 20 70 m (

h 25 t 75 p

e 30

D 80 35 85 40 90 45 95 50 100 Loleta Fire Station

G:\FORTUNA\LOLETA\R11_45.GRAG:\FORTUNA\LOLETA\R05_45.GRA G:\FORTUNA\LOLETA\R05_90.GRAG:\FORTUNA\LOLETA\R11_90.GRA G:\FORTUNA\LOLETA\R11.DTG:\FORTUNA\LOLETA\R05.DT G:\FORTUNA\LOLETA\R05.DTG:\FORTUNA\LOLETA\R11.DT NovDec 8,4, 2001 8:44:539:29:48 am NovDec 8,4, 2001 8:44:539:24:24 am

Figure A-12. Horizontal component record section (from impacts in opposite directions) superimposed for identification of S-wave onset. Approximate S-wave time picks are indicated by the hatch marks.

24 P-WAVE Time (sec) Time (sec) 0 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 0 50

5 55

10 60

15 65

) 20 70 m (

h 25 t 75 p

e 30

D 80 35 85 40 90 45 95 50 100 Loleta Fire Station

G:\FORTUNA\LOLETA\VERT\004_45.GRA G:\FORTUNA\LOLETA\VERT\004_90.GRA G:\FORTUNA\LOLETA\VERT\004.DT G:\FORTUNA\LOLETA\VERT\004.DT Dec 4, 2001 9:33:13 am Nov 8, 2001 9:25:47 am

Figure A-13. Vertical component record section. Approximate P-wave arrivals are indicated by the dots.

25 Time (sec) 0 0.05 0.1 0.15 0.2 0.25 0

20 ) s r 40 P S e t e m ( h t p

e 60 D

80

100 Loleta Fire Station

Figure A-14. Time-depth graph of P-wave and S-wave picks. Line segments are straightline interpolations of model predictions at the observation depths. The times for zero depth, not shown, are given by the horizontal offset (hoffset) divided by the velocity in the uppermost layer (see accompanying tables of velocities for specific values).

26 Loleta Fire Station S Velocity (m/sec) P Velocity (m/sec)

Age Lithology 200 400 600 800 1000 0 500 1000 1500 2000 2500

0 0-22 ft: 10YR6/8 to10YR 5/8 brown-yellow0 to yell-brown silt, sandy silt, and silty clay; friable to sl. stiff; sl. stick4y1, s5l. m/s 532 10 plastic, no CO 3; few fine carb. roots and tubular pores. 10 708 20 22-38 ft: 10YR5/8 yellowish brown silty-clayey gravel to 2.5 in.; massive, sl. hard; many wx. ss, slts clasts. 38-60 ft: 5Y3/1 v. dark gray lean silty clay (CL); dense, 1262 30 sl. sticky, sl. plastic, no CO 20

40 3 . 60-80 ft: 2.5Y6/4 light yell. brn. gravel, sand, silt and clay; 0 0 fines upward in 5-ft-thick beds; sl. sticky, sl. plastic, non- 50 effervesc8e2n-t9; 5g rfat:v 5eYl b4e/1d sd a~r6k ignr.a tyh isciklt; aFnradn lceiasnc asni3l tsy0o cularcye (.CL-ML) 1029 20 w/ few silty sand (SM) interbeds; compact; few org. silt laminae. 0 60 10 40 95-132 ft: Alternating beds of dark green4is0h gray clayey 256 m/s silt, silty clay, and silty sand; stiff, sticky, plastic, no CO 20270 60 466 20 80 132-225 ft: Mainly lean silty clay (CL) interbedded5 w0ith 80 some silt (ML) and a few thin brown and yellow sandy and 29809 silty sand beds; stiff, sl. sticky, sl. plastic, no CO3. 30 100 100 60 739 120 40 27 432 140 3. 70 Few fine org. fragments, incl. wood, reed fragments, and 16ch0arcoal. Fine grained intervals lack sand. No invertebrate 1737 50 fossils. 180 80 398 Pleistocene 60 200 Depth (meters)

Depth (meters) 225-240 ft: V. dark gray coarse pebbly sand (SW); easy9 0 2d2r0illing; few wood fragments; mod. sorting. 240-270 ft: 5Y4/1 dark gray silty clay (CH) and interbed- 70 ded silt Hookton Fm. (Ogle, 1953) (ML); stiff, sticky, plastic; sctd organics as pore 240 27 493 fillings and vegetal residues; occ'l charcoal fragments.100 226700-313 ft: 5YN/1 dark gray coarse lithic sand and 80 gravelly sand and gravel (SW, GW); v. dense, poorly sorted, well-graded, non-sticky, non-plastic, non-CO3; 28Fr0anciscan provenance for clasts. 557 300 1885 Total drilled depth = 313 ft 320 705

100

M--Depth--Ft

Figure A-15. S- and P-wave velocity profiles with lithology. Dashed lines represent plus and minus one standard deviation of velocities. 28 29 Figure A-16. Site location map for the borehole at Redwood Village Mall. The accelerograph is located approximately 10 meters from the borehole.

30 S-WAVE S-WAVE Time (sec) Time (sec) 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 45

5 50

10 55

15 60 )

m 20 65 ( h t

p 25 70 e D 30 75

35 80

40 85

45 90

Redwood Village Mall

G:\FORTUNA\RVM\C05_45.GRAG:\FORTUNA\RVM\C11_45.GRA G:\FORTUNA\RVM\C11_90.GRAG:\FORTUNA\RVM\C05_90.GRA G:\FORTUNA\RVM\C05.DTG:\FORTUNA\RVM\C11.DT G:\FORTUNA\RVM\C11.DTG:\FORTUNA\RVM\C05.DT NovDec 7,4, 2001 10:01:27 9:55:34 am am NovDec 7,4, 2001 10:00:37 9:55:34 am am

Figure A-17. Horizontal component record section (from impacts in opposite directions) superimposed for identification of S-wave onset. Approximate S-wave time picks are indicated by the hatch marks.

31 P-WAVE P-WAVE Time (sec) Time (sec) 0 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 0 45

5 50

10 55

15 60 )

m 20 65 ( h t

p 25 70 e D 30 75

35 80

40 85

45 90

Redwood Village Mall

G:\FORTUNA\RVM\VERT\RVMP_45.GRA G:\FORTUNA\RVM\VERT\RVMP_90.GRA

G:\FORTUNA\RVM\VERT\RVMP.DT G:\FORTUNA\RVM\VERT\RVMP.DT

Dec 4, 2001 9:50:32 am Nov 7, 2001 8:54:12 am

Figure A-18. Vertical component record section. Approximate P-wave arrivals are indicated by the dots.

32 Time (sec) 0 0.05 0.1 0.15 0

20 ) s

r 40 e t

e P S m ( h t p

e 60 D

80

100 Redwood Village Mall

Figure A-19. Time-depth graph of P-wave and S-wave picks. Line segments are straightline interpolations of model predictions at the observation depths. The times for zero depth, not shown, are given by the horizontal offset (hoffset) divided by the velocity in the uppermost layer (see accompanying tables of velocities for specific values).

33 Redwood Village Mall S Velocity (m/s) P Velocity (m/sec) Age Lithology 0 1000 2000 3000 0 Fill 0-3 ft: FILL:5Y5/1 gray gravelly sand (SWG). 829 m/s 3-22 ft: 10YR5/4 brown lean silty clay (CL); m7od13 stiff, sticky, plastic, no CO 10 Holo. 3; no orgs. or odors. 22-60 ft: 10YR5/3 brown sand (SW) and interbedded gravel (GW) w/ rare interbeds of sandy silt (MLS); poorly sorted; prob. multiple fining-up sequenc2es0. 60-92 ft: 5GY5/1 to 10GY4/1 dk. greenish gray lean1 702 silty clay (CL); stiff, sticky, plastic, no CO 0 0 30 2197 385 m/s 92-128 ft: 2.5Y5/3 lt. olive brown lithi3c; m-c sand (SW) & 20 Abundant 254 redwogoradv?e fl r(aGgWs; )t hwin/ isnatenrdb e7d3s-7 o5f flet.an silty clay (CL-ML); 10 poorly sorted; subrounded chert, ss, qtzite clas4ts0; 0 500 1000 401500prob. multiple fining-up sequences. 0 744 . 60 128-174 ft: N4/ gray silt and lean silty clay (CL); laminated, stiff, sl.sticky, plastic, no CO 20 50 458 80 10 1875 30 100 60

20 948 120 3 or fossils; 40 no apparent microfossils; UCS >4.5 T/sq.ft. 140 70 34 30 174- 220 ft: 5Y3/1 v. dark gray med-cse sand (SP) & 160 496 50 2g2r0a-v2e4ll0y fsta: n1d0 Y(S3/W1 Gdk); gnroene-nsitsichk gyr, anyo lne-apnla sitlitcy, cnloa yC (OCL); v. stiff, sticky, sl. plastic, USC >4.5 T/sq.ft. 80 180 3 or Pleistocene

40 Depth (meters) foss2il4s0; -c2la8s9t flti:t h1 0seYe 5m/1s glikraey m codaersren lEitehli cR s.and and 60 200 Depth (meters) 990 gravelly sand and gravel with silt interbeds (SW, SW9G0, GW); v. dense, poorly sorted, non-sticky, non-plastic, 50 22n0o CO

70 Hookton Fm. (?) of Ogle (1953) 34 733 240 100

60 260 2333 80 1275 280 70 290-302 ft: 5GY5/1 dark greenish gray sand and gravel 90 (S3W00G) w/ cobbles; fine sand and silt interbeds in basal 4 feet; nonsticky, nonplastic,no CO 80 320 3.

90 Total drilled depth = 302 ft 3 .

100 100

M--Depth--Ft

Figure A-20. S- and P-wave velocity profiles with lithology. Dashed lines represent plus and minus one standard deviation of velocities. 35 36 Figure A-21. Site location map for the borehole at Rio Dell. The highway (US 101) has been rerouted and is close to the borehole. The accelerograph is located approximately 10 meters from the borehole.

37 S-WAVE Time (sec) Time (sec) 0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4 0 50

5 55

10 60

15 65

) 20 70 m (

h 25 t 75 p

e 30

D 80 35 85 40 90 45 95 50 100 Rio Dell

G:\FORTUNA\RIO_DELL\R11_45.GRAG:\FORTUNA\RIO_DELL\R05_45.GRA G:\FORTUNA\RIO_DELL\R05_90.GRAG:\FORTUNA\RIO_DELL\R11_90.GRA G:\FORTUNA\RIO_DELL\R11.DTG:\FORTUNA\RIO_DELL\R05.DT G:\FORTUNA\RIO_DELL\R05.DTG:\FORTUNA\RIO_DELL\R11.DT NovDec 5,4, 2001 10:10:06 2:52:07 pm am NovOct 8, 5, 2001 2001 10:17:08 2:52:07 pmam

Figure A-22. Horizontal component record section (from impacts in opposite directions) superimposed for identification of S-wave onset. Approximate S-wave time picks are indicated by the hatch marks.

38 P-WAVE Time (sec) Time (sec) 0 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 0 50

5 55

10 60

15 65

) 20 70 m (

h 25 t 75 p

e 30

D 80 35 85 40 90 45 95 50 100 Rio Dell

G:\FORTUNA\RIO_DELL\VERT\VERT_45.GRA G:\FORTUNA\RIO_DELL\VERT\VERT_90.GRA G:\FORTUNA\RIO_DELL\VERT\004.DT G:\FORTUNA\RIO_DELL\VERT\004.DT Nov 5, 2001 3:25:04 pm Dec 4, 2001 10:12:58 am

Figure A-23. Vertical component record section. Approximate P-wave arrivals are indicated by the dots.

39 Time (sec) 0 0.05 0.1 0.15 0.2 0

20 ) s

r 40 e t e m (

h P S t p

e 60 D

80

100 Rio Dell

Figure A-24. Time-depth graph of P-wave and S-wave picks. Line segments are straightline interpolations of model predictions at the observation depths. The times for zero depth, not shown, are given by the horizontal offset (hoffset) divided by the velocity in the uppermost layer (see accompanying tables of velocities for specific values).

40 Rio Dell P Velocity (m/sec) S Velocity (m/sec) 0 200 400 600 800 Age Lithology 0 500 1000 1500 2000 2500 0 0 154 m/s 5Y4/2 olive gray silty clay & clayey silt; stiff, sticky, 353 m/s

Fill plastic; compacted fill at Painter St.- US 101. Holo. 644 5Y4/2 olive, 5GY4/1 dark greenish gray, and 2.5Y 4/3-/4 1451 267 olive brown silt with few sandy interbeds an1d0 silty clay beds; fines are slightly to med. dense, sl. sticky, sl. plastic to plas- tic; sands are loose to dense and poorly sorted. Probably overbank facies (?) of Eel River alluvial deposits 10 20 1211 2.5Y4/1 dark gray lithic scan and gravel w/ sctd. cobbles. 596 Channel deposits of Eel River (poss. L. Wisc. lowstand?). Erosional unconformity between alluvium and Rio Dell Fm. 20 30 Eel River Alluvium leist. and Holocene 5Y5/1 to 5Y4/1 gray to dark gray siltstone of Rio Dell Fm.

511 Late P Smooth, quiet drilling. Few thin clayey zones 1927 40 0 0

20 50 648 10 40

60 135 ft: Stiffness increases. 60 20 80 Hard bed ~6 inches thick at 220 ft. 41 70 30 30 100 Thin sandy silt interval

742 120 205 ft: Drilling rate decreases. 40 40 80 140 Depth (meters) Depth (meters) 160 50 50 90

180 Rio Dell Formation 2079 41 60 60 200 100

220 70 70 240

260 80 80 280 Late Pliocene and Early to Middle Pleistocene 90 90 300

320

Total drilled depth = 311 ft. 100 100

M--Depth--Ft

Figure A-25. S- and P-wave velocity profiles with lithology. Dashed lines represent plus and minus one standard deviation of velocities. 42 43 APPENDIX—B Poisson’s Ratios 44 45 46 47 48