Integrated Surface and Borehole Strong-Motion, Soil-Response Arrays in San Francisco, California

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1 Integrated Surface and Borehole Strong-Motion, Soil-Response Arrays in San Francisco, California R. D. Borcherdt, G. Glassmoyer, C. Dietel, and R.E. Westerlund INTERNATIONAL WORKSHOP FOR SITE SELECTION, INSTALLATION AND OPERATION OF GEOTECHNICAL STRONG-MOTION ARRAYS: WORKSHOP 1, INVENTORY OF CURRENT AND PLANNED ARRAYS. OCTOBER 14, 15, 2004 CONVENED BY THE CONSORTIUM OF ORGANIZATIONS FOR STRONG-MOTION OBSERVATION SYSTEMS (COSMOS) UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES, CA 90089

2 Integrated Surface and Borehole Strong-Motion Arrays in San Francisco, CA San Francisco Bay Fort Mason Marina (Winfield Scott Sch) Maritime Museum Longshoremen Assoc. Telegraph Hill Russian Hill Levi Plaza Embarcadero Plaza E&M Electric Bank America Pac Bell Stadium Bessie Carmichael Sch. Mission Rock Ch. Pump Station Potrero Hill Legend Gallop Courier Bldg. Integrated Strong Ground Motion Array San Francisco, CA Ground-Motion Recording Locations Borehole Array Surface Recording Site NEHRP Site Classes E -- Soft Soils (Bay Mud) D -- Stiff Clays and Sandy Soils C -- Gravely Soils and Soft Rock B -- Soft Rock 0 2 S Kilometers 4

3 Vs30 and Geologic Units Integrated Surface and Borehole Strong-Motion Arrays, San Francisco, CA GEOLSFP by AGELITH Tu-ss Tu-sm Tu-sl Tu-sc Tu-md Tu-ls Tu-fv Tu-bv Tl-ss Tl-sm Tl-sl Tl-md QT-ss QT-sm QT-md Q-ms p-s Mz-ss Mz-sp Mz-sm Mz-sl Mz-sch Mz-mv Mz-ms Mz-mm Mz-md Mz-ls Mz-gr Mz-fv Mz-bv h-wm h-s h-m 0 2 S Kilometers

4 Location of Borehole and Structural-Response Arrays San Francisco, CA Bessie Charmichael School Chevron Building Embarcadero Plaza Embarcadero 4 Bldg. Trans America Bldg. Levi Plaza Marina (WS School)

5 Location of Borehole Array at Bessie Charmichael School San Francisco, CA Bessie Charmichael School

6 Seismic and Geologic Logs for Array at Bessie Charmichael School Depth (m) P Velocity (m/s) S Velocity (m/s) FBA Bessie Charmichael School FBA PP FBA PP FBA VEL Sand (Fill) Holocene Clay,Silty Clay Sand Clay Sandy Clay, Loam Sand to sandy loam Clay (v. stiff to hard) Gravelly Sand Clay (hard) Serpentine Shale

7 Location of Borehole Array and Nearby Well-Instrumented Buildings near Embarcadero Plaza San Francisco, CA Trans America (USGS) Embarcadero Four (CDMG) Embarcadero Plaza Array (USGS)

8 Seismic and Geologic Logs for Array at Embarcadero Plaza 0 P Velocity (m/s) S Velocity (m) Embarcadero Plaza Clay, Sand, Debris Fill FBA PP FBA Holocene Clay Depth (m) FBA PP Sand Clay (v. stiff to hard) FBA Sandstone 90 90

9 Location of Borehole Array and Surface Recorder on Rock near Levi Plaza San Francisco, CA Telegraph Hill Levi Plaza

10 Seismic and Geologic Logs Levi Plaza Borehole Array P Velocity (m/s) S Velocity (m/s) Levi Plaza 0 Gravelly Sand (Fill) FBAVEL 10 FBAPP Holocene Clay Depth (m) 20 FBA PP Shelly Clay Dense Sand w Clay Layers 30 Sandy Clay 40 FBA Shale

11 Locations Near Marina Array in San Francisco, CA Telegraph Hill Fisherman s Warf Marina

12 Seismic and Geologic Logs for Array at Winfield Scott School 0 P Velocity (m/s) S Velocity (m/s) Winfield Scott School Sand FBA/ VEL Silty Clay Sand De pth (m ) FBA/ VEL Sandy Clay Sand Sandy Clay, Silty Clay Clay w shells FBA/ VEL Sandy Clay, Silty Clay

13 Instrumentation Configuration GOES Satellite GEOS GOES Receiver Menlo Park, CA

14 Epicenter and Shaking Intensity Yountville, CA Earthquake, M=5.1

15 Epicenter and Shaking Intensity Gilroy, CA Earthquake, M=4.9

16 Simultaneous Surface Recordings of Radial Acceleration and Velocity Yountville Earthquake, M=5.1 PRS Recorded Acceleration 21-APR-04 Soft Soil N2.CPS H181 PRS Recorded Velocity 21-APR-04 Soft Soil N5.CPS H N2.E0A H O2.C0A H N5.BMA H N2.BMA H N5.GAL H181 CM/S** N2.GAL H181 CM/S O5.M0V H O2.M0A H181 Stiff Soil - Soft Rock N2.MAR H181 Firm to Hard Rock O2.PBS H Stiff Soil - Soft Rock N5.MAR H181 Firm to Hard Rock O5.PBS H N2.P50 H N5.P50 H S N2.RHL H N2.FM3 H S N5.RHL H N5.FM3 H181

17 Surface Recordings of NS & EW Acceleration Gilroy Earthquake, M=4.9 PRS Recorded NS Acceleration 26-APR-04 Soft Soil PRS Recorded EW Acceleration 26-APR-04 Soft Soil P2.E0A H P3.E0A H P2.C0A H P3.C0A H Q2.L0A H Q3.L0A H Q2.BMA H Q3.BMA H CM/S** Q2.M0A H322 CM/S** Q3.M0A H Stiff Soil - Soft Rock Q2.MAR H322 Stiff Soil - Soft Rock 0 Firm to Hard Rock P2.PBS H Q3.MAR H052 Firm to Hard Rock P3.PBS H O2.ENM H O3.ENM H P2.RHL H Q2.FM3 H P3.RHL H Q3.FM3 H

18 Amplitude Spectral Ratio to Surface Rock (FM3- Radial -Yountville) Yountville Earthquake (M5.1) North-South Component Spectral Ratios 20 CPS/FM3 E0A/FM3 C0A/FM3 15 Spectral Ratio Spectral Ratio Spectral Ratio BMA/FM3 MAR/FM3 GAL/FM3 PBS/FM3 M0A/FM3 P50/FM RHL/FM3 M9A/FM3 E8A/FM3 15 Spectral Ratio Spectral Ratio C9A/FM Frequency (Hz) Frequency (Hz) Frequency (Hz)

19 Embarcadero Plaza Yountville Earthquake, M=5.1, 100 seconds Surface - Z N-S E-W 10 Meters - Z N-S E-W 49.4 Meters - Z N-S E-W 79.2 Meters - Z N-S E-W

20 Marina Velocity Borehole Array Orinda Earthquake M 4.1 Surface Vertical Radial Transverse 30.3 Meters Vertical Radial Transverse 88.4 Meters Vertical Radial Transverse

21 Embarcadero Plaza Yountville Earthquake, M=5.1, 50 seconds Surface - Z N-S E-W 10 Meters - Z N-S E-W 49.4 Meters - Z N-S E-W 79.2 Meters - Z N-S E-W

22

23 Embarcadero Plaza Spectral Ratio (Surface NS / 79 Meters NS) Yountville Earthquake, M=5.1

24 Embarcadero Plaza Spectral Ratio (Surface EW / 79 Meters EW) Yountville Earthquake, M=5.1

25 Embarcadero Plaza Spectral Ratio (10Meters NS / 79 Meters NS) Yountville Earthquake, M=5.1

26 Embarcadero Plaza Spectral Ratio (10Meters EW / 79 Meters EW) Yountville Earthquake, M=5.1

27 Embarcadero Plaza Spectral Ratio (50Meters NS / 79 Meters NS) Yountville Earthquake, M=5.1

28 Embarcadero Plaza Spectral Ratio (50Meters EW / 79 Meters EW) Yountville Earthquake, M=5.1

29 San Francisco Marina Acceleration Yountville Earthquake, M=5.1, 50 seconds Surface - Z N-S E-W 30.3 Meters - Z N-S E-W 88.4 Meters - Z N-S E-W

30 San Francisco Marina Recorded Velocity Yountville Earthquake, M=5.1, 50 seconds Surface - Z N-S E-W 30.3 Meters - Z N-S E-W 88.4 Meters - Z N-S E-W

31 San Francisco Marina Spectral Ratio (Surface NS / 88 Meters NS) Yountville Earthquake, M=5.1

32 San Francisco Marina Acceleration and Velocity Spectral Ratios Surface NS / 88 Meters NS; Yountville Earthquake, M=5.1 Ratio of Recorded Acceleration Ratio of Recorded Velocity

33 San Francisco Marina Spectral Ratio (Surface EW / 88 Meters EW) Yountville Earthquake, M=5.1

34 San Francisco Marina Spectral Ratio (30 Meters NS / 88 Meters NS) Yountville Earthquake, M=5.1

35 San Francisco Marina Spectral Ratio (30 Meters EW / 88 Meters EW) Yountville Earthquake, M=5.1

36 Bessie Carmichael School Acceleration Yountville Earthquake, M=5.1, 50 seconds Surface Z N-S E-W 36.9 Meters - Z N-S E-W 89.9 Meters - Z N-S E-W

37 Bessie Carmichael Spectral Ratio (Surface NS / 90 Meters NS) Yountville Earthquake, M=5.1

38 Bessie Carmichael Spectral Ratio (Surface EW / 90 Meters EW) Yountville Earthquake, M=5.1

39 Bessie Carmichael Spectral Ratio (37 Meters NS / 90 Meters NS) Yountville Earthquake, M=5.1

40 Bessie Carmichael Spectral Ratio (37 Meters EW / 90 Meters EW) Yountville Earthquake, M=5.1

41 Spectral Ratio (Russian Hill Surface NS / Embarcadero Plaza 79 Meters EW) Yountville Earthquake, M=5.1

42 Spectral Ratio (Russian Hill Surface EW / Embarcadero Plaza 79 Meters EW) Yountville Earthquake, M=5.1

43 Theoretical Response of a Viscoelastic Soil Layer as a Simple Model for Site Coefficients in Bldg. Codes Amplitude Response versus Frequency Homogeneous Linear S Wave, Vertical Incidence Soil Rock v Hs1 v Hs2 D 2 θ 2 γ 2 D 0 1 Q Hs Q 1 1 Hs 2 RQ2 = 0.02 RQ1 = 2 DR = 0.1 Inhomogeneous Linear S Wave Inhomogeneous Linear S Wave 8 Solution: D D 0 1 = F[ (inc. wave field par.),(material par.)] D0 f vhs ρ1 = F[ ( θ2, γ2, ),(,Q Hs,Q )] 1 Hs, 2 D1 f0 vhs ρ 2 2 where f =fundamental frequency. 0 D 0 /D f f v v Hs Hs 1 2

44 Amplitude Response versus Period, Shear Velocity, and Bldg. Code Site Class Anelastic Soil Layer Damping Ratio 5% Vertical Incidence RQ2 = 0.02 RQ1 = 2 DR= 0.1 Soil Homogeneous Linear S Wave Rock D 0 /D 1 0 /D T T 0 1 T T vhs 0.4 vhs Hs 1 vhs E D C B Site Class

45 Bldg. Code Site Coefficients Theoretical Response at 5 % Damping or I a ~ 0.1g Anelastic Soil Layer Damping Ratio 5% Ia ~ 0.1g Vertical Incidence RQ2 RQ2 = = RQ1 RQ1 = = 22DR= DR= Fa C Fa B Soil Homogeneous Linear S Wave Rock 4 4 D 0 /D 1 D 0 /D 1 2 Fa E 2 Fa D T T T T0 0 Fv E Fv D Fv D v v Hs v v EE Fv B Fv C Fv B DD Hs 1 Hs Hs 2 2 B C Site Site Class Class

46 Bldg. Code Site Coefficients and Theoretical Response 15 % Damping or I a ~ 0.4 g Anelastic Soil Layer Damping Ratio 15 % Ia ~0.4 g Vertical Incidence RQ2 = 0.02 RQ1 = 2 DR= DR= 0.3 Fa B Soil Homogeneous Linear S Wave Rock D 0 D /D 0 /D Fa E 0.5 Fa D T T 0 Fa C 1 Fv E 1.5 Fv D 2 Fv C 0.2 E Fv B 0.6 vhs v D Hs B C Site Class

47 Definition of Site-Dependent Response Spectra (log-log scale) (NEHRP, UBC, IBC, ASCE 7 Provisions) Response Spectral Acceleration S A (g) S A = I a F a S A = I v F v / T I x a F a F v Period (secs) I v / T x

48 Site-Dependent Response Spectra (linear (linear-linear scale) (NEHRP, UBC, IBC, ASCE 7 Provisions) Spectral Response Acceleration Sa (g) Sa (g) S DS DS S D I a = 2 S 3 S a I a a 2 2 S S S S S F a = IaFa = SDS = SMS = a 3 3 T F Iv T = Iv T I 2 2 S S = F = S = S = F T 3 3 T v 1 a v D 1 M 1 v 2 S 21 S1 3= T Iv 22S 1S 3I v T= = 33T T 1 a TL Sa( T : T TL ) = SD 1 2 T 0 0 T 0 T S 1 TLL Period T (secs)

49 Spectral Amplification Dependence on Shear Wave Velocity (Vs) Loma Prieta Earthquake; I a < 0.1g Average Spectral Amplification (a) Short-Period Band ( s) F = (997 m/s / v) % Confidence Limits for Ordinate Standard Error of Estimate Average Spectral Amplification (b) Intermediate-Period Band ( s) F = (1084 m/s / v) % Confidence Limits for Ordinate Standard Error of Estimate Mean Shear-Wave Velocity to 30 m (100 ft) (v, m/s) Mean Shear-Wave Velocity to 30 m (100 ft) (v, m/s) Average Spectral Amplification (c) Long-Period Band ( s) F = (1077 m/s / v) % Confidence Limits for Ordinate Standard Error of Estimate Mean Shear-Wave Velocity to 30 m (100 ft) (v, m/s) (Borcherdt, 1994) Average Spectral Amplification (d) Mid-Period Band ( s) F = (1067 m/s / v) % Confidence Limits for Ordinate Standard Error of Estimate Mean Shear-Wave Velocity to 30 m (100 ft) (v, m/s)

50 Short and Mid-Period Site Coefficients versus Vs30 F a and F v for I a < 0.1g Average Spectral Amplification Factors, F a and F v E Soft soils D Stiff clays and Sandy soils C Gravelly soils and Soft rocks Mean Shear-Wave Velocity to 30 m (100 ft) v (, m/s) Loma Prieta Strong-Motion Data Fa - 95% Fa = (997 / v )^0.36 Fa +95% Fv - 95% Fv = (1067 / v )^0.64 Fv + 95% Fa for Site Class Intervals Fv for Site Class Intervals B Firm to Hard rocks (Borcherdt, 1994)

51 F a versus Vs30 and Input Acceleration I a = 0.1, 0.2, 0.3, 0.4 g (linear scales) Short-Period Amplification F a wrt SC-Ib SC-IV Soft soils (a) SC-III Stiff clays and Sandy soils F a = (v SC-Ib / v ) m a = ( 1050 m/s / v) m a SC-II Gravelly soils and Soft rocks Mean Shear-Wave Velocity to 30 m (100 ft) (v, m/s) I=0.1g; ma = 0.35 I=0.2g; ma = 0.25 I=0.3g; ma = 0.10 I=0.4g; ma = Fa (0.1g) for Site Class Intervals Fa for Site Classes SC-Ib Firm to Hard rocks (Borcherdt, 1994)

52 F v versus Vs30 and Input Acceleration I v = 0.1, 0.2, 0.3, 0.4 g (linear scales) Mid-Period Amplification F v wrt SC-Ib SC-IV Soft soils (b) SC-III Stiff clays and Sandy soils F v = (v SC-Ib / v ) m v = ( 1050 m/s / v) m v SC-II Gravelly soils and Soft rocks Mean Shear-Wave Velocity to 30 m (100 ft) (v, m/s) I=0.1g; mv = 0.65 I=0.2g; mv = 0.60 I=0.3g; mv = 0.53 I=0.4g; mv = 0.45 Fv(0.1g) for Site Class Intervals Fv for Site Classes SC-Ib Firm to Hard rocks (Borcherdt, 1994)

53 Short-Period Site Coefficient F a (NEHRP, UBC, IBC, ASCE-7 7 Provisions) Site A a < 0.1 A a = 0.20 A a = 0.30 A a = 0.40 A a > 0.50 Class S s < 0.25 S s = 0.50 S s = 0.75 S s = 1.00 S s > 1.25 A B C D E * F * * * * * * Site-specific geotechnical investigation and dynamic site response analysis shall be performed.

54 Mid-Period Site Coefficient F v (NEHRP, UBC, IBC, ASCE-7 7 Provisions) Site A v < 0.1 A v = 0.20 A v = 0.30 A v = 0.40 A v > 0.50 Class S l < 0.1 S l = 0.20 S l = 0.30 S l = 0.40 S l > 0.50 A B C D E * F * * * * * * Site-specific geotechnical investigation and dynamic site response analysis shall be performed.

55 Empirical Measurements of F a at SF Array Sites F a versus Vs30 Inferred from Loma Prieta Sites Average Spectral Amplification Factor Fa Site Class E Soft soils Site Class D Stiff clays and Sandy soils Site Class C Gravelly soils and Soft rocks Loma Prieta Strong-Motion Data Fa - 95% Fa = (997 / Vs )^0.36 Fa +95% Fa (0.1g) for Site Class Intervals Fa Y&G SF Array Site Class B Firm to Hard rocks Mean Shear-Wave Velocity to 30 m (100 ft) (V s, m/s)

56 Empirical Measurements of F v at SF Array Sites F v versus Vs30 Inferred from Loma Prieta Sites Average Spectral Amplification Factor Fv Site Class E Soft soils Site Class D Stiff clays and Sandy soils Site Class C Gravelly soils and Soft rocks Loma Prieta Strong-Motion Data Fv - 95% Fv = (1067 / Vs )^0.64 Fv + 95% Fv (0.1g) for Site Class Intervals Fv Y&G SF Array Site Class B Firm to Hard rocks Mean Shear-Wave Velocity to 30 m (100 ft) (V s, m/s)

57 Conclusions Integrated Surface and Borehole SF Arrays provide unprecedented opportunity to measure in-situ high-strain constitutive properties of soft soils in SF region. Low-strain measurements to date on the array show large period-dependent amplification characteristics at sites underlain by thick layers of soft soil. Low-strain site response characteristics observed on SF arrays are consistent with those observed from previous low-strain comparative ground response measurements (Borcherdt et al., 1970, 1975, 1994). Bldg. code site coefficients, Fa and Fv, measured at some Thick, Soft-soil SF array sites are significantly greater, statistically, than those adopted in current code provisions. New site-specific procedure adopted for 2003 NEHRP provisions (Proposal 3-6 R; is recommended for purposes of seismic design and retrofit at Thick, Soft-soil, site-class E and D sites. Thick, Soft-soil, site-class E and D sites suggested for special-study considerations are those underlain by soils with Vs30 < 225 m/s, and interval Vs < 275 m/s to depths > 30 m.