Parameterization of Basin Response Based on
3D Simulations
by
PEER/SCEC 3D Ground Motion Project Team
PI: Steven M. Day
San Diego State University
March 25, 2004
03/25/04
NGA Workshop
1
Simulations Completed
– 85 different earthquake simulations
• 10 faults from SCEC Community Fault Model
• 6 rupture scenarios for each (hypocenter and slip model variations)
• 10 cross-check simulations (1 per fault)
• 15 1D reference simulations
03/25/04
NGA Workshop
2
Faults Modeled
•
•
•
•
•
•
•
•
•
•
03/25/04
NGA Workshop
1. Sierra Madre (7.0)
2. Santa Monica SW (6.3)
3. Hollywood (6.4)
4. Raymond (6.6)
5. Puente Hills I (6.8)
6. Puente Hills II (6.7)
7. Puente Hills (all) (7.1)
8. Compton (6.9)
9. Newport-Inglewood (6.9)
10. Whittier (6.7)
3
Six Rupture Scenarios Per Fault
• 2 hypocenters
– 1/4 fault-length from each end
– 7/10 fault-width down dip
• 3 slip models
– Constructed following Somerville
(1999)
– Constant rupture velocity (2.8
km/s)
– Rise time scaled to empirical
formula:
Log(Tr)=0.5(Mw+10.7) + log(2.9x10-9)
03/25/04
NGA Workshop
4
Coordination Scheme
UCB -LLNL UCSB
CMU
URS (RG)
S. Madre
F,R,S
C
S. Mon.
F,R
C
HollyW
F,R
C
Raym
F,R
C
URS (AP)
P.Hills6.8
F,R
C
P.Hills6.7
F,R
C
P.Hills7.1
F,R,R,S
C
Comp
F,R,S
C
N-I N.
R,S
F
C
Whit N.
R
F
C
F = 6 3D scenarios
C = single cross-check
03/25/04
NGA Workshop
R = 1D rock reference simulation
S = 1D basin-profile simulation
5
Output
• Full time histories
• 3 velocity components
• 1600 surface points per simulation
• Basin and rock sites sampled
• ~300,000 synthetic time histories
and associated metadata in digital
library
03/25/04
NGA Workshop
6
Cross-check (cont’d)
• Sierra Madre Scenario
• Compares FD and FE codes
at 16 sites (N-S component):
– FD (UCB/LLNL) red
– FE (CMU) green
03/25/04
NGA Workshop
7
Response Spectra Data Set
• synthetic Sa ordinates (2-10 second period range)
• source distances
• local basin depth measures (depths to 1.0, 1.5, 2.5, and 3.5
km/s isosurfaces)
• Sa files available on web
03/25/04
NGA Workshop
8
ln(Sa Ratio)
3D÷1D_rock Sa Ratios
Frequency (Hz)
Frequency (Hz)
03/25/04
NGA Workshop
9
ln(Sa Ratio)
Vertically Incident SH Response
Frequency (Hz)
Frequency (Hz)
03/25/04
NGA Workshop
10
Basin Depth Effect Curves
03/25/04
NGA Workshop
11
Curve Fits to Basin Depth Effect
(Separately Optimized at Each Period)
03/25/04
NGA Workshop
12
Curve Fits to Basin Depth Effect
(6-parameter model for Depth and Period Dependence)
03/25/04
NGA Workshop
13
Basin Effect Relative to 1-D Soil
(2000 m Depth to Isosurface)
03/25/04
NGA Workshop
14
Underprediction Factor
1D Rock Simulations vs A-S
Regression Model
Period (sec)
03/25/04
NGA Workshop
15
Transfer Function from “Very Hard
Rock” to Boore/Joyner “Generic Rock”
03/25/04
NGA Workshop
16
03/25/04
NGA Workshop
17
1.5 Km/s Isosurface Map
03/25/04
NGA Workshop
18
8 Sec Sa Mean Residual Map
03/25/04
NGA Workshop
19
5 Sec Sa Mean Residual Map
03/25/04
NGA Workshop
20
3 Sec Sa Mean Residual Map
03/25/04
NGA Workshop
21
RMS Residuals
03/25/04
NGA Workshop
22
8 sec Sa RMS Residual Map
03/25/04
NGA Workshop
23
5 sec Sa RMS Residual Map
03/25/04
NGA Workshop
24
3 sec Sa RMS Residual Map
03/25/04
NGA Workshop
25
Summary
• Source-averaged 3D effect is largely captured by basin depth
term (depth to 1.5 km/s isosurface)
• Mean and variance are period-dependent
• Results almost certainly double-count effects partially
represented in “rock” regression equations
• With ~500 m depth sites (instead of 0 depth) taken as “rock”
reference:
– absolute amplitudes at long period (5 sec) come into agreement with AS rock regression (i.e., under-prediction eliminated)
– Addition under-prediction at shorter periods probably partly a source
effect (which would be removed by our analysis of ratios)
– Maximum basin effect reduced to ~2 (@ 2 sec) to ~3 (@ 10 sec)
03/25/04
NGA Workshop
26
Summary (cont’d)
• Little or no systematic basin-edge effect in sourceaveraged residuals
• Likewise, no clear basin-edge effect in sourceaveraged standard deviations
03/25/04
NGA Workshop
27
Directions for Additional Work
• Analysis of current synthetic data set for
– Basin-specific (e.g., L.A., San Fernando, San Gabriel) variations
– Event-specific basin effects
• Simulations for additional regions (e.g., Santa Clara Valley?
Imperial Valley? others) to examine transportability of results
• Push simulations to ~1 Hz
03/25/04
NGA Workshop
28