Ground Motion Prediction for Southern California

The purpose of this project is to quantify how well our Earth structure model and our numerical wave propagation simulation methods can predict observed ground motion from earthquakes in Southern California. The ground-motion simulation area is the TeraShake V3 box, the highest frequency we are studying currently is 0.2 Hz.

1. Modeling Volume

2. Methodology

To compare observed and predicted ground motion, the following steps are executed in a semi-automatic fashion:

1. Once an earthquake in our modeling area happens, the waveform data recorded at CISN stations in our modeling box are retrieved. The retrieved waveform data are in SAC format and corrected for gain. The resulting seismograms are in velocity (cm/s).

2. The SAC files for the two horizontal components are rotated into Radial (R) and Transvers (T) components. The rotated seismograms together with the vertical component (R, T and Z) are then low-pass filtered using a 6-th order Butterworth filter with a corner at 0.2 Hz.

3. Our current ground-motion indicator is the Peak Ground Velocity (PGV). Therefore, the peak amplitude of each observed seismogram is picked. The PGVs picked at the stations were then interpolated to the whole area we are modeling using a stochastic interpolation algorithm similar to kriging.

4. The CMT solution for the earthquake is determined using an automated waveform inversion algorithm based on GSDF amplitude measurements and the receiver Green tensor (RGT) database constructed for our modeling volume.

5. Synthetic seismograms at the CISN stations are calculated using the CMT solution determined from the previous step and the RGT database by applying the reciprocity principle.

6. The PGVs for the synthetic seismograms are picked and interpolated to the whole modeling area using the same interpolation algorithm as used to interpolate the observed PGVs.

7. The predicted PGVs as well as the waveforms are then compared with the observed PGVs and waveforms.

3. Comparison Between CVM3.0 and CVM4.0

4. Ground Motion Prediction Experiments

Event ID: 14155260 (Ml4.9, 16 Jun 2005, "Yucaipa event")

Waveform Comparison Between CVM4.0 and CVM3.0 Synthetics
(blue wiggles: CVM3.0 synthetics; red wiggles: CVM4.0 synthetics)
Vertical Component zoom 1 zoom 2
Radial Component zoom 1 zoom 2
Transverse Component zoom 1 zoom 2

Waveform Comparison Between CVM4.0 and Data
(blue wiggles: data seismograms; red wiggles: CVM4.0 synthetics)
Vertical Component zoom 1 zoom 2
Radial Component zoom 1 zoom 2
Transverse Component zoom 1 zoom 2

Event ID: 9818433 (Ml4.8, Mw4.3, 3 Sep 2002, "Yorba Linda event")