Forward modeling of a transect of ground motion recordings of the 3 September 2000 M5.0 Napa/Yountville earthquake
We model a linear transect of recorded ground motions at five stations of the 3 September 2000 M5.0 Napa/Yountville earthquake in the Northern San Francisco Bay area, focusing on the tangential displacement component. The epicentral distances range from 6 km to 57 km. The waveforms at all five stations are characterized by a direct shear-wave (S0), a midcrustal reflection (S1), a surface-layer multiple (S2), and Love waves. Our one-dimensional (1D) and two-dimensional (2D)simulations have a grid spacing of 100 m and minimum velocity of 800 m/s and accurately model displacements at frequencies up to 0.8 Hz. We compare the fit of our synthetic seismogram to the 1D Berkeley Seismological Laboratory GIL7 model and the three- dimensional (3D) USGS San Francisco Bay Area velocity model. We find that a simple 1D velocity model composed of four layers sufficiently predicts the primary arrivals with the exception of the later arriving Love wave at all five stations. Our modeling indicates that the source layer must be faster than the velocities in the current 1D GIL7 and 3D USGS regional velocity model to account for the arrival time of S0. To explain the delay between the S0 and S2 arrivals, the velocities at depths extending from the surface to 5 km must be slower than the velocities indicated in the other regional models. Adding a 1 km deep trapezoidal basin with a shear-wave velocity of 800 m/s significantly improves the fit of the amplitude, phase, and duration of the surface waves.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 7205 Continental crust (1219);
- 7212 Earthquake ground motions and engineering seismology