HR: 10:35h
AN: S12B-02 INVITED     [Abstracts]
TI: Observations and Modeling of Microseisms in the Santa Clara Valley, California
AU: * Dolenc, D
EM: dolenc@seismo.berkeley.edu
AF: UC Berkeley Seismological Lab, 215 McCone Hall, UC Berkeley, Berkeley, CA 94720 United States
AU: Dreger, D
EM: dreger@seismo.berkeley.edu
AF: UC Berkeley Seismological Lab, 215 McCone Hall, UC Berkeley, Berkeley, CA 94720 United States
AU: Larsen, S
EM: larsen8@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550 United States
AB: Previous studies of the 3D velocity structure in the Santa Clara Valley (SCV) showed that teleseismic, local, and microseism data recorded by the 41-station Santa Clara Valley Seismic Experiment (SCVSE, 6/98-12/98) are all sensitive to basin structure and that they may be used to refine the velocity model of the basins. In our recent work we focused on constraining the source of the microseisms and used this for modeling the microseism observations in the SCV. We used an f-k array method on microseisms recorded during the SCVSE to determine if they are monodirectional and to see if their source can be localized. Our results showed that at low frequencies (0.1 to 0.3 Hz), wavefield observations in the SCV display directionality. At higher frequencies (0.3 to 0.5 Hz), wavefield directionality is lost, which may be due to scattering of the waves by the 3D structure in the SCV basins. The important result of these observations is that the source of the microseisms can be localized and can therefore be used in numerical simulations. We used the 3D finite-difference code E3D (Larsen and Schultz, 1995) and the UCB 3D velocity model (Stidham et al., 1999) to simulate the microseism wavefield. A vertically oriented CLVD source located about 27 km offshore was used to generate isotropic Rayleigh waves. We used the source time function that was a superposition of sine waves at discrete periods over the observed microseismic band. The f-k analysis of simulated waveforms agrees with observations in terms of directionality at low frequencies, and the loss of directionality at higher frequencies. We will attempt to refine the method to simulate microseism wavefield by including the source spectrum derived from the ocean wave data recorded at the Santa Cruz buoy. One objective of this research is to use the obtained results to develop a simultaneous inversion of the teleseismic, local, and microseism observations to constrain the internal velocity structure of the SCV basins.
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2004 AGU Fall Meeting