Analysis of Site Response Across the San Gabriel and San Bernardino Basins from Linear Seismic Node Arrays Using the Ambient Noise Spectral Ratio Method
Abstract
The San Gabriel and San Bernardino Basins are large, densely populated, sedimentary basins located in southern California that are bounded by a system of faults. Therefore, it is particularly important to understand the site response and subsurface structure of these areas for seismic hazard mitigation. Furthermore, if a major rupture occurs on the southern San Andreas Fault, the San Gabriel and San Bernardino Basins may form a seismic waveguide and funnel the energy into the Los Angeles Basin (Denolle et al., 2014), amplifying ground motions. To help characterize these basins and better understand amplification and resonance period, several lines of seismic nodes have been deployed to transect the San Gabriel and San Bernardino Basins. We have generated Horizontal-to-Vertical Spectral Ratio (HVSR) curves for ambient noise waveform data from 202 three-component nodes from these profiles and 7 permanent broadband seismometers. To determine the reliability of these HVSR curves and clarity of their peaks, the Site Effects Assessment Using Ambient Excitations (SESAME) guidelines have been applied to all processed data.
Analysis of the spectral ratio curves shows clear long period peaks (between 2 and 5 seconds), related to basin resonance, along large sections of the seismic lines. Significant changes in resonance frequencies and amplification factors are seen across both the San Gabriel and San Bernardino Basins. For nodes along a line in the Western part of the San Gabriel Basin, our results show peak frequencies above 1 Hz for sites that are located north of the Raymond Fault, while peak frequencies for nodes that are situated to the south of the Raymond Fault range from 0.2-0.3 Hz. Higher frequency peaks, indicating a shallower basin, are determined along the line in the Central part of this Basin. The peak spectral ratio amplitudes within the two Basins range from 2.0-4.5, which suggests the potential for substantial ground motion amplification. The nodes in the San Bernardino Basin, which includes the Chino Basin, indicate peak frequencies of 0.4 Hz and higher amplification values in the Southern half of the profile. We will compare the frequencies of the spectral ratio peaks with those predicted by basin models.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S23C0535T
- Keywords:
-
- 7203 Body waves;
- SEISMOLOGYDE: 7255 Surface waves and free oscillations;
- SEISMOLOGYDE: 7260 Theory;
- SEISMOLOGY