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Basin Amplification Seismic INvestigation: tracking the propagation of waves from the San Andreas Fault to Los Angeles

Robert W. Clayton, Marine A. Denolle, Kim B. Olsen, Patricia Persaud, & Jascha Polet

Published August 8, 2018, SCEC Contribution #8333, 2018 SCEC Annual Meeting Poster #099

Seismic amplification in sedimentary basins naturally arise from the contrast in elastic wave speeds between soft sediments and hard bedrock. Connectivity in sedimentary basins can thus act as seismic waveguides. The Basin Amplification Seismic INvestigation project aims to establish the presence of a coupling effect between the amplification due to seismic waveguides and that due to source directivity, which can enhance shaking intensity in sedimentary basins. The natural laboratory is the northern basins of the greater Los Angeles area (San Bernardino, Chino, San Gabriel) that may funnel long-period seismic waves from a San Andreas Earthquake to downtown Los Angeles. The BASIN project involves a multi-phase deployment of broadband seismometers and nodes between 2017 and 2018. Results from ambient noise spectral ratio analysis show clear long period (2-5 sec) peaks related to basin resonance, with significant variation in resonance frequencies and amplification factors across both the San Gabriel and San Bernardino Basins. Receiver functions show the Moho discontinuity, bottom of the basin, and intermediary sedimentary layers. Autocorrelation functions with nodes in the area exhibit reflectivity response that corresponds to transition between upper-lower crust and Moho. Preliminary ambient-noise cross correlations between permanent stations located on the San Andreas Fault and nodes contain anticausal Rayleigh waves with signal in the period range 2 – 10s.

Key Words
Basin structure, site amplification, waveguide

Clayton, R. W., Denolle, M. A., Olsen, K. B., Persaud, P., & Polet, J. (2018, 08). Basin Amplification Seismic INvestigation: tracking the propagation of waves from the San Andreas Fault to Los Angeles. Poster Presentation at 2018 SCEC Annual Meeting.

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