Imaging Seismic Attenuation across the Northern Los Angeles Basins with Dense Arrays

Chiara Nardoni, Patricia Persaud, Joses Omojola, & Robert Clayton

Published September 11, 2022, SCEC Contribution #12078, 2022 SCEC Annual Meeting Poster #248 (PDF)

In high seismic hazard regions, attenuation imaging is used jointly with velocity tomography to detect highly-fractured volumes and fine-scale crustal heterogeneities. Attenuation is also important for predicting site response and seismic wavefield amplitudes. The northern basins of the Los Angeles area (San Gabriel, Chino and San Bernardino basins) are characterized by complex fault networks and sedimentary layers that can focus and trap seismic energy from a large earthquake on the southern San Andreas fault. However, disagreement exists in the amount of seismic wave amplification predicted beneath the major population centers. Although the SCEC CVM-H v15.1 and CVM-S 4.26 Earth models provide P and S wave velocities for Southern California, anelastic attenuation is not included in these models. In the northern Los Angeles region, the Basin Amplification Seismic Investigation (BASIN) experiment deployed 10 dense nodal arrays that each recorded continuously for ~30 days providing a dataset of >1500 local earthquakes. A 3D shear wave velocity model based on ambient noise cross-correlation and a 3D model of the basin depths that integrates gravity data have been developed. The local earthquake data are being used to produce the first high-resolution attenuation model for the region. High-frequency (> 1 Hz) attenuation can be separated into its scattering and absorption contributions. The P- and S- phase picks from recorded earthquakes will be utilized to obtain peak delay times, which are a measure of forward scattering. The exponential decay of the coda wave envelopes quantified by the quality factor, Qc, can be used to invert for the absorption anomalies. Here we present results on the data selection and assess the data quality and coverage needed to image scattering attenuation and absorption at different frequencies.

Key Words
Earth Model, Seismic Attenuation, Basin Amplification, San Gabriel Basin, San Bernardino Basin

Citation
Nardoni, C., Persaud, P., Omojola, J., & Clayton, R. (2022, 09). Imaging Seismic Attenuation across the Northern Los Angeles Basins with Dense Arrays. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
San Andreas Fault System (SAFS)