Imaging the Northern Los Angeles Basins with Autocorrelations

Creators: Zou, Caifeng¹; Clayton, Robert W.¹

1. California Institute of Technology

Abstract

We show reflectivity cross sections for the San Gabriel, Chino, and San Bernardino basins north of Los Angeles (LA), California, determined from autocorrelations of ambient noise and teleseismic earthquake waves. These basins are thought to channel the seismic energy from earthquakes on the San Andreas fault to LA, and a more accurate model of their depth is important for hazard mitigation. We use the causal side of the autocorrelation function (ACF) to determine the zero-offset reflection response. To minimize the smoothing effect of the source time function, we remove the common mode from the autocorrelation to reveal the zero-offset reflection response. We apply this to 10 temporary nodal lines consisting of a total of 758 geophones with an intraline spacing of 250–300 m. We also show that the ACF from teleseismic events can provide illumination on the subsurface that is consistent with ambient noise. Both autocorrelation results compare favorably to receiver functions.

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Acknowledgement

The authors thank all the volunteers who helped with deploying the dense nodal arrays. This research was supported by the National Science Foundation Awards 2105358 and 2105320. The Basin Amplification Seismic Investigation (BASIN) project was partly supported by U.S. Geological Survey Awards GS17AP00002 and G19AP00015, and Southern California Earthquake Center Awards 18029 and 19033.

Data Availability

The primary data (node data) used in this study are available from the Incorporated Research Institutions for Seismology Data Management Center. The autocorrelation functions and processing code underlying this article are made public at https://github.com/caifeng-zou/BASIN_ACF (last accessed September 2024). The supplemental material to this article includes a list of shear‐wave velocities used to match the time and depth scales in Figures 5 and 6 (Table S1), an example image using a correlation length of one week (Fig. S1), an example ZZ autocorrelation function (Fig. S2), and the VS model plot (Li et al., 2023) for SB1 (Fig. S3).

Supplemental Material

Supplementary data (PDF)

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