Imaging the Northern Los Angeles Basins with Autocorrelations

TL;DR

This study demonstrates how autocorrelation of ambient noise and teleseismic waves can image subsurface reflectivity in Los Angeles basins, aiding seismic hazard assessment.

Contribution

It introduces a method to extract zero-offset reflection responses from autocorrelations, improving subsurface imaging using ambient noise and teleseismic data.

Findings

Autocorrelation reveals basin reflectivity consistent with receiver functions.

Method effectively images subsurface structures using ambient noise.

Results enhance understanding of seismic energy pathways in Los Angeles.

Abstract

We show reflectivity cross-sections for the San Gabriel, Chino, and San Bernardino basins north of Los Angeles, 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 Los Angeles and a more accurate model of their depth is important for hazard mitigation. We use the causal side of the autocorrelation function 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 in order 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 autocorrelation function from teleseismic events can provide illumination of subsurface that is consistent with ambient noise. Both autocorrelation results compare favorably to receiver functions.