Improved High-Resolution 3D Vs Model of Long Beach, CA: Inversion of Multimodal Dispersion Curves From Ambient Noise of a Dense Array

Abstract

Ambient noise recorded by a dense seismic array provides an opportunity to resolve detailed 3D shear wave velocity (Vs) structures. We utilize the frequency-Bessel transform (F-J) method to compute the dispersion spectrogram for ambient noise recorded by the Long Beach seismic array, extract multimodal dispersion curves with a deep learning approach, and invert multimodal dispersion curves with a gradient algorithm. The addition of higher-mode dispersion curves reduces nonuniqueness and provides an improved high-resolution 3D Vs model that shows good correlations with the known stratigraphic sequence and geologic features in the study area. Furthermore, the Richard fault between the Pacific Coast Highway and Newport-Inglewood faults, which have never been discussed in previous studies, is resolved. Our study demonstrates the potential of using the F-J method to extract multimodal dispersion curves and consequently retrieve an improved high-resolution 3D Vs model from a dense seismic array.