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Reverse-Time Migration of Fault Zone Reflected Waves: Methodology and Application to the Southern San Andreas Fault

Session: Recent Development in Ultra-Dense Seismic Arrays with Nodes and Distributed Acoustic Sensing

Type: Oral

Date: 4/20/2021

Presentation Time: 06:30 PM Pacific

Description: 

High-resolution imaging of fault geometry at depth is challenging. Velocity models derived from tomography methods that utilize travel times and waveforms of body and surface waves only provide smoothed images. In contrast, waves refracted along or reflected from the impedance contrast across major faults have the potential to illuminate the geometry of fault interfaces at depth with unprecedented resolution. Such waves have been observed in data recorded by near-fault stations and dense fault zone arrays. In this study, we develop a novel method to infer fault-related reflection interfaces by applying the cross-correlation imaging condition to reflected and transmitted waves recorded by dense linear arrays crossing major faults. Compared to traditional reverse-time migration methods, our approach does not require accurate source information and works particularly well in imaging near-vertical interfaces. Migration images obtained using a smoothed velocity model and synthetic reflected and transmitted waves computed for a flower-shaped fault zone model show accurate geometry of the fault zone edges. The developed migration method is applied to data recorded by a ~4-km-long dense linear 3-component nodal array crossing surface traces of the Mission Creek and Banning strands of the Southern San Andreas fault zone around the Thousand Palms Oasis Preserve, California. The resulting migration images from P and S waves generated by several regional earthquakes reveal high-resolution interfaces of the Mission Creek and Banning faults that are consistently dipping steeply toward the NE in the top 2-3 km.

Presenting Author: Benxin Chi

Student Presenter: No

Authors