ModellingPwaves in seismic noise correlations: advancing fault monitoring using train traffic sources

Korbinian Sager,Aurélien Mordret,Heiner Igel,Florent Brenguier,Victor C Tsai,Pierre Boué,Yixiao Sheng

doi:10.1093/gji/ggab389

Abstract

SUMMARYThe theory of Green’s function retrieval essentially requires homogeneously distributed noise sources. Even though these conditions are not fulfilled in nature, low-frequency (&lt;1 Hz) surface waves generated by ocean–crust interactions have been used successfully to image the crust with unprecedented spatial resolution. In contrast to low-frequency surface waves, high-frequency (&gt;1 Hz) body waves have a sharper, more localized sensitivity to velocity contrasts and temporal changes at depth. In general, their retrieval using seismic interferometry is challenging, and recent studies focus on powerful, localized noise sources. They have proven to be a promising alternative but break the assumptions of Green’s function retrieval. In this study, we present an approach to model correlations between P waves for these scenarios and analyse their sensitivity to 3-D Earth structure. We perform a series of numerical experiments to advance our understanding of these signals and prepare for an application to fault monitoring. In the considered cases, the character of the signals strongly diverges from Green’s function retrieval, and the sensitivity to structure has significant contributions in the source direction. An accurate description of the underlying physics allows us to reproduce observations made in the context of monitoring the San Jacinto Fault in California using train-generated seismic waves. This approach provides new perspectives for detecting and localizing temporal velocity changes previously unnoticed by commonly exploited surface-wave reconstructions.

Highlights

The retrieval of low-frequency (
More studies have shown that direct P waves travelling at distances of a few kilometres can emerge from the correlation of powerful, localized noise sources such as surf break (Roux et al 2005; Nakata et al 2016; Brenguier et al 2020) or car/train traffic (Nakata et al 2011; Brenguier et al 2019; Dales et al 2020; Pinzon-Rincon 2021)
The correlation of seismic waves generated by localized noise sources such as vehicle traffic breaks the assumption of uniformly distributed noise sources required for the process of Green’s function retrieval (Lobkis & Weaver 2001; Wapenaar 2004)

Summary

Introduction

The retrieval of low-frequency (1 Hz) P waves generated using active sources have been used to image sharp structural boundaries down to Moho depths (Davenport et al 2017). Nakata et al 2015 were among the first to report the retrieval of high-frequency direct and refracted P waves from the correlation of cultural noise in the Los Angeles basin. More studies have shown that direct P waves travelling at distances of a few kilometres can emerge from the correlation of powerful, localized noise sources such as surf break (Roux et al 2005; Nakata et al 2016; Brenguier et al 2020) or car/train traffic (Nakata et al 2011; Brenguier et al 2019; Dales et al 2020; Pinzon-Rincon 2021). This work aims at better understanding the origin of these interferometric body waves in the case of localized sources, including their 3-D sensitivity to velocity perturbations at depth

Objectives

Discussion

Conclusion