Train Traffic as a Powerful Noise Source for Monitoring Active Faults With Seismic Interferometry.

F Brenguier,A Mordret,E Beaucé,Y Ben‐Zion,O Coutant,P Boué,P.‐E Share,F Vernon,D Hollis,C.W Johnson,T Lecocq

doi:10.1029/2019gl083438

Abstract

Laboratory experiments report that detectable seismic velocity changes should occur in the vicinity of fault zones prior to earthquakes. However, operating permanent active seismic sources to monitor natural faults at seismogenic depth is found to be nearly impossible to achieve. We show that seismic noise generated by vehicle traffic, and especially heavy freight trains, can be turned into a powerful repetitive seismic source to continuously probe the Earth's crust at a few kilometers depth. Results of an exploratory seismic experiment in Southern California demonstrate that correlations of train‐generated seismic signals allow daily reconstruction of direct P body waves probing the San Jacinto Fault down to 4‐km depth. This new approach may facilitate monitoring most of the San Andreas Fault system using the railway and highway network of California.

Highlights

Recent observations of early deformation phases preceding moderate to large earthquakes (Bouchon et al, 2011; Kato et al, 2012; Niu et al, 2008) raise the hope that real‐time, continuous monitoring of fault zones will allow improved earthquake forecasting. Scuderi et al (2016) observed precursory changes of seismic wave speed in laboratory faults for the complete spectrum of failure modes found for tectonic faults
We show that seismic noise generated by vehicle traffic, and especially heavy freight trains, can be turned into a powerful repetitive seismic source to continuously probe the Earth's crust at a few kilometers depth
The cross correlation of seismic noise generated by extended sources in space and recorded at two sensors were shown to provide the impulsive response of the Earth between the two sensors as if a virtual source was emitted at each of the sensors

Summary

Introduction

Recent observations of early deformation phases preceding moderate to large earthquakes (Bouchon et al, 2011; Kato et al, 2012; Niu et al, 2008) raise the hope that real‐time, continuous monitoring of fault zones will allow improved earthquake forecasting. Scuderi et al (2016) observed precursory changes of seismic wave speed in laboratory faults for the complete spectrum of failure modes found for tectonic faults. Following the prediction of strong traffic‐generated noise in the Coachella Valley, we designed the location and separation (30 km) between two arrays (total of 400 seismic stations) located at the Piñon Flat Observatory and the Cahuilla Indian Reservation, so that the noise sources required for the reconstruction of direct P waves traveling through the fault at 4‐km depth between the arrays coincides with high‐traffic railways and highways in the Coachella Valley (Figure 1a). By filtering the raw seismograms of the Piñon Flat array (1–10 Hz) and by stacking all traces with an apparent velocity of 6 km/s for body waves in the direction of the stationary phase zone in the Coachella Valley (white circle in Figure 1), we observe about 25 daily tremor‐like signals lasting about 15 min (yellow trace in Figure 2) that fit very well with the timing of trains running through the Coachella Valley and recorded by seismic stations along the railway

Predicted Level of Train‐Radiated Body Waves Across California

Findings

Conclusions and Perspectives