Fiber‐Optic Network Observations of Earthquake Wavefields

Abstract

Our understanding of subsurface processes suffers from a profound observation bias: seismometers are sparse and clustered on continents. A new seismic recording approach, distributed acoustic sensing (DAS), transforms telecommunication fiber‐optic cables into sensor arrays enabling meter‐scale recording over tens of kilometers of linear fiber length. We analyze cataloged earthquake observations from three DAS arrays with different horizontal geometries to demonstrate some possibilities using this technology. In Fairbanks, Alaska, we find that stacking ground motion records along 20 m of fiber yield a waveform that shows a high degree of correlation in amplitude and phase with a colocated inertial seismometer record at 0.8–1.6 Hz. Using an L‐shaped DAS array in Northern California, we record the nearly vertically incident arrival of an earthquake from The Geysers Geothermal Field and estimate its backazimuth and slowness via beamforming for different phases of the seismic wavefield. Lastly, we install a fiber in existing telecommunications conduits below Stanford University and show that little cable‐to‐soil coupling is required for teleseismic P and S phase arrival detection.

The Potential of DAS in Teleseismic Studies: Insights From the Goldstone Experiment

“…In the supporting information, we further demonstrate the angle dependence of ε xx for P, SV, and SH particle motions (e.g., Benioff, 1935;Lindsey et al, 2017;Martin et al, 2018). In the supporting information, we further demonstrate the angle dependence of ε xx for P, SV, and SH particle motions (e.g., Benioff, 1935;Lindsey et al, 2017;Martin et al, 2018).…”

“…For example, Lindsey et al (2017) analyzed regional/teleseismic earthquake waveforms from three different DAS arrays in Alaska and California. Several field experiments have been carried out recently.…”

“…The great consistency of earthquake waveforms recorded by DAS and by conventional seismometers (e.g., Ajo-Franklin et al, 2019;Lindsey et al, 2017;Wang et al, 2018), the observations of broadband sensitivity on DAS (Ajo-Franklin et al, 2019;Becker et al, 2017), and the availability of existing telecommunication infrastructures (e.g., Ajo-Franklin et al, 2019;Jousset et al, 2018;Lindsey et al, 2017) motivate us to provide more in-depth analyses of DAS earthquake waveforms. Here we explore the potential applications of DAS to teleseismic studies using the Goldstone OpticaL Fiber Seismic (GOLFS) experiment in Goldstone, California.…”

On the Broadband Instrument Response of Fiber‐Optic DAS Arrays

“…Here, we restrict our focus to a single commercial instrument, the Silixa iDAS (Version 2), which is a time domain, single‐pulse, phase‐based DAS instrument (Parker et al, ). This particular DAS instrument is among the more widely utilized in the field of earthquake seismology (Ajo‐Franklin et al, ; Jousset et al, ; Lindsey et al, ; Wang et al, ; Yu et al, ). The following discussion of the relationship between ground motion and DAS data is a synthesis of many works including Bakku (), Bóna et al (), Dean et al (), Grattan and Meggitt (), Hartog (), Kreger et al (), Karrenbach et al (), Masoudi and Newson (), Posey et al (), Parker et al (), and Willis et al (), as well as U.S. patents on the technology (Farhadiroushan et al, ).…”

“…Generally, DAS studies have focused on seismic wave phase information, which is sufficient to model seismic wavefield velocities, for example, in vertical seismic profiling (Daley et al, ; Mateeva et al, ), ambient noise velocity inversions (Ajo‐Franklin et al, ; Dou et al, ; Zeng et al, ), and earthquake phase identification (Ajo‐Franklin et al, ; Jousset et al, ; Lindsey et al, ; Yu et al, ). However, true ground motion amplitudes are necessary for many other seismological processing tasks, including full‐waveform inversion, AVO analysis, moment tensor inversion, and attenuation analysis, which the DAS community will likely investigate in the near future (Cole et al, ; Paitz et al, ).…”