Ground motion response to an ML 4.3 earthquake using co-located distributed acoustic sensing and seismometer arrays

TitleGround motion response to an ML 4.3 earthquake using co-located distributed acoustic sensing and seismometer arrays
Publication TypeJournal Article
Year of Publication2018
AuthorsWang, HF, Zeng, X, Miller, D, Fratta, D, Feigl, KL, Thurber, CH, Mellors, RJ
JournalGeophysical Journal International
Pagination2020 - 2036
Date PublishedMay-03-2019
ISSN0956-540X
Abstract

The PoroTomo research team deployed two arrays of seismic sensors in a natural laboratory at Brady Hot Springs, Nevada in March 2016. The 1500 m (length) × 500 m (width) × 400 m (depth) volume of the laboratory overlies a geothermal reservoir. The distributed acoustic sensing (DAS) array consisted of about 8400 m of fiber-optic cable in a shallow trench and 360 m in a well. The conventional seismometer array consisted of 238 shallowly buried three-component geophones. The DAS cable was laid out in three parallel zig-zag lines with line segments approximately 100 m in length and geophones were spaced at approximately 60 m intervals. Both DAS and conventional geophones recorded continuously over 15 d during which a moderate-sized earthquake with a local magnitude of 4.3 was recorded on 2016 March 21. Its epicentre was approximately 150 km south–southeast of the laboratory. Several DAS line segments with co-located geophone stations were used to compare signal-to-noise ratios (SNRs) in both time and frequency domains and to test relationships between DAS and geophone data. The ratios were typically within a factor of five of each other with DAS SNR often greater for P-wave but smaller for S-wave relative to geophone SNR. The SNRs measured for an earthquake can be better than for active sources because the earthquake signal contains more low-frequency energy and the noise level is also lower at those lower frequencies. Amplitudes of the sum of several DAS strain-rate waveforms matched the finite difference of two geophone waveforms reasonably well, as did the amplitudes of DAS strain waveforms with particle-velocity waveforms recorded by geophones. Similar agreement was found between DAS and geophone observations and synthetic strain seismograms. The combination of good SNR in the seismic frequency band, high-spatial density, large N and highly accurate time control among individual sensors suggests that DAS arrays have potential to assume a role in earthquake seismology.

URLhttps://academic.oup.com/gji/article/213/3/2020/4942237?guestAccessKey=d836305e-809d-4abd-917e-0f19b4c76282
DOI10.1093/gji/ggy102