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Moment Magnitudes (Mw) of Smaller Events Using Distributed Acoustic Sensing (DAS)

Session: Fiber-Optic Seismology II

Type: Oral

Date: 4/23/2021

Presentation Time: 02:45 PM Pacific

Description: 

During a geothermal monitoring experiment at Brady Hot Springs, Nevada both Quantitative Distributed Acoustic Sensing (DAS) and nodal geophones were deployed on the surface for two weeks in March 2016. DAS array consisted of ~8 km of fiber-optic cable deployed in zig-zag pattern in shallow trench and the conventional seismometer array was composed of shallowly buried three-component geophones (Fairfield Nodal systems). Both DAS and geophones recorded continuously for fifteen days during which two moderate-sized earthquakes with a local magnitude of Mw=4.3 (3/21/16) and Mw=4.1 (3/22/16) were recorded. The epicenters of both events were at similar epicentral distances (129 km and 156 km) and backazimuth (172° and 159°) with respect to Brady Hot Springs. These earthquakes provided a unique opportunity to investigate coda amplitude response similarity of envelopes between DAS and geophone and potential to estimate Mw using coda waves. Several DAS line segments with co-located geophone stations were used to compare the amplitude variation using narrow-band S-wave coda envelopes. Initial calculations of DAS coda envelope decay at each point showed remarkable similarity with geophone coda envelopes at all frequencies. Final source spectra and Mw matched source spectra from regional stations without any major scatter. As coda waves arrive from a range of azimuths, the azimuthal sensitivity of DAS is somewhat ameliorated. We will also show the recent software toolkit for straightforward and faster processing using the necessary large datasets which would provide an easier source parameters and subsurface imaging.

Presenting Author: Rengin Gök

Student Presenter: No

Authors