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Poster #066, Seismology

Temporal Seismic Velocity Variations: Recovery Following from the 2019 Mw 7.1 Ridgecrest Earthquake

Joshua Boschelli, Morgan P. Moschetti, & Christoph Sens-Schönfelder
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Poster Presentation

2020 SCEC Annual Meeting, Poster #066, SCEC Contribution #10202 VIEW PDF
We investigated seismic velocity changes (dv/v) associated with the 2019 Ridgecrest earthquake sequence from high-frequency autocorrelations of ambient seismic noise data. Daily autocorrelation functions were computed for the entirety of 2019 for the permanent broadband stations within the region that experienced strong ground shaking, with a peak ground acceleration greater than 10 percent of g during the Mw 7.1 earthquake and for the temporary broadband stations installed during the aftershock deployment. Travel time shifts in the daily autocorrelation functions, relative to the mean autocorrelation, were computed to produce dv/v time series, which are sensitive to the evolving material p...roperties of the shallow crust surrounding the Ridgecrest fault zone (RFZ). A short-term velocity drop follows the Mw 7.1 earthquake at stations in the vicinity of the Mw 7.1 earthquake, while those greater than 50 km away showed no such drop despite recording peak ground accelerations of up to more than 22 % of g. Additionally, the maximum, absolute seismic velocity changes are proportional to the logarithm of distance from the fault rupture; the seismic velocity changes exhibit a weak correlation with peak horizontal ground accelerations, though variability is high and multiple sites are not explained by this relationship. For the stations that recorded a reduced seismic velocity, two distinctive temporal behaviors emerged. Near the areas of the highest coseismic slip within the RFZ, seismic velocities recovered over 3 months. However, in the vicinity of the nearby Garlock fault, where triggered slip manifested, and north of the RFZ, seismic velocities recovered within a month. We interpret the seismic velocity changes and their recovery to be largely due to changes in the physical properties of the shallow crust, such as fault zone damage recovery caused by the earthquake rupture process, and perhaps in response to the large dynamic stresses of passing seismic waves from the earthquake.