Detailed seismic imaging of the Mw 7.1 Ridgecrest earthquake rupture zone from data recorded by dense linear arrays

Hongrui Qiu, Yehuda Ben-Zion, Rufus D. Catchings, Mark R. Goldman, Amir A. Allam, & Jamison H. Steidl

Under Review November 1, 2020, SCEC Contribution #10905

We analyze seismograms recorded by four arrays (B1-B4) with 100-m station spacing and apertures of 4-8 km that cross the surface rupture of the 2019 Mw7.1 Ridgecrest earthquake. The arrays extend from B1 in the northwest to B4 in the southeast of the surface rupture. Delay times between P-wave arrivals associated with ∼1200 local earthquakes and four teleseismic events are used to estimate local velocity variations beneath the arrays. Both teleseismic and local P waves travel faster on the northeast than the southwest side of the fault for ~4.6% and ~7.5% beneath arrays B1 and B4, but the contrast is less significant at arrays B2 and B3. We identify several 1- to 2-km-wide low-velocity zones with more intensely damaged inner cores beneath each array. The damage zone at array B4 generates fault-zone head, reflected, and trapped waves. An automated detector, based on peak ground velocities and durations of high-amplitude waves, identifies candidate fault-zone trapped waves (FZTWs) in a localized zone for ~600 earthquakes. Synthetic waveform modeling of averaged FZTWs, generated by ~30 events with high-quality signals, indicate that the trapping structure at array B4 has a width of ∼300 m, depth of 3-5 km, S-wave velocity reduction of ∼20% with respect to the surrounding rock, Q-value of ∼30, and S-wave velocity contrast of ~4% across the fault (faster on the northeast side). The results show complex fault-zone internal structures that vary along fault strike, in agreement the surface geology (alternating playa and igneous rocks).

Citation
Qiu, H., Ben-Zion, Y., Catchings, R. D., Goldman, M. R., Allam, A. A., & Steidl, J. H. (2020). Detailed seismic imaging of the Mw 7.1 Ridgecrest earthquake rupture zone from data recorded by dense linear arrays. Journal of Geophysical Research, (under review).