Poster #063, Seismology

Detailed seismic imaging of the Mw7.1 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
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Poster Presentation

2020 SCEC Annual Meeting, Poster #063, SCEC Contribution #10186 VIEW PDF
We analyze seismograms recorded by four dense linear arrays oriented NE to SW with 100 m station spacing and apertures 4-8 km that cross the surface rupture of the July 5, 2019, Mw7.1 Ridgecrest earthquake in Southern California. The arrays extend from B1 in the NW to B4 in the SE 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 within the arrays. Both teleseismic and local P-waves travel faster on the northeast than the southwest sides of the fault beneath arrays B1 (~4.6%) and B4 (~7.5%), but the contrast is less significant at arrays B2 and B3. Several 1-2 km wide ...low-velocity fault damage zones are identified beneath each array. These low-velocity zones contain more intensely damaged inner cores (0.5-1.5 km wide) that produce additional 0.01-0.05 s delay in local P-wave arrival times. The damage zone at arrays B2 and B4 generate both fault-zone head and trapped waves. An automated detector based on peak ground velocities and durations of high amplitude waves identifies candidate fault zone trapped waves (FZTW) in a localized zone (300-400 m wide) for ~500 earthquakes. Synthetic waveform modeling of averaged FZTW generated by ~20 events with high-quality signals indicate that the trapping structure at array B4 has a width of ∼300 m, depth of ∼4 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 structures that vary along fault strike, in general agreement with the surface geology in the area (alternating playa and igneous rocks). Combining the observations with additional seismological results should provide a detailed multi-scale model of the rupture and surrounding area.