Co-seismic rupture process of the 2019 Ridgecrest earthquake sequence from joint inversion of geodetic and seismological observations
Abstract
On July 4th and 6th, 2019, two large strike-slip earthquakes with W-phase magnitudes MWW 6.5 (foreshock) and MWW 7.1 (mainshock) struck the eastern California shear zone, northeast of Ridgecrest. These earthquakes were very well recorded regionally by dense geodetic and seismological networks. We determine the faulting geometry and kinematic co-seismic slip distribution of both events by jointly inverting teleseismic body waves, local strong motions, and GPS static displacements. The fault geometry is constrained by measured surface rupture traces reported by the United States Geological Survey (USGS) and by the aftershock distribution from the USGS National Earthquake Information Center (NEIC). These define a prominent NW-SE trend with a secondary NE-SW trend activated during the foreshock.
For the final joint inversion, the foreshock fault system is parameterized with two nearly perpendicular faults with strikes of 227° (F1, 85° dip) and 316° (F2, 90° dip), accounting for a prominent "L" distribution apparent in the immediate aftershocks. The mainshock faulting extends along the NW-SE direction and includes four vertical rupture segments, labeled F1, F2, F3 and F4 with strikes of 315°, 334°, 312° and 316°, respectively. Fault F4 overlaps with F2 from the foreshock. The preferred fault systems are able to better account for all datasets than parsimonious single-segment planar fault models. The foreshock inversion indicates primary slip concentration along the surface rupture for F1, extending ~20 km along strike and ~10 km along dip with a maximum slip of ~1.1 m. Secondary slip occurred on F2, extending northwestward from the intersection with F1, during the first 5 s with a maximum slip of 0.8 m. The mainshock rupture indicates that slip initiated about 8 km depth near the end of the rupture during the foreshock, and propagated bilaterally with an average rupture velocity of ~2.0-2.5 km/s. The rupture process lasted about 40 s, with the primary moment release within the first 20 s, on faults F1- F3. The largest coseismic slip for the mainshock is over 4 m and is located just northwest of the hypocenter. The surface rupture shows a combination of strike-slip and dip-slip. The model dip-slip component is generally small at the surface, except on F2 and F3, where the slip has significant dip-slip component with slip of up to ~1.5-2 m. Both the foreshock and mainshock ruptures terminate in regions of complex surface offsets. High aftershocks productivity may correspond to rupture of relatively immature faults with complex distribution.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S31G0489L
- Keywords:
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- 7299 General or miscellaneous;
- SEISMOLOGY