Finite-Source Model of the 8 July 2021 M 6.0 Antelope Valley, California, Earthquake

Abstract

Abstract We present a finite-source coseismic slip model of the 2021 Mw 6.0 Antelope Valley earthquake based on the joint inversion of regional seismic waveforms, Interferometric Synthetic Aperture Radar (InSAR), and Global Navigation Satellite Systems data. The results show that the mainshock rupture was dominated by normal slip along a nearly north–south-trending fault dipping to the east. The rupture lasted for ∼10 s, with primarily unilateral propagation toward the south. Most coseismic slip is found to be within a depth range between 6 and 10 km, with apparently no slip reaching the surface. Surface projection of the modeled fault plane matches well with the southern extension of the previously mapped Slinkard Valley fault (SVF). Aftershocks one year after the mainshock are mostly distributed within a relatively narrow band of 2–3 km thickness around the up-dip portion of the inferred coseismic rupture plane. There is little aftershock activity below 10 km, suggesting a relatively shallow brittle-to-ductile transition in this area. Aftershocks are also clustered at shallow depth beneath several branches of the Antelope Valley faults to the east of the mainshock rupture, including the Mw 4.4 event on 27 August 2021, which produced clear coseismic surface deformation observed by InSAR. Most aftershocks, immediately up-dip of the coseismic rupture and to the east beneath the Antelope Valley faults, are in areas of substantial coseismic Coulomb stress increase, particularly when assuming that all faults in this area dip to the east. This suggests that like the SVF that hosted the mainshock, the Antelope Valley faults in this area also dip to the east. There is little to no postseismic deformation seen from InSAR observations ∼2 months after the mainshock. The lack of clear coseismic and postseismic slip on the shallow portion of the fault suggests the potential for future shallow seismic activity.