Surface Rupture Kinematics and Coseismic Slip Distribution during the 2019 Mw7.1 Ridgecrest, California Earthquake Sequence Revealed by SAR and Optical Images

Chenglong Li,Xinjian Shan,Dezheng Zhao,Yanchuan Li,Rui Jia,Jin Li,Zicheng Huang,Jing Nie,Guohong Zhang

doi:10.3390/rs12233883

Abstract

The 2019 Ridgecrest, California earthquake sequence ruptured along a complex fault system and triggered seismic and aseismic slips on intersecting faults. To characterize the surface rupture kinematics and fault slip distribution, we used optical images and Interferometric Synthetic Aperture Radar (InSAR) observations to reconstruct the displacement caused by the earthquake sequence. We further calculated curl and divergence from the north-south and east-west components, to effectively identify the surface rupture traces. The results show that the major seismogenic fault had a length of ~55 km and strike of 320° and consisted of five secondary faults. On the basis of the determined multiple-fault geometries, we inverted the coseismic slip distributions by InSAR measurements, which indicates that the Mw7.1 mainshock was dominated by the right-lateral strike-slip (maximum strike-slip of ~5.8 m at the depth of ~7.5 km), with a small dip-slip component (peaking at ~1.8 m) on an east-dipping fault. The Mw6.4 foreshock was dominated by the left-lateral strike-slip on a north-dipping fault. These earthquakes triggered obvious aseismic creep along the Garlock fault (117.3° W–117.5° W). These results are consistent with the rupture process of the earthquake sequence, which featured a complicated cascading rupture rather than a single continuous rupture front propagating along multiple faults.

Highlights

From 4 July to 6 July 2019, a sequence of damaging earthquakes (Mw > 5) struck the northeast region of Ridgecrest, in southern California
The derived multiple faults model of the Mw7.1 mainshock contains three secondary faults, which are fault I located on the northwest of the epicenter (Figure 11g, releasing bend shown in the Figure 2); fault II with the strike of 310◦, length of 10 km, and maximum slip 4 m distributed between the Mw7.1 and the Mw6.4 epicenter (Figure 11h); and fault III (Figure 11i) with a length of 15 km, strike of 319◦, and the slip peaking at 2 m west of the Mw7.1 main fault
The rupture process of the earthquake sequence could be a cascading rupture rather than a single continuous rupture propagating along multiple faults [45,46,47,48]

Summary

Introduction

From 4 July to 6 July 2019, a sequence of damaging earthquakes (Mw > 5) struck the northeast region of Ridgecrest, in southern California. The horizontal displacement field reconstructed by the subpixel optical image correlation provides valuable information on the near-fault (the region within 1 km of the seismogenic fault, where SAR images usually decorrelate) deformation patterns [17], which is of great help to reveal how the fault rupture broke the surface and gives robust constraints on the shallowest part of the fault slip model [18]. Utilizing InSAR line-of-sight (LOS) observations and the horizontal measurements of optical images to reconstruct surface displacements can obtain the kinematic rupture characteristics [19] and slip distribution in a fault model. We reconstructed the coseismic horizontal displacement field (north-south (NS) and east-west (EW) components) using Sentinel-2 optical images, and we computed the curl and divergence of the NS and EW components to quantitatively analyze and demonstrate the geometric complexity of the surface rupture produced by the Ridgecrest earthquake sequence. We used the derived multiple-fault slip model to calculate the static Coulomb stress changes, and investigated the possible triggering relationships between the seismic slip and aseismic slip involved in the earthquake sequence

Data and Methods

Multiple Faults Slip Distribution

Cascading Rupture Process

Conclusions