Present‐Day Deformation Mechanism of the Northeastern Mina Deflection Revealed by the 2020 Mw 6.5 Monte Cristo Range Earthquake

• Published in: Geophysical research letters Vol. 47; no. 22
• Main Authors: Zheng, Ao, Chen, Xiaofei, Xu, Wenbin
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.11.2020
• Subjects: Accommodation; Broadband; Data analysis; Data integration; Deflection; Deformation; Deformation mechanisms; Earthquakes; Fault lines; Geological faults; Interferometric synthetic aperture radar; Obliquity; Plate motion; Plate tectonics; Plates (tectonics); Radar data; Rupture; Rupturing; SAR (radar); Segments; Seismic activity; Seismic data; Seismological data; Seismology; Shear zone; Slip; Synthetic aperture radar; Tectonics
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL090142

The 15 May 2020 Monte Cristo Range Mw 6.5 earthquake occurred in the northeast of the Mina deflection, which accommodates approximately a quarter of the relatively dextral motion between the Pacific and North American plates. The Monte Cristo Range event provides an opportunity to study the present‐day regional deformation mechanism and active tectonics. In this study, we investigate the source rupture process of the event using joint inversion of interferometric synthetic aperture radar and broadband seismic data. We find that the rupture propagates almost simultaneously on two main segments. The fault motion changes from the predominantly sinistral slip near the epicenter on the eastern segment to the oblique slip on the western segment, with a maximum coseismic slip of 0.8 m. Our results suggest that the accommodation of slip transfer localized in the northeastern Mina deflection tends to transform from the wrench‐ to extension‐dominated transtension. Plain Language Summary The relative motion between the Pacific and North American plates is largely focused on the dextral San Andreas fault system. A complex array of strike‐slip and normal faults, known as the Walker Lane and the Eastern California shear zone, accommodates about a quarter of this plate motion. The 2020 Monte Cristo Range earthquake struck the Mina deflection, a right stepover between two parallel but noncoplanar faults. The Mina deflection is considered to transfer slip from the southern to central Walker Lane. Because of the obliquity between the plate motion and the fault orientation, the deformation across the Mina deflection is generally interpreted as wrench‐dominated transtension, commonly characterized by strike slip and block rotation. We reconstruct the spatial and temporal process of the source rupture by integrated geodetic and seismological data analysis and find that the accommodation of slip transfer in the northeast of the Mina deflection has a tendency to evolve into the extension‐dominated transtension, thereby harboring normal faulting. We suggest that this behavior is because the extensional pure shear accumulates more rapidly compared with the wrench simple shear. Key Points Source rupture process of the 2020 Monte Cristo Range earthquake is derived using joint inversion of geodetic and seismic data Two fault segments with varied orientations ruptured, producing oblique and sinistral slip on the western and eastern segments, respectively Accommodation of slip transfer in the northeastern Mina deflection tends to transform from wrench‐ to extension‐dominated transtension