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- Title
Fracture‐Mesh Faulting in the Swarm‐Like 2020 Maacama Sequence Revealed by High‐Precision Earthquake Detection, Location, and Focal Mechanisms.
- Authors
Shelly, David R.; Skoumal, Robert J.; Hardebeck, Jeanne L.
- Abstract
In August of 2020, an earthquake sequence initiated within the Maacama fault zone in northern California, raising questions about its relationship with the larger‐scale fault. To investigate the faulting geometry and its implications for physical processes driving seismicity, we applied an integrated, multi‐faceted seismic analysis including waveform‐correlation‐based event detection, relative relocation, and high‐precision focal mechanisms. To determine mechanisms for a large population of very small earthquakes (predominantly M < 1), we combined correlation‐derived polarity analysis with a recently developed technique to determine S/P amplitude ratios from single seismic components. Finally, we applied an iterative stress inversion to distinguish between the likely fault and auxiliary planes. This analysis reveals that although the sequence initiated on a right‐lateral fault, plausibly a strand of the Maacama Fault, it also activated numerous en echelon left‐lateral conjugate faults. Together, these interlocking faults form a fracture mesh, consistent with structures associated elsewhere with fluid‐induced faulting and earthquake swarms. Plain Language Summary: In August of 2020, an earthquake sequence initiated within the Maacama fault zone in northern California, raising questions about its relationship with the larger‐scale fault. To investigate the faulting geometry and its implications for physical processes driving seismicity, we applied multiple high‐resolution seismic analyses to determine precise locations and slip orientations. This analysis reveals complex fracture mesh faulting geometry consisting of interlocking faults with two primary orientations, consistent with structures associated elsewhere with fluids and earthquake swarms. Key Points: A swarm‐like earthquake sequence occurred in 2020 near the Maacama Fault in northern California, with magnitudes up to Mw 4.2We determined precise locations for 3,520 events and focal mechanisms for 3,253 events, expanding the routine catalog of 388 earthquakesAn iterative stress inversion distinguishes likely fault planes, revealing en echelon and conjugate faults forming a fracture mesh
- Subjects
CALIFORNIA; EARTHQUAKE swarms; EARTHQUAKES; FAULT zones; EARTHQUAKE aftershocks; EARTHQUAKE magnitude; NATURAL disaster warning systems
- Publication
Geophysical Research Letters, 2023, Vol 50, Issue 1, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2022GL101233