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Abstract Understanding the mechanisms of crustal deformation along convergent margins is critical to identifying seismogenic structures and assessing earthquake hazards for nearby urban centers. In the southern central Andes (28–33$$^{\circ }$$ S), differences in the style of middle to upper-crustal deformation and associated seismicity are highlighted by the January 19th, 2021 (Mw 6.5) San Juan earthquake. We integrate waveforms recorded at regional and teleseismic distances with co-seismic displacements calculated from local Global Navigation Satellite System time series, to re-estimate the source parameters of the 2021 San Juan earthquake, confirming a mid-crustal nucleation depth (21 ± 2 km) and right-lateral transpressional mechanism. Considered alongside decades of seismic observations and geological data, this event provides evidence for retroarc deformation partitioning among inherited basement faults and upper-crustal structures in response to oblique convergence of the Nazca and South American plates. As they may transfer shortening to active upper-crustal faults associated with historically devastating shallower earthquakes, a better understanding of seismogenic basement faults such as the mid-crustal structure activated during the 2021 San Juan earthquake earthquake could help future re-assessment of the seismic risk in western Argentina.
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Seismicity and Present‐Day Crustal Deformation in the Southern Puna Plateau
Abstract The Southern Puna plateau in the central Andes has a complicated tectonic history that includes episodes of distributed shortening and extension, lithospheric delamination, uplift and Quaternary backarc volcanism. In this study, the upper crustal structure and present‐day deformation in this area is investigated using a new regional earthquake catalog derived with a deep‐learning‐based phase picker. Results show abundant strike‐slip seismicity at shallow depths in the eastern Southern Puna plateau that reveals active fault systems in the area and indicates N‐S extension/E‐W compression that changes orientation and relative magnitude from north to south. A broad zone of seismic quiescence in the western plateau may indicate a zone of upper crustal decoupling from large‐scale deformation. The region separating the western and eastern plateau exhibits a complex stress field that can be related to the boundary of east/west oriented middle‐to‐lower crustal flow in the main volcanic arc. Southeast of the plateau in the Sierras Pampeanas, crustal seismicity deepens and is dominated by conjugate reverse faulting structures associated with the direction of plate convergence. Vp and Vs seismic velocity models of the upper crust obtained through local earthquake tomography with the improved seismic catalog show low‐velocity anomalies near intermontane basins, except in the Antofagasta basin where a high‐velocity anomaly possibly represents shallow intrusive component of Quaternary basaltic volcanism. Below the Cerro Galan caldera, an upper crustal 10‐day long earthquake swarm is observed which may indicate local stress perturbations from fluids at the top of the crustal magmatic system that feeds this volcano.
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- Award ID(s):
- 2020935
- PAR ID:
- 10587864
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 129
- Issue:
- 12
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2024JB028918
