Relocalización sísmica mediante determinación conjunta de hipocentros (JHD): Implicancias tectónicas en el norte de la Precordillera de San Juan, Argentina

Seismic relocation using joint hypocenter determination (JHD): Tectonic implications for the northern San Juan Precordillera, Argentina

Carolina Rivas1,2,3,* , Pablo A. Blanc2,4 , Laura Perucca1,2

1 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Ministerio de Ciencia, Tecnología e Innovación. República Argentina.

2 Gabinete de Neotectónica y Geomorfología. INGEO. Facultad de Ciencias Exactas, Físicas y Naturales. Universidad Nacional de San Juan, 5402, San Juan, Argentina.

3 Departamento de Geofísica y Astronomía. Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de San Juan. Av. Ignacio de la Roza Oeste 590, Rivadavia, San Juan, Argentina, CPA: J5402DCS.

4 Cátedra de Edafología. Facultad de Ciencias Agrarias. Universidad Nacional de Cuyo. Almte. Brown 500. Luján de Cuyo. CPA M5528AHB ‑ Mendoza ‑ Argentina

*Autor para correspondencia: (C. Rivas) This email address is being protected from spambots. You need JavaScript enabled to view it.

Cómo citar este artículo: 

Rivas C., Blanc, P. A., & Perucca, L. (2026). Relocalización sísmica mediante determinación conjunta de hipocentros (JHD): Implicancias tectónicas en el norte de la Precordillera de San Juan, Argentina: Boletín de la Sociedad Geológica Mexicana, 78(2), A171225. https://doi.org/10.18268/BSGM2026v78n2A171225

Manuscrito recibido: 1 de agosto, 2025. Manuscrito corregido: 14 de octubre, 2025. Manuscrito aceptado: 25 de octubre, 2025.

ABSTRACT

This study presents a detailed analysis of crustal seismicity in the northern sector of the Argentinean Andean Precordillera (29°–30.8°S), located above the flat-slab segment of the Nazca Plate subducting beneath South America, known as the Chilean-Pampean flat-slab. A total of 92 earthquakes recorded between 2000 and 2020 were relocated using the Joint Hypocenter Determination (JHD) method, incorporating both broadband and short-period seismic stations. Three regional velocity models were evaluated, with the Furlani model yielding the lowest misfit. Seismicity is primarily concentrated between 20 and 35 km depth, with a notable cluster around 30.4°S. Magnitudes range from ML 0.8 to 5.2 and MW 1.2 to 5.1. Focal mechanisms for 43 relocated events were determined based on P-wave first-motion polarities and P/S amplitude ratios, using the FOCMEC, FPFIT, HASH, and PINV programs. For the largest-magnitude event, a more detailed characterization of the seismogenic source (depth and faulting style) was achieved through seismic moment tensor inversion by modeling broadband waveforms and applying the DREGER technique. The resulting focal mechanisms indicate a predominantly compressive regime, although some events show oblique and strike-slip components. Regional stress tensor inversion reveals a nearly horizontal σ1 with an azimuth of 107° and a near-vertical σ3, indicating a tectonic setting dominated by compressive stresses. These results highlight the importance of refined hypocentral and focal mechanism data for interpreting active crustal deformation and its potential correlation with surface geological structures. This contributes new data toward a more robust seismotectonic characterization and improved seismic hazard assessment in the Andean back-arc region.

Keywords: seismogenic source, seismic relocation, focal mechanism, seismic moment tensor inversion, stress regime.