The Andean structure of the Sierras Pampeanas based on earthquake focal mechanisms in their Northwestern region

• Autores: Alvarado, P.; Ramos, V.A.
• Año de publicación: 2010
• Idioma: inglés
• Tipo de recurso: artículo
• Fuente: Rev. Asoc. Geol. Argent. 2010;67(4):461-472
• Materia: Andes; Compressive deformation; Decollement levels; Earthquakes; basement rock; compression; crustal structure; decollement; deformation; earthquake epicenter; earthquake magnitude; earthquake mechanism; focal mechanism; modeling; seismic moment; seismicity; seismotectonics; strain; strike-slip fault; waveform analysis; Ambato; Argentina; Catamarca; Sierras Pampeanas
• Institución: Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales

Modeling of broadband seismic waveforms recorded by global and Chilean networks for two moderate crustal earthquakes of the northwestern Sierras Pampeanas shows their focal mechanisms, depths and seismotectonic features. The magnitude Mw 5.8 earthquake on 28 May 2002, located in the eastern flank of the sierra de Velasco and the Mw 6.2 earthquake on 7 September 2004, with epicenter in the southwestern part of the sierra de Ambato, have shallow focal depths of 10 and 8 km, respectively. These results combined with the historical seismicity of the region allow us to estimate the deep structure of the Sierras Pampeanas in the study region. The seismic analyses together with interpretations of the surface structure and previous neotectonic studies ruled out extensional or strike slip deformation as the main responsible mechanism of the Present structure of this sector of the sierras de Ambato and Velasco in the northwestern Sierras Pampeanas. The comparison between the Nazca-South America plate convergence orientation as well as GPS velocities in the upper plate with the summation of the seismic moment tensor for the largest seismic energy released by crustal earthquakes of this region in the last 30 years, shows a clockwise rotation of 50° of the average P-axis orientation from the convergence orientation to the northeast suggesting important strain partition. This partition is controlled by the Eopaleozoic basement fabric, which has guided the orientation and vergence of the Andean faults.
Fil:Ramos, V.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.