HR: 1340h
AN: S23B-0239    [Abstracts]
TI: Source Characterization of the Historic and Modern Earthquakes in the Andean Backarc Region (28°S - 36°S)
AU: * Alvarado, P M
EM: alvarado@geo.arizona.edu
AF: Department of Geosciences, Univ. of Arizona, Gould-Simpson Bldg, #77, 1040E 4th St., Tucson, AZ 85719 United States
AU: * Alvarado, P M
EM: alvarado@geo.arizona.edu
AF: Univ. Nac. de San Juan, Meglioli 1160 S, San Juan, 5400 Argentina
AU: Beck, S
S23B-0239 AF: Department of Geosciences, Univ. of Arizona, Gould-Simpson Bldg, #77, 1040E 4th St., Tucson, AZ 85719 United States
AU: Zandt, G
S23B-0239 AF: Department of Geosciences, Univ. of Arizona, Gould-Simpson Bldg, #77, 1040E 4th St., Tucson, AZ 85719 United States
AU: Group, C
S23B-0239 AF: Department of Geosciences, Univ. of Arizona, Gould-Simpson Bldg, #77, 1040E 4th St., Tucson, AZ 85719 United States
AU: Group, C
S23B-0239 AF: Univ. Nac. de San Juan, Meglioli 1160 S, San Juan, 5400 Argentina
AU: Group, C
S23B-0239 AF: Inst. Nac. de Prevencion Sismica (INPRES), R. Ballet 47 N, San Juan, 5400 Argentina
AU: Group, C
S23B-0239 AF: Univ. de Chile, B.Encalada 2002, Santiago, 2777 Chile
AB: Crustal seismicity in the Andes backarc region between 28°S and 36°S is responsible for the largest damaging earthquakes in the Argentinean history. These events are related to the thin-skinned Precordillera fold and thrust belt, and the thick-skinned Sierras Pampeanas basement cored uplifts and their interaction. We have determined source parameters (source time function, focal mechanism and depth) for the 15 January 1944 and 11 June 1952 San Juan, Argentina earthquakes, the largest historic earthquakes of the last century in the eastern Precordillera region. In addition, we have determined the focal mechanism and depth for the two largest most recent damaging crustal earthquakes in the Sierras Pampeanas that occurred on 28 May 2002 and 7 September 2004. We found thrust focal mechanisms and shallow depths (< 11 km) for the 1944 (Mw 7.0), the 2002 (Mw 5.8), and the 2004 (Mw 6.2) earthquakes. The 1952 (Mw 6.8) event shows an oblique focal mechanism solution and a similar shallow focal depth. The most recent and largest (Mw 7.4) crustal earthquake occurred in the vicinity of the Sierra Pie de Palo (SP), part of the western Sierras Pampeanas, on 23 November 1977. Comparing the seismic sources for the 1944 earthquake (our study) and the 1977 event [Langer and Hartzell, Phys. of the Earth and Planet. Inter. 94 (1996) 121-132], we note that the 1944 earthquake had a simple source time function consistent with a rupture along a single major fault while the 1977 earthquake is characterized by multiple shocks of depths > 17 km along separate blind thrust faults [Langer and Hartzell, 1996]. Available focal mechanisms for moderate crustal earthquakes (Mw > 4.0) in this region, determined from regional broadband data (IRIS-PASSCAL CHARGE experiment 2000-2002), are consistent with roughly east-west directed compressional stresses. Moderate earthquakes in the vicinity of the SP have thrust focal mechanisms and depths between 14 and 25 km. Thus the source characterization of moderate-to-large seismicity can help provide more constrains to understand the style of deformation in the Andes backarc region of high seismic hazard.
DE: 7205 Continental crust (1219)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8107 Continental neotectonics (8002)
SC: Seismology [S]
MN: Fall Meeting 2005