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Crustal wedging triggering recent deformation in the Andean thrust front between 31°S and 33°S: Sierras Pampeanas-Precordillera interaction

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  • We document a new model of crustal structure of the Andean front in Argentina where numerous historic earthquakes destroyed the cities of Mendoza in 1861 (M[subscript s] = ~7) and San Juan in 1944 (M[subscript w] = 7.0). The Cerro Salinas anticline is formed above the west directed Cerro Salinas thrust. An east facing monocline with an amplitude of about 2 km folds the Cerro Salinas thrust and overlying Neogene succession. This monocline is formed above a blind crustal thrust in the basement. Its dip of 14° west is inferred from fold geometry. This thick-skinned east directed blind thrust and the thin-skinned west directed Cerro Salinas thrust define a tectonic wedge; the wedge tip occurs at a depth of 5.4 km. Growth of the monocline after ~8.5 Ma is revealed on multichannel seismic (MSC) profile 31017 (Repsol-YPF). Rates of Cerro Salinas thrust displacement are of the order of 1 mm/yr, whereas vertical uplift of ~0.45 mm/yr results from the combined displacement on the Cerro Salinas thrust and growth of east facing monocline. The lateral extent of the east directed crustal blind ramp corresponds with the along-strike extent of the Eastern Precordillera. When combined with the low displacement rate, a long earthquake recurrence interval is implied. Smaller magnitude earthquakes, however, indicate that segments of the blind thrust ramps ruptured in historic events. If all the segments of the blind thrust ruptured together the fault area is ~7000 km² and could produce a M[subscript w] ~ 7.7 earthquake. The crustal wedge model provides new constraints on the origin and potential size of earthquakes that threaten the densely populated region.
  • Keywords: tectonic structure, seismogenic implications, growth strata, Andes
  • Keywords: tectonic structure, seismogenic implications, growth strata, Andes
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  • Vergés, J., V. A. Ramos, A. Meigs, E. Cristallini, F. H. Bettini, and J. M. Cortés (2007), Crustal wedging triggering recent deformation in the Andean thrust front between 31°S and 33°S: Sierras Pampeanas-Precordillera interaction, Journal of Geophysical Research, 112, B03S15, doi:10.1029/2006JB004287.
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  • 112
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  • B03S15
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  • This work has been partially supported by 99AR0010 CSIC-CONICET project and Grups de Recerca Consolidats (II Pla de Recerca de Catalunya) Projects 1997 SGR 00020. A.J.M. was supported by U.S. NSF grants EAR-0232603 and EAR-0409443 and a Research Equipment Reserve Fund grant from Oregon State University.
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