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

• Published in: Journal of Geophysical Research. B. Solid Earth 2007-03, Vol.112 (B3)
• Main Authors: Verges, J, Ramos, V A, Meigs, A, Cristallini, E, Bettini, F H, Cortes, J M
• Format: Article
• Language: English
• ISSN: 0148-0227

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 sub(s) = similar to 7) and San Juan in 1944 (M sub(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 degree 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 similar to 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 similar to 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 similar to 7000 km super(2) and could produce a M sub(w) 6 7.7 earthquake. The crustal wedge model provides new constraints on the origin and potential size of earthquakes that threaten the densely populated region.