Evidence of active shortening along the eastern border of the San Rafael basement block: Characterization of the seismic source of the Villa Atuel earthquake (1929), Mendoza province, Argentina

Abstract

On the 30 May 1929, a massive earthquake occurred in the San Rafael area (southern Mendoza province) leading to the destruction of the Villa Atuel and Las Malvinas towns. The region affected by the ground shaking covers a large part of southern South America. Although no surface breaks have been detected on the surface, several authors have pointed out active faults that could be related to the event of 1929. Using satellite imagery and field observations, we investigated two active faults situated on the eastern border of the San Rafael Block (SRB) close to or within the epicentral area. The most prominent faults are the c. 40 km long Las Malvinas and c. 30 km long Cerro Negro reverse faults which are located near the epicentral area. Geological and morphological observations allow us to describe late Pleistocene activity and estimate the long-term slip rates of these faults. Possible ruptures that match our observations and which are compatible with the cartographic length of these faults would account for a seismic moment magnitude of M0 = 2.8×1019 N m and a moment magnitude of MW = 6.9. The morphological signatures of these fault segments and the occurrence of the San Rafael earthquake suggests that the southern Mendoza Province is still currently submitted to shortening.