The 1929 Las Malvinas - Villa Atuel earthquake: A deterministic seismic hazard assessment nearly a century later, Mendoza, Argentina

On May 30, 1929, an earthquake with an estimated ~ M_W6.5 caused 30-40 fatalities and destroyed the towns of Las Malvinas and Villa Atuel, in the Andean foreland of Mendoza province, Argentina. This region is characterized by low-rate M < 4 crustal seismicity owing to regional compressional stresses that uplift a basement block known as the San Rafael Block. The exact hypocenter and source fault of the 1929 event remain uncertain, with several disagreeing proposals in the literature. Studies based on the classical tectonic framework of an east-vergent uplift place the hypocenter on the proposed west-dipping frontal structure, known as Las Malvinas fault. However, interpretations derived from historical field observations of the damage caused by the earthquake, locate it east of that fault, revealing a major inconsistency between both approaches. Additionally, given nearly a century of urban growth since the historic earthquake, the elements exposed to a comparable event have increased substantially. This work provides a deterministic seismic hazard analysis (using OpenQuake Engine) in the center of Mendoza province by simulating three possible scenarios for the 1929 event, with the goals of i) shedding light on the discussion about the hypocenter location by testing which scenario would better fit both historical damage observations and structural features of the region; ii) finding out the approximate ranges of ground motion that would occur on specific sites of interest; iii) comparing the results with existing large-scale probabilistic studies and current building codes to evaluate possible improvements on risk mitigation in the area. Our results favor a hypocenter located east of the San Rafael Block, matching the historical proposal derived from field observations and reinforcing our alternative tectonic interpretation of a large-scale deep-seated ramp as the main structure driving its uplift, which would be west-vergent instead, together with major seismic activity in the region.