Evidence of site amplification from ground motion of the last two large crustal earthquakes in central-western Argentina

The present study has investigated site amplification effects from the analysis of peak ground accelerations (PGA) and spectral accelerations (SA) of the last two major crustal earthquakes in central-western Argentina. These data were obtained from 15 accelerometers and 57 seismoscopes, which recorded ground motions during the 1977 ( M w 7.5) San Juan earthquake, and the 1985 ( M w 5.9) Mendoza earthquake. PGA and SA measurements were compared with average values predicted by global attenuation empirical relationships for the same type of crustal earthquakes. The amplifications in ground accelerations were analyzed according to their distribution and compared with the average shear wave velocities at 30 m depth (Vs30) where the stations are located. Our results definitively show that site effects and direction of maximum surface wave radiation strongly amplify the ground acceleration during moderate to large earthquakes near San Juan and Mendoza (Argentina); this is of importance in seismic hazard analyses.