Evidence of site amplification from ground motion of the last two large crustal earthquakes in central-western Argentina
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Evidence of site amplification from ground motion of the last two large crustal earthquakes in central‑western Argentina Patricia Alvarado1,2 · Rodolfo Christiansen3,4 · Salvador Daniel Gregori2,3 · Mauro Saez1,2 Received: 23 March 2019 / Accepted: 17 April 2020 © Springer Nature B.V. 2020
Abstract 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 (Mw 7.5) San Juan earthquake, and the 1985 (Mw 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. Keywords Seismic hazard · Peak ground acceleration · Spectral acceleration · Surface wave radiation pattern
* Rodolfo Christiansen [email protected] Patricia Alvarado [email protected] 1
Centro de Investigaciones de la Geósfera y Biósfera CIGEOBIO (CONICET-Universidad Nacional de San Juan UNSJ), Av. Ignacio de la Roza 590, CP: J5402DCS Rivadavia, San Juan, Argentina
2
Departamento de Geofísica y Astronomía ‑ FCEFyN, Universidad Nacional de San Juan, San Juan, Argentina
3
Instituto Geofísico Sismológico Volponi (IGSV) ‑ FCEFyN, Universidad Nacional de San Juan, 5407 Rivadavia, San Juan, Argentina
4
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), CCT San Juan, Argentina
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Natural Hazards
1 Introduction Every detailed evaluation of the seismic hazard for a particular region involves attenuation relationships, which consider parameters of engineering interest, such as seismic intensity, peak ground acceleration (PGA) and spectral acceleration (SA). This practice necessarily assumes having an adequate number of records of the larger earthquakes obtained from strong motion instruments appropriately distributed over a study area. The central-western part of Argentina is recognized as the region exposed to the greatest occurrence of earthquakes and of greater magnitudes in this country (Gregori 1993; Alvarado and Araujo 2011; Gregori and Christiansen 2018) (Fig. 1). In this region a significant seismic activity, sometimes causing severe damage, is observed within the continental crust of the South American Plate with focal depths 3.5) from 1575 to 2017 according to the USGS (2018). c Dashed line rectangle represents the study area and black squar
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