Ver artículo

The high seismic hazard level of the city of Tapachula (Chiapas, Mexico) and observed geological differences in the urban area requires a VS surface structure estimate in order to know the characteristics of local seismic response. In this work we have used empirical methods to characterize earthquake ground motion in different zones of the city. The shallow VS structure at 6 sites of Tapachula has been calculated applying a joint inversion of the SPAC method and the horizontal-to-vertical spectral ratio (HVSR, Nakamura 1989) method from ambient noise. The obtained shear velocity models show that major differences among sites appear in the first 30 meters. The VS30 values are between 252 and 363 m· s-1. The results show VS30 values between 252 and 363 m· s-1. The ground predominant periods (Tp), estimated in 275 points from microtremor data (0.2-1.1 s), show four distinct areas of the city, similar to those established with VS30 values obtained with the SPAC method. These areas are: the largest one in downtown and south (Tp 0.2-0.4 s), two small areas surrounding previous one of 0.41 to 0.7 s, and 0.75 to 0.9 s, respectively, and other small areas at N and SW of the city and bordering Coatán river Tp> 0.9 s. The accelerograms with the best signal/noise ratio of 220 events (Mw 3.3 to 4.5 and distance 60 to 190 km) recorded by a temporal seismic network installed (by the UNAM) at 6 sites in Tapachula were used to estimate a set of key engineering ground-motion parameters (PGA, PGV, AI, SI and arms). The attenuation laws of each parameter as function of the magnitude and distance are a first approximation of ground-motion …