LAUSR

Local variations in soil type and (to a lesser extent) topography determine seismic amplification, thereby establishing spatial patterns in the damages caused by large earthquakes, such as the two that occurred in Chiapas, Mexico on 6 October 1975 and 7 September 2017. The latter, of Mw 8.2, was the region’s strongest during the last 100 years. Based upon damage patterns, an analysis was made to identify the effects of sediment thickness and type upon seismic amplification in the urban zone of Chiapa de Corzo, Chiapas. Salgado et al., (2004) had shown that the fundamental periods of soil vibration in the city vary from0.14 s to0.39 s. From those periods, and using the model presented in Newmark and Rosenbleuth (1976), with an average shear-wave velocity of 150 m/s, the variation of the sediment thicknesses that cause site effects in the area was determined. The thicknesses ranged between 7.12 and 14.6 m. Finally, through the use of a map prepared with GIS software, a spatial correlation was made with the historical earthquake damage recorded within the city.