SPAC: An alternative method to estimate earthquake site effects in Mexico City

Abstract

Microtremor recordings are a very useful tool for microzonation studies because of simple data acquisition and analysis. The Spatial Autocorrelation Method (SPAC) proposed by Aki (1957), may be used to constrain the velocity structure underlying the site with microtremor array measurements, and the site effect (dominant period and amplification) can be calculated. In this paper the SPAC method is applied to Ciudad Universitaria, Mexico City. Results are compared with those obtained by Kagawa (1996) with the F-K method. The velocity structure inferred using SPAC method is consistent with Kagawa's results. We compare the transfer function obtained from the velocity model estimated by SPAC method with the transfer function from Kagawa's velocity model, and from spectral ratios of earthquake data. We conclude that the velocity structure of a site can be estimated from microtremor recordings by the SPAC method.