Microtremor measurements to identify zones of potential fissuring in the basin of Mexico

Abstract

The potential for the apparition of fissures and cracks in the Basin of Mexico can be inferred from microtremor measurements. Most of the cracking in the basin occurs where there is a sharp gradient in the depth of the hard layer below the soft clay. It is well known that the depth of the hard layer is related to the dominant period, T₀, of the site by the relation T₀=4H/ V_s, where H is the depth and V_s is the average shear-wave velocity in the clay. If V_s is assumed roughly constant then the gradient of T₀ would reflect the gradient in depth. Thus, if we can measure T₀ then we can relate it to the potential of cracking in the basin. Nakamura's technique provides a simple, fast, and inexpensive way to estimate T₀, at least in the lake-bed zone. The manuscript validates this premise in San Lorenzo, Ixtapalapa, where cracking has been observed and estimation of H is available from geotechnical data.