Ground motion variability in the virgin Texcoco Lake area, Mexico

摘要

Spatial ground motion variability observed in the Texcoco lake region, in the surroundings of Mexico City, has been studied through the generation of sets of site specific response spectra developed performing several 1 -D stochastic site response analyses. The studied zone has an area of 19.0 by 5.5 km2, and has been instrumented with four seismological stations, which have recorded strong ground motions over the past years. This area presents unique geotechnical subsoil conditions consisting on very soft clays deposits, with low shear strength and high compressibility, randomly interbedded by sand lenses. The subsurface conditions prevailing at the instrumented sites, including shear wave velocity distribution with depth, were characterized using standard penetration, SPT, and cone penetrations, CPT, tests, combined with selective sampling of undisturbed soil specimens. Uncertainties associated with shear wave velocity measurements were considered allowing a random variation of +/-30% around the mean values. Series of resonant column and cyclic triaxial tests were carried out to obtain the dynamic soil properties. From this work, response spectra for the studied area were proposed. These can be used in future updates to the Mexico City building code.