Seismic parameters characterization at Texcoco lake, Mexico

Texcoco lake area, in the Valley of Mexico, presents particularly difficult geotechnical conditions due to the presence of thick deposits of soft, highly compressible lacustrine clay, randomly interbeded with sand lenses. In contrast to other sites in the valley, there is a lack of information regarding the geotechnical subsoil conditions, dynamic properties, and earthquake recordings at rock sites. Thus, the seismic environment is not completely identified. This paper describes field and laboratory investigations as well as analytical studies, aimed at characterizing the ground response of a particular site located in this region, where is planed to be built an strategic power station, which will be the driving force for the urban and industrial development of Mexico City northeast side. In situ measurements of shear wave velocity, using suspension PS logging, along with cone penetration, CPT, and standard penetration, SPT, resistance values, and results from series of resonant column and cyclic triaxial tests were used to obtain a 3-D representation of the subsoil characteristics found at the site, and the variation of dynamic properties with strain level. Predicted shear wave velocity profiles derived through empirical correlations compared well with measured values. Ground motion definition was achieved indirectly through empirically derived response spectra obtained from sets of earthquake ground motions recorded at a nearby station located in soft soil. Acceleration time histories representative of the design earthquake were obtained using time-domain spectral matching. 1-D shear wave deconvolution was used to obtain the corresponding ground motions in rock.