GEOMORPHIC ASSESSMENT OF ACTIVE TECTONICS IN THE ACAMBAY GRABEN, MEXICAN VOLCANIC BELT

Spatial variations of Quaternary deformation and tectonic activity of faults along the Acambay graben are assessed using geomorphic and morp hometric approaches. The Acambay graben is an east-west trending struc ture of apparent Quaternary age, located in the central part of the Me xican Volcanic Belt, which gives rise to pronounced scarps over a dist ance of about 80km. Continuing tectonic activity in the Acambay graben is confirmed by recent well documented seismic episodes. The intensit y of active tectonics has been interpreted through a detailed geomorph ic study of the fault-generated mountain fronts and fluvial systems. T he combined geomorphic and morphometric data provide evidence for rela tive variations in tectonic activity among the Acambay graben faults. Geomorphic indices suggest a relatively high degree of tectonic activi ty along the Venta de Bravo and the Acambay-Tixmadeje faults, followed , in order of decreasing activity, by the Pastores, Temascalcingo and Tepuxtepec faults. Spatial variations within faults have also been ide ntified, suggesting a higher level of tectonic activity at the tips of the faults. This pattern of variation in the relative degree of tecto nic activity is consistent with field evidence and seismic data for th e Acambay graben. Geomorphic evaluation of the Acambay graben faults s uggests that the Acambay-Tixmadeje and Venta de Bravo faults, and spec ifically the tips of these faults and a central segment near the town of Venta de Bravo, should be considered as areas of potentially high e arthquake risk. (C) 1998 John Wiley & Sons, Ltd.