TECTONIC GEOMORPHOLOGY OF THE ACADEMY GRABEN, MEXICAN VOLCANIC BELT

Tectonics and volcanism in the Mexican Volcanic Belt (MVB) arc related to the subduction of the Cocos Plate beneath southern Mexico. Analysi s of Landsat imagery employing digital enhancement shows that the Acam bay graben located in the central part of the MVB is characterised by Quaternary, generally east-west trending, seismically active normal fa ults. Fault system associated with the graben can be categorised on th e basis of the morphological features associated with them. Five syste ms are identified: 1) the Acambay-Tixmadeje faults, 2) the Tepuxtepec faults on the northern flank of the graben, 3) the Pastores fault, 4) the Venta de Bravo faults on the southern flank of the graben, and 5) the Temascalcingo faults located in the centre of the graben. A range of geomorphological evidence indicates neotectonic activity in the Aca mbay graben. Prominent fault scarps and triangular facets demonstrate normal faulting, while offset drainage, sag ponds and pull-apart basin s together with linear and compression ridges confirm an important lef t-lateral component to fault displacement, a motion which is accordant with regional left-lateral shear along the MVB.