ESI2007 ASSESSMENT OF PALEOSEISMIC FEATURES IN THE ACAMBAY AND IXTLAHUACA GRABEN, MEXICO: EVIDENCE FOR CAPABILITY ALONG THE PERALES FAULT

We compare published macroseismic data from the Nov. 19th, 1912, Ms 6.9 Acambay earthquake with new analyses of
paleoseismic evidence preserved in the stratigraphy and geomorphology of three Mid-Pleistocene to Holocene lacustrine
subbasins (San Pedro El Alto and San Bartolo Lanzados, in the epicentral area of the 1912 event; and Ixtlahuaca de Rayón, along
the Perales Fault, ca. 40 km S of the 1912 epicenter) using the ESI 2007 scale. In the Ixtlahuaca paleobasin (Mid Pleistocene?),
liquefaction, megaslumping features, and synsedimentary surface faulting are genetically associated, suggesting A) a seismically
induced origin, and B) a local earthquake source, at least for some of the observed deformational paleoevents. In the studied subbasins,
the preliminary intensity assessment from the paleoseismic environmental effects is comparable, and consistent with the
epicentral intensity of the 1912 event (Io = X in the Cancani scale). The three sub-basins are controlled by the growth of the same
system of extensional structures during the Quaternary, showing very similar tectonic and geomorphic features. This includes the
Pastores, Temascalcingo and Acambay-Tixmadejé faults, which ruptured during the 1912 earthquake, and the Perales Fault. We
argue that within such a coherent seismic landscape the ESI 2007 intensity assessed from paleoseismic features in the Ixtlahuaca
paleobasin indicates a seismic potential in the order of Mw 7 for the Perales Fault, equivalent to the one demonstrated by the
master faults of the Acambay graben.