Evidence of recent ruptures in the central faults of the Acambay Graben (central Mexico)

The Acambay Graben, within the central part of the Trans-Mexican Volcanic Belt, is one of the major sources of continental earthquakes in Mexico. To date, the activity and paleoseismological history of the axial faults of the graben are not well constrained. We provide morphological, structural and sedimentological evidence of the seismogenic nature of two of the axial structures, the Temascalcingo and the Tepuxtepec fault systems. Faults consist of multiple parallel scarps with en echelon and horse-splay patterns. Fault systems extend for 60 km and displace Quaternary to Upper Miocene volcanic edifices and volcano-sedimentary materials. Surface lengths of individual fault traces range between 3 and 25 km, and observed throws reach a minimum of 150-200 m. The long-term and short-term slip rate of the Temascalcingo fault system in the studied section presents similar values, ranging from 0.06 ± 0.02 (minimum long term) to 0.12 ± 0.02 mm y−1 (maximum value of average short-term). Only the long-term slip rate of the Tepuxtepec system could be constrained in 0.01-0.02 mm/y, being a minimum estimate. The Holocene fault rupture history at two sites provided evidence of six ruptures since 12,500-11,195 BCE, among which three ruptures should have occurred between 11,847 ± 652 BCE and 11,425 ± 465 BCE Variable single event displacements (SEDs, between 6 and 77) are interpreted as the result of fault interdependences and/or the interaction with the latest volcanic activity. Also, small displacements triggered by activity on other faults probably contributed to slip variability, i.e., faults display primary and secondary behavior