Paleoseismology of the southwestern Morelia-Acambay fault system, central Mexico

Abstract

Fr The Morelia–Acambay Fault System (MAFS) consists of a sequence of E–W and NNE–SSW trending normal faults within the Trans–Mexican Volcanic Belt. The fault system is associated to the Chapala, Zacapu, Cuitzeo, Maravatio and Acambay lacustrine depressions. The E–W faults of MAFS appear to be 7–9 million yr old while the NNW–SSE faults are older and were reactivated producing stepped east–west geometry with a transtensional–right hand deformation.
Seismic magnitudes of the E–W structures in the Morelia–Cuitzeo region are estimated. Cartography, structural geology, and trench stratigraphy of these faults suggest Holocene activity. Historical earthquakes disrupted paleosols containing Pirinda–Purepecha shards. These Historical earthquakes are also imprinted in seisms along E–W faults at Los Azufres geothermal field. In the Pátzcuaro region, the E–W structures are also linked to strong seismic events occurred during prehistoric and historical times. The Jaracuaro lacustrine sequence in the southern Patzcuaro Lake contains evidence at least three important earthquakes (PostClassic, 1845 and 1858) and a possible tsunami associated to the 1858 event. The magnitude of this earthquake was estimated at ~7.3. An earthquake of this magnitude would damage a density populated area of Michoacán State. On October 17, 2007, three small earthquakes were felt in Morelia associated to normal E–W fault mechanisms of Central Camionera Fault corroborating the seismic potential of MAFS in the TMBV.