Evidence for quaternary seismic activity of the La Alberca-Teremendo fault, Morelia region, Trans-Mexican Volcanic Belt

The La Alberca-Teremendo fault is a 26 km-long, complex fault composed of an en échelon array of short crustal fault segments, belonging to the Morelia-Acambay fault system. This fault system shows parallel scarps with morphological evidence of recent activity such as drainage alteration, maximum throws of 50 m and minimum throws of 1.4 m that displace the recent soils. The fault acted as a conduit for the formation of the La Alberca de Guadalupe maar (23000 to 21000 years ago) and displaced afterwards its phreatomagmatic sequences. The paleoseismic analysis indicates that the La Alberca-Teremendo fault moved three times in the past 23000 years (age of the maar); this activity caused an average vertical displacement of 87 cm, and might have generated earthquakes with magnitudes Mw between 6.6 and 7, as well as volcano-tectonic earthquakes with magnitudes Mw between 4 and 5.5. The displacements were identified on the fault through the superposition of soils differentiated by a disconformity and an anomalous increase in the percentage of clay and organic matter. The La Alberca-Teremendo fault has dominant dip slip with a minor left-lateral component, a slip rate of 0.114 mm/year, and an average recurrence interval of 7726 ± 68 years. According to scaling relations that use the surface rupture length, if we assume that the La Alberca-Teremendo fault moves tectonically, it could generate earthquakes with maximum magnitudes of Mw between 6.7 and 7.3, however because of the active volcanic processes in the area, we could expect moderate volcano-tectonic earthquakes (Mw 4–5.5) rather than catastrophic ones.