The Abanico del Quindio alluvial fan, Armenia, Colombia: Active tectonics and earthquake hazard

The Abanico del Quindío (AQ) fan, a volcaniclastic deposit from the Ruiz–Tolima volcanic complex (RTVC), Colombia, provides insight into recent deformation in the Central Andes. The use of geological observations, geophysical measurements, and estimates of fault-scarp ages constrain timing of recent tectonic activity. Gravity and magnetic analyses, along with geomorphologic cartography, allow the detection of lateral variations in basement distribution and at least three structural trends that cut the AQ: the Armenia fault (NNE), El Danubio fault (NNW), and Hojas Anchas fault (E–W). Recent deformation in the zone results from slip on the Armenia and El Danubio faults and suggests a maximum interval magnitude of 5.1 < Mw < 6.3, with ages ranging between 2560 ± 480 yr B.P. and 4120 ± 780 yr B.P. Although no surface ruptures are associated with historical events on the fault segments in this zone, blind structures may have influenced the hypocentral distribution of events recorded after the Armenia Earthquake (Mw 6.2, 25-01-1999). Further geophysical studies are needed to understand the Romeral Fault System and assess the earthquake hazard for the city of Armenia.