SEISMOTECTONIC ACTIVITY OF A FOOTHILL FAULT SYSTEM IN THE NORTHERN ANDES. THE ALGECIRAS FAULT, EASTERN CORDILLERA, COLOMBIA

The Algeciras Fault System (AFT) is located in the eastern foothill of the Colombian Eastern Cordillera. This fault system is composed of a set of dextral strike-slip faults ~N60°E strike and has an accumulated active segment of ~608 km. Historical macroseismic events in this zone evidence strong-motion destructive earthquakes in 1827 and 1917. Later, instrumental seismic records also show significant events such as the earthquake of February 9, 1967, Mw 7.2, with the epicenter located 190 km southwest of Bogotá, where caused damage to buildings and some fatalities. The most recent example of its seismogenic potential occurred on December 24, 2019, Mw 6.2, 13km-depth, and near to the municipality of Mesetas, 115 km south of Bogotá. The main aftershock occurred 19 minutes later, Mw 5.6, but a sequence of tens of aftershocks followed during the next three days, with at least 14 earthquakes Mw> 4.0. All events related to the AFT maintain consistency with a moment tensor related to a strike-slip fault. Around January 20, 2020, the Colombian Seismological Network (RSNC) had registered 2107 aftershocks with Mw <2.0. Around 5 km northeast from the main earthquake of 2019, another event was reported on July 2, 2017, Mw 4.7, <10 km-depth. In the same area, it is reported another on October 7, 2013, Mw 3.1. Having in consideration that the RSNC improved the density of stations in this region later than 2013, we expect that recent seismic activity of the Algeciras fault system becomes the manifestation of the permanent active tectonics related to the uplift of the Andean Cordillera. Satellite images in the area show evidence of recent pressure domes, fault scarps, cataclasis response, hanging valleys, V-valleys, among others. Geomorphic indexes also suggest that the AFS presents a very high tectonic activity. In this work, we offer geological and seismological data of this fault to contribute to the understanding of this sort of fault system, in particular concerning its seismic behavior.