Monitoring microseismicity at the Servita Fault System, Colombian Eastern Cordillera

The Servita Fault System is located in the eastern foothills of the Colombian Andes Eastern Cordillera. It is considered a key fault for detailed active tectonics studies by its capacity to generate destructive earthquakes which has been demonstrated historically and its short distance to Bogotá (7 million inhabitants), about 60 km. With the aim of increasing our knowledge on the active deformation pattern, the geometry and the seismogenic depth of the potentially active structures, a dense temporary seismic network was installed in the Servitá Fault region to register microseismic activity. The network consisted of 21 portable stations, 6 broadband and 15 short period sensors, recording in continuous mode and in-situ data storage. Four permanent stations of the National Seismological Network of Colombia (RSNC) installed in the same region were also used to locate events. A thousand events with local magnitude between 0.1 and 3.2 ML were registered in the region during about 10 months of observation from 2011 to 2012. We used an automatic detection algorithm to identify seismic events and picked P and S wave arrival times manually. Recorded seismicity follows the same trend as the fault system, SW-NE. A group of events located westward of its trace suggests a fault plane dipping to the west. Refined seismicity locations show various clusters, consisting of sequences of small earthquakes with very similar waveforms. The most important cluster is located near the rupture zone of the 2008 Quetame earthquake (Mw=5.9).