Faults delineation and stress orientations from the microseismicity analysis of the Servita Fault System, Colombian Eastern Cordillera

Abstract:

The Servita Fault System (SFS) is located in the eastern foothills of the Colombian Andes Eastern Cordillera. This region is a structurally complex area with high seismogenic potential. The refined analysis of the microseismicity registered by a portable seismic network allows to delineate the main active faults and to estimate the direction of the regional tectonic stress.

We analyzed a high quality microearthquake data-set consisting of 890 events occurred during 2011-2012 with a local magnitude range between 0.1 and 3.2 and depths up to 40km. The refined locations of the events show a general SW-NE trend that follows the trace of the SFS. Selected focal mechanisms show predominantly right-lateral strike slip motion.

Results show that seismicity to the northern sector of the SFS is distributed in two groups, one on the axial zone of the cordillera and the other on the eastern flank. Most of the microearthquakes are concentrated in the rupture zone of Quetame earthquake (2008, Mw=5.9). Alignment of hypocenters along the eastern flank and some focal mechanisms suggest a fault plane dipping to the west, which is interpreted as the Servita Fault plane. Southwards of the Rio Negro, seismicity decreases and loses continuity. This feature coincides with the trace of the WSW-ENE Rio Blanco Fault which possibly segments the Servita Fault. Southwards, seismicity is spread over a wider area and exhibits deeper hypocenters compared to the northern sector. Hypocenter distribution and focal mechanisms in this sector suggest two planes dipping to the west which we interpret as segments of the Algeciras Fault and another plane (northwards) steeply dipping to the southeast interpreted as the fault plane of the Altamira Fault.