Co-Seismic Slip Distribution Inversion Applied to the Mutata Earthquake, Colombia

Colombia is located on the South American plate with two zones of subductions, one to the west on the Pacific side (Nazca plate), and one to the North on the Caribbean side (Caribbean plate). This leads to the presence to large and complex fault system within Colombia. On September 14, 2016, a Mw 6.0 earthquake occurred in Northwestern Colombia on the Uramita fault close to Mutata at a depth of approximately 18 km. The moment tensor calculated by the USGS for this event shows a thrust fault focal mechanism with a fault plane dipping at 35° and a small right-lateral component. Interestingly, the moment tensor decomposition shows a double couple component of only 55%. This event is both one of the most superficial and one of the strongest seismic events that occurred in Colombia since the installation of the national seismological network (RSNC) in 1993. In this work, we invert for the slip distribution on the fault plane for this seismic event using a combination of broad-band and near-field data provided by the USGS and the RSNC. We first choose the fault plane using the moment tensor and the information on the fault system available. The fault plane is then divided in a number of rectangular sub-faults in order to calculate the contributions of slip from each patch in the source region. To solve the slip inversion, we finally use the multiple shock sequence method with a least-squares fit. The slip distribution is also compared with the aftershocks distribution in order to investigate their coseismic triggering by the mainshock. Very few earthquakes from Colombia were studied in order to determine their slip distribution. This study is then a first step toward a better understanding of their complex rupture, and to better estimate seismic hazards in the region.