An evaluation of the moment tensor and its non-double-couple component for the Mutatá earthquake in Antioquia, Colombia

Abstract:

The Mutatá earthquake is one of the strongest superficial events that occurred in Colombia during the last decade. This Mw 6.0 earthquake was located at a depth of approximately 18km, 32 km away from the town of Mutatá, the 14th of September 2016. According to the moment tensor (MT) solution calculated by the USGS, this event has significant non-double-couple (DC) components but there is no clear explanation for volumetric components for this fault system. We here study the influence of the fault geometry, event number and event locations on the presence or not of these non-DC components using regional broad-band seismograms.

In order to calculate the MT, two types of inversion were done: full MT and DC constrained. In the first case, the inversion is carried out for one and two sub-events while, for the second, only the two sub-events case was considered. The data provided by the Colombian Geological Service was analyzed with the software ISOLA. First, only stations within a 300 km radius from the epicenter were selected. Then, the data were corrected from the instrumental response and band-pass filtered between 0.01 and 10 Hz. The seismic source was then defined in two ways: as a single point line below the epicenter and as multiple point-source planes with orientations that correspond to local faults close to the epicenter: the Murindó, Murrí and Mutatá faults. The inversion was finally applied with a frequency range of 0.03-0.09 Hz. Full MT inversion results are similar to those reported by the USGS, both in terms of focal mechanism and MT components. However, the results of the different inversions with two sub-events show that non-DC components are not necessary in the source of this earthquake. The non-DC part is then attributed to the fact that two sub-events occurred at close distance and time on either the Murindó or Mutatá faults.