Determination of the Fault Plane of the 2013 Santa Cruz Earthquake, Bolivia, Through Relative Location of Aftershocks

Abstract:

The Central Andes of southern Bolivia is a highly seismic region due to the faults present in this area which eventually could generate earthquakes up to 8.5 Mw. Nevertheless most of them are shallow and have low magnitude. In 2013, an earthquake of 5.0 Mw ocurred in Santa Cruz de la Sierra, it was followed by five aftershocks in the two months after the mainshock. Distances between epicenters of the aftershocks and the mainshock are up to 34 km, which is greater than expected for an earthquake of this magnitude. Additionaly the uncertainty of the epicenters is around 20 km; this scenario is not suitable for studies looking to determine the seismogenic fault orientation. Using data from South American stations of the international network of the Incorporated Research Institutions dor Seismology (IRIS) and the relative location technique, that uses the surface waves (usually the clearest wave in noisy sismograms), the epicenters of five aftershocks of the Santa Cruz series were determinated in relation the mainshock. This method enabled to achieve epicentral locations with uncertainties smaller than 2 km, distances between the aftershocks and the mainshock are up to 7 km, in accordance with the magnitude of the earthquake. The result of the relative location showed a N - S trend of the epicenters in agreement with the location and orientation of the Mandeyapecua fault, the largest reverse fault in Bolivia.

Key words: Relative location, Surface waves