Possible structures of the old Urcunina Caldera, revealed by high precision relocation of VT earthquakes at Galeras volcano

Volcano-Tectonic earthquakes at Galeras Volcano were relocated using the waveform catalog waveform and preliminary phase arrival data compiled by the monitoring network at Observatorio Volcanológico y Sismológico de Pasto. Several routines were developed in MATLAB, mainly to prepare waveforms, calculate differential travel times, and identifying seismic families; and the HypoDD program was implemented, which allowed performing the relocations. The procedure resulted in the detection of 10 swarm-type families and 4 spatial-type families of earthquakes, which reveal a fault of 1.6 km bounding the Urcunina Caldera, and a ring fault of 1.8 km in diameter, adjacent to the crater. Reductions in the range 56.84% - 87.48% were achieved in the hypocentral parameters uncertainties as compared to uncertainties in traditional locations, to finally obtain an alternative image of the Volcano-Tectonic earthquakes distribution Galeras Volcano VG with a significantly lower uncertainty.