3D seismic tomography in the seismic nest of Bucaramanga (Colombia)

Seismic tomography is a set of techniques used to obtain an image of velocity fields inside the Earth, using waves measurements. In this work, this technique was used to generate a quasi-3D velocity model of the P wave of Bucaramanga's nest zone - a highly seismic zone in Colombia caused by the collision of the Caribbean and Nazca Plates under the South American plate, able to generate intermediate earthquakes (70 - 200km). For this research, 1223 earthquakes recorded by the seismic stations of "National Seismological Network of Colombia" were analyzed. They all occurred in Santander, Colombia, within 6 degrees - 8 degrees N and 72 degrees - 74 degrees W recorded from January 2012 to June 2016. Only 1138 events that met the seismic nest parameters - like latitude, longitude and depth - were used to generate a first 1D velocity model where only depth velocity variations were considered. Furthermore, a quasi-3D model with both horizontal layers of different depths and lateral variations was generated. Results show two continuous anomalies in the study zone: the first one, a negative one interpreted as partial melt of magma and, the second one, a positive anomaly interpreted to magma crystallization.