3D Velocity Structure around the Source Area of the Armenia Earthquake: 25 January 1999, Mw=6.2 (Colombia)

Abstract

Selected P wave arrival time data of 518 events (mainly aftershocks) of the 25 January 1999 Armenia Earthquake (Mw=6.2, Colombia), recorded by 23 temporary seismic stations during February, 1999 to July, 2001, have been inverted simultaneously for both hypocenter locations and three-dimensional Vp structure. The surface geology of this area suggests a complex disposition of tectonic flakes composed by diverse rocks and crossed by the Romeral Fault System (RFS). However, there is a good correlation between high-velocity zones and old oceanic rocks affected by plutonic rocks. Metamorphic belts that wrap these rocks are well correlated with low-velocity zones. The disposition of tectonic flakes in depth is solved with a flower structure where the Cordoba fault slipped in a contact between high- and low-density rocks during the Armenia earthquake. The low-velocity zones would correspond to the older rocks that constitute the nucleus of the Central range. We infer that the source volume of the Armenia earthquake sequence lies within 75.64o - 75.72o W, 4.38o - 4.52oN and a depth of 5 - 21 km; the source volume is approximately 2 200 km3. Most of the well-located aftershocks occurred above the hypocenter of Armenia earthquake.