Relocalization and Focal Mechanisms of Volcano-Tectonic Events at Colima Volcano, Colima, Mexico

Colima volcano (19.51 N, 103.62 W, 3860 m.a.s.l.) in western Mexico is well known for its frequent activity. Along with nearby Nevado de Colima, and Cantaro volcanoes are part of a volcanic complex rising in the middle of the Colima graben, a structure on the margin of the Jalisco Block, some one hundred km from the Middle America trench. The activity of Colima volcano is varied and usually accompanied by intense seismicity, mostly of volcano-tectonic events. To investigate several aspects of these earthquakes, we analyzed events recorded by the seismological network of Colima during the outbursts of 1998–1999, 2005, and 2009. Those periods, of varying intensity, lasted from several months to several weeks before and after a significant explosive event. The hypocenters, located with standard methods, appear in a broad region around the volcanic complex. To obtain a more accurate location of these events, we relocated the hypocenters using the method of double differences. A set of 1191 relocated events was obtained, providing improved locations, which show hypocenters clustered under the edifice of Colima volcano and do not seem to be related to any particular geological feature and, therefore, represent the volume stressed by magma’s intrusion. The focal mechanism of the relocated events shows a variety of fault plane orientations with a majority indicating dip-slip faulting.