STRUCTURE AND TECTONIC DEFORMATION OF THE TRANS-MEXICAN VOLCANIC BELT: CURRENT SITUATION AND FUTURE CHALLENGES (Invited Presentation)

The Trans-Mexican Volcanic Belt (TMVB is unusual volcanic arc. It is oblique to the plate interface and geologically complex. Background seismicity is very low, with few instrumentally recorded events. However, large earthquakes, magnitude greater than 6, have occurred in the past. Two large earthquakes were recorded instrumentally in 1912 and 1920. These two events caused important damage and loss of life in this highly populated region of Mexico. In the past, macroseismic data stemming from historical records indicate that in the past 450 years, several large earthquakes (Mw > 6) have occurred along the TMVB. Some of these earthquakes, like the one in 1912, have occurred in well mapped faults; in other cases, some of these events took place in blind faults that still need to be identified and mapped. Geological studies show that the deformation of the TMVB is extensional, with a small component of left-lateral, strike-slip motion. Several paleoseismological campaigns confirm this style of deformation and show that the recurrence interval between succesive events is highly variable, even in nearby faults. The reason behind the anomalous geometry of the TMVB has been well established; the contorted shape of the Cocos plate in central Mexico flattens and moves the TMVB to the inner region of the upper plate. The diversity of volcanic activity is still not understood. In some parts of the TMVB, there are large stratovolcanoes, typical of volcanic arcs. In the central part of the belt, however, numerous monogenetic cones populate large segments of the volcanic belt. Further geological studies are necessary to map active faults and paleoseismological studies are needed to understand better the style and rate of deformation of the TMVB. Approximately 40% of the population live in cities along the TMVB. This highlights the importance of understanding the seismic hazard in this highly populated area, supported by physics-based hazard estimates that combine geological and the geophysical data.