Seismic activity in the Gulf of Mexico. A preliminary analysis

摘要

The southwestern corner of the Gulf of Mexico (around the Isthmus of Tehuantepec) is exposed to intense deep (>100 km) seismic activity caused by the subduction of the Cocos Plate. Aside from this, the gulf has been considered a zone of low or no-seismicity. However, a sparse shallow seismic activity is observed across the Gulf of Mexico, even in the most distant areas from the plate boundaries. Some of these earthquakes have been strongly felt (e.g. 23/05/2007 and 10/09/2006), and the Jaltipan 1959 earthquake caused fatalities and severe destruction in central and southern Veracruz. In this study we analyze five relevant earthquakes that occurred since 2001. At the central Gulf of Mexico, focal mechanisms show inverse faults oriented approximately NW?SE with dip ~45o, suggesting a link to sediment loading and/or to salt tectonics. On the other hand, we analyzed in the southwestern corner of the gulf some clear examples of strike-slip faults and activity probably related to the Veracruz Fault. One anomalous earthquake, recorded in 2007 in the western margin of the gulf, shows a strike-slip mechanism indicating a transform regime probably related with the East Mexican Fault. The recent improvements of the Mexican Seismological broadband network have allowed the recording of small earthquakes distributed in the Gulf of Mexico. Although intermediate and large earthquakes in the region are infrequent, historic evidence indicates that magnitudes could reach Mw ~6.4. This fact should be taken in consideration to reassess the seismic hazard for industrial oil infrastructure in the region.