| 英文摘要: | The September 7 Chiapas, Mexico (M=8.1) and the September 19 Puebla, Mexico (M=7.1) earthquakes occurred along a subduction zone, where the oceanic Cocos Plate subducts beneath the continental North American Plate along the Middle American Trench. Both earthquakes caused significant damage and loss of life. Initial United States Geological Survey (USGS) results show that these intermediate depth (50-60 km depth) earthquakes did not occurred along the plates interface, but ruptured the subducting oceanic plate with extensional faulting. These were not the typical subduction plate boundary compressional events along the subduction interface of the Middle American Trench. Furthermore, the earthquakes were located about 640-km from each other, a far enough distance to suggest no link between them. We will investigate several questions remaining about these earthquakes including: Will these earthquakes load the upper plate and possibly trigger an equal or larger earthquake on the plate interface? Are these the result of plate bending? Do the aftershocks migrate to the locked zone in the subduction zone? Did these intermediate depth earthquakes rupture into the mantle? Why did the intermediate depth earthquakes create so much damage? Are these earthquakes linked due to dynamic stresses? We will address these questions by deploying seismic sensors around these two earthquakes and in between them and analyzing the data collected in coordination with our colleagues in Mexico.
We propose to immediately deploy 10 broadband and 50 UTEP-owned nodes (5-Hz, 3-component geophones) seismometers near the epicenters of the September 7 Chiapas, Mexico (M=8.1) and the September 19 Puebla, Mexico (M=7.1) earthquakes to record their aftershocks and to map shallow earth structure near heavily damaged regions. Initial United States Geological Survey (USGS) results show that the two largest earthquakes were unusual: neither earthquake occurred along the plate interface, both were at intermediate depth (50-60 km depth), and both earthquakes ruptured within the subducting oceanic plate with extensional faulting, not the typical subduction plate boundary compressional events along the Middle American Trench. Furthermore, the earthquakes were ~640-km apart, longer than two fault lengths, a distance at which static triggering forces tend to be very small, suggesting no link between them. The 10 broadband instruments will be deployed for 6 months, while the nodes will be deployed 30 days, since this is the extant of their battery life. The nodes, however, allow for numerous stations to be deployed rapidly in targeted regions, especially regions of extensive damage for site characterization, and this is the first test of these instruments for this type of deployment. We wish to address some key questions on the earthquakes, defined above. Analysis of the data collected will allow for fault plane identification from aftershock locations, stress release and orientation caused by the earthquakes from the determination of fault plane solutions, and for site characterization and site effects to be mapped in regions of extensive damage. Furthermore, the data can be used to image the region to better define the active plate boundaries. |