The project will address the processes of rupturing of continental lithosphere through seismic reflection and refraction survey of the Salton Trough. This is an ideal location to study the effect of magmatism and sedimentation on continental extension and the portioning of the strain vertically in the lithosphere. The objectives of the study are to investigate the nature of the transitional crust at rifted continental margins; the role of magmatism in final stages of breakup; the effect of synrift sedimentation on magmatism and extension mechanism; the portioning and displacement in highly oblique continental rifting; and 3D structure for earthquake hazard evaluation. The broader impacts include addressing important goals of the MARGINS RCL initiative and contribute towards the goals of Earthscope as well as GeoSwath initatives. It uses Earthscope instrumention. It will foster strong collaboration between MARGINS, Earthscope and USGS, and involve undergraduate and graduate students in the field experiment. It will also incorporate the experiment into a graduate level course, and involve students in the interpretation of the data once it is collected.
Normal 0 21 false false false ES-MX X-NONE X-NONE This project was a collaboration between Virginia Tech, Caltech, the US Geological Survey, and CICESE and UABC-Mexicali in Baja California, Mexico. During the field work for this project, we set out seismometers at 4000 locations in southeastern California and measured the speed and amplitude of seismic waves that traveled from a set of shallow underground explosions to the seismometers. 125 seismometers were also set out in Mexico to record the seismic waves from the explosions to the Mexicali Valley and adjacent regions. Mexican seismologists also set out additional instruments of their own, to record these explosions. Even those these are not earthquakes, the behavior of seismic waves traveling through the earth is the same, so the recordings are used to understand how earthquake waves would travel in this same region. The speeds of the earthquake waves change depending on what kinds of rocks are present at depth, so this information helps to tell us about the geological evolution of this area, and the kind of "crust" (rocks in the top 30 kilometers of the earth's surface) that is present here. We are interested in this because it is an area of rifting and active faulting, similar to what has happened elsewhere during earth's history, but easier to study because it is above sea level and currently active. Intellectual merit: Using these results we have improved the model of seismic wavespeeds underground in the Imperial and Coachella Valleys and along a zone from near San Diego to the Colorado River. This new information can be used by the southern California seismic network to obtain better locations of earthquakes when they happen in this region, especially shallow earthquakes that occur in the Imperial Valley along the active faults. Our results also show that the San Andreas fault is not vertical along the eastern edge of the Salton Sea, but rather it is inclined toward the east. The shaking that would result from a big earthquake along this fault depends on whether the fault is inclined, and which way it is inclined, so this information changes the models of where the shaking will be the worst if there is a big earthquake along this fault. For the region of the Imperial Valley we have now obtained a much more detailed seismic velocity model south of the Salton Sea including in the region of the Salton Buttes and Brawley Geothermal plants as well as the cities of Imperial, El Centro, and Calexico. Using this model we have relocated earthquakes that have occurred at shallow depths in this region and can better understand what faults are controlling these earthquakes, and how these are related to the geothermal resources. We also now have a better idea of the pattern of rocks that are present at depth below the surface of this rift, and better ideas of how the rift formed and developed. Broader impacts: Student training - Many students from 2-year and 4-year colleges and universities in southern California assisted with the field work for this project. The field work was based out of the city of El Centro so students from Imperial Valley College and from a local high school also helped with the field work. Many of these students were from ethnic groups traditionally underrepresented in the earth sciences. Volunteers from the local communities also helped with the field work. Graduate students from Caltech and Virginia Tech are using the data from this project for their PhD dissertation research. One graduate student from Mexico wrote his master's thesis using results from this project. Three Latino undergraduate student interns sponsored by the Southern California Earthquake Center worked on the data during the summer after the data were collected. Public awareness – We gave presentations to civil engineers and government officials in the Imperial Valley, at meetings in the City of Calexico and the City of El Centro, to discuss earthquake hazards and the results of this project. We also gave a presentation to scientists and government officials in the city of Mexicali in Baja California. Information about our project is available to the general public in a display at the Thousand Palms Oasis visitor center in the Coachella Valley near Palm Springs, California. Results were used for several teacher training workshops for middle school and high school earth science teachers from Riverside and San Bernardino counties, California, and for workshops for community college teachers in Southern California. Results were also discussed on National Public Radio and in some news interviews for Spanish language TV in Los Angeles.
