This award will support collaborative research between Prof. Karen McNally of the University of Santa Cruz and Dr. J. Gonzalez-Ruiz of the Centro de Investigacion Cientifica y de Educacion Superior de Ensenada (CISECE) in Mexico. Recent studies have focused on intermediate depth seismicity, looking at the stresses and geometries associated with subduction processes. Evidence has been found suggesting that subducting plates "tear" into segments at locations of sharp changes in either the geometry of the trench or the dip of the downgoing plate or both. Other evidence suggests that downgoing plates are highly deformable. The investigators plan to extend present studies to include a detailed study of the structure of the subducting Cocos plate at the Tehuantepec transition zone beneath Mexico. This region is of interest because, among other reasons, it may be the location of the triple junction between the Cocos-North America-Caribbean plates; it is transitional between shallow angle and steep angle subduction; volcano geometry, trench depth, plate age, and other features change at this location; it is a seismic gap with unknown potential; and fault mechanism and seismicity distribution change markedly from those of other areas of Mexico. The investigators will use an observational approach by assembling very accurate depths and focal mechanisms of regional earthquakes via synthetic waveform modeling. Based on this earthquake data set, the geometry and the nature and direction of stress and coupling between and within the overriding and downgoing plates will be determined. The work will lead to a significant publication regarding earthquake mechanisms, tectonic framework, and seismic risk.
