U.S.-Mexico Collaborative Research; Study of Benioff Zone Geometry and Stresses at the Tehauntepec, Mexico Transition Zone along the Middle America Trench

该奖项将支持圣克鲁斯大学的Karen McNally教授和墨西哥Cientifica y de Education acion Superior de Ensenada中心的J.Gonzalez-Ruiz博士之间的合作研究。最近的研究集中在中等深度的地震活动上，着眼于与俯冲过程相关的应力和几何形状。已发现的证据表明，俯冲板块在海沟的几何形状或下沉板块的倾角或两者都发生急剧变化的位置上“撕裂”成碎片。其他证据表明，下沉的板块具有很强的变形能力。调查人员计划扩大目前的研究范围，以包括对墨西哥特万特佩克过渡带俯冲科科斯板块结构的详细研究。人们之所以对该地区感兴趣，是因为除其他原因外，它可能是可可-北美-加勒比板块之间的三重连接点的位置；它是浅角和陡角俯冲之间的过渡；火山几何形状、海沟深度、板块年龄和其他特征在这个位置发生变化；它是一个潜在未知的地震空区；并且断层机制和地震活动分布与墨西哥其他地区显著不同。研究人员将使用观测方法，通过合成波形建模，收集非常精确的区域地震深度和震源机制。根据这一地震数据集，将确定俯冲和下行板块之间和内部的几何形状、应力的性质和方向以及耦合。这项工作将导致一本关于地震机制、构造框架和地震风险的重要出版物。

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.