Collaborative Research: An integrated GPS and Structural Study of the Cocos-Caribbean Boundary in Nicaragua and El Salvador

在这四年的大地测量和结构研究的可可-加勒比收敛边缘沿着太平洋海岸的萨尔瓦多萨尔瓦多和尼加拉瓜，斜收敛的组合，一个突出的弯曲的海沟，和弱或没有锁定的俯冲界面，威斯康星州和阿肯色州大学的研究人员正在研究如何火山弧和弧前银变形，以响应斜收敛。通过数字高程模型分析、结构实地工作、GPS观测以及使用三维几何真实俯冲/前弧有限元网格的正演和反演建模，该团队正在解决以下重要问题：（一）由于沟道中的弯曲而引起的会聚度的变化是否有效地转化为弧前运动或变形的变化，以及弧前裂片是否向沟槽（2）为什么两个弧前狭长带之间的弯曲，预期地壳增厚的地方，反而被地形凹陷所占据（3）两个前弧的运动是否由弧平行走滑断层、书架断层或两者的某种组合所调节;（4）萨尔瓦多火山弧内侧地壳的东西向拉伸特征是否也延伸到弧前，如果是，这种拉伸如何与银迁移相互作用并影响银迁移。最后，正在进行一系列模拟实验，以更好地了解俯冲/弧前楔系统的运动学和动力学，使用三维有限元模型和一系列合理的边界条件，包括在楔的基础上的倾滑牵引力，可变阻力滑沿着俯冲界面和弧前断层，和不同程度的扶壁在楔的前缘。通过这一综合办法，利用全球定位系统和实地结构工作研究中美洲西部的活动变形，正在建立理解该地区地震周期的概念和运动学框架。自1900年以来，该地区发生了许多中、大地震，造成数万人死亡。向萨尔瓦多和哥伦比亚合作者转让知识和技术将大大有利于两国今后的地震灾害研究。研究生正在接受利用结构地质学和高精度大地测量学研究地震周期的培训。

In this four year geodetic and structural study of the Cocos-Caribbean convergent margin along the Pacific coasts of El Salvador and Nicaragua, where a combination of oblique convergence, a prominent bend in the trench, and weak or no locking of the subduction interface, University of Wisconsin and University of Arkansas researchers are studying how a volcanic arc and forearc sliver deform in response to oblique convergence. Through Digital Elevation Model analysis, structural field work, GPS observations, and forward and inverse modeling using a three-dimensional, geometrically realistic subduction/forearc finite element mesh, the team is addressing the following important problems: (1) whether changes in convergence obliquity due to bends in trenches are efficiently transferred into changes in forearc motion or deformation and whether escape of a forearc sliver toward the trench (a free surface) is favored over crustal thickening at the leading edge of a forearc sliver; (2) why the bend between the two forearc slivers, where crustal thickening is expected, is instead occupied by a topographic depression (the Gulf of Fonseca); (3) whether the motions of the two forearcs are accommodated by arc-parallel strike-slip faulting, bookshelf faulting, or some combination of the two; (4) whether the east-west stretching characteristic of the crust inboard from the Salvadoran volcanic arc also extends into the forearc and if so, how this stretching interacts with and influences sliver transport. Finally, a series of modeling experiments are being conducted to better understand the kinematics and dynamics of the subduction/forearc wedge system, using a three-dimensional finite element model and a series of plausible boundary conditions, including dip-slip tractions at the base of the wedge, variable resistance to slip along the subduction interface and forearc faults, and varying degrees of buttressing at the leading edge of the wedge. Through this integrated approach to studying active deformation in western Central America with GPS and field-based structural work, the conceptual and kinematic framework for understanding the earthquake cycle in this region is being established. , Tens of thousands of deaths have occurred since 1900 during numerous moderate and large magnitude earthquakes in this region. Knowledge and technology transfer to El Salvadoran and Nicaraguan collaborator significantly benefit future earthquake hazard studies in both countries. Graduate students are being trained in the use of structural geology and high-precision geodesy for studying the earthquake cycle.