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

威斯康星大学和阿肯色大学的研究人员对沿萨尔瓦多和尼加拉瓜太平洋海岸的科科斯-加勒比辐合边缘进行了为期四年的大地测量学和结构研究，在那里，斜辐合、海沟的显著弯曲和俯冲界面的弱锁定或不锁定结合在一起，威斯康星大学和阿肯色大学的研究人员正在研究火山弧和弧前银条是如何响应斜辐合而变形的。通过数字高程模型分析、构造现场工作、GPS观测，以及使用三维、几何逼真的俯冲/弧前有限元网格进行正演和逆演建模，该团队正在解决以下重要问题：(1)海沟弯曲引起的辐合倾角变化是否有效地转化为弧前运动或变形的变化，以及弧前条向海沟（自由面）的逃逸是否比弧前条前缘的地壳增厚更有利；(2)为什么预计地壳增厚的两个前弧条之间的弯曲处被地形洼地（丰塞卡湾）所占据；(3)两个前弧的运动是否受到平行弧走滑断裂、书架断裂或两者的某种组合的调节；(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，这种拉伸如何与银块搬运相互作用和影响。最后，为了更好地理解俯冲/弧前楔体系统的运动学和动力学，研究人员进行了一系列建模实验，采用三维有限元模型和一系列合理的边界条件，包括楔体底部的倾滑牵引力、沿俯冲界面和弧前断层的可变滑动阻力以及楔体前缘不同程度的支撑作用。通过这种利用GPS和野外构造工作研究中美洲西部活动变形的综合方法，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，该地区发生了多次中大型地震，造成数万人死亡。向萨尔瓦多和尼加拉瓜合作者转让知识和技术大大有利于两国未来的地震灾害研究。研究生正在接受构造地质学和高精度大地测量学的训练，以研究地震周期。

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.