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萨尔瓦多和尼加拉瓜太平洋沿岸科科斯-加勒比海会聚边缘进行了为期四年的大地测量和构造研究，在那里，斜向会聚、海沟中的突出弯曲以及俯冲界面的弱锁定或没有锁定相结合，正在研究火山弧和弧前银子如何响应倾斜会聚而变形。通过数字高程模型分析、结构野外工作、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反向建模，该团队正在解决以下重要问题：(1)由于海沟弯曲造成的会聚倾角的变化是否有效地转化为弧前运动或变形的变化，以及弧前银条向海沟(自由面)的逃逸是否比弧前银条前缘的地壳增厚更受欢迎；(2)为什么预期地壳增厚的两个弧前银条之间的弯曲被地形凹陷(丰塞卡湾)占据；(3)两个前弧的运动是否受到弧形平行走滑断裂、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伸展特征是否也延伸到前弧，如果是，这种伸展是如何与银矿运移相互作用和影响的。最后，正在进行一系列模拟实验，以更好地了解俯冲/弧前楔体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，包括楔体底部的倾滑牵引力、沿俯冲界面和弧前断层的可变抗滑阻力以及在楔体前缘的不同程度的支撑。通过利用全球定位系统和实地构造工作研究中美洲西部活动形变的综合方法，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，在该地区发生的多次中、大型地震中，已有数万人死亡。向萨尔瓦多和尼加拉瓜的合作者转让知识和技术将大大有助于两国未来的地震风险研究。研究生正在接受利用构造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.