A GPS Study of the Large-Scale Neotectonics of Northern Central America

该项目是对中美洲北部大规模新构造的五年合作大地测量研究，加勒比板块的西端毗邻中美洲俯冲带和莫塔瓜-波罗契克走滑断层系统。科学目标如下：(1)估计沿科科斯-加勒比海俯冲界面的摩擦耦合的大小和分布，(2)测量穿过莫塔瓜-波罗契克断裂系统的一个或多个点的走滑运动速度，(3)测量横跨莫塔瓜-波罗契克断裂系统南部的中美洲“盆山”的延伸，(4)测量应变在中美洲火山弧中的断层上累积的速度，这些断层适应于斜向俯冲的右旋弧前剪切，(5)测试是否发生显著的区域抬升，可能是对该区域之下的板块假定的拆离的响应，(6)改进加勒比板块大地参照系的运动学模型。关于第一个目标的工作有助于对非地震过程在容纳俯冲方面的基本作用的新的理解。目标2-5的进展正在推动目前对加勒比海板块西部后缘的新构造和地震危险的认识不足。最终目标的工作有利于美国国家科学基金会赞助的多项关于加勒比海板块复杂变形边缘周围变形的GPS研究。这些目标是通过对分布在洪都拉斯、危地马拉和萨尔瓦多的50-100个GPS站点每年或更频繁占用的速度以及已经在这些国家运行的7个连续GPS站点的速度进行建模来实现的。建模是使用三维有限元代码完成的，该代码允许从构造上真实地表示研究区域，包括代表海洋-大陆俯冲边界的横向和垂直变化的材料特性。除了最初的网络侦察和安装之外，所有的测量都是由当地科学家进行的，这是一个合作的努力。该项目的结构是为了极大地促进洪都拉斯、危地马拉和萨尔瓦多科学家的研究事业，这些科学家正在与他们合作。预算包括年度业务资金、GPS接收器，以及洪都拉斯地震学家和危地马拉地震学家以及可能还有一名萨尔瓦多地球科学家的旅费。最终，在上述目标方面的进展将改善对在这一广泛地区构成地震危险的各种断层上可能发生重大地震的频率的估计。

This project is a five-year collaborative geodetic study of the large-scale neotectonics of northern Central America, where the western end of the Caribbean plate abuts both the Middle America subduction zone and Motagua-Polochic strike-slip fault system. The scientific objectives are as follows: (1) Estimate the magnitude and distribution of frictional coupling along the Cocos-Caribbean subduction interface, (2) Measure the rate of strike-slip motion at one or more points across the Motagua-Polochic fault system, (3) Measure extension across the Central American "basin-and-range" south of the Motagua-Polochic fault system, (4) Measure how quickly strain accumulates across faults in the Central American volcanic arc that accommodate dextral forearc shear in response to oblique subduction, (5) Test whether significant regional uplift occurs, possibly in response to the hypothesized detachment of the slab subducting beneath this region, and (6) Improve kinematic models of the Caribbean plate geodetic reference frame. Work on the first objective is contributing to an emerging understanding of the fundamental role of aseismic processes in accommodating subduction. Progress on objectives 2-5 is advancing the present poor understanding of the neotectonics and seismic hazards at the western, trailing edge of the Caribbean plate. Work on the final objective benefits multiple NSF-sponsored GPS studies of deformation around the complexly deforming margins of the Caribbean plate. These objectives are being accomplished through modeling of velocities determined from annual or more frequent occupations of 50-100 GPS sites distributed throughout Honduras, Guatemala, and El Salvador and velocities at seven continuous GPS sites that are already operating in these countries. Modeling is done using three-dimensional finite element code that allows for a tectonically realistic representation of the study area, including laterally- and vertically-varying material properties representative of an ocean-continent subduction boundary. All measurements are made by local scientists, except for the initial network reconnaissance and installation, which were a collaborative effort.The project is structured to benefit significantly the research careers of Honduran, Guatemalan, and Salvadoran scientists with whom are collaborating. The budget includes annual operating funds, GPS receivers, and travel funds for Honduran seismologist and Guatemalan seismologists, and possibly an earth scientist from El Salvador. Ultimately, progress on the goals above will improve estimates of the likely frequency of significant earthquakes along a variety of faults that present a seismic hazard in this extensive region.