Collaborative Research: GPS Measurements and Deformation Modeling of Oblique Subduction and Strain Partitioning in the Northeastern Caribbean

主要的走滑断层，通常在倾斜汇聚的俯冲带的上覆板块边缘发现，极大地影响了这些边缘的构造，并代表了历史性的地震危险源。走滑断层是斜辐合弧平行分量的轨迹，一般认为只有当上覆板块的剪应力大到足以激活走滑断层时才会发生。上覆板块剪切应力的大小一方面受板块辐合倾角的控制，另一方面受两个辐合板块沿板块界面的耦合程度和上覆岩石圈的强度，以及基底牵引力和板块拉力等因素的控制。这些因素的作用没有得到很好的理解，在开始划分之前必须达到的压力阈值也没有得到很好的理解。了解应变分配的机制对地震危险具有重要意义，因为它通常被认为与会聚板块之间增加的摩擦耦合有关，因此在板块界面发生大地震。应变分割也会导致在上覆板块的走滑断层上发生大地震，这些断层通常有大量的邻近人口。该项目通过将加勒比海东北部的全球定位系统（GPS）测量结果与变形模型相结合，解决了斜俯冲边缘应变划分的原因和后果。加勒比海东北部非常适合进行这样的研究。该区域由锋面俯冲带（小安的列斯群岛）、斜向俯冲带（波多黎各）和斜向俯冲带（伊斯帕尼奥拉岛）组成。调查人员正在多米尼加共和国和海地获取新的GPS数据，并为整个加勒比海东北部地区生成一个大地测量学上一致的速度场。GPS速度为运动学和动态变形模型提供了约束条件，这些模型旨在理解(1)在倾斜俯冲背景下，应力如何传递给覆岩板块，以及沿边缘的横向变化如何触发应变划分和弧前变形，以及(2)弧前走滑断层地震如何通过共震和震后应力传递与板块界面地震相互作用。这项研究与其他与东北加勒比地区具有构造相似性的地区有关，如地中海（如意大利南部、希腊西部）、西太平洋（如菲律宾、印度尼西亚、新几内亚）和南大西洋（斯科舍弧）。多米尼加共和国的历史记录显示，在过去的500年里发生了几次7级或更大的地震。该项目提供了加勒比东北部地震灾害分析所需的基本地球物理信息。

Major strike-slip faults, commonly found on the margin of overriding plates in obliquely convergent subduction zones, greatly influence the tectonics of these margins and represent sources of seismic hazard of historic proportions. The strike-slip faults, which are the locus of the arc parallel component of oblique convergence, are generally assumed to occur only if shear stresses in the overriding plate are large enough to activate strike-slip faulting. The magnitude of shear stress in the overriding plate is controlled in part by the plate convergence obliquity, but also by the degree of coupling of the two converging plates along the plate interface and the strength of the overriding lithosphere, as well as other factors, such as basal tractions and the slab-pull force. The role of these factors is not well understood, nor is the threshold of stress that must be achieved before partitioning will be initiated. Understanding the mechanics of strain partitioning has important implications for seismic hazard as it is often thought to be associated with increased frictional coupling between the converging plates, and therefore large earthquakes at the plate interface. Strain partitioning also leads to large earthquakes on strike-slip faults in the overriding plate, that often have large neighboring populations. This project is addressing the causes and consequences of strain partitioning at oblique subduction margins by combining Global Positioning System (GPS) measurements in the northeastern Caribbean with deformation models. The northeastern Caribbean is well suited to such a study. The region consists of neighboring zones of frontal subduction (Lesser Antilles), oblique subduction with no strain partitioning (Puerto Rico), and oblique subduction with strain partitioning (Hispaniola). The investigators are acquiring new GPS data in the Dominican Republic and Haiti and the generating a geodetically consistent velocity field for the entire northeastern Caribbean. The GPS velocities provide constraints for kinematic and dynamic deformation models aimed at understanding (1) how stress is imparted on an overriding plate in an oblique subduction setting and how lateral variations along the margin can trigger strain partitioning and forearc deformation, and (2) how strike-slip fault earthquakes in the forearc interact with the plate interface earthquakes through co- and postseismic stress transfer. This study is relevant to other areas sharing tectonic similarities with the northeastern Caribbean, such as the Mediterranean (e.g., southern Italy, western Greece), the western Pacific (e.g., Philippines, Indonesia, New Guinea), and the south Atlantic (Scotia arc). Historical records from the Dominica Republic reveal several magnitude 7 or greater earthquakes in the past 500 years. This project is providing basic geophysical information needed for seismic hazard analysis in the northeastern Caribbean.