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

主要走滑断层常见于斜向会聚俯冲带上覆板块的边缘，对这些边缘的构造影响很大，是历史上规模巨大的地震危险性的来源。走滑断层是斜向收敛的弧形平行分量的轨迹，通常认为只有当覆盖板块中的剪应力大到足以激活走滑断层时，才会发生走滑断层。上覆板块中剪应力的大小部分地受板块会聚倾角的控制，但也受两个会聚板块沿板块界面的耦合程度和上覆岩石圈的强度以及其他因素，如基座牵引力和板片拉力的控制。这些因素的作用没有得到很好的理解，也没有达到在启动分区之前必须达到的压力门槛。了解应变分配的机制对地震灾害具有重要的意义，因为它通常被认为与会聚的板块之间的摩擦耦合增加有关，因此与板块界面上的大地震有关。应变分割还会导致在俯冲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。该项目通过将全球定位系统(GPS)在加勒比海东北部的测量与形变模型结合起来，研究斜向俯冲边缘应变分配的原因和后果。加勒比海东北部非常适合这样的研究。该区域由额面俯冲(小安的列斯群岛)、斜向俯冲而无应变分割(波多黎各)和斜向俯冲而应变分割(伊斯帕尼奥拉)的相邻区域组成。调查人员正在多米尼加共和国和海地获取新的全球定位系统数据，并正在为整个加勒比海东北部生成一个大地测量一致的速度场。GPS速度为运动学和动态形变模型提供了约束，旨在了解(1)在斜向俯冲背景下，如何将应力施加到俯冲板块上，以及沿边缘的横向变化如何触发应变分配和弧前变形，以及(2)弧前走滑断层地震如何通过同震和震后应力转移与板块界面地震相互作用。这项研究与其他与加勒比海东北部在构造上有相似之处的地区有关，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。该项目正在提供加勒比海东北部地震危险性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.