Major strike-slip faults commonly found on the margin of overriding plates in oblique subduction zone settings greatly influence the tectonics of these margins and represent sources of seismic hazard of historic proportions. These faults, that facilitate the partitioning of strain into trench-parallel and trench-normal tectonics, 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 strength of interplate coupling and of the overriding lithosphere, as well as other factors such as basal tractions and the magnitude of 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 on seismic hazard as it is often thought to be associated with increased frictional coupling, and therefore large earthquakes at the plate interface as well as on intraplate strike-slip faults, that often have large neighboring populations.

Strain partitioning also has significant implications on the lateral transport of crustal slivers in plate boundary zones and their accretion to the margin of continents as it is a possible mechanism for plate boundary zone segmentation and terrane migration.

We propose to address the causes and consequences of strain partitioning on oblique subduction margins with a study combining GPS measurements and deformation models in the northeastern Caribbean. The northeastern Caribbean contains a fine example of neighboring zones of frontal subduction (Lesser Antilles), oblique subduction with no strain partitioning (Puerto Rico), and oblique subduction with strain partitioning (Hispaniola). We will acquire new GPS data in the Dominican Republic and Haiti and produce a geodetically consistent velocity field for the entire NE Caribbean. We will use these GPS velocities to constrain 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 (e.g., due to the subduction of a buoyant asperity) can trigger strain partitioning and, more generally, forearc deformation, and (2) how strike-slip fault earthquakes in the forearc interact with the plate interface earthquakes through co- and postseismic stress transfer.

Broader Impacts.

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).

Government officials and scientists in Haiti and the Dominican Republic (combined population 16.5~million) are becoming increasingly aware of seismic risk in their territories, where historical records shows several magnitude 7 or greater earthquakes in the past 500 years. This project will deliver basic geophysical information needed for seismic hazard analysis.

During the course of the project, collaborators from Haiti and the Dominican Republic will receive training in the use of GPS. Undergraduate and graduate students will participate in the fieldwork, benefit from exposure to the realities of field-based geophysics, and gain valuable skills that can be translated to the workplace or advanced degree programs.