STRAIN PARTITIONING AT THE NORTH AMERICAN-CARIBBEAN PLATE BOUNDARY AS REVEALED BY AN EARTHQUAKE SEQUENCE IN THE NORTHERN DOMINICAN REPUBLIC

The Northern Caribbean Plate Boundary Zone is a complex region that has been modified extensively by the relative eastward movement of the Caribbean Plate and the plate’s impact with the buoyant Bahama carbonate platform. The results include extensive subduction of oceanic crust belonging to the North American Plate, a broad zone of deformation to accommodate strain, the development of several new transform and normal faults to relieve stress after collisions, the formation and rotation of microplates, and the rearrangement and aggregation of crustal fragments into new islands.

On 22 September 2003, a large (m_W=6.5) earthquake struck the Dominican Republic, causing widespread damage that included partially collapsed buildings and bridges in the cities of Santiago and Puerto Plata and landslides in the mountainous outlying areas. Aftershocks reaching m_W =5.1 followed for weeks afterward. This earthquake sequence is the strongest to affect the Dominican Republic since a series of powerful thrust events, including five earthquakes ranging in magnitude from 7.1 to 8.1, occurred between 1943 and 1953. Prior to 1943, significant earthquakes occurred in 1564 (in which the city of Santiago was destroyed), 1783, 1842, 1887, and 1897.

Following the 2003 Puerto Plata main shock we deployed 10 broadband seismographs borrowed from the IRIS PASSCAL Instrument Center around the aftershock zone for a period of two months and analyzed the data jointly with data from two permanent seismic networks in the Dominican Republic. Analyses included estimating a new 1D model of earth structure, re-locating more than 300 aftershocks, producing a 3D tomographic model of the fault zone from phase arrivals, and computing focal mechanisms. We will report the results of these analyses and their implications for regional structure, tectonics and seismic hazard.