Puerto Plata Earthquake

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Posting Date: September 22, 2003, 11:00:00 AM

A strong earthquake struck the Dominican Republic at 12:45 a.m. local time on Monday, September 22, 2003. The moment magnitude of the quake was 6.4, according to the U.S. Geological Survey. The epicenter was located 9 miles (15 km) south of the city of Puerto Plata, a coastal resort, and 12 miles (20 km) north of Santiago, about 93 miles (150 km) north-northwest of the capital, Santo Domingo. Focal depth is estimated at about 6 miles (10 km). The earthquake was felt some 220 miles (354 km) to the east in Puerto Rico. There have been at least two aftershocks of magnitude 5.1 and 4.7. The seismicity of the island of Hispaniola, which includes the Dominican Republic and Haiti, is dominated by the interaction between the eastern North American and Caribbean plates. The seismo-tectonic process of the region is a complex transition from subduction, dominant in the east, to a transform boundary, defined by the Septentrional Fault Zone (SFZ), dominant in the west. The region includes both strike-slip and dip-slip faults that accommodate both parallel and perpendicular plate motions. The results of recent regional GPS modeling suggest an eastward relative motion of about 19 mm/yr for the Caribbean plate with respect to the North American plate. The moment tensor solution for the current earthquake suggests a dip-slip faulting mechanism. A recent paleoseismic study of the central SFZ in the Dominican Republic by Prentice et al. (2003) indicates past earthquake activity in this region with an estimated recurrence interval of 800 - 1200 years for M>7 earthquakes. The data suggests that an earthquake of such magnitude ruptured the SFZ some time before A.D. 1230. The historic seismic record of Hispaniola, although not well studied, suggests a large earthquake, with uncertain magnitude, on the western segment of the fault, occurring around 1842. However, there is no historic report of large earthquakes on the central and eastern segments. A joint rupture of these segments can produce a rather large magnitude earthquake on the SFZ. One office building in Puerto Plata collapsed and other buildings suffered some damage. Since the quake struck after midnight, most commercial buildings were deserted. A hospital in Santiago was evacuated due to cracked walls. There have been no reports of serious injuries or deaths.

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Posting Date: September 22, 2003, 11:00:00 AM