Technical Report - January 10, 2004

GPS Gampaign in the Dominican Republic,

October 12-18, 2003

Data Analysis and Preliminary Results

Report written by Eric CALAIS, Purdue University

Collaboration:

Paul MANN, Univ. of Texas, Institute for Geophysics

Pam JANSMA, Univ. of Arkansas

Glen MATTIOLI, Univ. of Arkansas

Abstract:

On September 22, 2003, a M6.5 earthquake struck the northern Dominican Republic in the Puerto Plata area. This event prompted a remeasurement of the northern portion of a 36-site GPS network previously observed in 1999 and 2001. The objective of this GPS campaign is to measure surface coseismic displacements that, in turn, will be used to constrain source model and determine whether this event may have triggered slip on the nearby Septentrional fault. The survey took place between October 12 and 18, 2003. A total of 12 sites were remeasured and we benefited from data from 4 continuous GPS sites operated by the Dominican Department of Justice.

After processing the data and combining the resulting solutions with previous surveys, we find significant and reliable coseismic displacements at 4 sites out of 12, all located within 50 km of the epicenter. The coseismic displacements are consistent with a rupture dipping shallowly to the southwest, with pure thrust motion. Our preferred coseismic model is a 11.5 km wide by 25 km long rupture plane striking in a N149E direction and dipping 15$^o$ to the southwest, located offshore at a depth of 2 to 6 km.

In addition to quantifying surface coseismic displacements, this GPS campaign provides a third measurement epoch for 12 sites, with important implications for the measurement of long-term interseismic strain in Hispaniola.