Ongoing Surface Deformation Studies of Dominica, BWI: GPS Results and Interpretations From the 2006 NSF-REU Campaign

The UARK 2006 NSF-REU campaign was the fourth trip to Dominica to collect GPS geodetic data. GPS observations were made at 24 different sites on the island, concentrating on the southern half, where 7 of the 9 potentially active volcanic centers are located. GPS code and phase data were collected at 30 s sync using choke ring antenna. Data were processed using GOAII with final, precise orbits, clocks, and EOP from JPL. We calculated velocities for 18 of the sites that had been occupied in previous campaigns in 2001, 2003, and 2004 along with the new observations of 2006. The site velocities were corrected for co-seismic displacement from the Nov. 21, 2004 Mw 6.3 earthquake, secular movement of the Caribbean Plate, and elastic strain accumulation along the plate interface leaving only the values likely caused by volcanic deformation. Our data analysis involved inverse elastic half-space modeling of the surface deformation field using a modified version of Simplex and forward models made with RNGCHN software to find the best fit for the data with potential Mogi or dike-like magma sources. We also ran forward models for the volcanic centers to identify possible trends for deformation in the future. Our results showed no strong correlation between the site velocities and potential magmatic deformation sources, but left open many possibilities, especially in the vicinity of the Plat Pays volcanic complex in the south. Of the two best-fitting models, one showed a Mogi source southeast of the Plat Pays peak and the other a dike to the east, between Plat Pays and the Foundland Volcano. Volcanic deformation may also exist in the north, but we have not established enough sites there to constrain source location or geometry. In addition to the preliminary modeling presented here, we also determined the optimal location of additional sites to install during future field campaigns to further monitor surface deformation on Dominica.