HR: 0800h
AN: G51A-0058    [Abstracts]
TI: Volcanic Deformation Interpretations From Campaign-Mode GPS Measurements of the Commonwealth of Dominica, Lesser Antilles, 2001-2003 Epoch I Data
AU: * Parra, J G
EM: jgparra@csupomona.edu
AF: Department of Geological Sciences, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768 United States
AU: * Parra, J G
EM: jgparra@csupomona.edu
AF: Department of Geosciences, University of Arkansas, 113 Ozark Hall, Fayetteville, AR 72701 United States
AU: Turner, H L
EM: hturner@uark.edu
AF: Department of Geosciences, University of Arkansas, 113 Ozark Hall, Fayetteville, AR 72701 United States
AU: Blessing, B C
EM: bcblessi@mtu.edu
AF: Department of Geological Engineering and Sciences, Michigan Tech, 630 Dow Environmental Sciences and Engineering Building, 1400 Townsend Drive, Houghton, MI 49931-1295 United States
AU: Davidson, R T
EM: rtdypb@umr.edu
AF: Department of Geological Sciences and Engineering, University of Missouri-Rolla, 125 McNutt Hall, Rolla, MO 65409 United States
AU: Fitzgibbon, K
EM: kfitzgi@uark.edu
AF: Department of Geosciences, University of Arkansas, 113 Ozark Hall, Fayetteville, AR 72701 United States
AU: Jansma, P
EM: pjansma@uark.edu
AF: Department of Geosciences, University of Arkansas, 113 Ozark Hall, Fayetteville, AR 72701 United States
AU: Mattioli, G
EM: mattioli@uark.edu
AF: Department of Geosciences, University of Arkansas, 113 Ozark Hall, Fayetteville, AR 72701 United States
AB: The Commonwealth of Dominica is located on the eastern margin of the Caribbean plate midway along the Lesser Antilles Arc. It is the most mountainous of the Lesser Antilles, primarily due to its seven potentially active volcanic centers. A shallow seismic swarm was recorded in southern Dominica from September 20, 1998 to June 30, 2001. This seismicity prompted geodetic investigation due to its relative shallow nature and arc-shaped distribution around the peaks of Morne Anglais, Morne Plat Paye, and Morne Patates. A second seismic swarm took place in 2003. This seismicity clustered in the north of the Island in the vicinity of Morne Aux Diable. Campaign GPS observations were done using Ashtech Z-12 dual frequency, code-phase GPS receivers, with choke ring antennae. Three types of mounting systems were used depending on differing site restrictions. A total of 18 established monuments now exist throughout Dominica: nine were constructed in 2001 after the first seismic swarm occurred and three in 2003 after a second seismic swarm. Six additional sites were installed in June 2004. This presentation will focus on data collected from the 2001 and 2003 campaigns. Absolute point positions were obtained and velocity vectors were resolved in June 2003 for the initial nine benchmarks. Each data point was then compared with previously measured locations in 2001. Seven of the nine sites are located in the south where much of the seismic activity had been concentrated. The remaining two sites are located in the north. The preliminary velocity field is complex. All of the sites showed some measure of local deformation over a 2-year period. In the southern portion of the island, a set of vectors located in the Gommier Estate (GOMM) and Wotten Waven School (WOTT) point toward each other as well as towards the largest concentration of 2001 seismic epicenters. The vector for GOMM exhibited a velocity of 4.21 mm/a trending N68.1øE. WOTT displayed a velocity of 5.38 mm/a trending S16.8øW. A similar occurrence is observed in the northern region of Dominica, where another set of vectors located in Cabrits National Park (CABR) and in Concord (CNCD) point toward the main collection of shallow earthquakes from the more recent seismic swarm in 2003. CABR velocity is 3.89 mm/a trending S68.8øE, while CNCD velocity is 3.70 mm/a directed in a N25.8øW trend. Both seismic episodes are arcuate in shape. The overall shape and depth of the two sets of seismicity on Dominica, when joined with the geometry of local deformation suggest reactivation of old caldera collapse structures. However, the possibility of a shallow magmatic source or hydrothermal activity as grounds for seismicity is not out of the question. Continued annual GPS monitoring is imperative in order to better constrain the nature of deformation on the island of Dominica.
DE: 8419 Eruption monitoring (7280)
DE: 1200 GEODESY AND GRAVITY
DE: 1242 Seismic deformations (7205)
DE: 1294 Instruments and techniques
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting