HR: 14:00h
AN: G43C-02    [Abstracts]
TI: Rapid Transient Deformation From a Shallow Magmatic Source at the Socorro Magma Body, NM, USA?
AU: * Newman, A V
EM: anewman@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences Div., MS D462, Los Alamos, NM 87545 United States
AU: Chamberlin, R M
EM: richard@gis.nmt.edu
AF: New Mexico Bureau of Geology and Mineral Resources, 801 Leroy Place, Socorro, NM 87801 United States
AU: Love, D W
EM: dave@gis.nmt.edu
AF: New Mexico Bureau of Geology and Mineral Resources, 801 Leroy Place, Socorro, NM 87801 United States
AU: Dixon, T H
EM: tdixon@rsmas.miami.edu
AF: University of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149 United States
AU: La Femina, P
EM: plafemina@rsmas.miami.edu
AF: University of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149 United States
AB: The Socorro Magma Body (SMB) lies within the central Rio Grande Rift (RGR) Valley and is one of the largest known magma bodies in the Earth's continental crust. Studies of local microseismicity and deep seismic soundings revealed an unusually strong reflector approximately 70 km wide at 19 km depth and identified it as a large active sill-like crustal magma intrusion. Using precision leveling (1912-80) and InSAR (1992-99), previous studies have found $\sim$2-4 mm/yr of averaged uplift centered near San Acacia, over the center of the reflector, and corresponding to about 10$^7$ m$^3$ of annual growth from an inflating sill at 19 km depth. We performed two GPS campaigns over the SMB on nine bedrock sites in 2002 and 2003. Vertical GPS velocities from six sites forming a transect over the central SMB are between $\sim$10 and 20 mm (1$\sigma \sim$10 mm) with the maximum measured surface uplift at two central stations near San Acacia. However, three sites forming a partial transect $\sim$12 km north show no uplift for this period. Additionally, continuous GPS 18 km south of the central transect shows 4-5 mm/yr uplift between 2001 and 2004. Collectively, these data suggest a significant and smaller body inflating between 5-10 km depth and corresponding to 0.5-5$\times 10^6$ m$^3$ between 2002 and 2003. Though horizontal velocities are all less than their individual errors ($\sim$5 mm) they generally radiate outward from the center of the SMB. These results indicate that the SMB may have considerable variation in the spatio-temporal pattern of deformation. This suggests that, though over several years to decades the SMB inflates at an average of 2-4 mm/yr, more frequent and widespread geodetic measurements are necessary to fully assess its complex sources. Additionally, because the southern portion of the SMB extends into the trilateration network of Savage et al. [1988], which found slow-to-no extension ($<$3 mm/yr) across the RGR, it may be that those results were contaminated by previously unknown transient effects of the SMB.
DE: 8434 Magma migration
DE: 8439 Physics and chemistry of magma bodies
DE: 1208 Crustal movements--intraplate (8110)
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 1243 Space geodetic surveys
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting