Structural Geodesy: Active Deformation of the Barrancas Anticline, Mendoza, Argentina

BROOKS, BENJAMIN; BEVIS, MICHAEL; KENDRICK, ERIC; EUILLADES, PABLO; BLANCO, MAURO; EUILLADES, LEONARDO; CABRERA, GABRIEL; SMALLEY JR., ROBERT; ARIAL, ARJUN; FOSTER, JAMES

San Francisco, CA, USA

Congreso; American Geophysical Union Fall Meeting; 2006

American Geophysical Union

AB: We analyze continuous and survey GPS and InSAR data from the south-central Andean thrust front in Mendoza, Argentina and focus on the Barrancas anticline, a blind thrust-related fold with evidence for Quaternary folding. In 2001 we installed a 43 station network in a ~50 km radius centered on the anticline in response to our regional analysis which suggested that the area might exhibit a displacement rate gradient twice that of the ~3-5mm/yr/100 km throughout the rest of the Andean backarc. Most stations have now been reoccupied at least 3 times. We process the data in a standard way using GAMIT and GLOBK software but adjust our analysis in order to elucidate smaller, more localized deformation patterns. We choose stations on the anticline´s backlimb and further to the west and find a local stable reference frame via a 6 parameter Helmert transformation in which horizontal velocities are minimized in a least-squares sense yielding residual rms velocities smaller than 1.7 mm/yr. In this reference frame, the majority of stations on the east of the anticline´s structural crest exhibit west-directed residuals ranging from ~1 - 4 mm/yr. Additionally, we analyze ERS-1 interferograms and a ~1.5 year stack of Envisat data and find no evidence that the GPS data are significantly affected by active oil pumping or fluid injection at the anticline. This is not necessarily a surprise as reservoir depths exceed 2 km here. Our combined analysis strongly suggests that the anticline has been the locus of active shortening in the absence of any earthquakes, although the data are not yet of sufficient resolution to allow differentiation between competing mechanical or kinematic models.