HR: 0800h
AN: T51D-1384    [Abstracts]
TI: Current Vertical Crustal Movements in Northern Baja California, Mexico
AU: * Outerbridge, K C
EM: kouterbridge@rsmas.miami.edu
AF: University of Miami RSMAS/MGG, 4600 Rickenbaker Cswy, miami, FL 33149 United States
AU: Dixon, T
EM: tdixon@rsmas.miami.edu
AF: University of Miami RSMAS/MGG, 4600 Rickenbaker Cswy, miami, FL 33149 United States
AU: Wdowinski, S
EM: swdowinski@rsmas.miami.edu
AF: University of Miami RSMAS/MGG, 4600 Rickenbaker Cswy, miami, FL 33149 United States
AU: Malservisi, R
EM: malservisi@geophysik.uni-muenchen.de
AF: Ludwig-Maximilians University, Theresienstrasse 41, Munich, 80333 Germany
AB: The observed topographic expression in the northern Baja California region is a challenging multipart problem that may give insight into other fault systems and tectonic mechanisms. Northern Baja California is a complex fault system with mechanisms of both strike-slip and normal faulting. This area is positioned close to the Pacific-North America plate boundary and is intimately associated with the spreading center within the Gulf of California as well as the southern extension of the San Andreas Fault. In this study we focus on the normal faulting components of the region. Over the last 7 years we collected campaign GPS data from a network of stations located throughout the area. The data show statistically significant vertical movements of up to 4.8 +/- 1.5 mm/yr, which correlate with high topography. In order to better understand the source of the observed uplift, we calculated the expected isostatic uplift magnitude and distribution in response to unloading that occurs along a normal fault due to crustal thinning. We obtained our solution using a two stage calculation procedure, the first of which was an elastic half space model utilizing the Poly3D software package. The second stage of calculations applied the calculated mass removal and uplift magnitude from purely kinematic means, to an elastic plate bending model. Our modeled results, however, did not fit the observed uplift signal in northern Baja California well. In particular the wavelength of the uplift distribution was misfit. This mismatch indicates an additional unmodeled uplift process, most likely with a deeper source. Using the same elastic plate bending model and a best fit approach we calculated the amplitude and distribution of the additional uplift. Our results show that the additional uplift centers 30 km west of the normal fault, beneath the highest topography. The parameters that varied within these models include rigidity, rate, locking depth of the fault, and the position of the center of negative mass for the additional source of isostatic uplift. The possibility that this uplift signal is due to a systematic error is being explored. However, although we don't yet have a quantitative model that explains this additional uplift, we attribute it to deep processes such as delamination of a dense root, analogous to delamination beneath the Sierra Nevada batholith to the north.
DE: 0545 Modeling (4255)
DE: 1218 Mass balance (0762, 1223, 1631, 1836, 1843, 3010, 3322, 4532)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8175 Tectonics and landscape evolution
SC: Tectonophysics [T]
MN: Fall Meeting 2005