HR: 1330h
AN: G43B-09    [Abstracts]
TI: 3-D Gravity modeling of the crust and uppermost mantle beneath southern California: implications for the deep structure of the San Andreas continental transform zone.
AU: * Bundalo, N
AF: Dept of Geosciences, University of Houston, Houston, TX 77204 United States
AU: Hall, S A
EM: sahgeo@uh.edu
AF: Dept of Geosciences, University of Houston, Houston, TX 77204 United States
AB: We have used a regional compilation of both onshore and offshore gravity data to investigate variations in crustal and upper mantle structure beneath southern California in order to better understand the tectonic development of the San Andreas continental transform zone. The seismic velocity model developed by the Southern California Earthquake Center (SCEC - version 3) was used to construct an initial 3-D, multilayer density model of the region for comparison with observed gravity data. The model uses vertical triangular prisms with non-parallel upper and lower surfaces to simulate lateral density variations. The model was divided into an upper portion that incorporates near surface lithologic information and topography and a lower portion that includes density variations in the deeper crust and uppermost mantle derived from the seismic velocity data. The broad scale agreement between the anomaly field generated by our model and the major features in the observed gravity data indicates that the overall structure is well defined. In several areas, however, differences between the modeled and observed data are significant. To address these differences we have modified our initial model using densities obtained from a range of published velocity-density relationships and rock sample measurements. Differences between the modeled and observed gravity are most apparent in the high frequency portion of the gravity spectra and can best be explained by the poorly constrained near surface density distribution. Other sources of the differences include those due to edge effects and those imposed by limits in the SCEC model data. Details regarding along-strike variations in the deep structure beneath the transform zone will be presented.
DE: 1219 Local gravity anomalies and crustal structure
DE: 8110 Continental tectonics--general (0905)
DE: 8122 Dynamics, gravity and tectonics
SC: Geodesy [G]
MN: 2005 Joint Assembly