HR: 1340h
AN: T33C-1398    [Abstracts]
TI: 2-D Lithospheric Density Modeling in Southern California
AU: * Romanyuk, T
EM: t.romanyuk@uipe-ras.scgis.ru
AF: US Geological Survey, 345 Middlefield Rd. MS 977, Menlo Park, CA 94025 United States
AU: * Romanyuk, T
EM: t.romanyuk@uipe-ras.scgis.ru
AF: Institute of Physics of the Earth, B. Gruzinskaya 10, Moscow, 123810 Russian Federation
AU: Mooney, W D
EM: mooney@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd. MS 977, Menlo Park, CA 94025 United States
AB: We report results from density modeling of the crust and uppermost mantle along the LARSE I and II transects across southern California. A linear gravity inversion technique was used to calculate crustal and mantle densities along a two-dimensional profile. We used borehole measurements, seismic velocities, and petrologic information to constrain the model where possible. We further assumed that the lithosphere is close to isostatic equilibrium in the deep ocean and east of the Mojave Desert. We used the linear equation $\rho$=a+bVp (where $\rho$ is density, Vp is seismic P-wave velocity) to approximate the mantle density-velocity ratio. A value of b=0-0.2 corresponds to a purely thermal effect on density in the mantle, whereas a coefficient of b $>$ 0.3 implies that petrological or metamorphic changes play an important role in determining density. Solutions with b=0.2-0.4 are considered optimal. It was noted that solutions without mantle density variations required an abnormally dense lower crust (3.1 g/ccm) beneath the Los Angeles basin. Analysis of the isostatic balance of the models and the average density of the consolidated crust did not allow us to clearly define a preferred density model. With this approach, we cannot distinguish if thermal or petrological and/or metamorphic processes cause observed density variations in the study area.
DE: 7260 Theory and modeling
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8159 Rheology--crust and lithosphere
DE: 7205 Continental crust (1242)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting