HR: 17:45h
AN: S34B-08    [Abstracts]
TI: SAsia3D: A New Crustal and Upper Mantle P- and S- Velocity Model in Central and Southern Asia from Joint Body- and Surface-Wave Inversion
AU: * Reiter, D
EM: delaine@westongeophysical.com
AF: Weston Geophysical Corp., 181 Bedford St., Ste 1, Lexington, MA 02420, United States
AU: Rodi, W
EM: rodi@erl.mit.edu
AF: Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences 77 Massachusetts Ave., Cambridge, MA 02139, United States
AB: Accurate travel-time and amplitude predictions for regional seismic phases are essential for locating and characterizing small seismic events with the accuracy needed for explosion monitoring decisions. Parameter estimates calculated through 3D Earth models have the best chance of achieving acceptable prediction errors, if the models are constrained by sufficient data. With this motivation, we have developed and applied a joint body- wave/surface-wave inversion method to produce a new 3D P and S velocity model (SAsia3D) for the crust and upper mantle to a depth of 400 km in the region of central and southern Asia between 10-50° N and 40- 110° E. The method uses Pn and Pg arrival times to determine the P velocity structure and Rayleigh-wave group velocities in the period range 10-150 s to constrain the S velocity structure and depth to Moho. The body- wave and surface-wave inverse problems are coupled through an assumed correlation coefficient between P and S velocity perturbations and the imposition of bounds on the velocities and Poisson's ratio as a function of depth. Both body-wave and surface-wave forward modeling are performed in 3D models with the aid of finite-difference numerical raytracing to calculate body-wave raypaths and 2D raytracing to calculate non-great circle surface-wave paths. Nonlinearity is addressed by iterating the inversion method with updated raypaths. The regional P-wave arrival-time observations used to obtain SAsia3D were collected from the Engdahl, van der Hilst and Buland (1998; EHB) bulletin, restricted to well-located earthquakes in the years 1988-2004. The group- velocity measurements were provided by groups at the University of Colorado and Lawrence Livermore National Laboratory. Our initial model for the inversion procedure was taken as a hybrid of the CRUST2.0 3D model (Bassin et al., 2000) and the upper mantle portion of the global 1D AK135 model (Kennett et al., 1995). SAsia3D was obtained with four iterations of our technique, achieving a fifty percent variance reduction for both the body- wave and surface-wave data. Relative velocity (in particular the P velocity) variations with respect to the AK135 mantle model are in good agreement with previous studies and reflect the major tectonic features across southern and central Asia. For example, at 250 km depth, P variations across new model range from -2.0 to +2.3%, while S variations vary from -2.1% to +1.5%. We have also noted intriguing differences between the P and S velocity models in regions of significant tectonic activity, such as the Tibetan Plateau and South Caspian Basin. Some of these variations may prove useful in explaining the tectonic evolution of the Indo-Asian collision zone. We have also completed a number of validation exercises to demonstrate the accuracy of SAsia3D in regional seismic event location. Most notably, SAsia3D performs well when both regional P and S phase arrivals are included in the location. The regional P/S location obtained with SAsia3D are frequently superior to the locations obtained with a large set of teleseismic and regional P arrivals and the AK135 reference model.
DE: 7219 Seismic monitoring and test-ban treaty verification
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7270 Tomography (6982, 8180)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: 2007 Fall Meeting