Preliminary Results From the Southern Sierra Nevada Continental Dynamics Project 1993: Wide-Angle Fan Profiles

by M M Fliedner (Stanford University) and SSCD Working Group

In September 1993 the Southern Sierra Nevada Continental Dynamics project (SSCD) acquired 'axial' (north-south) and 'transverse' (east-west) wide-angle reflection/refraction profiles across the southern Sierra Nevada mountains and western Basin and Range Province. One of the fundamental uncertainties about the Sierra Nevada batholith is the extent of the root to this mountain range: how deep (if it is present) and where (localised beneath the present mountains or also continuing east beneath the extended fragments of the batholith in the western Basin and Range).

In order to model the depth to the Moho in three dimensions, we recorded - in addition to the nineteen in-line shots - four overlapping broadside fan shots, two into each receiver line in the expected critical-distance range for reflections from the Moho. The design of the fan shots was based on our 3-D finite-difference travel-time models (using the code of J. Hole, JGR 97, 3417, 1992) of P_mP reflections using realistic 2.5 D velocity structures. Our models show that shooting with a fan geometry is best suited to distinguish between the different proposed structures of the Sierran crustal root, and that travel-time differences of up to 2.5 s at critical distance are to be expected between models with or without a crustal root.

In this poster we present the new fan-shot data from the 1993 field experiment, and compare these data with the results of travel-time modelling done before the experiment.

The SSCD Working Group includes representatives from Duke University, University of Nevada at Reno, University of California at Riverside, Lawrence-Livermore National Laboratory, Caltech, San Diego State University, Princeton University, the USGS, and Stanford University.