CONTRASTING LITHOSPHERIC STRUCTURE BETWEEN THE COLORADO PLATEAU AND GREAT-BASIN - INITIAL RESULTS FROM COLORADO PLATEAU - GREAT-BASIN PASSCAL EXPERIMENT

The Colorado Plateau - Great Basin (CPGB) PASSCAL experiment provides broadband seismic data that allow us to determine crustal and upper ma ntle structure in the Colorado Plateau and eastern Great Basin. Twelve portable broadband seismometers throughout Utah and Nevada are supple mented by permanent broadband stations in the region. Receiver functio ns indicate an average crustal thickness of 35 +/- 5 km in the Great B asin (GB) with a strong P-to-S (Ps) conversion from the Moho. The crus t in the transition between the Great Basin and Colorado Plateau (CP) produces a strong intracrustal conversion. The CP has somewhat thicker crust (42 +/- 5 km) and weaker Moho conversion. BR surface wave phase velocities are 3-4% higher than CP phase velocities in the 20-35 s ra nge, consistent with a thinner crust under the GB. The phase velocitie s at periods greater than 40 s are indistinguishable between the two p rovinces, indicating that differences between upper mantle velocities are minor. Shear wave splitting yields fast polarizations that paralle l the western and northern boundaries of the CP, with delay times decr easing towards the center of the Plateau.