CRUSTAL SHEAR-WAVE VELOCITY STRUCTURE ACROSS CALIFORNIA AND NEVADA FROM AMBIENT NOISE SURFACE WAVE MEASUREMENTS

We have inverted for three-dimensional shear-wave crustal structure across California and Nevada using surface wave group and phase velocity measurements derived from ambient noise techniques. Ambient seismic noise contains a significant component of Rayleigh and Love wave energy from which the Green's function between pairs of stations can be extracted by cross-correlating long noise sequences. Surface wave group and phase velocities are measured on the estimated Green's functions to provide broadband dispersion curves between station pairs with improved resolution compared to earthquake studies. Measurements below 10 seconds period are routinely made and provide greater information about upper- to mid-crustal shear wave velocities than are available from earthquake measurements. Rayleigh group and phase and Love phase velocity maps are constructed for the western US from 6 to 40 seconds period and show high resolution within the inversion region. A Monte Carlo inversion of the dispersion maps was carried out to estimate the crustal velocity structures across the region. Constraints on the inversion are imposed by receiver function measurements and sedimentary thickness estimates. Better constraints on the inversion will result in an improved model. We present a preliminary model for the thickness and shear-wave speeds of the California crust. The model allows examination of the crustal structure of the Basin-and-Range, the root of the Sierra Nevadas, and the mantle wedge and hypothesized southern edge of the Juan de Fuca plate.