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Regional Studies with Broadband Data.
Semi-Annual rept. no. 1, 13 Feb-30 Sep 85,
CALIFORNIA UNIV BERKELEY DEPT OF GEOLOGY AND GEOPHYSICS
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A laterally averaged one dimensional P and S wave velocity structure is obtained for Silent Canyon Caldera, located beneath Pahute Mesa at the Nevada Test Site. The velocity models are derived from a linearized damped least squares travel time inversion for slowness gradient perturbations. A total of 72 P wave and 20 S wave travel times generated from 13 different explosions, and obtained at scattered locations above the caldera, are used in the inversion. The structure is modeled using linear velocity gradients. The inversion produces a model which increases in velocity from 1.50 kmsec at the surface to 2.35 kmsec at 2.5 km depth for S waves. The P and S wave models produce travel time residuals which are typically less than 0.1 and 0.2 seconds, respectively, which is within observational error. However, P wave amplitude ratios and waveform characteristics of data collected from 7 explosions buried near 625 m depth indicate the presence of lateral variations within the caldera which may be significant to nuclear source studies. Keywords Seismic waves, Seismic data, Nuclear explosion, Velocity structure.
APPROVED FOR PUBLIC RELEASE