oa Near Surface S-Velocity Profiles At 30 Salt Lake Valley Sites From Inversion Of Surface Wave Dispersion And Analysis Of S-Wave Refraction Data

Surface wave and shear refraction data were collected at thirty Salt Lake Valley<br>sites using a Bison 9000 seismic recorder. Each experiment used 10 Hz vertical and 4<br>Hz horizontal geophones at group intervals of 5 feet, with spread lengths up to 1000<br>feet. Both horizontal and vertical 100 lb weight drop sources were used, as well as the<br>Bison EWG 500 lb source. Rayleigh waves, Love waves and shear refraction waves<br>were recorded and inverted for the shallow S-wave velocity structure. Results show<br>that the Rayleigh wave and refracted shear wave data were the most reliable and generally<br>provided similar velocity profiles; the Love wave data proved to be the least reliable,<br>although over half the sites showed that the Rayleigh, Love and refraction wave<br>velocity profiles agreed to a depth of about 30 meters.<br>These shallow S-velocity profiles were used to simulate the seismic amplification<br>from earthquake waves impinging on the basin floor. For all sites, it is shown that the<br>deep (about 1 km thickness) 2-D basin structure causes about 2-3 times more<br>amplification than the shallow S-velocity structure for frequencies from O-4 Hz. The<br>shallow velocity structure is important for amplification at frequencies greater than<br>about 5 Hz.