abstract

The travel times and amplitudes of Pg and Pc, a wide-angle reflection from the middle crust, are inverted into a P-velocity depth function of the upper part of the crust beneath the refraction profile DELTA-W in southwestern Utah. Special attention is paid to the question of whether or not a velocity reversal exists on top of the Pc reflector. The travel-time interpretation is performed with the hedgehog method and the amplitude interpretation by trial and error. Only after the amplitudes of Pc are included in the inversion does the evidence for a low-velocity zone on top of the Pc reflector become convincing. This zone extends between depths of about 7 and 12 km, the boundaries at the top and the bottom are transition layers with thicknesses of a few kilometers, and the minimum P-velocity in this zone is less than or equal to 5.4 km/sec.

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