Travel-time and amplitude interpretation of crustal phases on the refraction profile DELTA-W, Utah

The travel times and amplitudes of P_g and P_c, 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 P_c reflector. The travel-time interpretation is performed with the hedgehog method and the amplitude interpretation by trial and error. Only after the amplitudes of P_c are included in the inversion does the evidence for a low-velocity zone on top of the P_c 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.