Seismic reflection, refraction and gravity surveys of half-graben basin floor ramps and a central horst between Silver Island and Newfoundland Ranges:Great Salt Lake Desert, Utah, U.S.A

Three reflection seismic profiles used air shots over carbonate mud between the Silver Island and Newfoundland Mountains in the Great Salt Lake Desert, Utah. Here the flat terrain, sparse vegetation, lateral uniformity of carbonate clay, shallow water table, and use of point-source explosives yield excellent conditions for study of P-wave reflections and refractions. The west end of Line 1 is 40 km northeast of Wendover, Utah. The seismic signals generated by the Poulter method were detected by receiver arrays of 12 10-Hz geophones at intervals of 5 m and recorded by 24-channel truck-mounted recording instruments. The source-receiver offsets were 30 to 1433 m. After CMP sorting, the data were filtered, partially migrated before stack, gain recovered, normal moveout corrected, CMP stacked, and migrated. About 8 km east-southeast of Line 1, Line 2 was shot to obtain 1-fold reflection data and refraction data extended 6.4 km N57°E. Near the west end of Line 2, P- and S-wave velocities for unconsolidated sediments and Paleozoic dolomite bedrock were evaluated using vertical weight drops and massive horizontal hammer-heads. Here unconsolidated sediments were only as deep as about 275 m, but with intermediate layers, and likely pre-Tertiary rocks at a maximum here of only about 430 m deep. Lines 1 and 2 data for refraction, reflection, and gravity were interpreted and modeled. Line 3 near Crater Island's eastern edge used 48-channel portable recording instruments and extended of recording for about 23 km. The migrated section shows the western part of the Crater Island graben's east-dipping basin floor with rugosity and shallow faulting. The Crater Island graben flattens near CMP 540 at approximately 0.85 s. From there the half graben exhibits normal drag on the west of the narrow and buried Central Horst. The horst of Line 3 is 12 km south of a gravity profile by which Cook et al. (1964) interpreted this a buried horst. Normal drag is also exhibited within the West Newfoundland graben near the east end. Multicomponent walkaway-noise data were also recorded with triaxial inclined geophones. Those data were used to extensively study polarizations of Rayleigh wave modes and air-coupled Rayleigh waves as well as to develop methods of polarizing filtering for multicomponent data.