Abstract

On Aug. 11, 1960, sixty oil exploration and research seismograph crews attempted to record 2 shots detonated in the Texas Gulf Coastal Plain. Shotpoint A was located 16 mi. NW. of Cleveland, Texas. Shotpoint B was located 27 mi. NW. of Victoria, Texas. The shotpoint line is approximately parallel to the strike of the Cenozoic sediments, and the distance between shotpoints is 260.2 km. More than 3000 lb. of explosives were placed in 5 holes at each shotpoint. The top of the charge was at a depth of 95 ft. and the bottom at 250 ft. at each shotpoint. The regional Bouguer anomaly is -25 mgal. The shot instant was keyed to a 140 c.p.s. reference signal transmitted by radio station KTRH, Houston, Texas. First and later refracted arrivals were used to determine the velocity structure which was supported by events identified as reflections from the refractors. The results indicate the following thickness-velocity relationships: 2.0 km. of 2.3 km./sec. material, 5.3 km. of 3.94 km./sec. material, 12.5 km. of 5.38 km./sec. material, and 13.2 km. of 6.92 km./sec. material. The Mohorovicic discontinuity is represented by a velocity of 8.18 km./sec. and the total crustal thickness is 33.0 km. Possible geologic identities of the refractors are as follows: the 2.3 km./sec. and 3.9 km./sec. layers represent the Cenozoic and Mesozoic sediments, the 5.4 km./sec. layer represents Paleozoic and Precambrian rocks, the 6.9 km./sec. layer is the high-velocity crustal layer, and the 8.18 km./sec. zone represents upper mantle material. The S. Texas velocity section appears to correlate well with adjacent measurements in the Gulf of Mexico and in northeastern Arkansas.

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