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A gravity survey of the Coyote Creek fault in the Ocotillo Badlands, Ocotillo Wells, San Diego County, California
Porter, Allen D.
This thesis studies the relationships between the basement topology and the surface structures in the Ocotillo Badlands, in the western Salton Trough area of southern California. Gravity surveys were conducted during the summer of 1994 by Jerry Bell and Allen Porter under the direction of Dr. Monte Marshall. Three east-west lines between 4 and 7 miles long were surveyed, one immediately to the north of the badlands, one through the central badlands, and one just to the south. The topology of the gravity-inferred crystalline basement is an east-west trough in which the badlands lie over the northern side. This northern side slopes about 7° S from a depth of around 500 ft beneath the northern line along Hwy 78 to a depth over 2,500 ft beneath the southern line. The badlands are flanked by two en echelon strands of the right-lateral strike-slip Coyote Creek Branch of the San Jacinto Fault. These strands ruptured in the magnitude 6.8 Borrego Mt. earthquake on April 9, 1968. The obvious surface structure of the area is an east-west trending anticlinorium that makes up the core of the badlands. Computer modeling shows an east-west trending fault with 500-1,000 ft of throw and with the north side up. This fault is almost directly beneath the fold axis of the anticlinorium. One interpretation of this model is that this fault is responsible for the deformation in this area. Compression across the step causing thrust faulting is the probable mechanism for this uplift. This compressional uplift on the northern side is further expressed as a gravitational high and exposure of bedrock at Squaw Peak to the north of the study area. On the southern side of the thrust fault, the bedrock has been forced down creating a trough, which is reflected in the gravity.
San Diego State University
Bachelor of Science (B.S.) San Diego State University, 1995
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