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Interpretation of Subsurface Structure Using Gravity Data from Region of Appalachian Ultradeep Hole

R. T. Williams, P. Favret, L. Fabbri, S. Chavez-Perez

More than 5,000 new gravity measurements have been made over an area of 7,500 km2 in the region of the proposed ultradeep core hole in the southern Appalachians (ADCOH). Data were obtained mostly at surveyed elevations at approximately 0.5-km intervals along highways, and county and U.S. Forest Service roads in the study area. The data have been reduced to simple Bouguer anomaly values using a standard crustal density of 2.67 g/cc and the International Gravity Formula of 1967.

Simple Bouguer anomaly values range from about -10 to -80 mgal within the study area. Profiles crossing the outcrop of the Brevard fault zone (BFZ) at different locations reveal a characteristic gravity signature, with a decrease in gravity of more than 1.5 mgal. A profile along the route of ADCOH seismic line 3, located along U.S. Highway 64 west of Hayesville, North Carolina, crosses a gravity high with an amplitude of more than 50 mgal.

A contour map of simple Bouguer anomaly values reveals a linear gravity high of about 4 mgal, trending about N10°E, that crosses ADCOH seismic line 1 northwest of Westminster, South Carolina, and seismic line 3 at its intersection with the BFZ. This anomaly correlates with a family of basement faults having more than 0.5 km of throw, seen on both seismic lines 1 and 3, and is evidence that these faults are oblique to both the trend of surface structure and the direction of the seismic profiles. Low gravity values are observed near the Shooting Creek window and Tallulah Falls dome, indicating that these structures may be cored by low-density, possibly sedimentary rocks.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.