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Airborne Gradiometer Survey over the San Andreas Fault Drill Site
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, EGM 2007 International Workshop, Apr 2007, cp-166-00003
Abstract
An airborne gravity gradiometer survey was carried out over the San Andreas Fault deep drill site. The survey consisted of 40 lines each 10 km long and 200 meters apart and 10 cross lines also each 10 km long and 1 km apart. The topography ranged in elevation from 400m to 1100m, and the drape surface which was flown was nominally set with a clearance of 200m; in practice it ranged from 850m to 1300m. Because of the rough topography, the contribution of the terrain to the gradients was very large and comprised most of the observed gradient signal. After subtracting the terrain effect the contribution of buried structures was obtained. The residual anomalies substantiated the presence of a low density gouge zone associated with the fault, but because of the large uncertainties in removing the terrain effect, there are large variations in the values of residual anomalies which are not attributed to the fault.