Gravity Mapping Of Subsurface Structures In Batholithic Terrain

A regional gravity survey was conducted in the vicinity of March Air Force Reserve,<br>southern California with the objective of mapping basement topography that may directly<br>influence groundwater flow. The data set consists of 3500 gravity stations that cover an area of<br>670 square kilometers. The raw gravity data were converted to complete Bouguer gravity values<br>by using standard techniques that included Digital Elevation Models to perform the necessary<br>terrain corrections. The complete Bouguer values were gridded using a kriging method while<br>spectral filtering techniques were employed to generate residual anomaly maps. The resulting<br>anomaly pattern reveals three mappable orders of subsurface structures. Inverse modeling, as<br>constrained by well-log data and seismic interpretations, indicates that the primary, secondary,<br>and tertiary structures have axial depths of 1000, 100 to 300, and less than 100 meters,<br>respectively. The primary structure is a tectonic trough while the secondary and tertiary<br>structures are erosional channels.