MAGNETIC SIGNATURES OF SUBSURFACE FEEDER DIKES AND FAULTS, NEW HAVEN, CT - DURHAM, CT

Commonly observed large amplitude magnetic anomalies are nearly always the result of a large magnetization contrast, i.e. a change in lithology, such as the juxtaposition of Triassic-age arkoses with Jurassic dikes observed in the southern Hartford Basin. Strong boundary contrast (strong low amplitude anomalies) also appears to characterize areal faults.

Cesium magnetometer field surveys run in Winter 2003-2004, using the Geometrics 858 Magmapper, in selected areas from New Haven, CT, to Durham, CT, facilitated mapping of feeder dike systems and associated faults based on their magnetic (or lack of magnetic) signatures. Multiple north-trending and northeast-trending, near vertical diabase dikes were traced in the subsurface between outcrops, and bounding northeast-southwest trending faults identified in the vicinity of the Foxon Quarry, New Haven, CT. Primary and secondary (antithetic and synthetic) faults were identified in the area adjacent to the Eastern Border Fault, Durham, CT, demonstrating the usefulness of portable magnetometers as a subsurface mapping tool.