TRACING DEEP STRUCTURE: FRACTURE ANALYSIS IN THE FINGER LAKE REGION OF THE APPALACHIAN PLATEAU, NYS

The Finger Lakes region of the Appalachian Plateau is currently a target for gas exploration along faults that affect the Ordovician Trenton-Black River section. The location of these faults is controlled by structures in the Precambrian basement. We collected fracture data along a N-S transect in order to determine if deep structure observed in proprietary seismic and inferred from aeromagnetics is reflected in the surface fractures and lineaments. The fracture data include 9 characteristics recorded for over 2550 fractures observed in Devonian Catskill Delta sediments along the eastern side of Seneca Lake. We separated the fractures into sets and calculated the fracture frequency for each set. Modified rose diagrams that display fracture frequency in the upper half and fracture abutting relationships in the lower half reveal that the fracture patterns are not constant along the NS transect. In the southern part of the transect, the master fractures commonly strike NNW and are relatively closely-spaced; in addition, northerly-striking fracture intensification domains (FIDs)are evident. At many sites in this part of the transect ENE-striking fractures are subdominant. In the central and northern part of the transect, ENE-striking fractures are both master and closely spaced. ENE-strking FIDs are common. The locations of the ENE-striking FIDs are coincident with ENE-trending topographic, Landsat, and aeromagnetic lineaments, as well as soil gas anomalies reported by Nelson and others. This coincidence suggests that the Trenton-Black River faults guided fracture development in the Devonian section. These data also demonstrate that the trend of deep faults observed in single-line seismic can be extended away from the seismic line by the use of lineaments that have been groundtruthed by an integration of fracture analysis and soil gas analysis. We also observed a number of northerly-striking fractures along which small amounts of strike-slip motion occurred. This shear is consistent with Engelder's recent observation. The strike slip motion may indicate that the northerly-striking basement CSDs were reactivated during Alleghanian tectonism.