NEOTECTONIC STRUCTURES AND STRESSES ASSOCIATED WITH NEW YORK STATE FINGER LAKES BASINS: IMPLICATIONS FOR SUBSURFACE MINES AND CAVITIES

Limited subsurface bedrock data is publicly available beneath the glaciated troughs in the Finger Lakes region with the exception of the numerous wells associated with the abandoned solution salt mining activities in the Tully Valley, mines under Cayuga Lake, and from post-collapse studies related to the Akzo-Nobel mine disaster in the Genesee Valley. However, it is well documented in the literature that horizontal stresses in the upper 3000 ft (915 m) of the crust can exceed vertical loads by up to a factor of 3. Data collected from overcoring during the Genesee Valley salt mine planning studies by Akzo Nobel measured horizontal stresses at depths as shallow as 672 feet (205m) that are greater than twice the static vertical loads. The complications associated with neotectonic stresses can be found in numerous engineering reports, especially those involving dam foundations, but are less well represented in academic journals. The interesting “pop-up” structures associated with rock quarries and some deep bedrock foundations testify to active neotectonic stresses. Similar compressional features, including “valley anticlines,” are scattered across the Colorado Plateau in locations where excavations are not always a factor. Data from the abandoned Tully Valley solution mining borings suggest that east-west compression of the north-south valley axis has displaced the axial strata in excess of 200 ft (60 m) along opposing, north-south trending reverse faults. A seismic profile across Cayuga Lake near Lansing suggests that similar neotectonic compressional structures should be anticipated beneath other larger Finger Lakes valleys. The typical “floor heaves” in salt mines, such as the Retsof mine (Genesee Valley) and the Cayuga mine commonly are ascribed to vertical “pillar punching.” However, the simple “tepee” geometry of such floor heaves may be partially attributable to the influence of horizontal stresses that exceed the vertical rock loads. When combined with the existence of the mapped and extrapolated east-west striking thrust faults and associated tear faults in the Salina section within the Finger Lakes region, the potential complications introduced by east-west neotectonic stresses suggest that caution be advised for projects located beneath or near the valuable Finger Lakes water resources.