Paul J. Wolfe

Pre-Mount Simon basin under the Cincinnati Arch

A newly discovered sedimentary basin underlies the Mount Simon Sandstone (Upper Cambrian) below part of the Cincinnati Arch in southwestern Ohio. On the basis of preliminary examination of samples and geophysical data, the basin is tentatively traced for at least 160 km north-south and 48 km east-west in Ohio and adjacent Kentucky and Indiana. The basin is located in an area with sparse control in the deep subsurface, near the boundary of the Grenville and the Eastern granite-rhyolite provinces. Core recovered from the basin consists of a homogeneous, tightly compacted, grayish-red, lithic arenite. A seismic profile across the core site shows a layered sequence containing eastward-dipping seismic reflectors which extend to a depth of at least 5,200 m. Further work is required to determine the basins precise structural history.

Delineation of shallow stratigraphy using ground penetrating radar

Abstract Ground penetrating radar surveys were conducted at four sites to investigate the shallow stratigraphy and to determine the applicability and performance of the radar technique. A basic analog-recording radar system with a single 80 MHz antenna was used for all of the surveys. Good stratigraphic control existed at all of the sites so that the effectiveness of the radar could be evaluated. The four sites were distinctly different in composition and extent. At an upland farm site in the glaciated region of southwestern Ohio a clay-rich soil covers shallow bedrock. Some soil horizons were identifiable on the radar profiles, but only to a depth of 1.4 m. At a sand and gravel quarry in southwestern Ohio the depositional patterns of the unsaturated deposits were clearly imaged to a depth greater than 4 m. At a hydraulic fill dam in western Ohio the changes in the internal composition of the earthen fill were observed on the radar records to depths of 4 m. On San Salvador in the Bahamas radar profiles over partially consolidated carbonate sand revealed an extensive series of buried beach ridges to depths of 4 m. These data were useful in understanding the depositional history of the area, which could not be determined from surface and pit sampling alone. These studies show that ground penetrating radar is an important tool for studying shallow stratigraphy where the ground conductivity is low enough to permit radar reflections from depths of interest.

Analytical Modeling of Magnetic and Gravity Signatures of Unexploded Ordnance

The dominant cost and time driver in unexploded ordnance (UXO) cleanup is the necessity of digging (excavating) “false alarm” geophysical anomalies. As many as 75% of all the anomalies investigated are false alarms, e.g., scrap metal, ordnance debris, cans, wire, etc. The effort to develop capability to discriminate UXO anomalies from false alarm anomalies is a driver for the development of geophysical model-based signature modeling. The signature modeling is important for forward signature prediction and ultimately for geophysical inversion of buried object parameters from measured data. Researchers are actively developing forward and inverse modeling capability for time-domain and frequency-domain electromagnetic induction, ground penetrating radar, magnetic, and gravity anomaly signatures for realistic UXO shapes. This paper documents progress in developing forward gravity and total magnetic field analytical solutions. Gravity and magnetic methods are passive and share similarity in mathematical formal...

Integrated Geophysical Studies of Buried Valley Aquifers

Integrated geophysical studies of three buried valley aquifers in southwestern Ohio were made to compare the effectiveness of various geophysical techniques in outlining the extent and depth of these valleys. All of the areas have been overridden by two or more Pleistocene glaciers and each valley contains sequences of till and outwash. These buried valley deposits are the primary water source for the region. This paper summarizes the results of the geophysical studies and proposes a strategy for geophysical investigations of shallow buried valleys in glaciated areas. The techniques used in the integrated studies were gravity, magnetics, resistivity, ground‐penetrating radar, seismic refraction, and seismic reflection.Gravity, seismic refraction profiling, and seismic refraction fan shooting surveys were far superior to other geophysical methods in delineating buried valleys. Buried valleys show up as gravity lows of -2.7 to -0.7mGal due to the increased porosity of the fill materials relative to bedrock....

GEOPHYSICAL SURVEY TECHNIQUES FOR IDENTIFYING POTENTIAL COLLAPSE FEATURES UNDER HIGHWAYS

An abandoned coal mine under Interstate 70 in eastern Ohio collapsed and created a large crater along the highway a few years ago. A myriad of unmapped features under the States roadways threatens similar localized collapses. These catastrophic failures may cause loss of life and always cause traffic disruption and require extensive repair expenses. Identifying the zones, which are likely to fail, would allow remedial action to prevent future failure. Methods to locate these zones need to be inexpensive enough to allow widespread use but focused enough to target very specific problem areas. Geophysical survey techniques have the potential for meeting these requirements. The principal objective of the present research study was to develop a reconnaissance geophysical survey technique to delineate the zones that can be further investigated by borings or by localized geophysical studies to determine the nature and probability of significant failures. Accordingly, several different geophysical techniques were adopted during the summer of 1998. The results obtained from this study show that seismic refraction, resistivity imaging and surface wave profiling have the most potential for meeting the project objectives and should be studied further in phase two.

Resistivity interpretation near a trench

On Andros Island, Bahamas, fresh water is pumped from trench wells for shipment. The depth to the interface between fresh and salt water needs to be monitored in the well fields to prevent salt water contamination of the aquifer. Resistivity soundings are an effective way to measure the thickness of the fresh water layer. The presence of the trenches violates the horizontal layering assumption of usual 1D modeling programs. Finite element method modeling for a 2.5D case was used to determine the conditions under which 1D models are adequate and to provide a means to model salt water depth in situations where 1D is inadequate.

Precambrian Structures of Western Ohio

Ten wells in western Ohio, eastern Indiana, and northern Kentucky have penetrated pre-Mount Simon sedimentary rocks and several hundred kilometers of seismic data allow us to map units below the Mount Simon Sandstone in western Ohio. Most of the wells sampled a lithic arenite, the Middle Run Formation, but one well penetrated over 300 m of carbonate rocks. The seismic data reveal pre-Mount Simon basins that are about 25 km wide and are normally about 2000 m deep, but range in depth. They appear to be structural basins that formed primarily after the Middle Run Formation was deposited. Two basins are located on top of the Grenville Front and, therefore, are younger than Grenville rocks and older than Late Cambrian Mount Simon rocks. Thus the basins could be as young as Middle Cambrian, but at least post-date the Grenville Orogeny.

Delineation of a Coal Burn Edge With Seismic Refraction

Coal seams in many areas of western United States have ignited and burned for considerable distances underground. The boundary between the coal and clinker needs to be defined for determination of reserves. Field tests of a seismic refraction method were conducted at Kerr-McGee Coal Corps open pit Clovis Point mine near Gillette, Wyoming. Explosive sources were detonated in shot holes in the pit floor. Geophone lines, laid on the surface beyond the edge of the pit, crossed from an area of known coal to an area of clinker. Delays in arrival times correlated with the expected beginning of the clinker zone. Waves passing through the clinker also exhibit a significant attenuation. A magnetic survey concluded along the seismic lines showed anomalies in the regions where seismic data indicated the burn edge.