OFR2 Preliminary Report on Seismic Events in Northern Delaware

Earthquakes are an unfamiliar phenomenon in Delaware. Because of the great public and scientific interest in the seismic events that have recently affected northern Delaware, this Open File Report has been prepared to present currently available information concerning the earthquakes and the investigation pursued by the Delaware Geological Survey. This is not a final scientific explanation of the events. To many persons it is shocking to realize that the earth that they regard as stable is, in fact, an active body.

RI39 Earthquakes in Delaware and Nearby Areas, June 1973 - June 1984

Earthquakes in Delaware and surrounding areas have been well documented historically since about the early 1700’s and since 1972 by instrumental records. Most of the Delaware events have occurred in the Wilmington area immediately adjacent to or within rocks of the Wilmington Complex. Since the compilation of earthquakes by Jordan and others (1974) which lists events through May 1974, six felt earthquakes have occurred in northern Delaware and about 20 additional events in Delaware have been recorded on seismographs of the Delaware Geological Survey.

OFR30 Evaluation of Remote Sensing and Surface Geophysical Methods for Locating Underground Storage Tanks

Delaware Code, Title 7, Chapter 74, Section 7415 states in part: "The Delaware Geological Survey shall investigate the feasibility of utilizing aerial photographs and other new advanced techniques for locating abandoned tanks." In response to this charge, the Delaware Geological Survey has completed a survey of currently available remote sensing and geophysical tools to determine which methods may be utilized to locate underground storage tanks. Limited preliminary field testing has been performed.

B13 Geology, Hydrology, and Geophysics of Columbia Sediments in the Middletown-Odessa Area, Delaware

Columbia sediments in the Middletown-Odessa area are composed of boulders, gravels, sands, silts and clays. These sediments are exposed in four gravel pits where their structures and textures were studied. Subsurface geology was interpreted on the basis of the well-log data from 40 holes drilled in the area of study. Columbia sediments were laid upon a surface made up of the greensands of the Rancocas Formation (Paleocene – Eocene age). The contact between the Rancocas and Columbia Formations is an erosional unconformity.

RI31 Hydrocarbon Resource Potential of the Baltimore Canyon Trough

It is now possible to evaluate some of the earlier assessments and offer tentative conclusions about the hydrocarbon resource potential of the Baltimore Canyon trough, a major northeast-southwest trending sedimentary basin off the Mid-Atlantic coast of the United States.

RI25 Selected Logging Data and Examples of Geophysical Logs for the Coastal Plain of Delaware

Geophysical logging techniques have been used in Delaware for many years as a means of identification and correlation of Coastal Plain formations. Criteria for the recognition of those formations having distinctive types of logs are presented. Formation factors have been calculated using multiple-point resistivity logs, temperature logs, and ground-water quality data and range from 1.2 to 6.8 for various formations underlying the State. Formation factors in turn are used to estimate water quality in later test holes.

SP23 Earthquake Basics

This report provides a brief overview of the causes of earthquakes, how earthquakes are measured, and a glossary of earthquake terminology.

RI22 Hydrogeology of Selected Sites in the Greater Newark Area, Delaware

Additional sources of ground water have been located in the Piedmont Province as a result of a ground-water exploration program conducted by the Delaware Geological Survey at the University of Delaware in cooperation with the City of Newark. Drilling sites for relatively high-yielding wells were located through the use of geophysical investigations, air-photo interpretation, field mapping, and review of existing data.

RI16 Application of Geophysics to Highway Design in the Piedmont of Delaware

The feasibility of using geophysical techniques in determining the amount of overburden and the nature of the subsurface along a proposed highway was tested in the Piedmont area of Delaware. The area is underlain by crystalline rocks capped by varying amounts of unconsolidated material or regolith. Seismic refraction and surface resistivity methods were used at selected stations and the interpretations were later compared to results from test holes and to the material exposed in road cuts.

RI11 An Evaluation of the Resistivity and Seismic Refraction Techniques in the Search for Pleistocene Channels in Delaware

Pleistocene channels along the margins of the Atlantic Coastal Plain are developed in crystalline and Triassic sediments (Bonini and Hickok, 1958), or into the Cretaceous and Tertiary coastal plain sediments (Widmer, 1965). Deposits in these channels consist of sand and gravel with amounts of silt and clay. For example, the Bear area channel is 50 to 70 feet deep and contains up to 30 feet of sand and gravel overlain by sandy clay.