A Seismic Investigation Over A Near-surface Cavern

A field experiment was conducted over a near-surface cavern with the principal objective of obtaining a spatial definition of the associated Cavity Resonance phenomenon, as reported by Watkins et. al. (1967) and by Godson and Watkins (1968). The results of the experiment were inconsistent with those of the earlier investigators in that all seismic events recorded in the vicinity of the cavity, having vertical velocity components, could be readily identified as standard modes of seismic wave transmission. A persistence of strong horizontal motion was observed for late record times. This horizontal motion was consistently oriented parallel to the cavity boundary, occurred only over an extremely limited range of the traverse at approximately a 25° polar angle to the vertical axis passing through the center of the void, and did not appear to be propagating. This energy might qualify as a cavity resonance phenomenon. © 1975

The detection and mapping of subterranean water bearing channels - phase 2

Students supported: 4 Student Assistants"The research conducted under this Grant was directed towards the development of a method for the detection and delineation of subterranean cavities. Such cavities in the carbonaceous rocks of Missouri form a vast system of interconnected channels available for the transport of ground water. These channels play an important role in the water resources of Missouri and also constitute an undesirable means of transport and dissemination of polluted waters from mining districts and heavily populated areas. Such transport systems offer little opportunity for water purification by the natural process of filtering, and such waters may be transported over considerable distances with little change in their polluted state. Prior to this Grant, a reliable method for even the detection of large cavern structures like Onondaga Cave was unknown. Past attempts at cavity detection span a broad spectrum of geophysical exploration methods. While most of these attempts have yielded some degree of success, the general consensus of the authors has been that conventional geophysical approaches to the problem do not appear adequate."--Introduction.Project # B-087-MO Agreement # 14-31-000

The detection and mapping of subterranean water bearing channels

Students supported: 1 UndergraduateThis report presents the results of an experiment designed to determine the vibrational characteristics of subterranean voids. The objective of this research was to evaluate the resonance phenomenon, as reported by early investigators, as an appropriate mechanism for the development of a cavity detection and delineation tool. The results of this experiment, whiIe not entirely establishlng the existence of resonance per se, establishes a diagnostic reverberant seismic event that shows much promise as a detection mechanism. In addition, the use of three-component seismometers, and particle trajectory analysis, brings the reflection method back into the realm of practicality.Project # A-051-MO Agreement # 14-31-0001-352

A Computer-Automated Laboratory System In A University Environment

A computer-automated laboratory system at the University of Missouri-Rolla, Rolla, which serves a wide variety of instruction and research disciplines including Geophysics, Cloud Physics, and Computer Graphics, is described. The system serves as an example for campuses which are relatively small in geographic area and with budget limitations which dictate a step-by-step evolution. The paper describes 1) the constraints and economics realized in the development of the system, 2) the characteristics of the minicomputer network, and 3) an evaluation of the system philosophy and performance. Also included is a description of diverse laboratory projects supported by the computer-automated system. © 1975, IEEE. All rights reserved

Performance Evaluation Of A High-freqency Borehole Seismic Source

A simple, arc-discharge seismic source for application to the borehole environment is described. Test results from a performance evaluation in sedimentary, metamorphic, and igneous sections are presented. These results demonstrate repeatability of seismic signatures in a variety of geologic settings for a waveform with a dominant period of about 1.5 kHz and a half-power bandwidth in excess of 1 kHz. The ability of the sparker to operate in a borehole under hydrostatic heads in excess of 400 m, at lateral ranges in excess of 100 m, and at angular ranges in the vertical plane to 70 degrees is demonstrated

The One-Dimensional Elastic Wave Equation: A Finite-Difference Formulation for Animated Computer Applications to Full Waveform Propagation

A FORTRAN computer program for modeling full waveform propagation through a layered homogeneous one-dimensional medium is presented. The output synthetic seismograms are generated using a finite-difference approximation to the wave equation, as opposed to the more conventional approach of simply convolving the calculated reflection coefficient wavetrains with representative wavelets. The strength of the program in wavefront propagation is screen animated and can be captured on hard copy. The software is user-friendly, and was developed primarily as an instructional tool. Each of the finite-difference input parameters is explained in detail for those unfamiliar with the finite-difference theory

Observation Of Continuous Fracturing In Crosshole Seismic Experiments In Crystalline Rock

Crosshole seismic data were gathered in a metamorphic section. These data exhibited anomalous events that were ultimately attributed to the interaction of tube waves and converted tube waves with a continuous fracture connecting the transmitter and receiver boreholes. The pattern of the anomaly is distinctive and easily recognized in a crosshole seismic section and might prove to be useful in the evaluation of high volume inter-borehole fluid communication, or in the assessment of hydrofracture effectiveness

Crosshole Seismic Tomography and Borehole Logging for Engineering Site Characterization in Sikeston, MO, USA

This paper presents a geophysical investigation performed in the median separating the east and west bound lanes of U.S. Highway 60, approximately 15 km west from the town of Sikeston, MO, USA. Two boreholes, drilled at depth of 45 m, approximately located 6 m from the Wahite Ditch Bridge in U.S. Highway 60, were used to carry out the geophysical tests. The objective of the survey was to obtain the density distribution of soil materials and high-resolution compressional and shear wave velocities of the shallow subsurface for computation of elastic engineering properties of the unconsolidated material interposed between the two investigated boreholes. The studied site is located in the New Madrid Seismic Zone (NMSZ), one of the major seismic source zones in the eastern United States. Although no major seismic events have occurred in the New Madrid area since the catastrophic earthquakes of 1811-1812, more intensive studies in this area are required to better understand the local soil effects and the liquefaction potential of unconsolidated earth materials on strong ground motion. Joint interpretation of borehole logs and velocity images obtained by P- and S-wave traveltime inversions outlined shallow anomalies, which were interpreted as caused by variation in relative porosity and compactness of saturated unconsolidated soil materials. In the interval between 17 and 19 m of depth, a velocity anomaly with distinct characteristics is recognized. Analysis of traveltimes of P-wave energy propagated from common source-receiver depth positions at that depth interval delineated a low velocity zone (lower than estimated P-wave velocity in water) in which propagated S-wave energy was negligible. Analysis of porosity logs did not outline any porosity anomaly for that region. The anomaly is interpreted as caused by the presence of a gas-bearing zone extending for 1.5 m (+0.76 m from the top and the bottom of the depth interval), through which propagation of shear energy was almost prevented and compressional energy traveled a very low speed. Relative lower values of shear modulus were computed for the gas-bearing zone; the same depth interval also exhibited relative lower values of bulk modulus, relative higher values of compressibility and relative high porosity. However, the low velocity anomaly is not caused by relative increased porosity but rather to replacement of water by gas in the pore volumes of this zone. The presence of a shallow thin gas-bearing zone is interpreted as hazardous in the occurrence of strong motion in the New Madrid Seismic Zone. Shallow water table, as detected by seismic and log measurements in the area, increases the risk of liquefaction of the sampled soil under strong ground motions

New Sensors and Sensor Fusion for a Ground-based Land Mine Detection System

The complexity of the detection and discrimination problem for land mines requires that multiple sensors and algorithms be employed. We have been attempting to develop a range of new sensors and sensor combinations that will contribute to the solution to this problem. The sensors discussed in this paper include heated waterjets combined with infrared images, non- contact acoustic focusing, and the detection of electromagnetic emissions from smart land mines