Locating Abandoned Mines Using the Active Mining Operation as the Seismic Energy Source – Demonstration of a New Method
This study demonstrates a new method for detecting the margin of old mine works using the seismic energy generated by active mining in the coal seam. As the first test of this new concept, the method should not be viewed as a proven, off-the-shelf technology, but rather a demonstration of the fundamental concept which has promise for detecting the margins of old mine works. For the primary method a linear spread of vertical 4.5Hz geophones on the earth’s surface was distributed across the margin of old mine works (both flooded and air-filled locations) and to a position over the active mining nearby. The seismic vibrations associated with the underground mining were passively recorded across this spread, with individual records as long as 32 seconds. Through a process of crosscorrelation, using each seismic trace sequentially as the pilot sweep for correlation with each other trace in the recording, two distinct seismic wave arrival patterns emerged from the data. The direct arrival from the mining operation to the surface through the rock overlying the coal seam was distinct and well represented in
The Vibroseis source
Introduction. The Wavefield of a Surface Source in a Horizontally Layered Elastic Medium. Configuration. Basic relations. Decomposition into upgoing and downgoing wavefields. The local reflection of the wavefield at a layer interface. The propagation of the wavefield within a single layer. The global reflection response. The particle velocity and traction components at an arbitrary point in the medium. The transformation to the space domain. The elastic halfspace. The horizontally layered acoustic medium. Far field relations. The Seismic Vibrator. Mechanics of the land vibrator. The vibrator signal. The baseplate behaviour. The Combined Earth-Vibrator Model. The earth model. The combined earth-vibrator model. The numerical procedure. Numerical results. Test of the Theory By Experiment. The data set. The earth model. The vibrator model. The feedback signal on the seismic vibrator. The Marine Vibrator Source. Configuration. Vibroseis: land and marine. The earth model. The mechanical model of the marine vibrator. The combined earth-vibrator model. The numerical procedure. The distribution of pressure and displacement at the surface of the vibrator. The average power factor. Far field relations. Test of the theory by experiment. Processing of Vibroseis data. Description of the data set. Conventional processing. Proposed processing sequence. Concluding remarks. Appendices: Determination of Green's Matrices for Acoustic and Elastic Media. Solution of the Differential Equation Describing the Plate Bending. The Numerical Procedure for the Combined Earth-Vibrator Model. References. Author Index. Subject Index.
Shoeless Joe: Fantasy and the Humor of Fellow-Feeling
In his essay on Jean Paul Friedrich Richter, Thomas Carlyle writes of a humor that manifests itself in smile rather than laughter. "Richter is a man of mirth," says Carlyle, whose humor is "capricious . . . quaint . . . [and] heartfelt" (15). The three adjectives represent for Carlyle the essence of what he terms "true humor" because they suggest Richter's enormous respect for humanity. "True humor," he goes on to say, "springs not more from the head than from the heart; it is not contempt, its essence is love; it issues not in laughter, but in still smiles, which lie far deeper" (17). These smiles are not Hobbesian smirks of superiority1 but genuine signs of compassion for, sympathy toward, and empathy with the object of the humor. Carlyle further provides a direct link between humor and both pathos and nobility; the link is the smile of the caring man. For Carlyle, this smile is one of "fellow-feeling":