Some Stupid Shallow Seismic Experiments I Have Done

Don W. Steeples.  Provost Office & Department of Geology, The University of Kansas, Lawrence, KS 66045  [email protected]

While near-surface and classical seismic exploration obey the same laws of physics, the relative importance of those laws is different for the two types of surveys. These differences have led to some eccentric experiments with unexpected and occasional serendipitous outcomes. Progress attained by our research group has occurred through a mixture of stupid experiments that turned out to be clever, and clever experiments that turned out to be stupid. Shallow seismic methods have matured noticeably since the time 25 years ago when the worldÕs scientific literature contained few refereed papers on shallow reflection. Much of the maturation is related to the revolution in microelectronics and the associated several orders of magnitude decrease in computational costs, while developments in sources, seismographs, and field methods have all played a role to differing degrees. However, other driving factors in this improvement have included demonstrable attainment of objectives such as providing structural contour maps of bedrock beneath alluvium, delineating shallow faults, evaluating near-surface stratigraphy to detect preferential ground-water-flow paths, and detecting underground cavities. By 1999, we had demonstrated seismic-reflection images from depths of less than a meter, easily within reach of a marginally competent gravedigger. Detecting such shallow reflectors is expensive, however, because of the requirement to plant geophones at intervals of 10 centimeters or less. The effective resolution potential of classical seismic exploration data recorded on land is often determined by geologic conditions in the upper few tens of meters; in addition, the majority of statics problems commonly occur in the upper 30 meters. We are currently experimenting with methods of making near-surface three-dimensional seismic imaging more cost-effective.