CRUSTAL SCALE REFLECTION SEISMOLOGY USING A SINGLE VIBROSEIS SOURCE

The view is widely held that large numbers of vibroseis trucks are needed to obtain good seismic reflection data, but heavy vibrators are expensive to operate and maintain, generally too expensive for academic research. Pioneering work at Virginia Tech two decades ago demonstrated that a single vibrator can be used for crustal-scale research, but questions about the practicality persisted, in part due to limitations imposed by recording system and data processing technology available at that time. In this study, we re-examine questions related to using a single vibroseis source for academic research. What is the impact on data quality? What depth of penetration can be expected? How does data processing differ when only one vibrator is used? Results are presented from two overthrust terranes, the Appalachian Basin represented by the Valley and Ridge of East Tennessee, and the Kuban Basin in the foreland of the northern Caucasus Mountains. These are two quite different environments from the perspective of reflection seismology. In the Appalachians, the Paleozoic rocks exhibit uniformly high P-wave velocities, ~5-6 km/s from the surface to several kilometers depth, and the velocities in the upper portion of crystalline basement are only marginally higher than in the sedimentary section. The structures commonly involve complex folding and faulting. In contrast, the Kuban basin is younger, Cenozoic to Mesozoic, and poorly lithified pelites comprise a major portion of the sedimentary section. P-wave velocities are low at the surface (~1.8 km/s), increasing approximately linearly with depth. Despite major differences in lithologies and seismic properties, the depth of penetration in both basins was ~5 – 5.5 km. The travel times were different, ~1.8 s in the Appalachians vs. ~3.5 s in the Caucasus, reflecting the changes in average P-wave velocity. Using additional vibrators increases the speed at which data are acquired and thereby decreases the cost in a petroleum project. The economics of academic research are very different from petroleum exploration, however, and it may be cost effective to acquire data using a single vibrator and a student crew.