Seismic Data Acquisition in San Juan Volcanic Field: ABSTRACT

Abstract

The 1982, 1983, and 1984 Colorado School of Mines Geophysics Department summer field camp data acquisition was in the San Juan volcanic field between Monte Vista, Colorado, and the Continental Divide 30 mi west of Monte Vista. The objectives included (1) determining which techniques were most successful at retrieving data through volcanic layers, and (2) trying to see if there was seismic evidence for Cretaceous and older sediments beneath the volcanics. Both of these objectives met with success. Seven seismic lines (approximately 40 mi) were acquired in this area. Field tests were also conducted along these lines. Each of the three data sets (1982, 1983, and 1984) were acquired using two Vibroseis trucks, 110-ft shot and group intervals, off-end spreads, 48 groups per shot, and 12 to 24 fold. Number of sweeps, drive level, sweep frequencies, source and group arrays, and minimum and maximum offsets were changed for each data set. These changes were beneficial in some respects and harmful in others. Lengthening the group array helped cancel the ground roll but also attenuated higher frequency data. Increasing the low frequency cutoff helped cut out ground roll but resulted in less interpretable data character. Increasing minimum offsets helped to cut out ground roll but also re ulted in loss of some shallow reflections. A beneficial acquisition parameter for this area was the reduced energy level input into the ground. Variations in near-surface geology also caused data quality differences. The best data were acquired where a fairly consistent thickness of alluvium covered the volcanic rocks. End_of_Article - Last_Page 1042------------