F. Buker et al., SHALLOW 3-D SEISMIC-REFLECTION SURVEYING - DATA-ACQUISITION AND PRELIMINARY PROCESSING STRATEGIES, Geophysics, 63(4), 1998, pp. 1434-1450
A comprehensive strategy of 3-D seismic reflection data acquisition an
d processing has been used in a study of glacial sediments deposited w
ithin a Swiss mountain valley. Seismic data generated by a downhole sh
otgun source were recorded with single 30-Hz geophones distributed at
3 m x 3 m intervals across a 357 m x 432 m area. For most common-midpo
int (CMP) bins, traces covering a full range of azimuths and source-re
ceiver distances of similar to 2 to similar to 12.5 m were recorded. A
common processing scheme was applied to the entire data set and to va
rious subsets designed to simulate data volumes collected with lower d
ensity source and receiver patterns. Comparisons of seismic sections e
xtracted from the processed 3-D subsets demonstrated that high-fold (>
40) and densely spaced (CMP bin sizes less than or equal to 3 m x 3 m)
data with relatively large numbers (>6) of traces recorded at short (
<20 m) source-receiver offsets were essential for obtaining clear imag
es of the shallowest (<100 ms) reflecting horizons. Reflections rich i
n frequencies >100 Hz at traveltimes of similar to 20 to similar to 17
0 ms provided a vertical resolution of 3 to 6 m over a depth range of
similar to 15 to similar to 150 m. The shallowest prominent reflection
at 20 to 35 ms (similar to 15 to 27 m depth) originated from the boun
dary between a near-surface sequence of clays/silts and an underlying
unit of heterogeneous sands/gravels.