SEISMIC SOURCES FOR SHALLOW INVESTIGATIONS - A FIELD COMPARISON FROM NORTHERN GERMANY

A field test of 14 seismic P-wave sources was designed to show the cap abilities of several sources for shallow subsurface investigations in the quaternary landscapes of Northern Germany. The sources included ac celerated dropped weights, shallow blasts, a shotgun using blank cartr idges and controlled signal sources. Local changes in subsurface condi tions showed a strong influence on the recorded data: so it proved nec essary to record up to 120 shots per source in order to Set representa tive results and to compare not only single shot records but stacked s ections as well. Reducing the geophone spacing to 1 m, it became possi ble to trace very local features like fluctuations in travel times or in the recorded amplitudes. The amplitude spectra of the recorded trac es indicated energy at frequencies up to 200 Hz and showed remarkable spatial changes due to different subsurface conditions near the receiv er locations. Changes in signal form and amplitude due to compacting e ffects were visible in the first four impacts of strong sources. (C) 1 998 Elsevier Science B.V.