Shallow seismic investigation of a site with poor reflection quality

A shallow seismic reflection experiment was performed on a construction site to determine the feasibility of using reflection seismology to investigate the shallow structure in a weathered sand-gravel interlayered zone that was known to be a poor transmission of high-frequency seismic energy. Field-recording parameters were designed to fit the limited space of the urban construction survey area.A 7 kg sledgehammer was used to generate P-waves and SH-waves. Single 100 Hz geophones were deployed at 1.0 m/0.5 m group intervals, and 200/100-Hz low-cut filters were applied prior to A to D conversion to attenuate ground roll. For SH-wave reflections, single 14 Hz geophones and a 70-Hz low-cut filter on the seismograph were used. The dominant frequency bands ranged from 33 to 275 Hz and were centered around 110 Hz for P-waves. Lower dominant frequency bands 20 to 160 Hz with a dominant frequency of around 85 Hz were observed on SH-wave records. Four seismic lines, three P-wave recordings and one SH-wave recording, using different sets of recording parameters and an appropriate seismic-wave generation method produced reflections from varying depth ranges and at different resolutions.The results show that the techniques employed in this experiment may resolve the structure of a site with poor reflection quality. An f-k dip filtering and deconvolution were necessary in processing the reflection data to eliminate various types of unwanted energy. The seismic interpretations in this study were verified by drilling and by a nearby excavation.