The detection and identification of disturbances in the shallow underground using a combination of reflection seismics and CMP-refraction seismics

Disturbances in the shallow underground in the area of a motorway bridge were detected and identified by a combination of reflection seismics and CMP-refraction seismics. With the CMP-refraction seismic method, the shallow underground can be described in detail using all information (amplitude, frequency, phase characteristics) of the wavetrain following the first break (first-break phase). This method was used to determine the layering and additionally to identify faults and weak zones in a depth range from 0-6 m. For the detection of deeper horizons and disturbances, the reflection-seismic method was used. The results of both methods were combined and interpreted at one seismic section. Thus the stratigraphy and the tectonic for a depth range from 0-12 m could be identified, so that concrete could have been pressed at locations of weak zones and areas of disturbances into the underground to stabilize the motorway bridge. To analyze seismic refractors and reflectors within this very shallow underground range, seismic signals with high frequencies had been generated with a special kind of seismic vibrator, the air-sound source.