- 活断層研究 (ISSN:09181024)
- vol.1996, no.15, pp.73-86, 1996-11-29 (Released:2013-03-22)
Ground penetrating radar uses reflected electromagnetic waves to image the subsurface. Its investigation depth is 2-3m and its resolution is 20-30cm in soil. Because of its very shallow investigation depth, ground penetrating rbdar has been used for finding underground gas pipes, electric cables and buried remains.Ground penetrating ra d ar method has an advantage over the seismic reflection method in tenns of the spread density of sources and sensors. It is necessary in the seismic reflection method to spread sources and sensors in consideration of surface waves because the generation of surface waves makes it very difficult to distinguish reflected waves. However, in ground penetrating radar method, sources and sensors can be spread conveniently with high density for its high resolution because surface waves are not generated in the electromagnetic field.We have devised a new radar system to ap p l y the ground penetrating radar method to geological surveying. In the ordinary radar system, impulsive waves are used as transmission signals, but in the new radar system, sine waves are used with the frequency varied as a step function of the sweeping period of transmission signals. We can obtain the impulsive reception signals such as the ordinary radar system after the convolution integrals between sine-shaped transmission and reception signals. We call the new radar system the Step Continuous Wave Radar(SCWR) systen after the characteristics of its transmission signals. Its investigation depth is 10-15m in soil and 20-30m in rock with resolution of 50-60cm.The SCWR system will provide useful information because it can be carried out speedily and non-destructively on the ground around active faults, before trenching, down to about 10m in depth.In this paper, we will show the imaging of active faults with the SCWR system throu g h the results of the investigation around the Nojima faults which appeared in the Awaji Island with the 1995 Southern hyogo Prefecture Earthquake, and then we will pick up some current problems in the imaging, for example the effective arrangement of sources and sensors for the shorter period of field work and for the three-dimensional imaging with ground penetrating radar, and finally show a conception for the solutions of these problems.