Seismic reflection survey by the crooked line method applied to a coalfield in a mountainous region

In the past, seismic reflection surveys on land in Japan have usually been carried out along straight lines irrespective of surface terrain. However in Japan, where most of the areas are covered by mountainous terrain, it may require considerable time and cost to carry out field operations by the straight line method.From August to October in 1988, a reflection seismic survey was carried out at the Sarufutsu area in Hokkaido, Japan. The area is in a mountainous region where the straight line method was very difficult to conduct. A trial of the crooked line method was introduced to the area by laying out seismic lines along roads and valleys.Four test borings with VSP and extensive field geological surveys were carried out in this area by NEDO (New Energy and Industrial Technology Development Organization) prior to 1987, and the results show that there is a north-south trending syncline in the area and that the maximum depth of the main coal seam is approximately 600 m below the surface.The data acquisition system adopted was a 48-trace IFP digital recording system with one-millisecond sample interval.The result of the survey gives a good correlation with existing geological information.It has been concluded that seismic reflection surveys by the crooked line method are applicable for coal exploration in such a mountainous terrain.