Displacements of Triangulation Points in Northern Kyusyu.

Abstract

The revision of triangulation survey was carried out with regard to 106 triangulation points distributed in the northern part of Kyfisyu. As the results, the horizontal displacements of these triangulation points were worked out with reference to several points surrounding the area. These reference points are situated in the region covered with layers of older geological formation; i.e., the mesozoic and Paleozoic formations and the granitic layer, underlain the layers of the tertiary formation. The vertical displacements of these triangulation points were also worked out with reference to the bench-marks nearby, of which the heights and their changes were measured by means of precise levels. The horizontal and vertical displacements thus worked out are due to the time interval from 1897 to 1954. The distribution of the vertical displacements shows that there are several centres of subsidence, as shown in Fig, 3. These subsidence centres appear to be closely related with mining the coal field, the sinking exceeding 7 m at most. As for the horizontal displacements, we notice that (i) the amounts are larger at the points where the vertical downward displacements are large, and that (ii) the directions of the displacements are rather at random. Remarkable deformation of the earth's surface such as reported in the present manuscript is thought as has been caused by underground mining. But it may be a matter of further discussion whether the deformation has been caused simply by underground excavation.