大津市皇子が丘潜在断層群について

Abstract

The presence of two parallel faults concealed below the Alluvial fan deposits and running alongthe east foothill of the Hiei-Daimonji mountainland has been confirmed by surface geology, boring, and geophysical explorations. Another concealed fault has been also estimated under the coastalplain. Each fault dislocates the Pliocene-Pleistocene deposits by east side downthrow.By analysing the actual faults in the granite mass which constitutes the mountainland the con-cealed faults are considered to have been generated by uplifting of the mountainland by a east-west compression. The analysis ofjoint system of the granite, on the other hand, indicates a north-south compression. Most of lamprophyre dykes in the granite have been revealed to haveintruded along tensional joints of the same stress field, and this stress field is concluded to beolder than the stress that generated the concealed faults.