This paper provides some additional data on the surface deformation associated with the Nojima earthquake fault, that occurred on January 17, 1995. These data were obtained mostly in March 1995, and include: 1) detailed mapping of the fault trace at the Nashimoto and Nojima sectors ; 2) coseismic coastal uplift on the northern part of Awaji Island; and 3) tide gauge data and displacement of supporting columns of the bridge between Awaji Island and Honshu, across the Seto Inland Sea. The main results are as follows.: 1) En eshelon fault traces and cracks are particulaly well developed at Nashimoto, underlain by unconsolidated alluvial sand and gravels. Small-scale reliefs, such as minor pullapart basins and minor pushed-up bulges, associated with the right-step or left-step of the rightlateral displacement of the Nojima earthquake fault, are clearly seen at Nashimoto 2) Coseismic coastal uplift is revealed by displacement of tetrapods (concrete blocks for wave brakes) at Ezaki (Loc. O) and by emerged beach deposits, about 300m east of Ezaki (Loc. P). This indicates that the southeastern side (upthrown side) of the earthquake fault was uplifted at the time of the 1995 earthquake. 3) Examination of releveling results of benchmarks, tide gauge data, and displacement of supporting columns of the bridge across the Seto Inland Sea, as well as the general pattern of active faults in the Kobe area, suggest that the northern extension of the Nojima fault has subsided and this probably represents a large scale pull-apart basin, due to right-step of major faults, dominated by right-lateral offset.
The Nojima earthquake fault appeared along the recognized active fault in the northwestern part of Awaji Island in association with the 1995 Hyogoken-Nanbu Earthquake. This earthquake fault is dominated by right-lateral offset (max. 1.7m), with a high-angle reverse fault which has a maximum verlical displacement of 1.3m uplift on the southeastern side. We have repeated the measurement of seven profiles of the fault scarp at two areas (Hirabayashi, Ogura). The fault scarp of the Hirabayashi area (profiles 1-4) is composed of the Plio-Pleistocene Osaka Group at the base and is overlain by an unconsolidated gravel bed at the top. The Ogura area (profiles 5-7) is entirely underlain by the Plio-Pleistocene Osaka Group. The fault scarp in these two areas is characterized by an overhanging slope due to thrusting of the upthrown side. Scarp retreat at Hirabayashi occurred in association with the sudden collapse of the gravel bed and proceeded more quickly than at Ogura, where fault scarp retreat proceeded by exfoliation of the fault plane as well as partial collapse of the Osaka Group. These facts strongly indicate that the lithological control is most significant for the formation of original fault scarp as well as retreat. The retreat of fault scarp was very slow after March to June at Hirabayashi and June to July at Ogura, and proceeded more quickly than some of seismically generated normal faults.