Abstract
Following the Hyogoken Nanbu earthquake (Januray 17, 1995, Mw = 7.2), three drillholes were sunk through the Nojima Fault (Awaji Island, Japan). Textural andpetrographic studies of the Geological Survey of Japan (GSJ) drill cores allow recognition of two deformation episodes. The first one is older than the deposition of the Middle to LateEocene Kobe Group, corresponds to a left-lateral movement on the Nojima fault and is expressed by pseudotachylytes, kinking of biotite crystals in the low-strain rocks and anintense laumontite hydrothermal alteration. The second one displaces the basal unconformity of the Kobe group, corresponds to a right-lateral reverse displacement and is expressed atleast by carbonate-filled hydraulic fractures and thin gouge zones. Different important deformation mechanisms are recorded by the fault rocks, but questions relating to theattribution of deformation and alteration features to one or other deformation episodes remain unresolved.