Quaternary vertical offset and average slip rate of the Nojima Fault on Awaji Island, Japan

Drilling was carried out to penetrate the Nojima Fault where the surface ru pture occurred associated with the 1995 Hyogo-ken Nanbu earthquake. Two 500 m boreholes were successfully drilled through the fault zone at a depth of 389.4 m. The drilling data show that the relative uplift of the south-east side of the Nojima Fault (south-west segment) was approximately 230 m. The Nojima branch fault, which branches from the Nojima Fault, is inferred to extend to the Asano Fault. From the structural contour map of basal unconfo rmity of the Kobe Group, the vertical component of displacement of the Noji ma branch-Asano Fault is estimated to be 260-310 m. Because the vertical co mponent of displacement on the Nojima Fault of the north-east segment is a total of those of the Nojima Fault of the south-west segment and of the Noj ima branch-Asano Fault, it is estimated to total to 490-540 m. From this, t he average vertical component of the slip rate on the Nojima Fault is estim ated to be 0.4-0.45 m/10(3) years for the past 1.2 million years.