In this study, the author attempted to estimate trace of the northern concealed section of the Isurugi Fault, classified as a part of the western part of the Tonamiheiya Fault zone in Toyama Prefecture, central Japan, by examining stratigraphic columnar sections obtained from existing borehole log data. The results showed that, based on the lateral continuities of significant vertical differences in presumably identical sediments recorded in the borehole log data, the main part of the Isurugi Fault appears to extend northeast along the lower part of the Oyabe River, reaching Toyama Bay via the central part of Takaoka City. The total length on land of this fault was found to be about 30 km. Borehole log data thus appear to be potentially useful for estimating traces of a concealed active faults.