SEGJ Technical Conference

Large near-surface rupture along an active fault detected by electrical resistivity and radon surveys: a case of the Hanaore fault, Japan

Abstract In Japan, a number of surveys at various active faults using boreholes and trenches have been conducted for disaster preventions. However, the extensive borehole/trench surveys along a fault are hard to be done due to the cost and constraints of surveys. For overcoming the problem, as a case study, we conducted soil gas survey and electrical resistivity survey at the Hanaore Fault, in Kyoto city, Japan. Our surveys indicate that the surface trace of the active fault can be clearly detected from the spatial distribution of the radon concentration in the gas. In addition, a high resistivity zone of about 6 m in thickness and about 8 m in width was buried beneath the trace. Compared to the results of the nearby trench survey, it can be inferred that this high resistivity zone was once large topographic depression and buried in sandy river sediment. There are no corresponding present rivers along the fault but the inferred sandy sedimentary belt is elongated at least 150 m along! the fault, so that this large depression is possibly created by the past huge earthquake along the Hanaore fault.