Detection of geological faults using a nuclear method

It proved possible to detect the precise location of large geological faults using the amount of⁴⁰K and²²⁰Rn daughter gamma-rays and the amount of²²²Rn (measured in a scintillation chamber) which could be extracted from the soil using negative pressure. Both⁴⁰K and²²⁸Th appear to be concentrated in fault gouge. The²²²Rn content extractable from the soil is a measure of permeability and is very low in the region of the fault due to clay-like fault gouge. The method was demonstrated successfully on the large Wellington fault at Upper Hutt, New Zealand.