Abstract
An outline of geochemical studies for earthquake prediction starting from the end of 1973 in Japan is presented. In these studies most emphasis has been placed on the measurement of the radon concentration in groundwater, but variations in abundances and isotopic ratios of other elements, water temperature, water level of groundwater have also been measured.
At the present time a total of 30 observation sites for the periodical radon measurement are operated mainly by University of Tokyo and the Geological Survey of Japan. Among them the continuous measurement technique by using a recently developed ZnS(Ag) scintillation detection system has been adopted at five sites operated by University of Tokyo and Nagoya University. Tokyo Metropolitan Government runs the project of radon monitoring in groundwater at over 400 sites in and around the Tokyo area.
Two examples of continuous measurements of the radon concentration in groundwater obtained by using the above-mentioned system are given. Temporal changes of the radon concentration in groundwater in Izu and Tokai districts are compared with the occurrence of three earthquakes (M=5.5, 5.4, and 4.5) with the epicenter distances of some 20 to 130km.
