Figure 1
From: Increased radon-222 in soil gas because of cumulative seismicity at active faults
Location maps of seven active faults in western Japan and the associated distribution of earthquake epicenters. Fault traces are after a digital fault map (Nakata and Imaizumi 2002). Locations of measurement lines and the epicenters of earthquakes from January 2001 to September 2010 in the vicinity of the faults as recorded in the Seismological and Volcanological Bulletin of Japan (CD-ROM) and based on the observations of the Japan Meteorological Agency are depicted. The beginning of the earthquake data observation period was selected to comport with the commencement of Hi-net (the High Sensitivity Seismograph Network Japan, National Research Institute for Earth Science and Disaster Prevention), October 2000, for hypocenter determinations in the study areas. The color and shape of the epicenter indicators correspond to hypocenter depth and earthquake magnitude, respectively.