| Summary: | To clearly show the dangerous lunar phases during which giant earthquakes tend to occur at each subduction zone and to clarify the mechanisms of giant earthquake occurrences during neap tides at some subduction zones, the folded and double-folded lunar phase is introduced. The dangerous lunar phases for each subduction zone, represented as delays from spring tides, are 1 to 4 days for Peru, 3 to 5 days for Indonesia, 5 to 7 days for Tonga, 3 to 8 days for Japan, 8 to 11 days for Kuril, -3 to 0 days for Chile, -2 to 0 days for New Guinea, and -2 to 0 days for Alaska. Paying sufficient attention to foreshocks and various precursors such as GPS (Global Positioning System) anomalies during the dangerous lunar phase for each subduction zone will be a very useful way to reduce damage from giant earthquakes. The influence of the solid tidal stress on reverse faulting was investigated based on the strike of subduction zones, and prohibition of giant earthquakes caused by strength increase due to the rapid variation in tidal stress during spring tides at NS subduction zones was proposed as one reason why giant earthquakes occur not only at spring tides but also at neap tides at some subduction zones. The 6th International Symposium on In-situ Rock Stress, August 20-22, 2013, Sendai , JAPAN
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