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| | Abstract | | In February-March, 2003 and, February-March, 2011, we conducted two time-lapse experiments near the Nojima Earthquake Fault in Awaji Island. In the former experiment, water was injected into the ground of 540m depth, and in the second experiment, the 80 tons air was injected into the ground at 100m depth. In both experiments, seismic ACROSS sources and geophones were used. In the former experiment, the observed travel time changes are well explained by rain falls during the observation by the flow simulation. The water flow speed at 5m is well matched to the observed travel-time delay curve. In the latter experiment, we observed very large waveform changes at 31 surface geophones and one 800m deep borehole geophone. The changes were identified from immediately after the injection to 24 hour delay. The 2D Vp structure explains the travel times for down-dipping sedimentary layers from the east side to the west side. Using this dipping strata above the granitic layer around 100 m to 300 m depth, it is found that the very large flow speed such as 1 cm/sec can explain waveform changes at 100m distance at 24 hours delay |
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