M9.0の発生に伴う福井県における地震活動の特徴的変化

概要

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One of the largest earthquakes, M9.0, occurred in the Pacific Ocean off the coast of northeastJapan in 2011. The focal area of this event is 200km × 500km with an average slip of 14m. Thestress difference by the M9.0 event affects Fukui Prefecture. An induced swarm occurred in thenorthern Reihoku area in Fukui Prefecture about 3 hours after the occurrence of the M9.0 event.The characteristic of this swarm was high seismic activity around the time of the M9.0 event. Thepresent activity of this swarm is low. The typical orientation of the T-axis of the fault plane solutionin this swarm turns in the direction of northeast Japan. This orientation does not coincide with themechanism of the earthquake that occurred in the Reihoku area before the M9.0 event. However, inthe Reinan area, earthquakes have the same orientation of the P-axis before and after the occurrenceof the M9.0 event. This means that the effects of the M9.0 event did not reach as far as the Reinanarea.