Relationship of the <i>M</i>7.1 1948 Fukui and the <i>M</i>8.0 1891 Nobi Earthquakes to the Occurrence of Large Earthquakes in the Surrounding Areas

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  • 1948年福井地震 (<i>M</i>7.1) および1891年濃尾地震 (<i>M</i>8.0) の発生と周辺の地震の発生との関連について
  • 1948年福井地震(M7.1)および1891年濃尾地震(M8.0)の発生と周辺の地震の発生との関連について
  • 1948ネン フクイ ジシン M7.1 オヨビ 1891ネン ノウビ ジシン M8.0 ノ ハッセイ ト シュウヘン ノ ジシン ノ ハッセイ ト ノ カンレン ニ ツイテ

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Abstract

The seismic activity in the Chubu region of Houshu, Japan after the M8.0 Nobi earthquake of 1891 has been remarkably active, with 7 earthquakes of M≥6.5. A probabilistic test concludes that this series of earthquake occurrences for the relatively short-period is significant and not random. The Coulomb Failure Function (CFF) is used to evaluate effects of static stress loading on the neighboring faults for the earthquakes which occurred in the Chubu region of Honshu. Five of the seven events fall in positive area of change for the Coulomb Failure Function values (ΔCFF). This consistency suggests that the Nobi earthquake changed the stress field of the crust around the hypocenter, triggering many earthquakes. The ΔCFF values are calculated for ±10° range of fault strike and dip angles for models of each earthquake. The values are found to vary significantly depending upon fault parameters, but the sense of ΔCFF (positive or negative) is stable throughout the test of different fault orientations. Preceding the M7.1 1948 Fukui earthquake, an earthquake of M6.3 occurred in 1930, possibly on the northern extension of the Fukui eastern margin fault system. Along the Fukui earthquake fault, high microearthquake activity has been observed to diminish with time since 1976, when the local seismic network was established. Whether or not the Fukui eastern margin fault system was involved in the Fukui earthquake of 1948 is not certain, and future work is needed to resolve the issue.

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