阿寺断層付近の低い地震活動

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書誌事項

タイトル別名
  • Low Seismic Activity Associated with the Atera Fault, Central Japan
  • アジ ダンソウ フキン ノ ヒクイ ジシン カツドウ

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説明

An observation of microearthquakes was carried out near the Atera Fault for two and a half months, from July 14 to October 2, 1971, since the fault has been known as one of the most active faults in Japan.<br>In the south-western side of the Atera Fault, the focal depths of earthquakes were deeper than 30km, that is, earthquakes occurred in the mantle but not in the crust. In the northeastern side, however, only a few earthquakes were detected. Although three direct analogue recording systems of high sensitivity were used near the fault, very few earthquakes could be located near the fault. A comparison of daily frequency of earthquakes near the NeoValley Fault with the present observation showed that the seismicity near the Atera Fault was undoubtedly lower than that near the Neo-Valley Fault. The same tendency has been also observed for larger earthquakes. Number of earthquakes detected at one of the three stations was exceptionally large, though the sensitivity was the same for all stations. But most of distant earthquakes were equally detected.<br>Considering these facts, it might be concluded that the present seismic activity is very low and, in addition, seismic waves of high frequency are attenuated in the crust near the Atera Fault. Some focal mechanisms of microearthquakes were calculated. The pressure axis thus obtained was E-W direction as in the case studied by MATSUDA (1969) and ICHIKAWA (1971).

収録刊行物

  • 地震　第２輯

    地震　第２輯 25 (3), 232-242, 1972

    公益社団法人 日本地震学会

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