相模湾北西部およびその周辺地域の地震活動 Seismicity at Northwestern Sagami Bay

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神奈川県温泉地学研究所によって決定された1990年から1998年の9年間の震源データを用いて,「神奈川県西部地震」の想定震源域である相模湾北西部における地震活動と地質構造との関係について考察した.<br>地震活動の高い地域は,神奈川・山梨県境や箱根火山のカルデラ内に分布し,それぞれ丹沢山地の隆起運動や箱根火山の火山活動に関連していると見られている.箱根古期外輪山の山麓東部では,地震が深さ10~20kmに発生しており,震源の深さは箱根火山中央火口丘から山麓東部へと行くに従って徐々に深くなっている.この特徴は,火山体近くの熱的構造を反映し,地震発生層の厚み変化を表していると考えられる.<br>一方,伊豆地塊の衝突によって形成された足柄山地や,断層で囲まれた大磯丘陵,湯河原や多賀火山等の第四紀火山地帯では,地震活動は相対的に低い.また,神縄断層や国府津-松田断層などの活断層付近では,浅い地震は観測されていない.

It has been pointed that an M7 class earthquake might occur in the near future around northwestern Sagami Bay, southwest Kanto district, central Japan, and this hypothetical earthquake has been named the "Western Kanagawa Prefecture Earthquake (WKPE)". In order to investigate the mechanism of WKPE, the Hot Springs Research Institute of Kanagawa Prefecture (HSRI) has carried out continuous monitoring of seismicity and crustal deformation since 1989, covering the anticipated rupture zone estimated from historical data. In this paper, the relationship between seismicity and geological structure in and around northwestern Sagami Bay is investigated in detail based on a hypocenter precisely determined by the HSRI during the period 1990-1998.<br>Hypocenters of earthquakes are calculated from 16 stations for the present seismicity analysis. Seismic stations are deployed 2-10km apart. The accuracy of the hypocenter determination in this study area was within 2-3km with application of the method of prediction analysis. The minimum magnitude of observable earthquakes was estimated to be M0 in the Hakone area and M1 in northwestern Sagami Bay.<br>Comparison between seismicity and geological structure can be summarized as follows:<br>(1) The higher seismicity areas are located in the prefectural border between Kanagawa and Yamanashi, and in the Hakone area. This higher seismicity can be attributed to the uplift of the Tanzawa Mountains and to volcanic activity, respectively, in the two areas.<br>(2) The cutoff depth of seismicity becomes deeper from the center toward the eastern flank of Hakone volcano. The depth change of the seismogenic layer should be attributed to geothermal effects of the Hakone volcano.<br>(3) The lower seismicity areas are located in the area (Ashigara Mountains and Oiso Hills) where the Philippines Sea plate is colliding with central Honshu, and in Quaternary volcanic areas (Yugawara and Taga).<br>(4) Seismicity shallower than 10km has not been observed around active faults, such as Kannawa and Kozu-Matsuda faults, during observation periods.<br>(5) Two remarkable seismic events occurred in 1990 (M5.1) and 1994 (M4.8), the first earthquakes in 57 and 74 years, respectively. Some researchers had postulated a period of seismic quiescence in the area, but this seems unlikely.

収録刊行物

  • 第四紀研究  

    第四紀研究 38(6), 461-467, 1999-12-01 

    Japan Association for Quaternary Research

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各種コード

  • NII論文ID(NAID)
    10004721306
  • NII書誌ID(NCID)
    AN0034136X
  • 本文言語コード
    JPN
  • 資料種別
    ART
  • ISSN
    04182642
  • NDL 記事登録ID
    4927017
  • NDL 雑誌分類
    ZM49(科学技術--地球科学--地質)
  • NDL 請求記号
    Z15-67
  • データ提供元
    CJP書誌  NDL  J-STAGE 
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