• Search Research Projects
  • Search Researchers
  • How to Use
  1. Back to project page

1994 Fiscal Year Final Research Report Summary

The mechanism of the Iriomote earthquakes swarms

Research Project

Project/Area Number 05452377
Research Category

Grant-in-Aid for General Scientific Research (B)

Allocation TypeSingle-year Grants
Research Field Natural disaster science
Research InstitutionKYOTO UNIVERSITY

Principal Investigator

ANDO Masataka  Kyoto Univ.DPRI.Prof., 防災研究所, 教授 (80027292)

Co-Investigator(Kenkyū-buntansha) BABA Hisatoshi  Tokai Univ.IRD Research Associate, 沖縄地域研究センター, 助手 (80256180)
OHKURA Takahiro  Kyoto Univ.CLAS Research Associate, 総合人間学部, 助手 (40233077)
KATAO Hiroshi  Kyoto Univ.DPRI Research Associate, 防災研究所, 助手 (80221878)
OHSHIMAN Naoto  Kyoto Univ.DPRI Associate Prof., 防災研究所, 助教授 (70185255)
ITO Kiyoshi  Kyoto Univ.DPRI Associate Prof., 防災研究所, 助教授 (80022721)
Project Period (FY) 1993 – 1994
KeywordsIriomote / Earthquake swarm / Normal fault / Extensional stress / Taiwan / Back arc / Geothermal actin'ty / Ryukyu trench
Research Abstract

The Iriomote swarm activity which started suddenly in November, 1991 had been intermittently occurred in the northern part of the island. The largest event of M5.2 happened in November, 1993. Since then the activity had decreased gradually. Nevertheless events of M>3 sometimes had occurred, sugeesting the swarm holding still its activity. From this reason, the present program was initiated in the last fiscal year. In the last year installation of instruments and the examination of the data thus obtained were made.
Events of the earthquake swarm is distributed like a plane, with a dimension of 20 km x 10 km, which strikes N35W and dips to the southwest with an angle of 70 deg.The focal mechanism of relatively large events M>3.5 have dominantly normal fault component that implies the earthquake swarm have been manifested under tensional stress.
This year have conducted observations and analyzes of the data on the swarm activity. We conclude the process of the earthquake swarm beneath the island as follows : Under the NEE-SWW tensional stress field water (liquid phase) intruded from the upper mantle causing an increase of pore pressure leading to the earthquake swarm activity. A more detailed geochemical study is necessary on the origin of the water although a chemical analysis has implied the upper mantle as an supply source of the water. The plane-like distribution of earthquakes on which the micro-earthquakes are concentrated during the swarm activity is a basically fault plane. The dip and strike of the plane are consistent with the regional pattern of faults throughout the southern Ryukyu trench and the mechanism of several M6 class earthquakes near Taiwan.
In conclusion the tensional stress field caused the Iriomote swarm activity and then the medium-size earthquakes near Taiwan. With the occurrence of the series of Taiwan events the activity completed and died out to the normal level.

  • Research Products

    (10 results)

All Other

All Publications (10 results)

  • [Publications] 清水 公一、伊藤 潔 他3名: "1992年西表島群発地震" 京都大学 防災研究所年報. 36. 253-262 (1993)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 京大防災研 地震予知研究センター: "西表島群発地震域での全磁力観測" 地震予知連絡会報. 50. 586-587 (1993)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 安藤 雅孝: "続発する西表島群発地震の調査・研究" 月刊「地球」. 15. 193-196 (1993)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 大志万 直人: "地磁気観測から見た西表島群発地震" 月刊「地球」. 15. 212-217 (1993)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] 清水 公一, 大倉 敬宏, 片尾 浩, 伊藤 潔: "1992年西表島群発地震" 月刊「地球」. 15. 202-206 (1993)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] M.Ando: "The distribution pattern of micro-earthquakes and active faults in the inner southern Japan as revealed by the relocated hypocenters from seismological networks of Kyoto University." Proceedings of Third ROC and Japan Joint Seminar on Natural Hazards Mitigation, national Cheng-Kung University. 1-15 (1993)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] H.Katao et.al.: "Ocean Bottom Seismometer (model IV of Kyoto University) ." Bull.Disast.Prev.Res.Inst., Kyoto Univ.Vol.44. 191-198 (1994)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] K.Obana et.al.: "Ocean Bottom Seismometer Handled by Submerse Vessel and Its Observation Prior to the 1993 Hokkaido Earthquake." Bull.Disast.Prev.Res.Inst., Kyoto Univ.Vol.44. 199-210 (1994)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] K.Shimizu et.al.: "1992 Iriomote Island earthquake swarm." Annuals, Disas, Prev.Res.Inst., Kyoto Univ.No.36 B-1. 253-262 (1993)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] RCEP.DPRI.Kyoto Univ.: "Observation of the Geomagnetic Total Intensity in the Area of the Earthquake Swarm in Iriomote Island." Rept.coordi.comm.Earthg. Predct. Vol.50. 586-587 (1993)

    • Description
      「研究成果報告書概要(欧文)」より

URL: 

Published: 1999-03-16  

Information User Guide FAQ News Terms of Use Attribution of KAKENHI

Powered by NII kakenhi