Earthquake Mechanism within the Philippine Sea Plate Subducting beneath the Kanto District, Central Japan

• HORI Sadaki

  National Research Institute for Earth Science and Disaster Prevention

Bibliographic Information

Other Title

• 関東地方下のフィリピン海プレート内地震の発生機構
• カントウ チホウカ ノ フィリピンカイ プレートナイ ジシン ノ ハッセイ キ

Abstract

The upper mantle earthquakes occurring within the Philippine Sea plate subducting beneath the Kanto district, Japan, were investigated for their hypocentral distribution and focal mechanisms. Earthquakes located above the double seismic plane, which is formed in conjunction with the subducting motion of the Pacific plate, were picked up on a graphic display with an “on-map selection” method. Hypocentral parameters were re-determined with removing stations far from the epicenter and with introducing station corrections to the observed arrival time data. Based on the relocated hypocenters, the focal mechanism solutions were also re-determined. Examining the hypocentral distribution in detail, we found that the earthquakes occurring within the Philippine Sea plate are classified into three groups and that their focal regions form a triple-layered structure. The earthquakes in Group I, which are located at the uppermost part of the slab, were found to occur in the oceanic crust of the Philippine Sea plate from their waveform analysis. The focal mechanism analysis showed remarkable difference between the earthquakes in Groups II and III. The down-dip compression type events are predominant for the earthquakes in Group II, while most of the focal mechanisms in Group III showed the earthquakes are occurring under the down-dip extension. We proposed a model to explain the earthquake mechanism within the Philippine Sea plate, where the “forced unbending” by the underlying Pacific plate causes compressional and extensional stress fields in the upper and lower portion of the slab, respectively.

Journal

• Zisin (Journal of the Seismological Society of Japan. 2nd ser.)

  Zisin (Journal of the Seismological Society of Japan. 2nd ser.) 50 (2), 203-213, 1997

  SEISMOLOGICAL SOCIETY OF JAPAN

Keywords

• Philippine Sea plate
• Pacific plate
• Focal mechanism
• Kanto district

Details

• CRID: 1390001204307245440
• NII Article ID: 10002501289
• NII Book ID: AN00305741
• DOI: 10.4294/zisin1948.50.2_203
• ISSN: 18839029
• ISSN: 2186599X
• ISSN: 00371114
• NDL BIB ID: 4292598
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I4292598
• Web Site: https://www.jstage.jst.go.jp/article/zisin1948/50/2/50_2_203/_pdf
• Data Source:
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  • NDL
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  • CiNii Articles
• Abstract License Flag: Disallowed