pure and applied geophysics

, Volume 126, Issue 2–4, pp 447–463 | Cite as

Downward migration of seismic activity prior to some great shallow earthquakes in Japanese subduction zones—a possible intermediateterm precursor

  • Kiyoo Mogi
Seismologic and Geodetic Precursors

Abstract

Before the 1944 Tonankai earthquake along the Nankai Trough, seismic activity increased in the shallow depths, and then the activity gradually migrated downwards. When it reached its limit (a depth of approximatelty 70 km), the main shock occurred. Several deep earthquakes, including one ofM5.3, occurred several months prior to the Tonankai earthquake. A similar downward migration pattern also can be recognized regarding the 1952 Tokachi-oki earthquake. In this case the deepest earthquakes reached about 400 km. This may be one of the intermediate-term precursory phenomena of great thrusttype earthquakes in subduction zones. Recent observations in the Tokai district along the Suruga Trough, where a large earthquake is expected to occur in the future, suggest a similar downward migration pattern in the land area.

Key words

Intermediate-term precursor downward migration seismic gap doughnut pattern subduction zone Tonankai earthquake Tokachi-oki earthquake Tokai earthquake 

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Copyright information

© Birkhäuser Verlag 1988

Authors and Affiliations

  • Kiyoo Mogi
    • 1
  1. 1.Earthquake Research InstituteUniversity of TokyoTokyoJapan

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