Crustal deformation of northeastern Japan based on geodetic data for recent 120 years

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  • Nishimura Takuya
    Geospatial Information Authority of Japan, Geography and Crustal Dynamics Research Center

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Other Title
  • 測地観測データに基づく東北日本の最近120年間の地殻変動
  • ソクチ カンソク データ ニ モトズク トウホク ニホン ノ サイキン 120ネンカン ノ チカク ヘンドウ
  • Crustal deformation of northeastern Japan based on geodetic data for recent 120 years [in Japanese with English abstract]

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Abstract

We accumulated geodetic triangulation, trilateration, leveling, tide-gauge, and continuous GPS data to clarify the nature and temporal variation of crustal deformation in northeastern Japan for the 120-year period preceding the 2011 Mw 9.0 Tohoku-Oki earthquake. Horizontal, regional strain is characterized by north–south extension and east–west compression for ∼90 and 10 years, respectively. Large compressional strain in an east–west direction was observed in the deformation zone in the central axis of northeastern Japan and along the eastern margin of the Japan Sea. Vertical deformation is the result of subsidence along the Pacific coast. The subsidence rate was roughly constant for 120 years, except for the Pacific side of the Fukushima prefecture where uplift was observed for ∼20 years beginning from 1939. Continuous GPS observations were collected from 1994 and show deceleration of east–west compressional velocity in the Fukushima prefecture around 2000. Interplate coupling estimates suggest that deceleration was caused by weakening of the coupling offshore of Fukushima and Ibaraki prefectures. This implies that the plate interface in part of the source region to the Tohoku-Oki earthquake was unlocked, contributing to the seismic rupture. There is a well-known discrepancy between geodetic deformation and geological deformation; there is also a large temporal variation even within geodetic strain rate. The giant Tohoku-Oki earthquake event did not resolve the discrepancy between strain rates. Ongoing post-seismic deformation may be the key to resolving this discrepancy.

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