Three Dimensional P and S Wave Velocity Structure beneath the Northeastern Japan Arc

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  • OBARA Kazushige
    Observation Center for Earthquake Prediction, Faculty of Science, Tohoku University
  • HASEGAWA Akira
    Observation Center for Earthquake Prediction, Faculty of Science, Tohoku University
  • TAKAGI Akio
    Observation Center for Earthquake Prediction, Faculty of Science, Tohoku University

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Other Title
  • 東北日本における地殻・上部マントルの三次元P波及びS波速度構造
  • 東北日本における地殻・上部マントルの3次元P波及びS波速度構造
  • トウホク ニホン ニ オケル チカク ジョウブ マントル ノ 3ジゲン Pハ

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Abstract

Three dimensional P and S waves velocity structure of the crust and the uppermost mantle beneath the northeastern Japan arc is investigated by an inversion of P and S waves arrival times observed at the seismic network of Tohoku University from local earthquakes.<br>The results show that, in the uppermost mantle, there exists a dipping high velocity zone of P and S waves which corresponds to the descending Pacific plate. Beneath active volcanoes low velocity zones of P and S waves are clearly seen, which are dipping westward and extend to a depth of about 100km.<br>Although the pattern of P wave velocity distribution is very similar to that of S wave velocity distribution, change in absolute value of S wave slowness perturbation is bigger than that of P wave slowness perturbation, indicating the spatial change in VP/VS value. Within the Pacific plate VP/VS values are generally low, whereas the low velocity zones existing beneath active volcanoes have high VP/VS values.

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