Crustal strains in the Japanese Islands as deduced from dense GPS array

Data from the nationwide continuous GPS network, operated by the Geographical Survey Institute of Japan, were used to estimate crustal strains in the Japanese islands. We used horizontal velocity vectors at 610 sites for the period April, 1996 to March, 1997, and employed the Least Squares Prediction method to interpolate the velocities to a uniform 7km × 7km grid over Japan. The gridded velocities were then differentiated in space to calculate principal components of strains. Results clearly portray tectonic strainings of the Japanese islands in one year; (1) Dilatational strains show that the Japanese islands are under a compressive strain regime induced by the subducting oceanic plates, (2) Distribution of high maximum shear strains coincides with the regions of crustal activities, and (3) Principal axes of the strains indicate influences of E‐W and NW‐SE compression due to the converging oceanic plates. North‐south extension in Kyushu is also visible.

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