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GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L02311, doi:10.1029/2005GL025270, 2006

Dynamic deformation of the accretionary prism excites very low frequency earthquakes

Yoshihiro Ito

National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan


Kazushige Obara

National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan


Abstract

We have detected anomalous very-low-frequency earthquakes within the accretionary prism along the Nankai Trough, southwestern Japan. Centroid moment tensor inversion analysis reveals that the earthquake hypocenters are distributed at ∼10 km depth above the upper surface of the subducting Philippine Sea Plate, and within 50–70 km landward of the trough axis. The focal mechanisms indicate reverse faulting. Their hypocenters are distributed beneath a deformation zone of an accretionary prism in sea-floor topography. These observations suggest that the occurrence of very-low-frequency earthquakes is related to numerous reverse fault systems within the accretionary prism, and that the earthquakes reflect the dynamics of deformation within this accretionary prism.

Received 19 November 2005; accepted 20 December 2005; published 25 January 2006.

Index Terms: 3045 Marine Geology and Geophysics: Seafloor morphology, geology, and geophysics; 7215 Seismology: Earthquake source observations (1240); 7230 Seismology: Seismicity and tectonics (1207, 1217, 1240, 1242); 8118 Tectonophysics: Dynamics and mechanics of faulting (8004); 8170 Tectonophysics: Subduction zone processes (1031, 3060, 3613, 8413).

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Citation: Ito, Y., and K. Obara (2006), Dynamic deformation of the accretionary prism excites very low frequency earthquakes, Geophys. Res. Lett., 33, L02311, doi:10.1029/2005GL025270.