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  • Letter
  • Open Access

Spatial distribution of centroid moment tensor solutions for the 2004 off Kii peninsula earthquakes

Earth, Planets and Space201457:BF03352575

  • Received: 30 November 2004
  • Accepted: 22 March 2005
  • Published:


Two large intraplate earthquakes (MW 7.0 and 7.3) occurred off the southeastern Kii Peninsula on September 5, 2004. We determined the centroid moment tensors of these earthquakes and their aftershocks. Earthquakes can be divided into two categories: (1) the reverse-fault type with a range in focal depth from 5 km to 20 km; and (2) earthquakes with a near-vertical nodal plane and a focal depth shallower than 5 km. Earthquakes of type (1) are distributed inside the Philippine Sea plate beneath the Nankai trough, while normal-fault events predominate in the other regions along the trough. The distribution of type (2) events shows two clear lineaments with strikes of NNW-SSE to the north and NE-SW to the west of the focal area. These lineament strikes coincide approximately with strikes at the nodal planes of such events.

Key words

  • Centroid moment tensor
  • broadband seismometer
  • tiltmeter
  • seismicity