Upper boundaries of the Pacific and Philippine Sea plates near the triple junction off the Boso Peninsula deduced from ocean-bottom seismic observations 4. Seismology

Aki Ito, Hiroko Sugioka, Koichiro Obana, Ryota Hino, Daisuke Suetsugu, Kazuo Nakahigashi, Masanao Shinohara, Masaru Nakano, Yojiro Yamamoto

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

We determined hypocenter distributions and focal mechanisms of earthquakes off the Boso Peninsula, Japan, based on seafloor observations using ocean-bottom seismometers (OBSs). From OBS data, we detected and located earthquakes that were closer to the trenches than had previously been reported. The determined focal depths of relocated hypocenters were systematically shallower than those in the Japan Meteorological Agency catalog determined from land-based data. The hypocenter distribution was separated into two groups: one associated with the Pacific plate (PAC) and the other with the North American and/or Philippine Sea plates (PHS). For the former group, both the focal depths and mechanisms of low-angle thrust-faulting earthquakes were consistent with the geometry of the PAC determined by previous studies. Among the latter group, we selected low-angle thrust-faulting earthquakes with a slip direction parallel to the direction of PHS subduction or with a dip direction parallel to the PHS to delineate the upper boundary of the PHS. The depth of the plate upper boundary off the Boso Peninsula was found to be approximately 6 km shallower than previously reported estimates.

Original languageEnglish
Article number30
Journalearth, planets and space
Volume69
Issue number1
DOIs
Publication statusPublished - 2017 Dec 1

Keywords

  • Boso Peninsula
  • Hypocenter distribution
  • Ocean-bottom seismometer
  • Pacific plate
  • Philippine Sea plate

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science

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