A triple-planed structure of seismicity and earthquake mechanisms at the subduction zone off Miyagi Prefecture, northern Honshu, Japan

Details A triple-planed structure of seismicity and earthquake mechanisms at the subduction zone off Miyagi Prefecture, northern Honshu, Japan A triple-planed structure of seismicity and earthquake mechanisms at the subduction zone off Miyagi Prefecture, northern Honshu, Japan

Sep 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981e%26psl..55...25s&link_type=abstract

Earth and Planetary Science Letters, Volume 55, Issue 1, p. 25-36.

Mathematics

Logic

18

Scientific paper

A detailed cross-section of seismicity combined with types of earthquake mechanisms was constructed for the subduction zone off Miyagi Prefecture, northern Honshu, Japan, where a large Ms = 7.5 earthquake occurred on June 12, 1978. Nodal-plane solutions were determined for fourteen earthquakes with body wave magnitudes >=5.4 using data recorded at WWSSN and Japanese stations. For smaller-magnitude events, the types of focal mechanism were analysed using P-wave first-motion data recorded at regional stations.
The results obtained are:
(1) For the area 150-200 km landward from the trench axis, the cross-section suggests a triple-planed seismic zone; that is, the zone of thrusting overlaps the so-called double-planed seismic zone. The upper and lower planes of the double-planed seismic zone are characterized by down-dip compression and down-dip tension, respectively.
(2) Thrusting terminates at a depth of 60 km, where the aseismic front in the area is located, and it merges into the zone of down-dip compression in the deeper part, in a down-dip direction. In contrast, the depth of the zone of down-dip compression appears to shift by 10 km at the aseismic front.
(3) The extension of the zone of down-dip compression seaward beyond the aseismic front and the shift of the depth of the zone may be caused by loading within the descending slab through a mechanical coupling between the plates at the focal area of the 1978 earthquake prior to its occurrence.
Present address: Meteorological Department, Bangkok 11, Thailand.

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