Geophysical Center of Russian
Academy of Sciences, Moscow, Russia
World Data Center for Solid Earth Physics
The Geotraverse Project
The Japan Sea Geotraverse
FINE STRUCTURE OF JAPAN SUBDUCTION ZONE SEISMICITY
V. VADKOVSKY
Moscow State University, Russia, vad@dynamo.geol.msu.ru
Abstract |
Short description of studied area |
Methods of the studies |
Data sourses
What's the "nail"? |
How the "nail" grows |
Why the "nail" forms?
Conclusion |
Bibliography
Abstract
The study of the seismofocal zone structure conducted in the Japan
Islands' area. Spatial distribution of the earthquake hypocentres in the
depth range 0-120 km considered according to the data of the most entire
and reliable Japan Meteorological Agency (JMA) catalogue for the period of
1983-1990. In the hanging wedge of the crust and mantle, where strong
anisotropy of P- and S-waves velocities were established by many scientists,
the existence of almost vertical, isometrical in Earth surface projection,
short-life buildups of the earthquake hypocentres has been found. Such
buildups I named seismic "nails" .
The "nail" length comes from 15 to 30 km in depth. The upper part
of a "nail" either comes out to the Earth surface or not. The depth of the
"nail" middle can reach up to 100 km. A preferable direction (upwards or
downwards) of a "nail" forming in time is absent. Earthquake hypocentres
fill the "nail" body with equal probabilities on any depth in the process
of its forming.
The direct correlation of "nails" with strong earthquakes with
magnitudes Mb (JMA) >5.0 and with recent active volcanoes
doesn't exist. "Nails" compact, their almost vertical position in the range
of depth from 0 to 100 km and their short-time forming is led to the
conclusion of possible significance of fluids in this process. Processes
of serpentinite dehydratation and releasing of free water during partial
melting of wet amphibolite in the upper part of subduction zone are fluid
contributors. The existence of "nails" testifies the strong anisotropy of
the crust and upper mantle above the subducting plate.
URL:
http://zeus.wdcb.ru/wdcb/sep/traverses/Japan_Geotraverse/paper2.html
Last revision June 15, 2002