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Abstract |
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Many large earthquakes have been recently occurring in Japan and worldwide. The risk of Tokai earthquake
has also been increasing day by day. Earthquakes cause huge loss of lives as well as properties and result in
tremendous social and economical damage.If earthquake prediction can be done,it will result in not only saving lives
but also minimizing the damaging effects of earthquakes.
In this study,an interpolation technique of finite element method proposed by Aydan［Aydan,2000;Aydan,2003］
is first outlined and it is used to compute the strain rate and consequently stress rate in the tangential plane to the
surface of the earth’s crust from crustal deformation measurements by Global Positioning System (GPS).The stress
rates derived from the GPS deformation rates for Turkey indicated that they can be effectively used to locate the
areas with high seismic risk.
The method is then applied to the daily GPS measurements in the northern part of Miyagi prefecture during the
period between 1998and 2003.The computed variations of various components of strain and stress clearly indicated
that remarkable changes started after the beginning of 2003before the M7.0Kinkazan earthquake that occurred on
May 26, 2003and M6.2Miyagi-ken Hokubu earthquake on July 26, 2003. Changes occurred within 3months before
the M6.2earthquake.The computed strain-stress variations clearly indicated that they tend to increase exponentially
before large events.This type behaviour resembles to the tertiary stage in creep tests of geomaterials.They may be
useful for near future earthquake prediction.However,they can not be used for very near future predictions,say,in
the order of several hours to days unless their sensitivity of measurements is substantially improved.
The method is also used to compute the strain rate and consequently stress rate in Tokai and Kanto regions of
Japan using GPS observation points operated by JGSI between 1997and 2004.The computations indicated that there
are high stress concentrations in Sagami Bay and at the northern part of Tokyo Bay.The stress and strain rates for
the area in the close vicinity of the epicentres of anticipated Tokai are compared with seismic activity, and their
implications are discussed.The stress variations since 1997in Suruga Bay,where M8Tokai earthquake is expected,
are directly correlated with seismicity. |
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