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In most cases, large earthquakes are usually accompanied by aftershocks,
the magnitudes of which are smaller than that of the mainshock. Aftershocks
are believed to occur due to induced stress changes in the peripheral
area that are caused by fault movements of the mainshock. Regions are
prone or non-prone to aftershocks depending on how much the stress changes.
A system will be developed for predicting aftershock activities in the
short term using the source mechanisms, stress drops and induced changes
in stress immediately after an earthquake.
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 Figure showing stress changes in the area
surrounding the fault of the Tottori-ken Seibu Earthquake (2000)
The fault slip of the mainshock causes the earth crust to distort
with the result of induced stress change in surrounding areas, and
consequently separates the areas into those that are prone and those
that are less prone to aftershocks.
The areas shown in orange suffered an increase of stress making the
area prone to aftershocks. The areas shown in blue are the opposite.
Such immediate calculation after a large earthquake may lead to the
estimation of areas prone to large aftershocks.
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National Research Institute
for Earth Science and Disaster Prevention