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wavelike movement observed on the surface of
the tidal fl ats. Liquefaction occurred just after the
earthquake before tsunami. Liquefaction is a
phenomenon in which the strength and stiffness
of a soil are reduced by earthquake shaking.
The water spurted from the cracks, which looked
like a jet of water. I observed many fi ssures moving and a jet of water from liquefaction coming to
the surface around the Yatsu tidal fl ats (Okoshi
2012a , b , 2013 ; Okoshi et al. 2014 ) (Fig. 3 ).
Twenty minutes after the earthquake, clear
water changed to muddy water. Sanbanze tidal
fl ats are connected with Yatsu tidal fl ats through
two channels.
Fig. 2 Imaginary picture of the Jogan-Sanriku Tsunami in 869 illustrated by Kaiki Okoshi
Fig. 3 Yatsu tidal fl at in Tokyo Bay. ( a and b ) 14:43, 11th of March 2011, 3 min before the earthquake. The water was clear
to the bottom at low tide. ( c and d ) 22 min after the earthquake. Clear water changed to muddy water (From Okoshi 2012b )
Impact of Repeating Massive Earthquakes on Intertidal Mollusk Community in Japan