Mechanisms for Damage and Failure from the Great East Japan Tsunami - Tohoku, Japan Earthquake and Tsunami of 2011 - page 63

3.11 Subsidence: Regional and Local

Large earthquake-induced displacement of the sea bottom may generate not only
tsunamis but also tectonic deformation (uplift and subsidence) in the impacted coastal
zones and inland regions. Earthquake-related subsidence can lower or submerge
beaches, tidal flats and coastal facilities, and waterfronts both on a regional and a
local scale due to the tectonic shifting of the submerged geological plates and
potential liquefaction of the soft upper soils. The coastal structures team visited
location with subsidence on the order of 0.5 to 1.2 meters in vertical settlement and
up to one meter in horizontal displacement. Values in this range expose coastal areas
and coastal structures to future damage from extreme tides, waves, and tsunami
occurrences. Reports cited subsidence in many locales of 0.5 to 0.8 meters. Figures
76 - 79 shows subsistence areas.

Figure 76. Kojirahama Port —
Waterfront area subsided by 0.5 to 0.8m

Figure 77. Kesennuma Port —
Waterfront area subsided by as much as
1m

Figure 78. Onagawa Port — Subsidence
of port structures and overturned
buildings/structures)

Figure 79. Gamo tidal flats —
Subsidence of entire tidal flats shown in
background