Environmental Engineering Reference
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450 × 200 km, generated a tsunami that struck Japan from Hokkaido to Kyushu as
well as various locations around the Pacifi c Ocean.
The tsunami fi rst reached the Japanese mainland about 20 min after the
earthquake and ultimately affected a 2,000 km stretch of Japan's Pacifi c coast
(The
2011
Tohoku Earthquake Tsunami Joint Survey Group 2011). The Tohoku
region consists of several prefectures ranging from north to south, Aomori
Prefecture, Iwate Prefecture, Miyagi Prefecture, and Fukushima Prefecture, which
border the Pacifi c Ocean. Sendai is the largest city in the region. The southern part
of Tohoku is relatively fl at, especially the Sendai plain. The coastal geomorphol-
ogy of northern Tohoku features ria coasts, which are steep, narrow bays.
The northeastern part of Pacifi c side of Tohoku is known by the name of Sanriku
region starting from North Miyagi Prefecture to South Aomori Prefecture. As of
August 8 in 2012, offi cial fatalities were 15,867 with an additional 2,903 missing
(National Police Agency of Japan). The major cause of death was the tsunami, and
most fatalities occurred in Tohoku, 58 % in Miyagi Prefecture, 33 % in Iwate
Prefecture and 9 % in Fukushima Prefecture. There were 126,631 totally damaged
and 272,653 partially damaged buildings, along with 116 bridges (National Police
Agency
2014
).
Before this event, the risk of earthquakes and tsunamis off the Tohoku coast
was believed to be high. The Japanese government reported that magnitude 7.5
and 7.7 earthquakes along a 200 km fault offshore of Sendai in southern Sanriku-
Oki were expected to occur with 99 % probability and 70-80 % probability within
30 years, respectively (The Headquarters for Earthquake Research Promotion
2005
). The 1896 Meiji Sanriku earthquake (Mw 8.2-8.5) and tsunami caused
21,915 deaths, the 1933 Showa Sanriku earthquake (Mw 8.1) and tsunami caused
3,064 deaths, and smaller tsunamis have occurred roughly every 10-50 years.
Thus, earthquake and tsunami disaster countermeasures, such as seawalls, gates
and offshore tsunami breakwaters, planted trees as a natural tsunami barrier, verti-
cal evacuation buildings, and periodic evacuation training were implemented and
practiced in these areas. Therefore, we emphasize that Tohoku was an area highly
prepared for tsunamis. Nevertheless, the tsunami disaster countermeasures were
insuffi cient against the 2011 event. Tsunami barriers (onshore and offshore break-
waters, and natural tsunami barriers) were severely damaged, some reinforced
concrete buildings were totally destroyed, and the extent of inundation was under-
estimated in several areas.
This event is important for future tsunami preparation to classify various modern
counter measures against mega-tsunami. Therefore, understanding the effectiveness
of countermeasures and estimation of error of impact assessments are critical. First,
this paper re-analyzed the tsunami inundation heights and run-up heights by the
three different numerical models at Kamaishi bay where offshore breakwater was
installed before the event. The effectiveness of offshore breakwater and error of
numerical model is discussed in comparison with the survey data. The relation
between damage and tax revenue is discussed to understand long-term impact on
the catastrophic event and its protection.
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