Tsunami Evacuation: Lessons from the Great East Japan Earthquake and Tsunami of March 11th 2011

The Great East Japan moment magnitude (Mw) 9.0 earthquake occurred at 14:46 (Japanese
Standard Time) on March 11th 2011. Significant seabed displacement generated the
subsequent tsunami, which caused significant damage in Iwate, Miyagi, Fukushima and
Ibaraki Prefectures. As a result of this event over 19,000 people are dead or missing, with
over 295,000 collapsed buildings along 600 km of affected coastline.
Reconnaissance-level analysis of evacuation preparedness and actions related to the
tsunami has been carried out using semi-structured interviews with local disaster prevention
officials and emergency services officials. Interviews were carried out in Taro Town,
Kamaishi City, Ofunato City (Iwate Prefecture) and Kesennuma City, Minami-Sanriku Town,
Ishinomaki City and Natori City (Miyagi Prefecture). The interviews covered tsunami
awareness, observations and response to natural and informal warnings; style and derivation
of evacuation maps; official warning timing and dynamics; evacuation timing, mechanisms
and issues; and vertical evacuation buildings – availability, designation, public awareness,
utilisation, relationship to maps, and post-event review. The report also presents examples of
hazard and evacuation maps and signs employed in the Tohoku region.
Experiences in Tohoku during this event are relevant to tsunami mitigation activities in the
State of Washington and in New Zealand, which co-funded this research. These areas have
local earthquake and tsunami risk posed by the Cascadia Subduction Zone and the offshore
Hikurangi subduction margin, respectively. This report provides recommendations for further
development of tsunami mitigation activities in these areas, based on findings from the
interviews.
Overall there was a 96% survival rate of those living in the inundated area of the
municipalities visited. This can be attributed to mostly effective education and evacuation
procedures. Schools education, hazard maps and exercises appear to be the most common
forms of education. Community involvement in planning of evacuation maps, routes and
buildings is common, with many places conducting regular community-level exercises.
Hazard and evacuation maps lacked consistency and both maps and safe locations were
generally designed for a tsunami height that under-represented the worst case scenario.
The natural warning of long ground shaking (reported as more than two minutes, and often
more than three) was widely agreed as enough by itself to have triggered evacuation. Sea
walls reduced effective observation of the natural warning of unusual ocean behaviour in
many places, and fostered a false sense of security in some locations.
Although an early warning system is often seen publicly as key infrastructure in enhancing
tsunami resilience, the expectation of official warnings (and their content) may have slowed
the time taken for people to initiate evacuation in Tohoku, compared to if there had been total
reliance on natural warnings. Exposure to previous false ‘major tsunami’ warnings apparently
led to complacency in this event, despite this earthquake feeling much larger than anything
previously experienced. The philosophy of tsunami tendenko was shown to be a positive
education tool which promoted immediate self-evacuation and save many lives.
Peoples’ movements during and after evacuation reveal that many people died unnecessarily
due to delayed evacuation or non-evacuation as a result of social or parental responsibility,
lack of education or scepticism of warnings. Widespread use of motor vehicles caused traffic congestion in some areas, when walking, running or cycling would have been much more
effective and saved lives.
Many people returned to the evacuation zone too early in some places because they had not
seen the wave arrive at the expected time given in official warnings, or because they
expected no more waves to arrive. It is critical that people have the awareness that the first
wave may come later than estimated by rapid scientific analysis, and the largest wave may
not be the first.
The evacuation strategy in place at March 11th 2011 was appropriate in that it sent people to
safe locations, used maps and community involvement and was regularly exercised in many
places. Some evacuation centres were not located far enough inland or on high enough
ground because they were not designated using the worst-case tsunami inundation.
There was extensive effective use of both designated and informal vertical evacuation
buildings. The most important considerations for effective use are sufficient height (in relation
to expected inundation depth), reinforced concrete construction, community engagement,
owner agreement, signage, 24-hour access and evacuee welfare. More than one building
owner considered use of their building in evacuation as corporate social responsibility. To
enhance evacuee safety it is prudent to minimise the opportunities for spilled accelerants
such as oil, and debris such as logs in tsunami-prone locations.