Messages from Departments and Centers of NILIM

Improvement of ability of coastal regions towithstand large-scale tsunami
SUZUKI Takeshi (Dr. Eng.),DirectorCoastal, Marine and Disaster Prevention Department(Key words) Large-scale tsunami, marine radar, tsunami evacuation

1. Introduction
The Nankai Trough Giant Earthquake Model
Research Committee established in the Cabinet Officehas defined the maximum class tsunami that could
possibly occur as a tsunami with maximum height of34m inundating a maximum of 100,000 hectares ofland. The Central Disaster Prevention Council
published Nankai Trough Giant Earthquake
Countermeasures (Final Report) in May 2013, inwhich, concerning its basic views concerning tsunami
it states, “The goal of tsunami countermeasures is to‘protect human life’ from tsunamis. And premised onbuilding and maintaining coastal preservation facilities
etc., focusing on the evacuation of residents byincluding establishing information transmission
systems, evacuation sites, evacuation facilities, andevacuation routes, with their most important goal
being ensuring that every resident voluntarily,
promptly, and correctly evacuates. This requires thatcomprehensive measures including disaster prevention
education, evacuation training, and support for persons
requiring assistance during disasters be promoted”.
The legal framework concerning measures forprotection from large-scale earthquakes and tsunami
was established with the proclamation in November
2013 of the Act For Special Measures Against a
Capital Inland Earthquake (Capital Inland Earthquake
Measures Act) and Act to Partially Revise the Act on
Special Measures concerning Advancement ofCountermeasures against Disasters of Tonankai andNankai Earthquakes (Tonankai and Nankai
Earthquake Measures Act), followed in December
with the proclamation of the Basic Law to Strengthen
the National Land to Contribute to Prevent or Mitigate
Disasters to Realize Strong and Flexible Life for thePeople (Strengthening the National Land Act).
In the future, earthquake and tsunami
countermeasures will be taken in conformity with theCapital Inland Earthquake Measures Act, Tonankai
and Nankai Earthquake Measures Act, andStrengthening the National Land Act. So to prepare
for tsunami, it is considered important to ensure that
evacuation be performed and that it be effective insaving human lives by ensuring a stipulated level ofprotection based on facilities that prevent theoccurrence of damage. To technologically support
these, the Coastal, Marine and Disaster Prevention
Department is making efforts to develop [1] tsunami
measurement technologies based on marine radar, and[2] tsunami evacuation simulation technologies.
2. Measuring tsunami with marine radar
The NILIM successfully used marine radar toclarify the flow velocity field of the tsunami triggeredby the Great East Japan Earthquake (2011). This
verified tsunami detection using marine radar, which
had been theoretically and numerically studied bymany researchers since the 1970s. The NILIManalyzed the data from marine radar installed in theMinato District of Wakayama City, areally clarifying
the height, speed of advance etc. of the tsunami, anddetermining that tsunami waves 1 to 3 were travelingwaves, and that it is highly likely that later waves werecaused by secondary undulations in the channels.
If it were possible use marine radar to stably measureapproaching tsunami or secondary undulations in realtime, this ability would be extremely useful in preparing
tsunami countermeasures. For example, if tsunami
traveling offshore could be measured, it would bepossible to use the results to prevent over orunder-estimation of Meteorological Agency predictions
or to support residents’ evacuation. In coastal seas(channels or enclosed inner bays), water level
fluctuations caused by secondary undulations continued
for several days after the earthquake. In the Kii Channel,
there are places where the maximum water level wasmeasured the next day on March 12. In this way, along
the coast, monitoring secondary undulation is useful for
judging the correct time to cancel alerts or start work toreopen channels. The fact that the earthquake ortsunami caused the discharge of heavy oil or chemicals
from shoreline industrial zones into coastal waters isalso considered. To clarify these dispersions, it isimportant to measure wind-blown currents, density
currents, or tidal currents, which fluctuate on timescales ranging from several hours to several days, rather
than tsunami or secondary undulations. This means that
it is necessary to simultaneously measure short-cycle
tsunami or secondary undulations and long-cycle flows.

3. Evacuation simulation
In ports and fishing harbors, outside the seawall
there are sections used for loading and unloading or
boarding or getting off ships, for parking vehicles
visiting the port, disposing or storing cargoes or fish
products, and sections where shoreline businessoffices stand. These sections are submerged even bytsunami that would not be described as huge, so it isimportant to plan them carefully considering
evacuation from tsunami and to closely follow thisplan.
In December 2004, a giant magnitude 9.1
earthquake struck offshore west of the northern part of
the Island of Sumatra in Indonesia, causing large-scaletsunami that resulted in about 300,000 fatalities or
missing in the countries surrounding the Indian Ocean.
In August 2005, large-scale Hurricane Katrina struck
the southeastern United States. It breached the dykes
in the City of New Orleans, submerging 80% of thecity. More than 1,400 people died in the center of New
Orleans and more than 1 million were forced toevacuate, making it one of the most destructive natural
disasters in American history.
In response to such tragic events outside of Japan,
the NILIM has developed tsunami evacuation
simulation technology. Thanks to later research, in2011, it became possible to perform a specified levelof tsunami evacuation simulations. An investigation of
the reproducibility of tsunami evacuation simulations
developed to obtain actual tsunami evacuation data
based on the tsunami caused by the Great East Japan
Earthquake has confirmed that it they can perform
highly realistic reproductions.
Tsunami evacuation must be strengthened toprepare for the feared Tonankai and Nankai
earthquake tsunamis. In order to ensure more reliabletsunami evacuations, it is necessary to enact effective
tsunami evacuation plans, to execute them, andincrease the effectiveness of evacuations by providing
regular training or by constructing facilities. Tsunami
evacuation simulations are tools of great use when
conducting studies or performing verifications to enact
effective tsunami evacuation plans, or plans forevacuation training or evacuation facilities. At thistime, we are making improvements to more
realistically reproduce evacuation activities in port andharbor districts.
4. Responding to mega-risk type coastal disasters
In response to the Indian Ocean tsunami ofDecember 2004 and to the Hurricane Katrina disasterof August 2005, the NILIM conducted “research onevaluation of countermeasures with diverse effects
taken to deal with low-frequency mega-risk type
coastal disasters”, and completed the manuscript of a
project research report immediately before the Great

East Japan Earthquake of March 2011.
When a tsunami with extremely low probability ofoccurring actually does occur, it inflicts catastrophic
damage in regions it strikes, endangering the lives andeconomies of the people of the region. Concepts of
response were organized assuming that such damage
is a “low-frequency mega-risk type coastal disaster”.
Firstly, regarding a tsunami that causes catastrophic
damage even though its occurrence frequency is
extremely low, it is not the case that countermeasures
for it are not studied only because its occurrence
frequency is extremely low. Secondly, excessive
investment is not made in order that it be impossible toaccept later that it was investment matched to needs,
just because it was done to prepare for a giant tsunami.
Considering the result of combining these two
administrative policies to be a Japanese version of a
“No regret policy”, it was the foundation of studying
countermeasures in preparation for giant tsunamis. Inorder to realize preparations for giant tsunami,
considering the various problems which Japan faces,
application to policy development with a high degreeof freedom and double-track organization use withpriority on workability is probably more necessary
than ever.
5. Conclusions
Fears of the occurrence of a giant tsunami following
the Nankai Trough Earthquake and people’s sharedmemories of the tsunami triggered by the Great East
Japan Earthquake of 2011 have increased public
interest in strengthening the ability of coastal regions
to withstand giant tsunamis. The tsunami which would
be caused by the predicted Nankai Earthquake would
be far higher than any tsunami considered up till thepresent time. How to protect people’s lives andproperty and regional economies and industries fromthis tsunami, and how to overcome the time against
time scale said to be once every thousand years, arequestions which are not easily answered. Concrete
initiatives to deal with such problems from a numberof perspectives are beginning. It is difficult to takeinitiatives predicting the answer from the beginning,
but we wish to exercise our imaginative powers andapply our capabilities to proceed one step at a time toresolve the problems.