Special Session 24.4 Great East Japan Earthquake
15th World Conference on Earthquake Engineering
Lisbon, Portugal, September 24, 2012

Tsunami and Damage to Coastal Facilitiesof the March 11, 2011, Tohoku, Japan Earthquake
Taro ARIKAWA
Port and Airport Research InstituteDamage of Otsuchi

Taken by residentOtsuchiTsunami profiles acquired by
GPS buoys around Japan(Kawai, et. al. 2011)
Earthquake Highest crest
1m

North-Iwate
0.24m
Central-Iwate(1)(2)(3) (4)(5) (6)(7)0.54mSouth-Iwate

Mean line before earthquake
Mean line after earthquake

North-Miyagi

0.66m
0.95mCentral-Miyagi
0.38m
Fukushima
Shizuoka-Omaezaki
Mie-OwaseSouthwest-Wakayama
Tokushima-Kaiyo
121518March 11

210Time (h)369March 121215

Detailed profiles of the first crest off the Tohoku region coast
Processed in real-time(Kawai, et. al. 2011)

Added later

North-Iwate
Whole wave crest
Local peakCentral-Iwate

Quick rise
Slow rise

1m+6.1m (6.7m before the correction
for ground subsidence)

South-Iwate
Earthquake effect
North-Miyagi

Central-Miyagi-6.0m (-5.1m)
Fukushima
14:40

14:50

15:00
15:10
15:20
Time (h, March 11)

15:30

15:40

The appearance time was earliest at Central‐Iwate and South‐Iwate among totally six sites off
the Tohoku region coast. The top height was 2.6‐6.7 m at these sites and was largest at South‐Iwate

Tsunami source models derived frominversion of observed tsunami waveforms.
(Takagawa and Tomita, 2012)

B’

Colored lines are contours of 1 m uplift in thesemodels
purple: Fujii et al., 2011
red: Central Disaster Prevention Council, 2012
green: Tsushima et al., 2011orange: Saito et al., 2011
blue: Takagawa and Tomita, 2012
Colored squares indicate maximum uplifted pointof these models. The star indicates epicenter ofmain shock. Open circles indicate geodetic
observation points of sea bottom.

BMaximum uplift is located on the east of
epicenter of main shock and near the Japan
Trench in all models except model Ts.

Snapshots of tsunami propagation(Takagawa and Tomita, 2012)plane (upper) and bird’s‐eye view (lower).

Disturibution of trace of tsunami height by the 2011 Tohoku earthquake tsunami
joint survey groupDifference with overflow above the seawalls(wind waves & tsunami)Wind waves:

Tsunami:Offshore wave height 0.5m
Period 4.0s

Offshore wave height 0.5m,Period 20.0s

Type of Tsunami ForceType 1 Overflow

Flooding Velocity isLow.

Type 2 BoreType 3 Breaking

IF theHeight ofTsunami issame, thenbreaking isthemaximum.

Flooding Velocity ishigher than theoverflow. That issupercritical flow.

Very close to the coastline
Flooding Velocity is high with
the Impulsive load.

LargeOverflow（Miyako Port）

Miyako weather TV（by courtesy of NHK）

Bore (Sand beach at Sendai)

By courtesy of NHK

Breaking （Kuji fishery port）

taken by a residenceTypical time histories of tsunami Force
Impulsive Bore Force

Force

Type 3 Breaking(kN)Type 2 BoreType 1 OverflowTimeMaximum Sustainable Force(s)Bore Type Tsunami

Tsunami Height in front of the wall is 2.0m

thickness 60mm

Kamaishi Tsunami Breakwater
Kamaishi Port

HirataSuga

Mouth of Port

Tsunami Breakwaters

Izumi

Topography of Sea Bed at Kamaishi after tsunami
25th , March, 2011
North SideSouth Side

Failure of Breakwater at North PartTOHOKU REGIONAL BUREAU MINISTRY OF LAND , INFRASTRUCTURE AND TRANSPORTOutsideof Port

Inside ofPort

Fromvideo
bypublicpeople
15:18 (1 positive wave, 32 minutes after)
st15:28( negative tsunami started, 42 minutes after)North side of Kamaishi breakwater

Experimental Video under overflow tsunami

22

Experimental Video under overflow tsunami
Plan View

23

24

Failure of Breakwater at North PartTOHOKU REGIONAL BUREAU MINISTRY OF LAND , INFRASTRUCTURE AND TRANSPORT
Outsideof Port

Inside ofPort

Effect of breakwater (Tomita et. al, 2012)

With Breakwater

Water surface elevation (m)Without Breakwater
Arrival time
6 minutes delay(tsunami height of 4 m)with breakwater
without

Tsunami height (m)Tsunami height
13.7 m → 8.0 m

Time after earthquake (min)26

Design policy of physical countermeasures
It is necessary to estimate two levels of tsunamis, and develop measures
to mitigate damage for both of them.
Tsunami Level

Definition

Planning or design

TsunamiPrevention Level（L1）

Tsunamis that occur frequently
and cause extensive damage
even though they are not highTo prevent the protected lowlandfrom being flooded, it plans and itdesigns.
⇒Continued mitigation throughphysical countermeasures

TsunamiReduction Level（L2）The largest class of tsunami,
which occurs at an extremely
low frequency, but which causes
enormous damage when it does

It plans and it designs so that it ismade easily not to destroy and tocollapse, and damage should not
expand though the flood of theprotected lowland is permitted.
That means ‘resilient’ structures⇒Disaster mitigation by evacuation

New Earthquake
Model(Nankai Trough)the Disaster Management Councilof the Cabinet Office, 2012

Resilient city against Tsunami"hardware" (disaster prevention facilities, etc.) and "software" (disaster prevention training,etc.) measures

Image of Coastal Area

Buildings as
Residential tower, hotel and so onSeawall

Breakwater

Office building as Evacuation tower

multiple protective structure

Against Human bodyInundation height is about 50cm, Inundation speed is about 4.0m/s

Lessons from The Great East Japan
Earthquake• The power of the tsunami is greatly different
depending on the place and the condition• The breakwater and seawall cannot preventthe tsunami perfectly, but can help people toevacuate.
• It is important to mitigate the tsunami disasterby using the hardware and software measures.
• Even if the tsunami is very small, people may
be washed away by tsunami.