Reconnaissance in Chiba after “Reconnaissance in Chiba after “The 2011 off the Pacific coast of Tohoku Earthquake”The 2011 off the Pacific coast of Tohoku Earthquake”Mohsin U. Qureshi and Ikuo Towhata Mohsin U. Qureshi and Ikuo Towhata

Department of Civil Engineering, The University of Tokyo, Tokyo, Japan. Department of Civil Engineering, The University of Tokyo, Tokyo, Japan.

1. Introduction1. IntroductionA reconnaissance was made in Chiba (prefecture

lies next to Tokyo in NE) after a massive

earthquake of magnitude 9.0 on 11 March 2011,

14:46 JST, off the Pacific coast of the northeastern

part of the Japanese Archipelago which also raised

a devastating tsunami. Epicenter is located at

38.322°N, 142.369°E, which is 373km NE of

Tokyo. This magnitude places the earthquake as the

fourth largest in the world since 1900 and the

largest in Japan since modern instrumental

recordings began 130 years ago.

2. Tsunami2. Tsunami

5. Concluding remarks5. Concluding remarks

CONTACT: Mohsin Usman Qureshi (Ph. D. Student)Geotechnical Engineering Laboratory, Department of Civil Engineering, The University of Tokyo7-3-1, Hongo, Bunkyo-ku, 113-8656, Tokyo, JAPAN , Email: qureshi@geot.t.u-tokyo.ac.jp

4. Ground displacement4. Ground displacement

6. References6. References

Tsunami warning

followed the

earthquake whose

height exceed 10m

in northeastern

coasts of Japan.

Chiba was also

highly affected by

the tsunami.

As a consequence of liquefaction, marks of sand

boils, subsidence, uplifting of manholes and ground

cracks were observed. Infact the shaking was not

too strong but its frequency was too high.

Widespread liquefaction in some areas can be

inferred to; 1) located on reclaimed land, 2)

historically rivers were flowing through that area,

3) shallow ground water table. Pictures shown here

were taken on 13th and 14th of March, 2011

A huge disaster left with directions to improve our

efforts in tackling with natural disaster. Survey was

conducted with objectives to collect information

about the type of damage with respect to the

location of area. The authors focused on the

following points;

• Tsunami devastation in coastal areas

• Widespread liquefaction on reclaimed land

• Embankment subsidence along the river

“A Bridge over another Bridge”

Tsunami warning

CHIBA

M9.0

Issued on 11 March 2011

Coastal protection remained safe as compared to roads

Water level

Coastal protections are designed to resist wave action

3. Liquefaction3. Liquefaction

Location map of Chiba

TOKYO

Tokyo Disneyland

M9.0

CHIBA

NARITA AIRPORT

Liquefaction Embankment subsidence Tsunami Damage

0km 105

“Devastation of coastal town”

Force of Tsunami is higher when it flows back to the sea

The “Otori” performed well like the piers of bridge

Scenes at harbor and beach

Ships floated over the docks Partially submerged ship in shallow waters near the beach

April 3-8, 2011 Vienna, AustriaApril 3-8, 2011 Vienna, Austria 東京大学東京大学

• Japan meteorological agency http://www.jma.go.jp/jma/indexe.html• April Issue of ISSMGE Bulletin 2011http://www.issmge.org/web/page.aspx?refid=430

After such an extreme experience of disaster, future research of Geotechnical Engineering has been provoked, few remarks are as follow, however many to come;

• Revision in Ground improvement techniques as a countermeasure against liquefaction.

• Extreme scenario of tsunami should be envisioned for urbanization along the coast.

Sand boils

Thickness at the origin: 15-20cm

Traces of seashell in boiled sand

Unforeseen uplifting of man holes near Disneyland

2m

1m

Few signs of liquefaction near Narita Airport area

0.5m

Sand boils

An interesting example of continuous horizontal

ground displacement was observed on the levees of

Tone River. The beams supporting the side walls of

a drain running parallel to the levee were failed due

to the subsidence of levee as illustrated below. The

hydraulic structures along the river showed no

damage.

Ground Displacement along southern levee of Tone River

1m

Continuous