Reconnaissance in Chiba after “The 2011 off the Pacific coast of Tohoku Earthquake” Mohsin U. Qureshi and Ikuo Towhata Department of Civil Engineering, The University of Tokyo, Tokyo, Japan. 1. Introduction A 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 °N, °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. Tsunami 5. Concluding remarks CONTACT: Mohsin Usman Qureshi (Ph. D. Student) Geotechnical Engineering Laboratory, Department of Civil Engineering, The University of Tokyo 7-3-1, Hongo, Bunkyo-ku, , Tokyo, JAPAN, 4. Ground displacement 6. 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 13 th and 14 th 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. Liquefaction Location map of Chiba TOKYO Tokyo Disneyland M9.0 CHIBA NARITA AIRPORT LiquefactionEmbankment subsidenceTsunami Damage 0 km 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, Austria 東京大学 Japan meteorological agency April Issue of ISSMGE Bulletin 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