Geo-environmental issues induced by the 2011 off the Pacific Coast of Tohoku Earthquake and tsunami

The 2011 off the Pacific Coast of Tohoku Earthquake of March 11, 2011, caused devastating geotechnical and geo-environmental issues mainly in the coastal area of the Tohoku and North-Kanto Regions, Japan. As a result of the earthquake and subsequent tsunami, approximately 23,000 Gg (23,000,000 t) of disaster debris was generated, with more than 12 million m3 of tsunami deposits left in the flooded area. The geotechnical utilization of the soil fraction in the disaster debris and tsunami deposits has presented a huge challenge to geotechnical engineers since (1) the clearance of debris and tsunami deposits is an urgent task which must be completed within a few years and (2) although a large amount of waste-mixed soil can be used in the construction of new embankments and levees to protect the coast from future tsunamis, their geotechnical properties have temporal and spatial variations. This paper summarizes the current status on the generation, clearance, and treatment and utilization of disaster debris and tsunami deposits from geotechnical and geo-environmental viewpoints. In addition, the environmental monitoring data on soil and groundwater quality conducted over the affected area is briefly reviewed. The results of several wide-area monitoring efforts conducted by different organizations indicate that no significant soil or groundwater contamination has occurred. However, the localized contamination near industrial plants where toxic chemicals leaked due to the earthquake and tsunami needs to be carefully taken into consideration during future revival and redevelopment works. Another serious geo-environmental issue is the management of the radioactive contamination of surface soils caused by the accident at the Fukushima First Nuclear Power Plant. This paper summarizes the distributions and expected behaviours of radioactive Caesium in soils and groundwater, and outlines the possible remediation options for dealing with this contamination.