The 11 March 2011 magnitude 9.0 Tohoku, Japan earthquake, with its ensuing tsunami, surprised many in the research and practicing professions. An earthquake of this size was not anticipated; the Japan Trench subduction zone had been assumed capable of a magnitude 8.0 earthquake but not much greater. Early reports indicate the constructed environment survived the ground shaking reasonably well given the magnitude of the event. However, the tsunami overpowered coastal defenses and caused wide-spread devastation along Japan's northeast coast. This event is an important learning opportunity for U.S. researchers due to (1) the many similarities between this event and a possible Cascadia subduction zone earthquake and tsunami that could affect western U.S. coastal communities and (2) the paucity of knowledge currently available on the effects of a catastrophic disaster in a developed country with many engineered structures designed or retrofitted for earthquake loads. The U.S. and Japan are both highly industrialized and advanced economies with many commonalities in their built infrastructure. This Rapid Response Research (RAPID) award builds on the Earthquake Engineering Research Institute's (EERI) long-term relationships with Japanese researchers and practicing engineers to organize the rapid collection of perishable data and early field reconnaissance from this 2011 event as a fully collaborative effort. Researchers supported on this award will team directly with respective Japanese colleagues to undertake field investigations followed by jointly authored reports. The primary collaborating organizations are the Architectural Institute of Japan, the Disaster Prevention Research Institute at Kyoto University, and the Japan Association for Earthquake Engineering. Three research themes have been identified for the rapid collection of perishable data: transportation systems, particularly bridges; engineered buildings, including the large inventory of retrofitted structures and use of modern technologies such as base isolation; and government and community response, in the areas of emergency response, social capital, institutional frameworks, and rebuilding, for a disaster of this extraordinary scale and complexity.
The data from this reconnaissance will be used to advance knowledge in seismic bridge retrofit and design requirements; seismic performance of structures with protective systems and concrete and steel buildings; and resilience, response, and recovery for a catastrophic event. Findings from the reconnaissance investigations will be shared widely with the broader research and practicing earthquake engineering community through EERI's clearinghouse web site, short research summaries posted on the clearinghouse and in inserts to the EERI monthly newsletter, and a web cast.
EERI sent several reconnaissance teams to Japan with funding support from this RAPID grant. Three primary areas were investigated--damage to bridges, social science, community and government response, and damage to buildings. A joint EERI/FHWA/GEER bridge reconnaissance team visited the affected area from June 2 to June 6, 2011. An 11-member social science team consisting of academics as well as practicing emergency managers and urban planners, and staff of an international non-governmental organization was in the field from June 19-26, 2011, roughly 100 days after the earthquake. Hosted by Japanese counterparts with the Institute for Social Safety Science (ISSS), the team visited 11 communities affected by the tsunami in Iwate and Miyagi prefectures, ranging from small towns to metropolitan Sendai. The EERI reconnaissance team deployed to evaluate structure damages was split into three groups: reinforced concrete buildings, structural steel buildings, and buildings with protective systems. The paragraphs below summarize observations from each of these teams. Bridges About 200 highway bridges and numerous rail bridges were damaged during the March 11th earthquake by effects ranging from span unseating, ruptured bearings, and column shear failures, to foundation scour and approach fill settlements. The causes can be broadly classified in two categories: ground shaking, including ground failure (liquefaction); and tsunami inundation. The tsunami was responsible for the damages in about one-half of the bridges. The reconnaissance team investigated 11 bridges, of which two had extensive bearing failures, two had column failures, two had combined bearing and column failures, and four suffered tsunami-related damage (unseated spans, scour, loss of approach fill). The performance of five of the bridges is summarized in the report available here: www.eqclearinghouse.org/2011-03-11-sendai/files/2011/03/East-Japan-Bridge-Performance-web.pdf. Social Impacts The scale and severity of losses—human, economic, debris generated--were extraordinary, creating unprecedented challenges for emergency management, sheltering, housing, and recovery planning. Estimates indicate 22,626 persons were killed or missing nationwide (of which 15,534 are confirmed deaths), 107,000 buildings collapsed, and another 111,000 partially collapsed. Communities had high levels of tsunami awareness, pre-disaster mitigation (including structural works) and preparedness; however, they had assumed and planned for a smaller tsunami, in part because of expectations set by seismologists regarding the maximum size event possible on their section of the subduction zone. The size of the actual event overwhelmed communities’ pre-disaster risk reduction efforts. In many communities the tsunami killed community leaders and the destroyed government buildings, emergency centers, designated emergency shelters, hospitals, and other emergency facilities and resources; therefore, it was extremely difficult for local jurisdictions to respond quickly and effectively. The simultaneous impacts of earthquake, tsunami, and nuclear power plant crises greatly impaired the capacity of governments to respond, and the multiple disasters now challenge their efforts to facilitate recovery. Detailed observations from the social science team are available in this report online: www.eqclearinghouse.org/2011-03-11-sendai/files/2011/03/Japan-SocSci-Rpt-hirez-rev.pdf Buildings Three separate teams visited Japan to document building damage--looking at reinforced concrete, steel and buildings with protective systems. The final report discussing all this damage is available here: www.eqclearinghouse.org/2011-03-11-sendai/files/2011/03/Japan-eq-report-Buildings-medrez.pdf. Damage to RC buildings was relatively light in the most affected prefectures, with only a small fraction of them heavily damaged or collapsed. In general, damage was concentrated in pre-1970 buildings, buildings of less than ten stories, and in unusual buildings (long-span, flexible diaphragm). In some cases, damage was focused in pockets, presumably because of soft soil conditions and higher shaking intensities. Significant damage, typically diagonal cracking, was observed in reinforced concrete partition walls that were used as nonstructural walls. Mid-rise multistory buildings did not show evidence of damage due to higher modes of vibration, although damage was concentrated at vertical structural discontinuities. Structural damage was concentrated in steel structures designed according to older Japanese seismic provisions. Typical failure modes included 1) net section fracture of braces; 2) gusset plate fractures due to low cycle fatigue, a consequence of the long-duration ground motions; and 3) foundation uplift in braced frames as well as panel zone yielding in steel moment-resisting frames. Among the thousands of buildings shaken by the earthquake in eastern Japan were many buildings that incorporate special protective systems, for example, seismic isolation or supplemental damping systems. It is probably not an exaggeration to say that more buildings with protective systems were affected by the Tohoku earthquake than had been in all previous global earthquakes combined. Since many of these buildings were instrumented, the earthquake created an unprecedented body of performance data for the structures. In Japan, protective systems for buildings (seismic isolation, supplemental damping, and hybrid systems) are much more widely used than in the United States. There are fewer than 100 seismically isolated buildings in the United States, but in Japan there are more than 2,600 commercial buildings, and more than 3,800 single-family homes, with seismic isolation systems, according to the Japan Society for Seismic Isolation.
