CEE Seminar: The Role of Urban Development Patterns in Mitigating the Effects of Tsunami Run-Up
Chief Executive Officer
ImageCat, Inc.
Long Beach, CA
Abstract:
This NSF-sponsored RAPID grant study sought to understand the relationship between urban development patterns and the extent of physical damage caused by widespread tsunami run-up. The March 11, 2011, Tohoku, Japan earthquake caused significant damage all along the northeastern coast of Japan, with almost all of it resulting from tsunami waves that reached heights in excess of 20 meters. In order to understand how the built environment can affect the performance of communities in a tsunami, we studied 12 communities in the Miyagi/Chiba/Ibaraki Prefectures – areas ranging from minor to moderate damage to complete devastation. Our central research question was: Can the urban topology of a community mitigate the effects of a tsunami by isolating the more damaging surge effects to a few well-designed and well-placed buildings, thus limiting damage to “protected” buildings to just rising water effects? Previous research on the 2004 Indian Ocean earthquake and tsunami (Chang et al., 2006) clearly showed that the presence of healthy natural ecosystems can indeed impede the progress of strong wave fronts, thus limiting damage to rural coastal communities. We designed our investigation of the built environment to explore if there were similar benefits to urban communities by examining data from the Tohoku earthquake.
Knowing the answer to the question above could have significant ramifications. Reconstruction can incorporate either higher design standards for buildings or specific neighborhood configurations that may serve as a first or second line of defense in future events. Knowing that particular buildings will be safer because of the type of construction and where they are located relative to other buildings may provide important evacuation points for residents who cannot quickly escape from an area (conditions that may be exacerbated because of traffic concerns). And, data and observations from this event will help to inform future vulnerability models especially ones that consider the impact on small and moderate-sized communities. For example, classifying towns or communities by vulnerability grade based on projected tsunami heights and community configurations would be an improvement over current standards, such as those that focus primarily on the performance of individual buildings (FEMA, 2008).
After studying 12 communities in Japan, we discovered several important lessons that should influence our understanding of community resilience to tsunami effects. First, we found out that there is a statistically significant trend between damage ratios (number of buildings destroyed over total number of buildings) and flood depth or inundation height. This trend was not unexpected; significant damage ratios (over 50%) generally occurred at flood depths of 2 to 5 meters or higher.
Another interesting trend is that residential areas that are protected from strong tsunami wavefronts by large industrial and/or commercial buildings are four times less likely to be destroyed by the tsunami. The hypothesis, stated above, is that damage can be mitigated to protected structures by limiting the wave forces to static (i.e., rising water) and buoyancy effects, as opposed to hydrodynamic forces when rushing water is unimpeded. Nine residential areas in four cities affected by the tsunami experienced maximum flow depths between 5m and 10m: five were located in areas deemed to be unprotected; four were located in areas that had large buildings between them and incoming tsunami waves. The percent of destroyed buildings in the unprotected zones ranged from 72% to 97%, with an average of 84%. The percent of destroyed buildings in protected zones ranged from 13% to 32%, with an average of 23%. See Figure 1 below.
Large structures (industrial and commercial) performed much better than residential construction across most flow depths. This was especially true for very high (maximum) flow depths, i.e., greater than 10m. Based on data from 15 zones in 10 cities, the percent of destroyed industrial/commercial buildings roughly doubles every 5 meters between maximum flow depths of 5m and 20m. For residential structures (unprotected), 7 meters appears to be a reliable threshold for catastrophic damage, i.e., 75% or more of the buildings are completely destroyed.
In addition to the findings above, the study also investigated the efficacy of “crowdsourcing” techniques in accurately identifying building damage in tsunami affected zones. The research team conducted several experiments to explore the relationship between user experience and collective accuracy in crowdsourced remote sensing applied to post-disaster building damage assessments. We learned that the reliability of a “completely destroyed” determination was quite high, however, we also learned that a significant omission error is present when the analyst attempts to identify damage at lower damage states, i.e., significant damage but not completely destroyed.
We believe that the outcomes from this study will be useful in supporting the investigation of landuse and building construction practices that will mitigate the effects of moderate to large tsunami events. In California, where a significant tsunami hazard is present, understanding the role of community configurations in either mitigating or exacerbating tsunami effects will help in preparedness planning as well as post-event response activities.
Speaker Bio:
Ronald T. Eguchi is president and CEO of ImageCat, Inc., a risk management company specializing in the development and use of advanced technologies for risk assessment and reduction. Eguchi has over 30 years of experience in risk analysis and risk management studies. He has directed major research and application studies in these areas for government agencies and private industry. He currently serves or has served on several editorial boards including the Natural Hazards Review published by the American Society of Civil Engineers and the Natural Hazards Research and Applications Information Center, University of Colorado; the Journal on Uncertainties in Engineering Mechanics published by Resonance Publications, Inc.; and the Earthquake Engineering Research Institute’s Journal SPECTRA. He is a past member of the National Research Council’s Disaster Roundtable whose mission it is to identify urgent and important issues related to the understanding and mitigation of natural, technological, and other disasters. He is a past member of the Scientific Advisory Committee of the U.S. Geological Survey, a committee that reports to Congress on recommended research directions for the USGS in the area of earthquake hazard reduction. In 1997, he was awarded the ASCE C. Martin Duke Award for his contributions to the area of lifeline earthquake engineering.
Eguchi remains active in the ASCE Technical Council on Lifeline Earthquake Engineering serving on several committees and having chaired the Council’s Executive Committee in 1991. In 1992, Eguchi was asked to chair a panel, established jointly by the Federal Emergency Management Agency and the National Institute of Standards and Technology to develop a plan for assembling and adopting seismic design standards for public and private lifelines in the U.S. This effort has led to the formation of the American Lifeline Alliance, currently managed by the National Institute of Building Sciences. In 2006, he accepted an ATC Award of Excellence on behalf of the ATC-61 project team for work on An Independent Study to Assess Future Savings from Mitigation Activities that showed that a dollar spent on hazard mitigation saves the nation about $4 in future benefits. He was recognized by EERI as the 2008 Distinguished Lecturer where he discussed the topic of “Earthquakes, Hurricanes, and other Disasters: A View from Space.” He was also invited as a keynote speaker to the 14th World Conference on Earthquake Engineering, held in Beijing, China in 2008. Recently, he gave keynote talks at the 10th International Conference on Urban Earthquake Engineering held in Tokyo, Japan (2013) and the 12th Americas Conference on Wind Engineering held in Seattle, WA (2013). In December 2014, he delivered a keynote talk at the 14th Japan Earthquake Engineering Symposium held in Chiba City, Japan. He has authored over 300 publications, many of them dealing with the seismic risk of utility lifeline systems and the use of remote-sensing technologies for disaster response.
