The tsunami triggered by the 11 March 2011 magnitude 9.0 earthquake off Tohoku, Japan, created widespread structural damage in cities along the Japanese coastline. Careful documentation of flow depth and structural response resulting from this tsunami will provide data that can be used to validate tsunami inundation models and corresponding methodologies for calculating structural response due to the inundation. The primary objective of this Rapid Response Research (RAPID) award is to collect time sensitive impact data in Japan from this March 2011 tsunami that will soon be lost, as buildings and infrastructure in the affected areas are repaired or demolished. The investigation team includes researchers and students from the University of Hawaii and Oregon State University. This study will focus on collecting detailed, localized data in several of the most severely damaged areas of the coastline in the Miyagi and Iwate Prefectures, rather than a general survey of all of the inundation areas, which has been undertaken by other local and international reconnaissance teams. Through this award, the reconnaissance team will collect high resolution, ground based LIDAR data. The LIDAR data will be used to generate virtual models that can be queried for measurements such as flow depths, observed maximum run-up, and scour depths at key sites. These will be complemented with manual measurements and analysis of videos and photographs. The LIDAR data will also provide detailed dimensional data for the structures to be studied. The focus in specific areas of study will provide the data needed for validation of the tsunami inundation model. Furthermore, the structural properties of both damaged structures and undamaged structures will be used to determine hydrostatic, hydrodynamic, and impact forces applied during the tsunami inundation. This field reconnaissance will help resolve several key questions in the tsunami design provisions regarding flow velocities and momentum of tsunami bores and/or wave surges over land and scouring, as well as gain information on overarching questions on risk-based design criteria and the ultimate capabilities of structures to resist a maximum credible tsunami. This team will coordinate reconnaissance activities with the UNESCO-led International Tsunami Survey Team.
Such data are important for understanding how to design buildings to resist earthquakes and tsunamis for public safety. Many parts of the United States and other places in the world that face similar hazards will benefit from such discoveries, which will help shape building design codes, which are important for public safety. These new standards, validated by information collected on this project, could also provide data in the near future to assist Japan in the recovery phase of their disaster stricken coastal areas. This project will also enable graduate students to observe sites impacted by tsunamis and learn from this event so that they will be better prepared to lead future generations of engineers in reducing seismic and tsunami risk.
This project provided funds for a team of researchers from University of Hawaii at Manoa and Oregon State University to travel to the Tohoku region of Japan to perform Light Detection and Ranging (LIDAR) surveys of topography and structures damaged by the March 2011 tsunami. LIDAR technology uses laser pulses to accurately model the geometry of a scene, creating a virtual world that can be explored and digitally preserves the site as a 3D model called a point cloud. LIDAR scanners can acquire tens to hundreds of thousands of data points in a second. Data can be acquired at centimeter-level resolution, enabling one to see extreme detail in the point cloud. The team assembled LIDAR scan and engineering data on 26 structures that suffered severe damage during the tsunami. In addition, the team also acquired LIDAR scans of topography in two affected coastal communities. This project demonstrated the value of capturing LIDAR scans of post-disaster conditions so as to preserve data that would be quickly lost during cleanup efforts. The non-intrusive nature of the LIDAR scan enables data collection to proceed without interfering with search, recovery and cleanup activities. The enormous amount of high-precision measurement data collected enables researchers to re-visit the sites virtually, long after the field survey, to determine dimensions and damage conditions that may not have been accessible during the survey. The topographic data have already be used to model tsunami inundation for Onagawa, Japan, showing excellent match with the measured inundation depth and run-up heights for this community. Research is ongoing for inundation models of Rikuzentakata and Sendai. LIDAR scans of a number of damaged structures have been used to validate hydrodynamic loading expressions proposed for tsunami design codes. Figure 1 shows typical exterior and interior LIDAR scans of a reinforced concrete building damaged by a direct strike form a tsunami bore on the coastline South of Sendai Harbor. Figure 2 shows the relative deformation of the concrete wall determined using the LIDAR data. This deformed shape is compared graphically in Figure 3, with a computer analysis of the building considering tsunami bore loading. The good agreement between measured and computed results helps to confirm that the tsunami bore loading expression developed from laboratory experiments can be applied to tsunami design of full-scale structures. LIDAR scans of a three story steel-framed building in Onagawa that was damaged during tsunami drawdown enabled accurate measurement of the relative displacement of each floor (Figure 4). These displacements could then be compared with the results of a computer analysis of the building to determine the approximate blockage caused by cladding or debris accumulation that would have been required to cause the observed damage. Prior to this project, only low resolution topographical data was available for many of the coastal communities along the Tohoku coastline. This affected the accuracy of tsunami modeling studies of coastal inundation. Figure 5 shows how a composite of numerous LIDAR scans of Onagawa taken during this study can be used to develop a high-resolution topographical map of the area. The LIDAR scans capture topography, debris and remaining buildings. This model is cleared of buildings and debris to produce the topography shown in the right image. This high-resolution topography is then available for tsunami modeling inundation studies. The LIDAR scans of topography and structural damage after the Tohoku tsunami have generated a vast data set that is available for research on coastal inundation modeling and structural response evaluation. Because of the enormous size of the dataset, only a limited number of buildings have been analyzed thus far. This valuable data can continue to be queried and explored as a virtual time capsule by a wide variety of scientists and engineers, enabling new discoveries related to earthquakes and tsunamis.
