The 11 March 2011 magnitude 9.0 earthquake off Tohoku in Japan triggered a transpacific tsunami that had basin-wide impact of varying severity. Both the earthquake and tsunami magnitudes are unprecedented in Japan's long historical records of over 1,000 years. This award supports a reconnaissance survey team to investigate the effects of this tsunami along coastlines in Japan, the Pacific Islands, and the western United States. The team will conduct the reconnaissance with Japanese researchers from Tohoku University in Sendai, the University of Tokyo, and the Port and Airport Research Institute, and coordinate with the UNESCO-organized International Tsunami Survey Team. The 2011 event in Japan presents a unique research opportunity since there are now three historic tsunamis with significant impact on the same Sanriku coastline, which may allow differentiating between tectonic and potentially superimposed landslide tsunami sources. The tsunami sources and magnitudes of historic and geologic events inferred from tsunami deposits such as the 869 event need to be revisited. The tsunami survey team supported on this award will collect high quality inundation measurements that will allow the research community to infer the predictive capability of different tsunami models. Tsunami eyewitness videos will be calibrated in situ to extract time series of flow depth and velocity. The obtained field data will be analyzed closely with the existing laboratory data collected by past experimental projects. The primary project deliverable will be a comprehensive multi-scale, geo-referenced database of tsunami damage and flood zone characteristics combined with numerical model results. Education and outreach lectures and briefings will be given at villages surveyed and to eyewitnesses interviewed. The reconnaissance team will coordinate with the UNESCO-led International Tsunami Survey Team.
Tsunami reconnaissance of an estimated 1,000-year event will transform tsunami modeling and mitigation with broad implications beyond engineering. Post-disaster reconnaissance following major natural events has yielded significant new insights into both the characteristics of the events as well as the behavior of landforms and performance of infrastructure subjected to these catastrophic events. Through such research into the Tohoku tsunami, researchers may be able to understand the causes of the significant death toll that resulted from this disaster. The measurements and observations will also provide important information that will be used to influence both evacuation and building procedures for the prevention of loss of life and property damage in Japan and in other areas of the world susceptible to tsunamis, such as the impact of a tsunami generated on the Cascadia subduction zone on communities along the U.S. Pacific Northwest and northern California coastlines.
On March 11, 2011, a magnitude Mw 9.0 earthquake occurred off the coast of Japan’s Tohoku region. This represents the fourth largest earthquake instrumentally recorded. The earthquake and tsunami caused substantial damage and loss of life along Japan’s coastline followed by multiple melt-downs at the Fukushima nuclear power plant. The bulk of the 19,447 fatalities were concentrated in the coastal regions of Myagi, Iwate and Fukushima prefectures. The majority at 92.5% of the fatalities are attributed to the tsunami. The 2011 Tohoku tsunami represents Japan’s deadliest tsunami since the 1896 Meiji-Sanriku tsunami earthquake. For the 2011 Tohoku tsunami we measured a maximum tsunami runup exceeding 38 m along the Sanriku coast in a narrow valley at Aneyoshi, Iwate Prefecture (TETJSG, 2011; Mori et al., 2011; Shimozono et al., 2012). Forecasts by the Earthquake Research Committee (ERC) for the Tohoku region were based on historical earthquakes. Tsunami mitigation and evacuation plans, coastal structures and vertical evacuation sites were designed based on these too conservative forecasts. Several tsunami reconnaissance trips were conducted in Japan starting early April 2011. The mid-afternoon tsunami arrival combined with survivors equipped with cameras on top of vertical evacuation buildings provided spontaneous spatially and temporally resolved inundation recordings. This report focuses on the surveys at 9 tsunami eyewitness video recording locations along Japan’s Sanriku coast and the subsequent video image calibration, processing, tsunami hydrograph and flow velocity analysis. Intellectual Merit: Selected tsunami video recording sites were explored, eyewitnesses interviewed and some ground control points recorded during the initial tsunami reconnaissance in April, 2011. A follow-up survey in June, 2011 focused on terrestrial laser scanning (TLS) at locations with high quality eyewitness videos. We acquired precise topographic data using TLS at the video sites producing a 3-dimensional "point cloud" dataset. A camera mounted on the Riegl VZ-400 scanner yields photorealistic 3D images. Integrated GPS measurements allow accurate geo-referencing. The original video recordings were recovered from eyewitnesses and the Japanese Coast Guard (JCG). The analysis of the tsunami videos follows an adapted four step procedure originally developed for the analysis of 2004 Indian Ocean tsunami videos at Banda Aceh, Indonesia (Fritz et al., 2006). The first step requires the calibration of the sector of view present in the eyewitness video recording based on ground control points measured in the LiDAR data. In a second step the video image motion induced by the panning of the video camera was determined from subsequent images by particle image velocimetry (PIV) applied to fixed objects. The third step involves the transformation of the raw tsunami video images from image coordinates to world coordinates with a direct linear transformation (DLT) procedure. Finally, the instantaneous tsunami surface current and flooding velocity vector maps are determined by applying the digital PIV analysis method to the rectified tsunami video images with floating debris clusters. Tsunami currents up to 11 m/s per second were measured in Kesennuma Bay making navigation impossible (Fritz et al., 2012). Tsunami hydrographs are derived from the videos based on water surface elevations at surface piercing objects identified in the acquired topographic TLS data. Further we analyzed the complex effects of coastal structures on inundation, outflow hydrographs and flow velocities. Broader Impact: The field data set has already become a benchmark for field work and validation of the combination of earthquake, tsunami and runup models. The complete database has become (part of) the official data base for the event (Government of Japan, UNESCO, and NGDC). Post tsunami field survey experience provided to local and international graduate students and senior scientists. More than half the participants trained were local Japanese graduate- and undergrad-students. This represents true capacity building in one of the world's most tsunami prone countries. Using the opportunity of working with field data, a few of the participants were trained in tsunami numerical tsunami simulations using MOST. The survey team did numerous outreach presentations to tsunami survivors, coastal communities, government agencies, universities during the Japan surveys, the Japan Geoscience Union Meeting and during multiple visiting semesters at the University of Tokyo by two PIs. Several news articles in the printed and online media including Japan's main newspapers. Prime time live interviews and documentaries on international and national radio and tv broadcasts including CNN. We have raised the tsunami awareness and we educated communities at risk about tsunamis and tsunami hazard mitigation. This event provides invaluable lessons learned, which will specifically benefit any forthcoming event triggered by the rupture of the Cascadia subduction zone, anticipating similar effects to the coastal communities in Pacific Northwest and Northern California. Main Reference: Fritz, H.M., Phillips, D.A., Okayasu, A., Shimozono, T., Liu, H., Mohammed, F., Skanavis, V., Synolakis, C.E., Takahashi, T. (2012). 2011 Japan tsunami current velocity measurements from survivor videos at Kesennuma Bay using LiDAR, Geophys. Res. Lett., 39, L00G23, doi:10.1029/2011GL050686.
