This collaborative U.S.-Japan Grant for Rapid Response Research (RAPID) award will investigate unanticipated and poorly understood geotechnical phenomena observed following the April 2016 Kumamoto earthquake sequence (KES) in Japan. The Geotechnical Extreme Events Reconnaissance (GEER) organization mobilized a U.S. reconnaissance team to explore the affected area immediately following the KES. The U.S. team in collaboration with Japanese investigators identified significant case histories that warrant further investigation due to their unique, unanticipated, and poorly understood nature, as well as their important potential implications for seismic design and safety in the U.S. and around the world. These case histories include, among other things: an unexplained 10km-long depression zone within the Mount Aso volcano caldera that caused significant damage to structures and transmission lines; a fault rupture through the spillway of a large dam impounding a full reservoir; and surprisingly limited observations of soil liquefaction and its effects for an earthquake of this size and apparent site conditions. This RAPID award supports a detailed study of the underlying causes behind these observations through: (1) the use of state-of-the-art remote sensing techniques to collect perishable surface topology, soil deformation, and structure settlement or tilt information from known liquefaction and major landslide sites; (2) the collection of preliminary geotechnical, seismic, geologic, and topographic information from potential case history sites of interest; and (3) the performance of a comprehensive set of laboratory tests on retrieved samples followed by preliminary simulations to evaluate the soil's resistance to liquefaction and response under cyclic loading. In doing so, this award contributes to the state of knowledge and practice in critical areas of geotechnical earthquake engineering and hence, the resilience of geotechnical structures and infrastructure globally. Collaboration with Japanese researchers through this study will improve the relationship and cooperation between the two countries, and will provide valuable international research experience for the PIs and the graduate students involved in this project.
This grant will advance the science and practice of geotechnical earthquake engineering by enhancing the fundamental understanding of seismic-induced ground deformations and liquefaction triggering. This RAPID project will enable the collection of valuable and perishable information related to landslides, liquefaction triggering and effects, and earthquake-induced ground deformations from the 2016 KES in Japan. There are a number of phenomena observed after the KES that cannot be explained by the existing state of knowledge or current analytical and/or empirical prediction models. These phenomena could have important implications for seismic design in locations with similar geology and geomorphology in the U.S. Information collected from the affected sites followed by laboratory testing and analysis will increase our understanding of the underlying causes of the geotechnical phenomena observed following the KES, which will ultimately impact the state of geotechnical earthquake engineering practice. The engineering community will benefit from learning why soil liquefaction did not occur to the extent that it was predicted in this region. Joint application of 3D digital surface modeling using UAV-based aerial photography and terrestrial LiDAR techniques will advance the science and art of remote sensing in geotechnical engineering and will improve the way surficial evidence of geotechnical earthquake phenomena is collected. Further, preliminary field and laboratory data collected from this RAPID will guide and inspire a larger international collaborative research effort to more thoroughly investigate the observed unique geotechnical phenomena and damage from this series of earthquakes.
