1 Jul 2017
1 Dec 2017 (Extended to 10 Jan 2018)
15 Jan 2018
16 Apr 2018 (Extended to 15 Jun 2018)
From 16 July 2018
By 17 September 2018
Professor at Department of Advanced Energy, Graduate School of Frontier Sciences, And Department of Aeronautics and Astronautics, School of Engineering, The University of Tokyo
Thu-02 Nov 2018 | 09:45 – 10:15 | Summit 2
"The Roles of Higher-Frequency Waves in "Unexpected" Problems of Earthquakes"
Utilizing the theories of continuum mechanics, etc., the research work in seismology has been trying to establish more rational relations between (earth-)"quakes" (recorded "shaking" or "vibrations") and "waves" that are initiated at seismic sources and propagated underground (and sometimes in the sea and the atmosphere). Like other dynamic fracture (rupture) phenomena in solids, however, an earthquake or rupture of solid Earth mostly occurs at a "concealed" place and even when dynamic rupture can be observed, its high-speed development cannot be followed by normal video recording devices. In addition, the multi-scale complexity of dynamic rupture in rocks and rock-like materials makes the comprehension of the fundamental mechanism of rupture development and related physical events much harder. Hence, in the normal treatment of seismology, the precise mechanical process around rupturing seismic sources is not straightforwardly taken into account and kinematic source parameters are mainly estimated from seismograms. Although valuable findings have been obtained by the traditional methods, there exist not a few earthquake-induced structural failures that cannot be explained via the classical kinematic approach. In this lecture, by handling some instances of "unexpected" earthquake-related failures, ranging from the collapse of underground facilities to the commencement of spontaneous crustal rupture at depth, we shall investigate the mechanics behind the "extraordinary" earthquake disaster. Rigorous but plain dynamic analyses show that the "abnormal" failures are produced in fact for clear reasons. These obvious causes may remain unnoticed if conventional geophysical and geotechnical techniques are employed and only kinematic features of the lower-frequency components of seismic waves below 1 Hz are studied. Our analyses suggest that, in place of kinematics, dynamics considering the impact of higher-frequency waves over 1 Hz is required to systematically explain the "unusual" phenomena and reduce in the future the damage "unexpectedly" generated by earthquakes.
After obtaining Master of Engineering degree in aeronautics and astronautics from the University of Tokyo, Japan, in 1995, Koji Uenishi started his research career as a research associate at the Institute of Mechanics, Vienna University of Technology in Austria where he received Doctor of Science degree in mechanics and geophysics in 1997. He became an assistant professor at Kobe University, Japan, in 1998 and worked with Professor Shunsuke Sakurai, at that time the President of the International Society for Rock Mechanics. He was promoted to an associate professor of the same university in 2006. In the meantime, from 2000 to 2002, he was a visiting scientist at the Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences of Harvard University in the United States of America. He moved back to the School of Engineering of the University of Tokyo in 2012. By using engineering methodologies in applied and experimental mechanics, he is investigating fracture (rupture) dynamics of solid materials, more specifically, that of the solid Earth and physics of earthquakes. He is concurrently developing efficient and practical techniques for exactly controlled fracture in solids. He was awarded, inter alia, the Leopold Mueller Award of the Austrian Society for Geomechanics in 1999, the Excellent Contributions Award of the International Association for Computer Methods and Advances in Geomechanics in 2008, the Young Scientists' Prize of the Ministry of Education, Culture, Sports, Science and Technology of Japan in 2009, and the JSPS Prize in 2016.