1. Contents of study
The solid Earth physics laboratory aims to clarify the basic laws governing a changing solid Earth structure, fault ruptures, propagation characteristics of seismic waves, volcanic eruptions, and various solid earth phenomena by making full use of theory, observation, data analyses, numerical simulation, and other means, particularly addressing the heterogeneity and complexity of the solid Earth.
Earthquakes are considered to be brittle failures of heterogeneous materials in the Earth. The heterogeneities make the growth of the failures become so complex that seismic waves radiate in a broad period range. We study the short-period seismic wave radiation from intermediate to large earthquake in the world. We try to make use of the results for predicting strong ground motions and mitigating earthquake disasters.
Various kinds of volcanic and eruptive activities are produced through interaction between magma comprising mixed phases of gas, liquid, and solid and surrounding rock bodies. We study the dynamics of volcanic eruptions on the basis of modeling of magma ascent process and eruption dynamics as well as analyses of geophysical data obtained at active volcanoes around the world.
Seismic waves provide us with useful information related to Earth's interior structure that has been formed over a long period of time: Earth's subsurface, crust and mantle are spatio-temporally changing and are full of small-scale heterogeneities that cannot be described in terms of a classical spherical shell structure. We study these heterogeneous structures by using seismic interferometry methods and seismic scattering/attenuation modeling.
2. Cooperative commissioned course
(Solid earth physics course)
We have hosted researchers from the National Research Institute for Earth Science and Disaster Prevention as commissioned staff since 1996. The commissioned staff introduce observations, research, and results related to earthquakes and volcanoes promoted nationwide, with efforts associated with reduction (disaster prevention) of seismic and volcanic disasters, which are important activities with respect to society, as an intensive course. The commissioned staff also take the role of research guidance for students in studies using the large-scale earthquake database of the National Research Institute for Earth Science and Disaster Prevention.
The commissioned Prof. Hiroyuki Fujiwara and Assoc. Prof. Eisuke Fujita are the commissioned staffs of the course for this fiscal year.
3. Research exchange
We promote research exchanges actively with domestic and overseas research institutes.
[ Domestic research institutes ]
- National Research Institute for Earth Science and Disaster Prevention:
- In very close cooperation such as that with establishment of a cooperative commissioned course.
- Earthquake Research Institute, The University of Tokyo:
- Participated in a collaborative research program related to seismic wave scattering and contributed to progress in studies in cooperation with researchers nationwide. The program continued from fiscal 1995 through fiscal 2005. Meanwhile, a special topic "A short-wavelength heterogeneous structure and seismic wave scattering" is explored in an academic journal "Earthquake 2". In fiscal 2006, the program is renovated into a workshop and has been continued to the present day.
[ Overseas research institutes ]
- Leipzig University, Germany:
- Through the Japan Society for the Promotion of Science (JSPS) / Japan-Germany collaborative research (2002-2004) has been advanced. Research cooperation including mutual visits of researchers has continued with the Geophysics and Geological Science Research Laboratory (Dr. Korn) of Leipzig University in Germany. It originated from study with Dr. Wegler and has progressed since. He was a researcher at the university and stayed in this course for one year until February 2000 as a special foreign research student of JSPS.
- Grenoble University, France:
- Through the Japan Society for the Promotion of Science (JSPS), the Japan-France collaborative research Sakura Program (2007-2008), Japan-France collaborative research (2009-2011) and J-RAPID (2011-2013) approval and research cooperation have progressed to include mutual visitation of researchers with the Earth's Interior Physics and Tectonics Research Laboratory (Prof. Campillo) of France's Grenoble University.
4. Historical Sketch
At Tohoku University, geophysical studies started with the creation of the Chair of Geophysics in 1922, which was presided by Professor Shirota Kusakabe for 1922-1924, and by Professor Saemontaro Nakamura for 1924-1945. In 1945, the Chair was expanded to the Division of Geophysics that was composed of the Chairs of Seismology, Geo-Electro Magnetism, and Meteorology. In 1949, regular publication of the "Tohoku Geophysical Journal" (Fifth Series of the "Science Report of Tohoku University") started, which has published important scientific achievements at the Department. As of 1999, five laboratories covering various fields of geophysics are under the umbrella of the Department of Geophysics, among which the Solid Earth Physics Laboratory succeeds the half-century endeavor of promoting research and education on seismology and the physics of Earth's interior at Tohoku University. The professors and their terms at the laboratory since the creation of the Chair of Seismology are: Saemontaro Nakamura (1945-1951), Hirokichi Honda (1951-1960), Ziro Suzuki (1961-1986), Hiroyuki Hamaguchi (1986-1988), Masakazu Ohtake (1988-2003), and Haruo Sato (1997-present).
In the past five decades, the laboratory promoted intensive researches to deepen the scientific understanding of an earthquake by theoretical and observational approaches. One of the most important contributions to the scientific community was theoretical research to establish the double couple mechanism of an earthquake. The elaborate works are summarized in Honda (1962). It was followed by a proposal of circular crack model of Sato and Hirasawa (1973). In the early 1950s, this laboratory conducted a number of pioneering observations of microearthquakes and artificial explosions by using newly developed high sensitivity seismometers of moving-coil type. The results of observations are fully reflected in a series of articles on earthquake statistics by Suzuki (1953, 1955, 1958, 1959).
- Honda, H., Earthquake mechanism and seismic waves, Geophysical Notes, Tokyo University, 15, Supplement, 97 pp, 1962.
- Sato, T. and T. Hirasawa, Body wave spectra from propagating shear cracks, J. Phys. Earth, 21, 415-431, 1973.
- Suzuki, Z., A statistical study on the occurrence of small earthquakes, Ⅰ, Ⅱ, Ⅲ, Ⅳ, Tohoku Geophys. J., 5, 177-182, 1953; 6, 105-118, 1955; 10, 15-27,1958; 11, 10-54, 1959.