Prof. Eiji OHTANI [Tohoku University, Japan]

Title: Sound velocity measurements at high pressure and their implications to the Earth's core

Time: 10:00 - 11:00 AM, May 21, 2024

Language: English

Place: Conference room 410, HPSTAR (SH) 

Online: Tencent Meeting: ID: 622-478-881 

Host:  Li Zhang

Abstract: 

There are several debated issues on the inner core. One of the debated issues is the ambiguity of the pressure scale. There are inconsistency among the pressure scales when we argue the inner core, since significant extrapolation and approximations are needed especially at the inner core pressures. Here, I discuss these debated issues and show limitation of present understanding of the inner core.

Establishing pressure scale has been a subject of intensive research but still involves significant extrapolation and approximations, especially at the inner core pressures. In order to solve the problem, we developed techniques to measure the sound velocity at high pressure by using Inelastic X-ray scattering (IXS). We performed sound velocity measurements in diamond anvil cell with an improved anvil design (a stepped bevel DAC) under extreme pressures of the inner core boundary (ICB) at the RIKEN beamline BL43LXU of SPring-8. We doubled the static pressure conditions for IXS and successfully measured the sound velocity of metallic iron under a pressure equivalent to ICB (~330 GPa) [1].

We developed a primary pressure scale extending to the multi-megabar pressures of the core by measuring vP, vS, and density of rhenium with using IXS and XRD. Our new pressure scale agrees with previous primary scales at lower pressures and also shock compression experiments, but is significantly different from previous secondary pressure scales at Earth’s core pressures: previous scales have overestimated, by at least 20%, laboratory pressures at 230 GPa. Our new pressure scale suggests the density deficit of the inner core is doubling the light-element content [2].

Reference:

[1] Ikuta, Ohtani, Fukui et al. (2022) Nature Communications 13:7211

[2] Ikuta, Ohtani, Fukui et al. (3023) Science Advances 9, eadh8706

Biography of the Speaker:

Prof. Eiji OHTANI 

Education:

Faculty of Science, Tohoku University, Sendai, Japan, 1969-1973: B. Sc. Petrology, 1973

Graduate school of Science, Nagoya University, Nagoya, Japan, 1973-1978

M. Sc., Geophysics, 1975

D. Sc., Geophysics, 1979

Research and professional experience:

1978.4.1-1980.3.31 Post-doctoral fellow from Japanese Association of Promotion of Science at Department of Earth Sciences, Nagoya University, Nagoya 464 Japan

1980.7.16-1982.3 Assistant Professor at Department of Earth Sciences, Faculty of Science, Ehime University, Matsuyama 790, Japan

1982.4-1984.3 Research Fellow at Research School of Earth Sciences, The Australian National University (Petrochemistry group), Canberra A.C.T., 2601, Australia

1984.4-1987.3.31 Assistant Professor of Geophysics at Department of Earth Sciences, Faculty of Science, Ehime University, Matsuyama 790, Japan

1987.4.1-1988.9.31 Associate Professor of Geophysics at Department of Earth Sciences, Faculty of Science, Ehime University, Matsuyama 790, Japan

1988.10.1-1994.6.30 Associate Professor of Mineral Physics at Institute of Mineralogy, Petrology, and Economic Geology, Tohoku University, Sendai 980, Japan

1994.7.1-2016.3: Professor of Mineral Physics at Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Tohoku University, Sendai 980, Japan

2002-2007: Project leader of 21st century COE program of Earth Science, Tohoku University in Sendai

2008.4-2011.3: Distinguished Professor of Tohoku University    

2011.8- 2014.3: Distinguished Professor of Tohoku University

2008.4-2013.3:  Project leader of Global COE program of Earth and Planetary Science, Tohoku University in Sendai

2011.4- 2013.3: Trustee of Tohoku University (elected on Jan. 26, 2011 by Faculty of Science)

2013-2016: Visiting Research scientist of Sobolev Institute of Geology and Mineralogy, Russian Academy of Science, Novosibirsk, Russia.

2015.4-2016.3: Distinguished Professor of Tohoku University

2015.10.2-2020.9: Guest professor, China University of Geosciences (Wuhan), China.

2016. 2.17-2021-2.16: Distinguished Affiliated Professor at the University of Bayreuth

2016.4-present: Professor Emeritus of Tohoku Uuniversity

2016.4- 2021.3: Research Fellow (Professor Emeritus), Tohoku University

2016.4-present: Visiting Researcher, RIKEN SPring-8 center, RIKEN

2018.3-present: Distinguished Visiting Chair, Institute of Earth Science, Academia Sinica, Taiwan

2018.4-present: Visiting Professor, Graduate School of Science, Shizuoka University

2021.4-present: Visiting Researcher (Professor Emeritus), Tohoku University

Honors, Awards:

Post-doctoral fellowship from JSPS (Japanese Association of Promotion of Science), 1978-1980

Visiting Professor Award of Bayerisches Geoinsitut from DFG (German Science Foundation) 1995.4-1995.10.

Mineralogical Society of Japan Award 1997

Reimei Research Award from Japan Atomic Energy Research Institute, 1998

Fellow of Mineralogical Society of America, 2002

Fellow of American Geophysical Union, 2006

N.L. Bowen Award from VGP section of AGU, Dec., 2007.

N.L. Bowen Lecturer, 2007AGU Fall Meeting, Dec. 2007.

Distinguished Professor of Tohoku University, 2008.4.-2011.3, 2011.8-2014.3, 2015.4-2016.3

Medal with Purple Ribbon from Japanese Government, 2010, 11.03

Mega-grant Award, Ministry of education and science of Russian Federation, 2013-2016.

Visiting Professor Award of University of Paris, 2015. 6-2015.9.

Geochemical Fellow of Geochemical Society (USA) and European Association of Geochemistry (EAG), 2015.

Urey Award from European Association of Geochemistry, Goldschmidt conference in Paris, 2017. 8.

Humboldt Research Award from Alexander von Humboldt-Stiftung, Nov. 27, 2017.

Miyake Prize from Japan Geoscience Union, April 10, 2018.

International Mineralogical Association (IMA) Medal from IMA, October 2019.

Fellow of Japan Geoscience Union, June 1, 2021

Honorary Member of Japan Association of Mineralogical Sciences, Sept. 17, 2022.

Research Interests:

1.     Global circulation of water and other volatiles in the earth’s interior

2.     Melting behavior of Earth and planetary materials, properties of melts at high pressures, and early differentiation of the Earth

3.     Phase transformation kinetics and discovery of high-pressure minerals in shocked meteorite

4.     Mineralogy, geochemistry, and physical properties of the core and core-mantle boundary

5.     Development of novel techniques for high pressure generation