Matuyama Motonori

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MATUYAMA MOTONORI

(b. Usa, Oita Prefecture, Japan, 25 October 1884; d. Yamaguchi, Japan, 27 January 1958),

physics, geophysics, theoretical geology.

Some discoveries are made before their time in the sense that there is a long delay from the time of discovery to the time when it is generally accepted. A good example is the paleomagnetic research by Japanese geophysicist Matuyama Motonori. In 1929 he proposed that the most recent reversal of the geomagnetic field took place in the early Quaternary. The chronology of geomagnetic reversals over the last five million years was established during the 1960s, contributing to the success of the theory of ocean floor spreading. These investigations identified four intervals of geomagnetic polarity, named the Brunhes normal, Matuyama reversed, Gauss normal, and Gilbert reversed epochs. The name of the Matuyama reversed epoch commemorates Matuyama’s discovery three decades earlier.

Early Life . Matuyama Motonori changed his family name two times in his life. He was born in small village near the Usa Shrine in Oita prefecture on 25 October 1884. His name was at first registered as Suehara Motonori after his mother’s family name, Suehara Kou. His father, Sumie Tengai, was a Zen Buddhist priest. When Tengai became the chief priest at an eminent Zen Buddhist temple in Yamaguchi, Tengai with his family migrated from Oita to Yamaguchi. At this time, Motonori changed his family name to Sumie. Finally, when he married in 1910, he changed his family name to Matuyama by adopting the name of his father-in-law.

Gravimetric Studies . Matuyama’s research activity incorporates a wide range of geophysical research, including early papers on seismology, glacial ice deformation, and volcanology. Although his most influential work was investigating the remanent magnetization of basaltic rocks in Japan and neighboring countries, his major work was related to a gravimetric study. He entered the Imperial University in Kyoto (now Kyoto University) in 1908 and graduated in 1911. Then he was accepted in postgraduate school. His mentors were Shida Toshi and Shinjyo Shinzo, with whom he began his investigation of gravitation. He published his first report “On the Elasticity of the Earth and Earth’s Crust,” in 1912, coauthored with Shida.

In 1913 Matuyama was appointed lecturer at the Physical Institute of Kyoto University. He began studying coral reefs in 1915, when he noticed uplift in the Mariana Islands and subsidence in the Marshall Islands in the West Pacific. He stressed the importance of measuring the seabed shift and its angle of these areas. By a recommendation of Terada Torahiko, member of the Imperial Academy of Japan, to the Japanese Association for the Advancement of Science, tide gauge stations in the Saipan and Jaluit islands were established for that purpose.

In 1916 Matuyama became an assistant professor at the Geophysical Institute. His doctoral dissertation was published as “Determination of the Second Derivative of the Gravitational Potential on the Jaluit Atoll,” in 1918. It suggested that minute features in the gravity field could reveal subsurface structure.

In 1919 Matuyama was sent abroad for two years. At the University of Chicago he performed experimental geology. Matuyama made laboratory models of glaciers, and by subjecting them to pressure and other variables, he studied deformation in ice. The paper detailing his findings was “On Some Physical Properties of Ice,” published in Journal of Geology in 1920. On the basis of this work, he was recommended for membership in the honorary scientific society, Sigma Xi. Also in honor of his work, the Matuyama Rocks (66°40' S, 66°35' W) in the British Antarctic Territory were named in his honor. On his return to Japan in 1921, he was appointed the first professor at the Institute of Theoretical Geology in the Geological Institute.

Research on Earth’s Magnetic Field . Matuyama was the first paleomagnetist to investigate the important questions of the timing of the reversal of Earth’s magnetic field. In surveying magnetic anomalies in Japan, he found that the

magnetic field was less intense over certain volcanic formations than it was elsewhere. This surprised him because volcanic formations contain magnetite, which might be expected to enhance the strength of the local magnetic field. The anomaly inspired him to investigate the matter. He collected samples from many parts of Japan and measured their magnetism. Early in April 1926, a specimen of basalt from Genbudo in the Hyōgo prefecture, a celebrated basalt cave, was collected for the purpose of examining its magnetic properties. When this block was tested by bringing it near a freely suspended magnetic needle, its magnetic north pole was found to be directed to the south and above the horizontal direction. This is nearly opposite to the present geomagnetic field at that locale. In May of the same year, four specimens of basalt were collected from Yakuno in Kyoto prefecture. When tested, their magnetic axes were found to nearly coincide with the present geomagnetic field. Genbudo and Yakuno are not very far from each other and have nearly the same magnetic field. Their basalts probably resulted from lavas of Quaternary eruptions. Subsequently, he collected more than one hundred specimens of basalt from thirty-six locations in other parts of Japan, in Tyosen (Korea), and in Manchuria (the northeastern region of China).

His most significant work based on these collections is “On the Direction of Magnetization of Basalt in Japan, Tyosen, and Manchuria” (1929). In this article he noted that the magnetism of the rocks fell into two distinct groups. One group, including the rocks from Yakuno, was directed toward the present geomagnetic field (normal magnetization). The other group, including rocks from Genbudo, was opposite the present field (reversed magnetization). His acute observation that the polarity of a rock correlated with its stratigraphic position or age led him to propose that long periods existed in Earth’s history during which the polarity of the magnetic poles was the opposite of what it is now. However, for a long time his proposal was not accepted because geophysicists still did not have a sensible theory for the origin of the geomagnetic field. The response of his fellow scientists was neither disbelief nor outrage, but, rather, silence.

Gravity over the Japan Trench . From 1927 through 1932, Matuyama extended his determinations of gravity to new regions, notably Korea and Manchuria. He also explored the oceanic abyssal regions near the Caroline and Mariana island groups in the West Pacific and found free-air gravity anomalies in both of these tropical areas.

In 1934 and 1935 Matuyama led a gravity survey of the Japan Trench, a deep depression on the Pacific Ocean floor near Japan, in a submarine using instruments perfected by F. A. Vening Meinesz. This could be submerged to depths where the effects of waves on swinging pendulums became negligible. The Japan Trench is the site of frequent seismic activity, and the undersea earthquakes there trigger tsunamis. Later, one of his successors correlated the earthquakes with gravity anomalies.

Matuyama retired from Kyoto University in 1944. In his postretirement years he became the first president of Yamaguchi University. At both universities he actively engaged a large group of assistants and students in his research. He was well known as a devotee of Noh plays, the classic form of Japanese dance drama. He died of leukemia on 27 January 1958 at Yamaguchi.

Posthumous Vindication . The works of Matuyama played a dramatically important role in the progress of plate tectonics theory. A few years after Matuyama’s death, Allan Cox began his research on geomagnetic reversals. The main result of his research was to corroborate Matuyama’s conclusion of thirty years earlier, that the geomagnetic field had reversed its polarity at some time in the early Quaternary. Cox and others developed the remarkable geomagnetic polarity time scale. They named the most recent epochs Brunhes and Matuyama to honor two geophysicists who were among the first to perceive the significance of reversed magnetization in rock. Consisting of rock, the ocean floor produced—as it newly emerged from the midocean ridges—the pattern of the zebra stripes shown in oceanic magnetic anomaly profiles.

BIBLIOGRAPHY

WORKS BY MATUYAMA

With Shida Toshi. “On the Elasticity of the Earth and Earth’s Crust—Part 3—Note on Hecker’s Observation of Horizontal Pendulums.” Memoirs of the College of Science and Engineering, Kyoto Imperial University 4, no. 1 (1912): 187–224.

With Shida Toshi. “On the Elasticity of the Earth and Earth’s Crust—Part 6—Change of Plumb Line Referred to the Axis of the Earth as Found from the Result of the International Latitude Observations.” Memoirs of the College of Science and Engineering, Kyoto Imperial University 4, no. 1 (1912): 277–284.

“Determination of the Second Derivative of the Gravitational Potential on the Jaluit Atoll.” Memoirs of the College of Science, Kyoto Imperial University 3 (1918): 17–68.

“On Some Physical Properties of Ice.” Journal of Geology 3 (1920): 607–631.

“On the Direction of Magnetization of Basalt in Japan, Tyosen, and Manchuria.” Proceedings of the Imperial Academy Japan 5 (1929): 203–205.

[Letters from Konjian]. Yamaguchi, Japan: private publication, 1954.