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Research about Japan

Source-linked reports with geographic coverage including Japan.

At least 127 records · Page 7Linked to original sources
USGS1988

The fir trees have moved

Trees show a record of the great Kanto earthquake of 1923 in Japan. Two minutes before noon on the morning of September 1, 1923, the Great Kanto earthquake occurred with a magnitude of 7.9 in the northern part of Mizukuma in Sagmi Prefecture, Japan. Fires broke out immediately following the earthquake, causing great damage in Tokyo and in Kanagawa. Deaths totaled 99,331 persons, with 43,476 missing; 128,266 houses partially destroyed, and 447,128 houses were destroyed by fire. Large earth movements occurred and there were innumerable landslides. Along the Kanto coastline, waves came crashing into the harbors; at Misaki the height of the waves was six meters, and 8.1 meters at Sunozaki. At Tokyo the amplitude of the vibrations renged from 14 to 20 centimeters and at Odawara they were estimated to have reached 80 centimeters.

Earthquakes & Volcanoes (USGS)↗
USGS1984

Unzipping of the volcano arc, Japan

A working hypothesis for the recent evolution of the southern Volcano Arc, Japan, is presented which calls upon a northward-progressing sundering of the arc in response to a northward-propagating back-arc basin extensional regime. This model appears to explain several localized and recent changes in the tectonic and magrnatic evolution of the Volcano Arc. Most important among these changes is the unusual composition of Iwo Jima volcanic rocks. This contrasts with normal arc tholeiites typical of the rest of the Izu-Volcano-Mariana and other primitive arcs in having alkaline tendencies, high concentrations of light REE and other incompatible elements, and relatively high silica contents. In spite of such fractionated characteristics, these lavas appear to be very early manifestations of a new volcanic and tectonic cycle in the southern Volcano Arc. These alkaline characteristics and indications of strong regional uplift are consistent with the recent development of an early stage of inter-arc basin rifting in the southern Volcano Arc. New bathymetric data are presented in support of this model which indicate: 1. (1) structural elements of the Mariana Trough extend north to the southern Volcano Arc. 2. (2) both the Mariana Trough and frontal arc shoal rapidly northwards as the Volcano Arc is approached. 3. (3) rugged bathymetry associated with the rifted Mariana Trough is replaced just south of Iwo Jima by the development of a huge dome (50–75 km diameter) centered around Iwo Jima. Such uplifted domes are the immediate precursors of rifts in other environments, and it appears that a similar situation may now exist in the southern Volcano Arc. The present distribution of unrifted Volcano Arc to the north and rifted Mariana Arc to the south is interpreted not as a stable tectonic configuration but as representing a tectonic “snapshot” of an arc in the process of being rifted to form a back-arc basin.

Tectonophysics↗
USGS1984

The “anomalous cedar trees” of Lake Ashi, Hakone Volcano, Japan

On the bottom of Lake Ashi at Hakone, Japan, there stand great trees that, since ancient times, have been widely known as the "Anomalous Cedar Trees" of Ashi. It is not known why these trees grow on the bottom of the lake, and it remains one of the mysteries of Hakone. It was formerly thought that, at the time Lake Ashi was born, a great forest of cedar trees which was growing in the caldera of the volcano sank into the water. From radioactive carbon dating techniques, it is known that a steam explosion in the Kami Mountains created the caldera approximately 3,000 years ago. The age of the "Anomalous Cedars" is placed at approximately.

Lake Ashi↗
USGS1982

Triggering of large earthquakes by magma-chamber inflation, Izu Peninsula (Japan)

A close spatial and temporal association between three aseismic uplift episodes and subsequent large (M ≈ 7) earthquakes on the Izu Peninsula, Japan, suggests a causal relation. Quaternary geology, as well as studies by other workers, indicates a volcanic origin for the observed uplift, and we use a simple inflation model constrained by leveling data to compute the expected increments in normal and shear stress across faults that ruptured in the earthquakes. Using a Mohr-Coulomb criterion, we find that in two cases out of three, stress changes induced by inflation are in the correct sense to trigger failure. Although changes are no more than a few bars, they represent the equivalent of several decades to a century of secular stress buildup.

Izu Peninsula↗
USGS1969

Lead and strontium isotopes in volcanic rocks from northern Honshu, Japan

Isotopic compositions of lead and strontium and concentrations of lead, uranium, thorium, rubidium, and strontium were measured in a suite of volcanic rocks, ranging from basalt to rhyodacite in composition, and in granite and gabbro xenoliths from a traverse across northern Honshu. The observed 238 U/ 204 Pb (μ) ratio ranges from 2.4 in tholeiitic basalt at the east end of the traverse to 11.6 in alkalic basalt from the west end. The isotopic composition is slightly less radiogenic to the west. The 87 Sr/ 86 Sr ratios of most of the samples fall within the range observed in oceanic basalts, but the granite xenolith and the rhyodacite are slightly more radiogenic.

Honshu↗
USGS1969

Isotopic composition of lead in volcanic rocks from central Honshu — with regard to basalt genesis

The isotopic composition of lead and concentrations of lead, uranium, and thorium were determined in tholeiitic and high-alumina basalts, and their calc-alkali rock series, from central Japan. The isotopic composition of lead of high alumina basalts is similar to that of tholeiites from adjacent areas, whereas their silicic differentiates (calc-alkali rock series) are rich in 207 Pb and 208 Pb. This is interpreted as a result of crustal contamination. The isotopic composition of lead in the primary basalts gradually decreases in radiogenic character from the Pacific Ocean side to the Japan Sea side, whereas the observed 238 U/ 204 Pb and 232 Th/ 238 U ratios in the basalts increase in the same direction. This inverse correlation can be interpreted as resulting from differentiation of the upper mantle about 3.6b.y. ago, with tholeiite (Pacific side) generated from a shallower zone than the alkali basalt (Japan Sea side). The magma generation is associated with a process which extracts Pb preferentially to U and Th at shallower depth and U and Th preferentially to Pb at deeper depth in the past (multi differentiation for the source region) or at the magma generation stage. An alternative interpretation of this inverse correlation is that the ocean floor is being thrust under the Japanese Island arcs and the isotopic difference is produced by the degree of mixing of mantle material under the arcs with thrust material.

Honshu↗
USGS1957

Volume I: Introduction and engineering aspects

This series of military geology reports on Okinawa is part of the Corps of Engineers Post Hostilities Mapping Program. The purpose of this survey is twofold. The first is to collect scientific information through field study; the second is to publish it in a form that is usable by the United States Armed Forces and Civil Administrators.

Okinawa↗
USGS1955

1950 and 1951 eruptions of Mihara Yama, O Shima Volcano, Japan

Mihara Yama is the active central cone of O Shima Volcano on the island of O Shima, Tokyo Prefecture, Japan. The outer slopes of O Shima Volcano compose most of the island. Their crest is a somma, about 600 km in altitude and 3 km in diameter, which encloses a caldera. Mihara Yama rises from the southern part of the caldera to an altitude of 755m. It is a truncated cone with a crater 800 m in diameter. Before the eruption in 1950 the crater contained an inner pit approximately 300 m in diameter and 165 m deep. Mihara Yama erupted on July 16, 1950, after 10 years of quiescence. Activity continued until September 24. Eruption resumed on February 4, 1951, and continued until April 2, after which activity was intermittent until the eruption ceased on June 28. In 1950 molten basalt was ejected explosively accompanied at times by flows. Two successive cinder cones formed from the accumulation of ejecta, some of which were hurled as high as 500 m. Lava filled the inner pit and crater, and a small amount overflowed into the caldera. About 52,000,000 metric tons of material was erupted. In 1951 six successive small cones developed. Beginning February 21 the principal cone formed. Lava overflowing the crater rim solidified mostly as aa and covered nearly 2 square km of the caldera floor. The intermittent activity during the final 3 months consisted of nine brief periods of eruption, a few of which were relatively violent. Between eruptions and especially after the final eruption the crater floor subsided. In 1951 about 20,000,000 metric tons of material was erupted.

O Shima Volcano↗
USGS1950

The appraisal of ore reserves at a Japanese copper mine

Estimates of ore reserves at major Japanese metal mines seem, at first glance, to be readily understandable to American engineers and geologists. Close scrutiny, however, generally reveals unexpected features at each mine. For example, the Hitachi copper mine formerly segregated its developed ore reserve into positive and probable on the basis of the possibility of high-grade and low-grade production from individual stopes. Tests were made by the writer at Hitachi on the accuracy of the original reserve estimates of a few ore blocks by comparing those figures with the final production data. The results suggesthat the average reserve estimate of positive ore may be accurate within 20 percent, plus or minus. A ten-year supply of proved ore at the big mines is not unusual; hence Hitachi is not much concerned with the additional categories of probable and possible ore, unless the positive ore has become inaccessible because of caving of the workings. For the sake of comprehensiveness, however, the writer studied the assay maps and stope maps in collaboration with the mine management and estimated tonnages of probable and possible ore, qualified by lower reliability ratings. Exploration prospects also were described in actual figures, subject to a variation of plus-or-minus 75 percent.

Ibaraki Prefecture↗
USGS1950

Summary of Kinoshita's kuroko deposits of Japan

Summarized translation of a report by Kameki Kinoshita, published in Japanese in 1943, on kuroko deposits (black ore deposits) of Japan. "Kuroko means two things. One is the common mixture of sphalerite, galena, and barite which is ordinarily black to grayish white, depending on the proportion of barite. The other meaning is the unusual assemblage of separate bodies of: 1, sphalerite-galena-barite; 2, massive pyrite; 3, disseminated chalcopyrite in silicified rock; and 4, massive gypsum. Rarely are all four of these ore bodies present in any one mine, yet the assemblage is still called kuroko, regardless of color."

Hokkaido, Honshu↗
USGS1950

Seismology in Japan in 1939-1947

In the latter half of this period the seismology in Japan was so much affected by the war that retrogressions in the instrumental seismology became very remarkable. Much regretted three leading seismologists, professors Ishimoto, Sezawa, and Inamura died in this period. But the seismic activities in this well-known land of earthquakes were not less active than usual as will be seen in the annexed table of destructive earthquakes. Seismologists in this country are now endeavoring to restore its former prosperity in this bitter circumstance.

Report↗
USGS1948

Petrography of Iwo Jima

The rocks of Iwo Jima are augite and augite-hornblende trachyandesites, distinctly more alkalic than the ordinary andesites of Japanese volcanoes or the average world andesite. They are described, and chemical analyses are listed. Fumarolic gases have altered some rocks to a mixture of opal and clay minerals and have cemented tuff with opal, calcite, zeolite, and iron oxides.

Iwo Jima↗