Akira Ikami

The University of Tokyo

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Kiyoshi Ito

Tohoku University

Takeo Moriya

Hokkaido University

Katsutada Kaminuma

National Institute of Polar Research

Kiyoshi Ito

Aizawa Hospital

Toshikatsu YOSHII

The University of Tokyo

Harumi Aoki

Nippon Dental University

Shuzo Asano

Obayashi (Japan)

Toshikazu Tanada

National Research Institute for Earth Science and Disaster Resilience

Kazuo Shibuya

National Institute of Polar Research

Yoshimi Sasaki

Tokyo University of Technology

Cooperative Institutions

The University of Tokyo

Kyoto University

Association for the Development of Earthquake Prediction

Earthquake Engineering Research Institute

Nagoya University

Prevention Institute

Hokkaido University

National Research Institute for Earth Science and Disaster Resilience

Tohoku University

Geophysical Division of the Earth Science Institute of the Slovak Academy of Sciences

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Deep crustal structure along the profile between Syowa and Mizuho Stations, East Antarctica

Akira Ikami Kiyoshi Ito Kazuo Shibuya Katsutada Kaminuma

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Citations (16)

Amplitudes of seismic waves on ice sheet in East Antarctica

Kiyoshi Ito Akira Ikami

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Citations (2)

Crustal structure of the Mizuho Plateau, East Antarctica from geophysical data

Journal of Geodynamics (1986)

Kiyoshi Ito Akira Ikami

10.1016/0264-3707(86)90045-1

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Citations (11)

Attenuation of Seismic Waves beneath the Volcanic Front in Japan

Zisin (Journal of the Seismological Society of Japan 2nd ser ) (1975)

Akira Ikami

Seismic intensity maps reported by the Japan Meteorological Agency are used for the study of seismic wave attenuation. Intensity maps between 1961 and 1964 were more detailed than now, because the observation of intensity by unofficial stations as well as those by the Japan Meteorological Agency were avairable. Some intensity maps show such a remarkable distribution that felt area is bounded by the volcanic front. It seems that waves cannot go across the volcanic front. Judging from the distribution of volcanoes, it would be better to think that this low-Q zone may not be homogeneous beneath the volcanic front. The Q value must be lower beneath the active volcanoes than the less active volcanoes.The abnormal intensity distribution by shallow earthquakes may not be due to the high-Q lithosphere but to the heterogeneity in the crust. From the seismograms recorded at Inuyama seismolgical observatory, it is concluded that the low-Q zone exists beneath the volcanic front near the Izu peninsula where volcanic activity is high. A Q-model under the southern part of the Chubu district, central Japan, is proposed to account for both characteristics of seismograms and abnormal intensity distribution. The model consists of two low-Q zones. A shallower one may be related to the volcanic activity, and the other, to the down going lithosphere. There remains a high-Q zone between two low-Q zones.

Seismogram

Intensity

10.4294/zisin1948.28.1_61

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Citations (7)

Crustal structure in the Mizuho Plateau, East Antarctica, by a two-dimensional ray approximation

Journal of Geodynamics (1986)

Akira Ikami Kiyoshi Ito

10.1016/0264-3707(86)90044-x

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Citations (16)

Upper Crustal Structure of Soya Coast, Antarctica Revealed by Explosion Seismology

Zisin (Journal of the Seismological Society of Japan 2nd ser ) (1980)

Akira Ikami Katsutada Kaminuma Yoichiro Ichinose

The summer-field party of the 20th Japanese Antarctic Research Expedition (JARE) carried out observations of explosion seismology to investigate the crustal structure of Soya Coast in Antarctica in January 1979. This was the first for JARE to carry out the explosion seismology for study on the crustal structure in Antarctica.The objectives of the measurements by JARE-20 are to establish the techniques of explosion seismology in Antarctica, such as the laying of lines and instrumentation, development of ice drills, dynamite for the use at low temperatures, etc. JARE-21 will continue the observation along the 250km measurement line during the winter of 1980.An upper crustal model is presented in this report. An overlaying thin layer of 4-5km/s P wave volocity is firstly estimated in the structure model of East Antarctica.

10.4294/zisin1948.33.3_379

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Citations (2)

Velocity distribution on ice sheet in Prince Olav Coast, East Antarctica

Akira Ikami Katsutada Kaminuma

East coast

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Evidence for the existence of a mid-crustal reflector in the Beppu-Shimabara Graben, Kyushu, Japan

Geophysical Research Letters (1993)

Takashi Iidaka Katsumi Miura Akira Ikami

The Beppu‐Shimabara graben, in Kyushu, Japan, has active seismic regions and active volcanoes. Studies using triangulation, gravity surveys and mechanism solutions of large earthquakes show that the graben is in a state of extensive stress associated with rifting. A temporary seismic study was carried out from February 20 to March 8 in 1992 in the region, during which time many seismic signals were observed. The microearthquake seismograms recorded inside the graben have a later phase dominant on the horizontal component following the direct S‐wave. Two‐dimensional ray‐tracing was applied to investigate the cause of the later phase. The phase was identified as an S‐reflected S phase (SxS‐phase) from a discontinuity with a depth of 20 km. The reflection points are located inside the Beppu‐Shimabara graben that is in a state of extensive stress associated with rifting.

Seismogram

Microearthquake

Focal mechanism

Horst and graben

Epicenter

10.1029/92gl02800

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Citations (4)

Low Seismic Activity Associated with the Atera Fault, Central Japan

Zisin (Journal of the Seismological Society of Japan 2nd ser ) (1972)

Akira Ikami Tsutomu ANKYU Harumi Aoki

An observation of microearthquakes was carried out near the Atera Fault for two and a half months, from July 14 to October 2, 1971, since the fault has been known as one of the most active faults in Japan.In the south-western side of the Atera Fault, the focal depths of earthquakes were deeper than 30km, that is, earthquakes occurred in the mantle but not in the crust. In the northeastern side, however, only a few earthquakes were detected. Although three direct analogue recording systems of high sensitivity were used near the fault, very few earthquakes could be located near the fault. A comparison of daily frequency of earthquakes near the NeoValley Fault with the present observation showed that the seismicity near the Atera Fault was undoubtedly lower than that near the Neo-Valley Fault. The same tendency has been also observed for larger earthquakes. Number of earthquakes detected at one of the three stations was exceptionally large, though the sensitivity was the same for all stations. But most of distant earthquakes were equally detected.Considering these facts, it might be concluded that the present seismic activity is very low and, in addition, seismic waves of high frequency are attenuated in the crust near the Atera Fault. Some focal mechanisms of microearthquakes were calculated. The pressure axis thus obtained was E-W direction as in the case studied by MATSUDA (1969) and ICHIKAWA (1971).

Elastic-rebound theory

10.4294/zisin1948.25.3_232

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Citations (4)

Upper crustal structure beneath the Ongul Islands, East Antarctica

Kiyoshi Ito Akira Ikami Kazuo Shibuya Katsutada Kaminuma

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Citations (5)