Masataka Ando

Yokohama National University

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K. Tadokoro

Meiji Pharmaceutical University

Mamoru Nakamura

University of the Ryukyus

Ryoya Ikuta

Shizuoka University

Ikuru Iwata

National Astronomical Observatory of Japan

G. M. Besana

Nagoya University

Kentaro Aoki

National Astronomical Observatory of Japan

Kouji Ohta

Kyoto University

Masayuki Akiyama

Tohoku University

K. Nishigami

Kyoto University

Cheng‐Horng Lin

Academia Sinica

Cooperative Institutions

The University of Tokyo

Kyoto University

Nagoya University

Association for the Development of Earthquake Prediction

Tohoku University

National Research Institute for Earth Science and Disaster Resilience

Hokkaido University

Prevention Institute

Graduate School USA

Institute of Earth Sciences, Academia Sinica

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Seismic observations in the DPRI 1800 m borehole drilled into the Nojima Fault zone, south‐west Japan

Island Arc (2001)

K. Nishigami Masataka Ando K. Tadokoro

Abstract Seismometers were installed at three depths in the Disaster Prevention Research Institute, Kyoto University (DPRI) 1800 m borehole drilled into the Nojima Fault zone, southwest Japan. The waveforms recorded by these seismometers are rather simple compared with those recorded at the DPRI 800 m borehole or on the ground surface. These data should be well suited for detecting fault zone‐trapped waves and estimating the fault zone structure and its temporal variation related to the healing process of the ruptured fault. Typical waveforms trapped in the fault zone were observed by a surface seismographic array across the Nojima Fault just after the 1995 Hyogo‐ken Nanbu earthquake (Kobe earthquake). Among the wave data recorded in the DPRI 1800 m borehole, however, clear evidences of fault zone‐trapped waves have not yet been found, and further studies are continuing. The present study outlines the observation system in the DPRI 1800 m borehole, which will make it easier to access and analyze the borehole data.

Seismometer

10.1111/j.1440-1738.2001.00327.x

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Citations (16)

Very low frequency earthquakes along the Ryukyu subduction zone

Geophysical Research Letters (2012)

Masataka Ando Yoko Tu Hiroyuki Kumagai Yoshiko Yamanaka Cheng‐Horng Lin

A total of 1314 very low frequency earthquakes (VLFEs) were identified along the Ryukyu trench from seismograms recorded at broadband networks in Japan (F‐net) and Taiwan (BATS) in 2007. The spectra of typical VLFEs have peak frequencies between 0.02 to 0.1 Hz. Among those, waveforms from 120 VLFEs were inverted to obtain their centoroid moment tensor (CMT) solutions and locations using an examination grid to minimize a residual between the observed and synthetic waveforms within an area of 11° × 14° in latitude and longitude and at depths of 0 to 60 km. Most of the VLFEs occur on shallow thrust faults that are distributed along the Ryukyu trench, which are similar to those earthquakes found in Honshu and Hokkaido, Japan. The locations and mechanisms of VLFEs may be indicative of coupled regions within the accretionary prism or at the plate interface; this study highlights the need for further investigation of the Ryukyu trench to identify coupled regions within it.

Seismogram

Moment tensor

Accretionary wedge

10.1029/2011gl050559

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Citations (53)

｢しんかい2000｣による沖縄トラフ中部熱水域の地形・鉱床・生物の観察 / Study of Topography, Hydrothermal Deposits and Animal Colonies in the Middle 0kinawa Trough Hydrothermal Areas Using the Submersible "SHINKAI 2000" System

政昭木村武男田中正憲許雅孝安藤保大森

Trough (economics)

Source

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Introduction to the Special Issue of the M7.1 1948 Fukui Earthquake

Zisin (Journal of the Seismological Society of Japan 2nd ser ) (1999)

Masataka Ando Kojiro Irikura

10.4294/zisin1948.52.1_109

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J‐Array Project seismic data now on CD‐ROM

Eos (1999)

Takuo Shibutani Masataka Ando Kazuro Hirahira

Two CD‐ROMs containing seismic waveform data obtained from the J‐array Project are now available.The J‐array was a large‐aperture seismic array extending over all of Japan. It consisted of 14 regional seismic networks and more than 200 stations. The project was concerned with detecting small‐amplitude waves that are refracted, reflected, converted, or scattered from seismic velocity discontinuities existing deep within the Earth, and with studying the detailed structure and regional variations of the core, lower mantle, and upper mantle. Continuous digital seismic waveform data were recorded at the rate of 20 Hz with short period seismometers developed under Japan's national program for earthquake prediction. The J‐array project began in April 1991 and continued for 3 years at most of the networks. Many studies have been done with the data, including investigations of the structure of the upper mantle, lower mantle discontinuities, D″ layer, and core. Anyone interested in using the data can refer to J‐array Group [1993] for more information.

Seismometer

Seismic array

Classification of discontinuities

10.1029/99eo00049

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Earthquake Geology and Tectonophysics around Eastern Tibet and Taiwan

Atmosphere, earth, ocean & space (2020)

Ching‐Hua Lo Xiwei Xu Wen‐Yen Chang Masataka Ando

Tectonophysics

10.1007/978-981-15-6210-5

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Error evaluation in acoustic positioning of a single transponder for seafloor crustal deformation measurements

Earth Planets and Space (2014)

Takuji Yamada Masataka Ando K. Tadokoro Kazutoshi Sato Takashi Okuda

The observation of seafloor crustal deformation is very important to understand plate motions, nucleation processes and mechanisms of great interplate earthquakes as well as the activities of submarine volcanoes. We have been developing an observation system for seafloor crustal deformation. This system consists of two main components; (1) kinematic GPS positioning of an observation vessel and (2) accurate acoustic measurements of distances between a transponder attached on the side of the vessel (onboard station) and one located on the ocean bottom (seafloor station). In this study, we performed numerical simulations to estimate measurement errors with acoustic positioning assuming acoustic velocities in the sea water and the distribution of observation points around the single seafloor station. We found that the position of the seafloor station which we can obtain by analyzing travel-time data might have around 18-cm discrepancy with respect to its "true" position. Colombo et al. (2001) reported that the position of the vessel can be determined with about 10-cm error by kinematic GPS positioning. These results indicate that the system should be able to detect seafloor crustal deformation much larger than 28 cm, including pre-, co-, and post-seismic slips due to the large earthquakes at subduction zones, slow and silent earthquakes, etc. Therefore, we emphasize the importance of continuous observations with a nationwide geodetic observational network for seafloor crustal deformation.

Seafloor Spreading

Transponder (aeronautics)

Seabed

Position (finance)

10.1186/bf03352435

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Citations (53)

Interseismic seafloor crustal deformation immediately above the source region of anticipated megathrust earthquake along the Nankai Trough, Japan

Geophysical Research Letters (2012)

K. Tadokoro Ryoya Ikuta Tsuyoshi Watanabe Masataka Ando Takashi Okuda

We monitored seafloor crustal deformation using the GPS/acoustic seafloor geodetic observation technique at three sites on the Kumano Basin, off southwestern Japan, which is located immediately above the source region of the anticipated Tonankai megathrust earthquake. We directly measured landward crustal movements of ∼40 mm/y in the ∼N80°W direction with respect to the Amurian Plate on the seafloor. The directions were found to be the same as those measured at the on‐land GPS stations. The magnitudes of the velocity vectors indicated significant crustal shortenings of approximately 10–20 mm/y between the Kumano Basin and the southeastern coast of the Kii peninsula of the Japanese Islands. The present observational results show strong and direct evidence for interplate locking during the interseismic period. Coupling ratios were roughly estimated at ∼0.6–0.8 on the plate interface up to at least 10 km in depth.

Seafloor Spreading

Trough (economics)

Peninsula

10.1029/2012gl051696

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Citations (36)

Seismic anisotropy near source region in subduction zones around Japan

Physics of The Earth and Planetary Interiors (1996)

Yoshihiro Hiramatsu Masataka Ando

Seismic anisotropy

10.1016/0031-9201(95)03119-7

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