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Most of the large earthquakes (magnitude greater than 8.0) observed in Japan fall into the subduction plate- boundary category. Based on the results of previous Nankai Trough research efforts, further research opportunities have been... more
Most of the large earthquakes (magnitude greater than 8.0) observed in Japan fall into the subduction plate- boundary category. Based on the results of previous Nankai Trough research efforts, further research opportunities have been proposed under the umbrella of the IODP scientific drilling proposal 603 (NanTroSEIZE: Nankai Trough Seismogenic Zone Experiment) ranked as the top level proposal in IODP. IODP
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Addressing Geologic Hazards Through Ocean Drilling: An IODP International Workshop; Portland, Oregon, 27-30 August 2007; How can Integrated Ocean Drilling Program (IODP) drilling contribute to the understanding of highly hazardous... more
Addressing Geologic Hazards Through Ocean Drilling: An IODP International Workshop; Portland, Oregon, 27-30 August 2007; How can Integrated Ocean Drilling Program (IODP) drilling contribute to the understanding of highly hazardous geologic events, such as great earthquakes, submarine landslides, and volcano collapses, all of which can generate devastating tsunamis and threaten huge parts of Earth's coasts? Eighty-nine participants from 18 countries
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In 2000 and 2001, the seafloor borehole seismological observatories WP-1 and WP-2 in the northwestern Pacific were installed. The WP-1 site is in the west Philippine Basin, and the WP-2 observatory is situated on a normal oceanic Mesozoic... more
In 2000 and 2001, the seafloor borehole seismological observatories WP-1 and WP-2 in the northwestern Pacific were installed. The WP-1 site is in the west Philippine Basin, and the WP-2 observatory is situated on a normal oceanic Mesozoic crust in the northwestern Pacific Basin. The seismic network with 1000-km interval in the western Pacific has been completed by the construction of these stations. Each observatory had two identical broadband seismometers (Guralp, CMG-1T), which were cemented in a igneous rock section. The WP-1 has a water depth of 5710m and all the necessary power was supplied from the Lithium Battery System. For the WP-2 observatory, a water depth is 5566m and the Sea Water Battery (SWB) System mainly supplied the power to the system. We operated only one seismometer for both the observatories to reduce the consuming power of the system. The WP-1 observatory was activated in March 2002 using the ROV KAIKO and long-term observation was started. In June 2006, the n...
The Sumatra Andaman earthquake of 26 December 2004 (Mw = 9.3) ruptured over a distance of 1300 km from offshore northern Sumatra to the Andaman Islands. Two months after the earthquake we conducted a research cruise over the trenchward... more
The Sumatra Andaman earthquake of 26 December 2004 (Mw = 9.3) ruptured over a distance of 1300 km from offshore northern Sumatra to the Andaman Islands. Two months after the earthquake we conducted a research cruise over the trenchward edge of the outer arc high in the area off Sumatra where co-seismic uplift of the seafloor was believed to be particularly high. Our observations from a remotely operated subsea vehicle discovered a surface break of the co-seismic rupture on the edge of the outer arc high. The seafloor was intensively and freshly shattered, particularly on the hanging wall of the thrust. Aftershock distribution obtained by OBS across the study area support us to interpret that the co-seismic rupture was displaced along the splay fault to be propagated from a low-angle detachment. To account them we propose `play fault model'. Our tsunami inversion model by that splay fault is taken into consideration suggested that the seafloor, particularly in the area above the ...
Geophysical networks provide data for better understanding of the dynamics in the Earth. For uniform distribution of stations on the Earth, we need to construct observatories in the sea. The western Pacific area had been selected for... more
Geophysical networks provide data for better understanding of the dynamics in the Earth. For uniform distribution of stations on the Earth, we need to construct observatories in the sea. The western Pacific area had been selected for installation of ocean-bottom observatories because it is ideal for problems related to plate subduction. Boreholes give best environment for geophysical observations in the sea. The observatories WP-1 and WP-2 are effectively located to complete a 1000-km span network in the western Pacific area. The WP-1 site is in the west Philippine Basin west of the Kyushu-Palau Ridge. The WP-2 observatory is situated in the northwestern Pacific Basin. Both the stations fill gap for global seismic networks. The WP-1 observatory was activated in March 2002 using an ROV and long-term observation started. In June 2006, an ROV dived to the WP- 1 (fourth visit) and recovered the data. At this visit, data recording was discontinued. Seismic records of 692-days (Mar. 2002 ...
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The hydroacoustic monitoring by the International Monitoring System for CTBT (Comprehensive Nuclear- Test-Ban Treaty) verification system utilizes hydrophone stations (6) and seismic stations (5 and called T- phase stations) for worldwide... more
The hydroacoustic monitoring by the International Monitoring System for CTBT (Comprehensive Nuclear- Test-Ban Treaty) verification system utilizes hydrophone stations (6) and seismic stations (5 and called T- phase stations) for worldwide detection. Some conspicuous signals of natural origin include those from earthquakes, volcanic eruptions, or whale calls. Among artificial sources are non-nuclear explosions and airgun shots. It is important for the IMS system to detect and locate hydroacoustic events with sufficient accuracy and correctly characterize the signals and identify the source. As there are a number of seafloor cable networks operated offshore Japanese islands basically facing the Pacific Ocean for monitoring regional seismicity, the data from these stations (pressure and seismic sensors) may be utilized to increase the capability of IMS. We use these data to compare some selected event parameters with those by IMS. In particular, there have been several unconventional a...
Most of the large earthquakes (magnitude greater than 8.0) observed in Japan fall into the subduction plate- boundary category. Based on the results of previous Nankai Trough research efforts, further research opportunities have been... more
Most of the large earthquakes (magnitude greater than 8.0) observed in Japan fall into the subduction plate- boundary category. Based on the results of previous Nankai Trough research efforts, further research opportunities have been proposed under the umbrella of the IODP scientific drilling proposal 603 (NanTroSEIZE: Nankai Trough Seismogenic Zone Experiment) ranked as the top level proposal in IODP. IODP
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Since 1997, Japan Marine Science and Technology Center (JAMSTEC) started a project to develop submarine cable systems for building a series of geophysical observation network at active seismogenic zones around Japan. These cabled systems... more
Since 1997, Japan Marine Science and Technology Center (JAMSTEC) started a project to develop submarine cable systems for building a series of geophysical observation network at active seismogenic zones around Japan. These cabled systems are very powerful tool for real-time and long-term geophysical observation. However, it has weakness in mobility compared to a land or a free-fall, pop-up ocean bottom
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Recent progress of seismic wave form inversion revealed overlapping asperities of large earthquakes in the Japan Trench, e.g., the 1994 Sanriku-Haruka-Oki earthquake (M=7.5) and 1968 Tokachi-Oki earthquake (M=7.9). It is also recognized... more
Recent progress of seismic wave form inversion revealed overlapping asperities of large earthquakes in the Japan Trench, e.g., the 1994 Sanriku-Haruka-Oki earthquake (M=7.5) and 1968 Tokachi-Oki earthquake (M=7.9). It is also recognized that the epicenters (initial break) of both earthquakes are situated at the trench-ward edge of the asperities, and the aftershocks were observed only around the asperities. Investigating structural
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ABSTRACT We located hypocenters for more than two years, using combined datasets from land-based observations and ocean-bottom seismological data acquired by a permanent cable geophysical observatory system (JAMSTEC system), installed off... more
ABSTRACT We located hypocenters for more than two years, using combined datasets from land-based observations and ocean-bottom seismological data acquired by a permanent cable geophysical observatory system (JAMSTEC system), installed off Kushiro-Tokachi in July 1999. Hypocenter distribution characterizes that: 1) double seismic zone just east of the cabled observatory system, 2) a relatively low seismicity west of the cabled system, and 3) characteristic shallow seismic activity below the cabled system.
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We deployed an OBS network in February–March 2005 in the rupture area of the Sumatra Andaman earthquake on 26 December 2004. We placed 17 short-term OBSs and two long-term OBSs, and recovered OBSs after observation for 19–22 days. The... more
We deployed an OBS network in February–March 2005 in the rupture area of the Sumatra Andaman earthquake on 26 December 2004. We placed 17 short-term OBSs and two long-term OBSs, and recovered OBSs after observation for 19–22 days. The hypocenter distribution from 10-day data of 17 OBS revealed the detailed structure of aftershock seismicity offshore of Sumatra Island. Aftershock seismicity associated with the subducting slab starts 40 km inward from the Sunda trench axis; it ceases at 50 km depth beneath the Aceh Basin, approximately 240 km inward from the trench axis. Aftershocks in 120–170 km from the trench axis consist of a surface with a dip of 10–12° dominated by a dip-extension type mechanism. Beyond the southwestern edge of the Aceh Basin, the aftershock activity becomes higher, and dominated by dip-slip type earthquakes, with a slightly increased dipping angle of 15–20°. Three along-arc bands of shallow seismicity were identified at 70 km inward from the Sumatra trench, 110...
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ABSTRACT In 2000 and 2001, the seafloor borehole seismological observatories WP-1 and WP-2 in the northwestern Pacific were installed. The WP-1 site is in the west Philippine Basin, and the WP-2 observatory is situated on a normal oceanic... more
ABSTRACT In 2000 and 2001, the seafloor borehole seismological observatories WP-1 and WP-2 in the northwestern Pacific were installed. The WP-1 site is in the west Philippine Basin, and the WP-2 observatory is situated on a normal oceanic Mesozoic crust in the northwestern Pacific Basin. The WP-1 observatory was activated in March 2002 using the ROV KAIKO and long-term observation was started. In June 2006, the new ROV KAIKO-7000II dived to the WP-1 (fourth visit) and recovered the data. At present, seismic records of 692-days (Mar. 2002 - Feb. 2004) have been obtained from the WP-1. The WP-2 observatory was activated in October 2000 using the KAIKO. In June 2005, the KAIKO-7000 made fourth visit to the WP-2 and recovered the data. Recording at the WP-2 has been suspended from the fourth ROV visit. In total, 436-days data (Oct. 2000 - Jan. 2001, Aug. 2001 - July 2002) were retrieved. The long-term variations of broadband seismic noise spectra (3 mHz -10 Hz) in oceanic basins were revealed. The stable ambient seismic noise levels enable us to record many teleseismic events uniformly in time. Especially, events with magnitudes greater than 6.5 were clearly recorded with a good signal to noise ratio.
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Digital broadband seismometer networks and GPS networks are the recent sources of rapid progress in solid Earth geophysics. But they do not exist beneath the oceans. The lack of observatories in deep oceans that cover 71% of the... more
Digital broadband seismometer networks and GPS networks are the recent sources of rapid progress in solid Earth geophysics. But they do not exist beneath the oceans. The lack of observatories in deep oceans that cover 71% of the Earth's surface has been considered a major deficiency in the seismic network by the scientific community. About 80% of the present plate
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Microearthquake observation using Ocean Bottom Seismometers (OBSs) was carried out to obtain a detailed distribution of microearthquakes beneath the area off Fukushima, in the middle section of the Japan Trench in the summer of 1997. The... more
Microearthquake observation using Ocean Bottom Seismometers (OBSs) was carried out to obtain a detailed distribution of microearthquakes beneath the area off Fukushima, in the middle section of the Japan Trench in the summer of 1997. The observation period spanned approximately one month. Almost all of the well-determined hypocenters occurred in the vicinity of the plate boundary in this region (approximately 100 km landward of the trench axis), while seismicity is markedly lower between this area and the trench itself. The seaward limit of the high seismicity region is close to the western end of the zone of direct contact between the oceanic crust and the overriding landward crust. Twenty-nine earthquakes were recorded within the overriding landward plate. Twelve earthquakes were recorded about 30 km below the plate boundary, and form a landward dipping plane that appears to be an up-dip continuation of the lower plane of the double seismic zone. The microseismicity characteristic...
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... Deepwater multibeam sonar surveys along the southeastern Hawaiian ridge: Guide to the CD-ROM. Auteur(s) / Author(s). SMITH John R. (1) ; SATAKE Kenji (2) ; SUYEHIRO Kiyoshi (3) ; Affiliation(s) du ou des auteurs / Author(s)... more
... Deepwater multibeam sonar surveys along the southeastern Hawaiian ridge: Guide to the CD-ROM. Auteur(s) / Author(s). SMITH John R. (1) ; SATAKE Kenji (2) ; SUYEHIRO Kiyoshi (3) ; Affiliation(s) du ou des auteurs / Author(s) Affiliation(s). ... Desmoronamiento tierra. ; Rift. ; ...
Seismological networks provide critical data for better understanding the dynamics of the Earth; however, a great limitation on existing networks is the uneven distribution of stations. In order to achieve a more uniform distribution of... more
Seismological networks provide critical data for better understanding the dynamics of the Earth; however, a great limitation on existing networks is the uneven distribution of stations. In order to achieve a more uniform distribution of seismic stations, observatories must be constructed in the ocean basins. The best configuration for oceanic seismic observatories is thought to be placement of seismometers in deep boreholes drilled into oceanic basement rocks. We constructed four borehole geophysical observatories in the western Pacific area, where plate-consuming boundaries are concentrated, from 1999 to 2001. The four seafloor borehole observatories, which were installed in cooperation with Ocean Drilling Program, are situated at three sites. The geophysical observatories were designed to work as stand-alone systems. The system of these observatories is basically identical except for geophysical sensors and the power supply. From an analysis of the data from broadband seismometers, we confirm that seismic observation in deep-sea borehole gives the best environment for long-term, low-noise, high-resolution earthquake observation in marine areas. Two observatories were collecting the data from the tiltmeter which recorded the earth tides clearly. It is not so difficult to connect the borehole system to a seafloor cable system, because the borehole system works with low voltages of power supply. It is important to cooperate with Integrated Ocean Drilling Program (IODP) for establishment of standard technology of connecting a borehole observation system to a seafloor cable system.
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ABSTRACT JAMSTEC has launched a new underwater cable network project (DONET) to cover the seismogenic zone offshore Kii Peninsula, central Japan. This project builds on lessons from past cable projects and aims to construct a core... more
ABSTRACT JAMSTEC has launched a new underwater cable network project (DONET) to cover the seismogenic zone offshore Kii Peninsula, central Japan. This project builds on lessons from past cable projects and aims to construct a core observation system composed of seismometers and pressure sensors. The planned infrastructure allows for future expansion of sensors to observe ocean processes to diagnose the condition of the Earth system. Furthermore, we believe the success of this project will mean expanding the cable network to the surroundings of Japan.
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... Couverture sédimentaire. ; Zone subduction. ; Structure vitesse. ; Sismographe fond sous marin. ; Serpentinisation. ; Couverture sédimentaire. ; ... Zone subduction. ; Croûte océanique. ; Mots-clés espagnols / Spanish Keywords. Asia.... more
... Couverture sédimentaire. ; Zone subduction. ; Structure vitesse. ; Sismographe fond sous marin. ; Serpentinisation. ; Couverture sédimentaire. ; ... Zone subduction. ; Croûte océanique. ; Mots-clés espagnols / Spanish Keywords. Asia. ; Sismógrafo fondo submarino. ; Serpentinización ...
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In August 2000, the seafloor borehole seismological observatory WP-2 in the northwestern Pacific Basin was installed successfully during the ODP leg191. The magnetic lineations in this area show the lithosphere was formed in Late Jurassic... more
In August 2000, the seafloor borehole seismological observatory WP-2 in the northwestern Pacific Basin was installed successfully during the ODP leg191. The magnetic lineations in this area show the lithosphere was formed in Late Jurassic to Early Cretaceous. In July 2002, we visited the WP-2 site to recover the data from the borehole seismometer. During this visit, we conducted a seismic survey with ocean bottom seismometers (OBSs), the borehole station and a controlled source to obtain the seismic crustal structure around the WP-2 observatory. Six OBSs were deployed on a 120-km-long line perpendicular to the magnetic lineations (Line1) and an 80-km-long line in the east-west direction (Line2). An airgun array with total volume of ~100 L was fired every 100 m. The data from the borehole observatory for the experiment will be recovered during a next ROV visit. All OBSs were retrieved after the shooting the airguns. The OBSs recorded the airgun signals at offset distances of more tha...