Fig 6 - uploaded by Junzo Kasahara
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M s = 6.1 earthquake, November 1, 1999, which occurred off Taiwan. NS (34.4 × 10 − 5 m/s full scale), EW (the same scale as NS) and Z (14.1 × 10 − 5 m/s). Horizontal axis: 20 min record.
Source publication
A multidisciplinary Ocean Bottom Observatory (MDOBO) was installed on VENUS (Versatile Eco-monitoring Network by Undersea-cable System) a depth of 2,170 meters on the slope of the Ryukyu Trench. In this context, “Eco-“ refers to both economic (e.g., earthquake hazard mitigation) and ecological motivation. The first step in this instillation was to...
Context in source publication
Context 1
... number of earthquakes, including two large events in Southern California (Ms=7.3) on October 16 and the Taiwan earthquake (Ms= 6.1) of November 1, 1999, were observed ( fig. 6) (Kasahara and Sato, 2000). The Taiwan event was one of the aftershocks of the September 21, 1999 Chi-Chi (Taiwan) Earthquake (Ms=7.7). The noise levels in data obtained from the broadband seismometers seem to be extremely high (e.g., ≅5 µm/s at 300 s for horizontal com- ponents) (fig. 7). The change in amplitudes with time is several ...
Similar publications
A MultiDisciplinary Ocean Bottom Observatory (MDOBO) was installed on VENUS (Versatile Eco-monitoring Network by Undersea-cable System) at a depth of 2170 m on the slope of the Ryukyu Trench. In this context, «Eco-»refers to both economic (e.g., earthquake hazard mitigation) and ecological motivation. The first step in this instillation was to inse...
Citations
... This has allowed investigations of geophysical processes at both global and regional scales in the Pacific Ocean and the European margin, under different programs from the United States, Canada, Japan, and the European Community (see Delaney et al. 2000; Stutzmann et al. 2001; Shirasaki et al. 2003; and Romanowicz et al. 2006; for a review, see also Favali and Beranzoli 2006). Japan was the first country to work on the extension of its geophysical monitoring to the ocean floor (Kasahara et al. 2006), and now has eight cabled seafloor observatories operating to date within the framework of the ARENA (Advanced Real-time Earth Monitoring Network in the Area) project. At the present feasibility study stage, ARENA is designed to deploy a mesh-like network of underwater cables that connects both terrestrial and underwater observatories all around the Japanese archipelago (Massion et al. 2004). ...
... In spite of this, in many of the most seismically hazardous and highly populated areas (e.g., off Chile, Mexico, and in Mediterranean countries such as Portugal, Italy, Greece, and Turkey), geohazard monitoring systems still remain exclusively land-based, with seafloor data generally acquired only on a temporary basis during episodic periods. The major causes that at present limit the extensive implementation of seafloor networks for geohazard monitoring relate to the need for the huge investment of funds, high management costs, and the technical and logistical difficulties involved in the deployment and maintenance of monitoring systems on the seafloor (Kasahara et al. 2006). For instance, the logistical elements—including ships, submersible vehicles, and specialized teams of operators—are too expensive for a single research institution, and assembling them thus demands cooperative efforts and cost sharing. ...
Geohazards monitoring can benefit greatly from the integration of seafloor and land observations, because many of the most seismogenic zones and active volcanoes are situated in oceanic basins. Similarly, many volcanic and seismic areas located in coastal zones extend their activities into nearby marine sectors. The known features of these marine activities are restricted to episodic events, and nothing much is known about the long-term processes. However, marine technology has advanced over the past two decades to the point where long-term and permanent observatories and networks are under development on the seafloor. CUMAS. 10.1785/gssrl.80.2.203
Japanese ocean science community has installed eight cabled observatories in Japanese water in the past. Japan started installing cabled observatories in the middle of 1970's for disaster mitigation as countermeasure to possible megathrust earthquake in the Tokai region, about 100 km away from Tokyo. Their first system composed of metal wires used frequency modulated signal transmission for carrying data acquired on the seafloor to land. The first Japanese cabled observatory was installed in 1978, i.e., five years after the initiation of engineering development. Since 1990, all newly installed cabled observatories have used fiber optic communication lines following the technological development in the telecom industry. Obviously, the development of scientific cabled observations adjusted their stride with that in the industry. Since the major telecom cables have been installed in a pointtopoint configuration, scientific cabled observatories have been developed in the same way. In general, they have a land station and a line of cable along which observational instruments or junction boxes are connected inline in the place of repeaters. Recently, scientists started trying to expand their observations in a way to enhance observational capabilities using multidisciplinary sensors as the growth of their understanding to invisible processes in the sea. Cabled observatory projects are now underway to enable nextstep data acquisition on the seafloor with much wider spatial coverage and dense observational instruments. Technological development from a pointtopoint configuration to a network, whose topology could be either ring or star shape, has become necessary. Power supply and communication mechanisms to all of sensors attached to observatory need to be revisited as well.
