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Suyehiro, K.
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- PublicationOpen AccessDeep-sea borehole seismological observatories in the western Pacific: temporal variation of seismic noise level and event detection(2006-03-20)
; ; ; ; ; ; ; ; ; ;Shinohara, M.; Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan ;Araki, E.; Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan ;Kanazawa, T.; Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan ;Suyehiro, K.; Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan ;Mochizuki, M.; Institute of Industrial Science, University of Tokyo, Tokyo 153-8505, Japan ;Yamada, T.; Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan ;Nakahigashi, K.; Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan ;Kaiho, Y.; Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan ;Fukao, Y.; Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan; ; ; ; ; ; ; ; 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 marine areas. The best configuration for oceanic seismic observatories is thought to be placement of seismometers in deep boreholes. Two deep-sea borehole seismological observatories (WP-1 and WP-2) were constructed in the western Pacific and form the initial installations of a 1000 km span network. At present, seismic records of more than 400 total days were retrieved from both the WP-1 and WP-2. Long-term variations in broadband seismic noise spectra (3mHz - 10 Hz) in the western Pacific were revealed from these records, and the data showed that ambient seismic noise levels in borehole observatories are comparable to those of the quietest land seismic stations. In addition, there is little temporal variation of noise levels in periods greater than 10 seconds. Due to this low seismic noise environment, many teleseismic events with magnitudes greater than 5 were recorded. It is confirmed that seismic observation in deep-sea borehole gives the best environment for earthquake observation in marine areas.257 453 - PublicationRestrictedGEMS: the opportunity for stress-forecasting all damaging earthquakes worldwide(2006-09-28T11:48:26Z)
; ; ; ; ; ; ; ;Crampin, S.; School of GeoSciences, University of Edinburgh, Edinburgh, Scotland UK; also at Edinburgh Anisotropy Project, British Geological Survey, Edinburgh, Scotland UK ;Zatsepin, S. V.; School of GeoSciences, University of Edinburgh, Edinburgh, Scotland UK ;Browitt, C. W. A.; School of GeoSciences, University of Edinburgh, Edinburgh, Scotland UK ;Keilis-Borok, V. I.; International Institute of Earthquake Prediction and Mathematical Geophysics, Russian Academy of Sciences, Moscow, Russia; also at Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California USA ;Suyehiro, K.; JAMSTEC, Yokosuka, Japan ;Gao, Y.; Institute of Earthquake Science, China Earthquake Administration, Beijing, China ;Walter, L.; Geospace Engineering Research International, Texas, USA; ; ; ; ; ; A new understanding of rock deformation allows the accumulation of stress before earthquakes to be monitored by using shear-wave splitting to assess stress-induced changes to microcrack geometry. Using swarms of small earthquakes as the source of shear-waves, such stress accumulations have been recognised with hindsight before some fifteen earthquakes worldwide. On one occasion the time, magnitude, and fault-break of an M 5 earthquake was successfully stress-forecast in a comparatively narrow magnitude/time window. However, suitable swarms of small earthquakes are very uncommon, and routine forecasting requires measurements of controlled-source observations at bore-hole Stress-Monitoring Sites (SMSs). A prototype SMS confirmed that both science and technology are effective for monitoring stress changes before earthquakes, and the sensitivity is such that a network of SMSs, on a 400 km-grid, say, could stress-forecast all M ≥ 5 earthquakes, that is all damaging earthquakes, within the grid. This paper suggests that a Global Earthquake Monitoring System (GEMS) could forecast all damaging earthquakes in both developing and developed countries worldwide.173 11