Scientific results from underwater earthquake monitoring using cabled observatories

Scientific results started appearing in the literature using realtime and continuous time series of data obtained on the seafloor for seismic and micro-tsunamic observations. JAMSTEC has developed three out of a total of eight cabled observatories in the Japanese water. The installed observatories are all operating to aid earthquake studies for disaster mitigation at the future potential hazards, which take place at plate boundaries surrounding the Japanese islands. Along with earthquake activity monitoring purposes, it has become clear that there are potentially and scientifically meaningful outcome from such observations. We summarize the latest scientific results from monitored data produced by our cabled observatories and, then, to demonstrate advantages of such underwater seismic and tsunamic stations. Until now, three main areas could be pointed out as meaningful scientific products from cabled observations: (1) fine mapping of offshore seismicity, (2) modeling of micro-tsunamic pressure fluctuations caused by deep earthquakes, and (3) constraining earthquake source parameters such as source depths of offshore events using tsunami simulation. They are all interesting scientific results from the observational data could also readily be exploited for earthquake studies on deformation processes at the plate boundaries and on early tsunami warning system as a part of future disaster mitigation methodologies. It is obvious that newly deployed monitoring systems have revealed, at least partially, meaningful phenomena, which have been invincible due to lack of observations in the offshore. Technical and theoretical developments for offshore earthquake monitoring must be well considered for profound perception of geophysical processes associated with offshore seismic activities.