Monitoring earthquakes using submarine cables Transitions from Passive to Active Monitoring

Eight cabled observatories are all installed to aid earthquake studies for disaster mitigation at the future potential hazards that could take place at plate boundaries surrounding the Japanese islands. Scientific results started appearing in the literature using passive, real-time and continuous time series of data acquired on the seafloor for seismic and tsunami signals. The knowledge about earthquake source mechanisms has been deepened in terms of seismic asperity with respect to hydrogeological findings at seismogenic zones. We are now expecting possible extension of observations to use active sources to monitor changes in physical properties of plate boundary interface. In this paper, we try to summarize the latest scientific achievements in this seismogenic studies from cabled observatotions and, then, to discuss advantages of detecting such changes in physical properties at depth in time and space. The development of offshore monitoring system and active monitoring/mapping must be well considered for profound understanding of earthquake generation processes..