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R&D Center for Earthquake and Tsunami (CEAT)

Real-time seismic analysis

Real-time analysis by ocean floor network system

The technology of oceanic observation has been drastically developed over the last decade. Our institution has installed cabled observatory systems near the Nankai and Sagami Troughs, and the Kuril trench zone. At the 2003 Tokachi-oki earthquake, we successfully recorded seismic and tsunami waveforms just above the focal region, which improves our understanding of the generation process of earthquake, geodetic deformation, and tsunami.

We are now challenging the deployment of cabled "network" observatory (DONET) with real-time recording systems in the seismogenic zone of M8 class, Tonankai, mega-thrust earthquake. The figure below shows the assignment of the network system and an example of methodology analysis using waveform data to issue early warnings for mitigation and disaster prevention. In this methodology, after detecting signals immediately from earthquake, we gather and select data and then execute the source analysis by grid search and/or inversion method. For advancing more accurate analysis, we implement structure models constructed by compiling the results of seismic surveys in and around the seismogenic zone into this method. We will provide the analysis results on the source elements, e.g. magnitude, focal mechanism and location of asperity, by using our network data before arriving strong motion and tsunami in populated land areas.

Additionally, the hypocenters of earthquakes that occurred around the Nankai trough have been determined by using the data obtained from DONET. Intensive seismic activity off the Kii Peninsula was found. The earthquakes are mainly distributed in three clusters, of which locations well overlap with the aftershock distribution of the 2004 off the Kii Peninsula earthquakes (M_JMA=6.9 and 7.4). Thus, it is considered that most earthquakes in the present activity are aftershocks of the 2004 earthquakes.