Seismological data assimilation
Our project DONET makes full use of this ocean-network observatory system not only as real-time monitoring but also the predictions of the mega-thrust earthquake generation. For examples, we would like to know whether the Tokai or Nankai earthquake occurs immediately after the sandwiched Tonankai earthquake, or the physical process and character of precursory change such as crustal deformations or seismic activities just before the mega-thrust earthquake. Note that these phenomena are observed for some previous great earthquakes. Recently, we have been able to qualitatively demonstrate some recurrence patterns of earthquake cycles all over the Nankai Trough.
For the next step, we aim to evaluate observational phenomena quantitatively from numerical simulation results. Such as postseismic deformation, slow slip events (SSE), and small repeating earthquakes is thought as objective data. The postseismic deformation and SSE have crustal changes significant to be observed. The small repeating earthquakes have recurrence intervals less than several years, which enables us to see the whole process of earthquake cycles. These advantages help us to narrow the value range of physical parameters for numerical simulations. When we put the narrow-ranged value of physical parameters into numerical models, the numerical simulation results can give a nearer way to observe the geophysical phenomena more clearly. The more clarified observational data analysis can give the more narrow-ranged value of physical parameters. That is assimilation of data analyses between observation data and simulation results.