8:30 AM - 8:45 AM
[J04-5-01] Tsunami data assimilation including effects of coseismic deformation for real-time tsunami forecasting using pressure gauges
Recent developments of dense networks of ocean-bottom pressure gauges are expected to bring us highly reliable, fast warnings of tsunami attacks. Among wide variety of proposed methods for tsunami forecasting, data assimilation (DA) approach provides a successive estimation of tsunami wavefield rather than estimates of seismic source fault slip or initial sea height, which is suitable for real-time monitoring. The ocean bottom pressure gauge records, however, contain an offset due to coseismic deformation beneath the sensor. Here I propose a new method on the tsunami DA with separation of the coseismic deformation to estimate the true tsunami height.
In the original DA method, the pressure gauge data are directly assimilated to the shallow-water equation. The tsunami height at a step away is forecasted by numerical simulation, and the residual between forecasted and observed tsunami heights at the station location is used to assimilate the surrounding tsunami wavefield by the optimum interpolation kernel. Since the data assimilation uses the tsunami height estimated by pressure gauges, the assimilated tsunami wavefield should be contaminated by the coseismic deformation.
In the proposed method, we estimate the coseismic deformation in addition to the tsunami height. It is shown that the coseismic deformation can be approximately expressed as a solution of an inhomogeneous Laplace equation having pressure height as a source term. This equation is numerically solved for estimation of coseismic deformation term. A numerical experiment for this method with a real station layout was performed. By applying the proposed method to hypothetical observations, it correctly separated the coseismic deformation. It is noteworthy that the initial tsunami rise-up at very early time due to the coseismic deformation was clearly detected by this separation, which could be useful for shortening the necessary time for forecasting tsunami.
In the original DA method, the pressure gauge data are directly assimilated to the shallow-water equation. The tsunami height at a step away is forecasted by numerical simulation, and the residual between forecasted and observed tsunami heights at the station location is used to assimilate the surrounding tsunami wavefield by the optimum interpolation kernel. Since the data assimilation uses the tsunami height estimated by pressure gauges, the assimilated tsunami wavefield should be contaminated by the coseismic deformation.
In the proposed method, we estimate the coseismic deformation in addition to the tsunami height. It is shown that the coseismic deformation can be approximately expressed as a solution of an inhomogeneous Laplace equation having pressure height as a source term. This equation is numerically solved for estimation of coseismic deformation term. A numerical experiment for this method with a real station layout was performed. By applying the proposed method to hypothetical observations, it correctly separated the coseismic deformation. It is noteworthy that the initial tsunami rise-up at very early time due to the coseismic deformation was clearly detected by this separation, which could be useful for shortening the necessary time for forecasting tsunami.