[1] We have developed a method to compute the total energy transmitted by tsunami waves, to the case where the earthquake source is unknown, by using deep-ocean pressure measurements and numerical models (tsunami source functions). Based on the first wave recorded at the two closest tsunameters (Deep-Ocean Assessment and Reporting of Tsunamis (DART)), our analysis suggests that the March 11, 2011 Tohoku-Oki tsunami generated off Japan originated from a 300-400 km long and 100 km wide area, and the total propagated energy is 3 Â 10 15 J (with 6% uncertainty). Measurements from 30 tsunameters and 32 coastal tide stations show excellent agreement with the forecasts obtained in real time. Our study indicates that the propagated energy and the source location are the most important source characteristics for predicting tsunami impacts. Interactions of tsunami waves with seafloor topography delay and redirect the energy flux, posing hazards from delayed and amplified waves with long duration. Seafloor topography also gives its spectral imprint to tsunami waves. Travel time forecast errors are path-specific and correlated to the major wave scatterers in the Pacific. Numerical dissipation in the propagation modeling highlights the need of high-resolution inundation models for accurate coastal predictions. On the other hand, it also can be used to account for physical dissipation to achieve efficiency. Our results provide guidelines for the earliest reliable tsunami forecast, warnings of long duration tsunami waves signals and enhancement of the experimental tsunami forecast system. We apply the method to quantify the energy of 15 past tsunamis, independently from earthquake magnitudes. The small tsunami to seismic radiation energy ratios, and their variability (0.01-0.8%), reinforce the importance of using deep-ocean tsunami data, the direct measures of tsunamis, for estimates of tsunami energy and accurate forecasting.

[1] This study applies tsunami forecast models developed for NOAA's Tsunami Warning and Forecast System to investigate the May 2006 Tonga Tsunami. Inversion of the Deep-ocean Assessment and Reporting of Tsunamis (DART) measurements estimates a tsunami magnitude equivalent to an earthquake moment magnitude of 8.0. The DARTconstrained modeling forecasts show good agreement with observations at eight coastal tide stations in Hawaii, U.S. West Coast, and Alaska, including first arrival times, wave periods, wave amplitudes, and decay during the day following the earthquake. The forecast system correctly reproduces the reflected waves from North America and the scattered waves by the bottom topography in the South Pacific, which arrived in the Hawaiian Islands 16 and 18.5 h after the earthquake, respectively. Wavelet analysis of the tsunami waves suggests that harbor and local shelf resonances may be predominantly responsible for the late occurrence of the maximum wave observed in some coastal areas. These results suggest expanding the operational use of the real-time forecast models and demonstrate the applicability of the forecast results for ''all-clear'' evaluations, search and rescue operations, as well as event and postevent planning. This research highlights the value of high-resolution inundation models in real-time forecasts during a long-duration hazard for coastal communities. It also provides a rigorous and successful test of the performance and accuracy of the forecast models when run in real-time mode.Citation: Tang, L., V.

The ability to accurately forecast potential hazards posed to coastal communities by tsunamis generated seismically in both the near and far field requires knowledge of so-called source coefficients, from which the strength of a tsunami can be deduced. Seismic information alone can be used to set the source coefficients, but the values so derived reflect the dynamics of movement at or below the seabed and hence might not accurately describe how this motion is manifested in the overlaying water column. We describe here a method for refining source coefficient estimates based on seismic information by making use of data from Deep-ocean Assessment and Reporting of Tsunamis (DART r ) buoys (tsunameters). The method involves using these data to adjust precomputed models via an inversion algorithm so that residuals between the adjusted models and the DART r data are as small as possible in a least squares sense. The inversion algorithm is statistically based and hence has the ability to assess uncertainty in the estimated source coefficients. We describe this inversion algorithm in detail and apply it to the November 2006 Kuril Islands event as a case study.

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