Direct propagation energy estimation of the 2011 Japan tsunami using deep-ocean pressure measurements
Abstract
The total energy transmitted by tsunami waves is one of the most fundamental macroscopic quantities for interpreting the size of a tsunami, as well as for understanding the physical processes of tsunami propagation and predicting coastal impacts. We develop a real-time method to compute the tsunami propagation energy by inversion of deep-ocean pressure measurements with numerical models (tsunami source functions). The 2011 Japan tsunami was the first, and the largest, tsunami for which deep-ocean tsunameter (Deep-ocean Assessment and Reporting of Tsunamis, DART) data were available in the near and far fields from multiple well-positioned tsunameter stations. It provides sufficiently high quality tsunameter data for a thorough test of the real-time method. Based on the first wave recorded at the two closest tsunameters, 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 × 10^15 J. Measurements from 30 tsunameters and 32 coastal tide stations show excellent agreement with the forecasts obtained in real time. The near-field modeling study is also validated by the inundation patterns along the most severely impacted Japanese coast. 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 for many hours. 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 delayed tsunami waves and enhancement of the experimental tsunami forecast system. Reliable regional forecasts may be achieved from a first wave recorded at a single near-field tsunameter. The first wave recorded at two near-field tsunameters with different directionalities can provide accurate forecasts basin-wide. Adding the third tsunameter has little effect in far-field but it may lead to some improvement in the near-field. We apply the method to quantify the energy from more than 30 tsunamis in the period of 1946-2011, 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, a direct measure of tsunamis, for estimates of tsunami energy and accurate forecasting.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMNH33A1648T
- Keywords:
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- 4562 OCEANOGRAPHY: PHYSICAL / Topographic/bathymetric interactions;
- 4564 OCEANOGRAPHY: PHYSICAL / Tsunamis and storm surges;
- 4313 NATURAL HAZARDS / Extreme events;
- 4315 NATURAL HAZARDS / Monitoring;
- forecasting;
- prediction