The 2004 Sumatra tsunami was an unprecedented global disaster measured throughout the world oceans. The present study focused on a region of the southeastern Pacific Ocean where the westward circumferentially propagating tsunami branch converged with the eastward branch, based on data from fortuitously placed Chilean DART 32401 and tide gauges along the coast of South America. By comparison of the tsunami and background spectra, we suppressed the influence of topography and reconstructed coastal spectral ratios that were in close agreement with a ratio at DART 32401 and spectral ratios in other oceans. Findings indicate that even remote tsunami records carry spectral source signatures (birth-marks). The 2004 tsunami waves were found to occupy the broad frequency band of 0.25-10 cph with the prominent ratio peak at period of 40 min related to the southern fast-slip source domain. This rupture hot-spot of approximate to 350 km was responsible for the global impact of the 2004 tsunami. Data from DART 32401 provided validation of model results: the simulated maximum tsunami wave height of 2.25 cm was a conservative approximation to the measured height of 2.05 cm; the computed tsunami travel time of 25 h 35 min to DART 32401, although 20 min earlier than the actual travel time, provided a favorable result in comparison with 24 h 25 min estimated from classical kinematic theory. The numerical simulations consistently reproduced the wave height changes observed along the coast of South America, including local amplification of tsunami waves at the northern stations of Arica (72 cm) and Callao (67 cm).

Tsunami forecasting with real-time models and real-time data has always been one of the main goals of tsunami research. The February 27th, 2010 Chile tsunami provided the challenge and the opportunity to test the modern state of the science in tsunami forecasting. By contrast with the previous basin-wide tsunami generated by the third largest 2004 Sumatra earthquake, the fifth largest Chilean earthquake occurred at the time and in the area where a variety of real-time measurements and model forecast models have been available to assess the generated tsunami in real-time.

The impact of the 2010 Chilean tsunami along selected coastlines is studied using the NOAA high-resolution tsunami flooding forecast model augmented to include modeled tide heights in addition to deep-water tsunami propagation as boundary-condition input. This Chilean tsunami was observed at the Los Angeles tide station at mean low water, Hilo at low, Pago Pago at mid tide and Wake Island near high tide. Because the tsunami arrived at coastal communities at a representative range of tide stages, the 2010 Chile tsunami provides an opportunity to study the tsunami impact on different communities at different tide levels. The current forecast models are computed for mean higher high water as a worst case scenario. The evaluation of techniques for including predictable fluctuations due to the local tide in this study provides the opportunity to improve tsunami forecasting. To model tides together with tsunami waves in the NOAA flooding model, a medium-resolution tidal model (Egbert and Erofeeva 2002) and the NOAA tsunami propagation model are combined to generate boundary conditions for a high-resolution tsunami flooding model. At the initial time step, the tidal results are interpolated over the entire tsunami propagation grid. At all future time steps, the combined tide and tsunami amplitudes are incorporated into the numerical model from the boundary locations.

Los Angeles County hosts two of the busiest container ports in the United States. The ports are adjacent to one another in San Pedro Bay but are operated separately by the cities of Long Beach and Los Angeles. Due to their importance to United States commerce, the hazard posed by tsunami is of great concern as the potential devastation and impact would likely interrupt commerce and marine activities. Furthermore, a tsunami would be hazardous to both the resident coastal population and the tourist trade for which these cities rely on for income. The Maritime Museum, Aquarium of the Pacific, and Queen Mary would all potentially be impacted by a tsunami. The seismic history of the Southern California Bight is well documented and confirms the tsunami generating potential of the region. A comprehensive study of the threat from near-field generation was conducted by Borrero et al. (2001, 2004). Dykstra and Jin (2006) and Moffatt and Nichol (2007) expanded these near-field studies by inclusion of tsunamis generated in the far-field along the Cascadia Subduction Zone. Prior to the Kuril Islands event in November 2006, most studies focused on wave heights as the dominant measure of hazard. However, the impact of Kuril Islands tsunami at Crescent City, CA demonstrated that distant sources have the potential of inducing strong currents in harbors. To investigate the hazard posed by currents, a sensitivity study is performed for 322 tsunami sources for Mw 9.3 earthquakes along Pacific Rim subduction zones using the Method of Splitting Tsunamis model (Titov and Synolakis, 1998). Of the scenarios investigated, eleven sources in Alaska, Chile, Philippines, Manu, New Zealand and Vanuatu are identified as potentially hazardous to Ports in Southern California. Initial study results suggest that a Mw 9.3 earthquake can potentially trigger a tsunami with wave amplitudes reaching up to 2 m and currents exceeding 8 knots in Los Angeles Harbor. This study also suggests that Pacific Basin subduction zones in addition to those in Alaska and along the Aleutians are capable of generating tsunamis that pose a threat to Southern California harbors.

Over the period October 1999-January 2001, there were four separate occasions in which real-time reporting tsunami DART systems, deployed by NOAA in the North Pacific, were set into tsunami event reporting mode by regional earthquakes. Fortunately, none of these generated a dangerous tsunami. To go into event mode, the high-frequency fluctuations in the bottom pressure (BP) had to exceed a pre-programmed threshold of 3 cm H2O. An explanation for the events was found by examining the seismic surface waves generated by earthquakes. By Newton's third law, they produced BP fluctuations in response to the vertical bottom acceleration induced as the waves propagated along the water-bottom interface. This hypothesis was verified for the 1999 Hector Mine, California, earthquake by analyzing seismic data from the nearby SAO seismic station and the travel time for the seismic surface waves to reach a DART system deployed off Monterey Bay, California. These results are consistent with previous studies of BP fluctuations due to seismic waves. They further suggest that the 3 cm H2O threshold, applied to 15-second averaged BP data, works well to activate the DART tsunami event mode for earthquake magnitudes ≥7.0 and epicenter distances ≤610 km, while ignoring much smaller magnitude earthquakes (M ≤ 6) in the region.

Summary form only given. NOAA has a goal to mitigate the tsunami hazard to Hawaii, California, Oregon, Washington, Alaska, and U.S. possessions in the Pacific region. Fulfilling this goal requires research, development and implementation of tsunami forecasts (with increased accuracy and speed) and the creation of state-of-the-art inundation maps. The strategy is to focus research and development on advanced technologies for: (a) field measurements using a real-time tsunami warning network and (b) numerical modeling-pre-computed databases of tsunami simulations for rapid forecasting of tsunami heights (tuned to particular tsunami events using data assimilation from the real-time buoy network) and inundation maps for threatened coastal communities (generated in cooperation with various institutions and agencies). The Project has also taken the lead in the creation of Web-based Tsunami Community Modeling Activities to share software, data, simulations, and expertise among institutions and agencies involved in tsunami modeling. This broad approach to tsunami mitigation is both necessary and a challenge since it requires the coordination and integration of instrument development, numerical modeling and Web-based implementation. The authors present examples of this work for Pacific tsunamis that are incident on Hawaii and the Oregon Coast