History and features of trans-oceanic tsunamis and implications for paleo-tsunami studies

Abstract

Far-field tsunamis and their features, as well as methods to quantify trans-oceanic tsunamis are reviewed, with examples of instrumental and historical data. Tsunamis from the 1854 Nankai earthquakes, the 1946 Aleutian tsunami earthquake, the 1960 and 2010 Chile earthquakes, as well as the 2011 Tohoku earthquake, were recorded around the Pacific Ocean. The 1883 Krakatoa volcanic eruption caused volcanic tsunami in the Indian Ocean and meteotsunami in the Pacific Ocean. The 2004 Indian Ocean tsunami was also recorded in the Pacific Ocean. When a tsunami amplitude is larger than that of ocean tides, which usually requires the parent earthquake to be gigantic (Mw ~ 9), it can cause damage and may be historically documented. The trans-Pacific tsunamis described in historical documents include those from the 1700 Cascadia earthquake, the 1730, 1751, 1837, and 1877 earthquakes off Chile, and the 1687 and 1868 earthquakes off Peru. The tsunami record in Japan from the 1586 Peru earthquakes was found to be incorrect and should be discounted. The tsunami magnitude scale relates the tsunami heights to the earthquake size. Tsunami travel time can be computed from actual bathymetry, and the tsunami ray tracing provides relative amplitudes, due to focusing/defocusing caused by irregular bathymetry. Numerical computations from fault models produce tsunami amplitudes and waveforms, and indicate strong directivity due to strike of fault or orientation of subduction zones. Far-field tsunamis are often long-lasting, due to multiple reflections across the basin or on continental shelf, or due to resonance in bays/harbors. These features would provide important criteria to estimate tsunami sources from paleo-tsunami data.