The June 15, 1896 Sanriku earthquake generated devastating tsunamis with the maximum run-up of 25 m and caused the worst tsunami disaster in the history of Japan, despite its moderate surface wave magnitude (Ms=7.2) and weak seismic intensity. This is a typical tsunami earthquake, which generates anomalously larger tsunamis than expected from its seismic waves. Previously proposed mechanisms of tsunami earthquakes include submarine slumping and slow rupture in the accretionary wedge or in the subducted sediments. In this paper, we estimate the fault parameters of the 1896 tsunami earthquake by numerically computing the tsunami and comparing the waveforms with those recorded at three tide gauge stations in Japan. The result indicates that the tsunami source is very close to the Japan trench and the fault strike is parallel to the trench axis. The fault width is about 50 km, suggesting that the tsunami earthquake is a slow rupture in the subducted sediments beneath the accretionary wedge.

Fault parameters of the 1896 Sanriku tsunami earthquake estimated from tsunami numerical modeling

Review on Near-Field Tsunami Forecasting from Offshore Tsunami Data and Onshore GNSS Data for Tsunami Early Warning

Tsunami research has been advanced by developments in theory and in the methods of observation. Coastal records such as tide gauges and inundation surveys have played an important role for a long time. Offshore observations have been undertaken widely across deep oceans. After the 2011 Tohoku-Oki earthquake, dense and wide offshore tsunami observation was begun. We now expect tsunami generation to be observed inside the focal areas of huge earthquakes. New observations require new theoretical frameworks. In Sect. 1.1, we briefly introduce the development of offshore observation using ocean-bottom pressure gauges. Section 1.2 illustrates the 2011 Tohoku-Oki earthquake tsunami. This is to show what we know and what we do not know about that huge earthquake and tsunami. Section 1.3 introduces a new observation network that was deployed after the Tohoku-Oki earthquake. This observation network is designed for the detection of tsunamis inside the focal area. In Sect. 1.4, we present the focus of this book. The wide use of ocean-bottom pressure gauges and the construction of new observation network can greatly advance our understanding of tsunami. This book is aimed to illustrate theoretical frameworks in analyzing these records.

http://link.springer.com/content/pdf/10.1007/978-4-431-56850-6.pdf

Tsunami Generation and Propagation

This study is an attempt towards understanding the sources of long oscillations observed within the Pacific Ocean following the 11 March 2011 Tohoku earthquake. We present evidence that extremely long modes of the Pacific Ocean in the range of 2–48 h were excited by this giant tsunami. A numerical approach was employed to calculate the basin-wide modes of the Pacific Ocean, resulting in 49 modes in the range of 2–48 h. We studied 15 tide-gauge records around the Pacific Ocean in order to extract basin-wide modes of the Pacific Ocean excited by this transoceanic tsunami. Spectral analysis of these tide-gauge records showed that some of the calculated basin-wide modes were indeed excited by the Tohoku tsunami. The observed modes ranged from 2 to 49.8 h. We attributed the long oscillations of the Pacific Ocean during the 2011 Tohoku tsunami to the excitation of these basin-wide modes, which can be grouped into global modes (15–48 h) and regional modes (2–15 h). We classified the signals on the tide gauges into three groups: (1) basin-wide modes (>1.5 h), (2) the tsunami source periods (20–90 min), and (3) local bathymetric effects (<20 min). The average contributions to the total tsunami energy were 6.4 % for the basin-wide mode, 64.1 % for the tsunami source, and 29.5 % for the local bathymetry, although the ratios varied from station to station. Simulations suggest that the amount of contribution of basin effects to the total tsunami energy depends on the location of the tsunami source.

https://purehost.bath.ac.uk/ws/files/242429995/Heidarzadeh_Satake2014_Article_ExcitationOfBasin_WideModesOfT.pdf

Excitation of Basin-Wide Modes of the Pacific Ocean Following the March 2011 Tohoku Tsunami

A simple parameterization of the loading deformation of the seafloor is incorporated into a tsunami simulation model in order to realistically calculate tsunami travel time, especially at regions far from the source. The parameterization uses one scalar parameter that is optimized effectively by far-field, deep-sea records of recent giant tsunamis: the 2011 Tohoku and the 2010 Chilean tsunamis. Using this parameterization with the optimal values, the observed tsunamis are realistically simulated in both near and far fields. The optimal values seem equivalent for both giant tsunamis, and are relatively smaller than those previously verified for ocean tide modeling, which is reasonable because of the shorter wavelengths of tsunamis.

https://link.springer.com/content/pdf/10.5047%2Feps.2013.03.010.pdf

Simulation of distant tsunami propagation with a radial loading deformation effect

A tsunami coda lasting more than 5 days was clearly recorded across the Pacific Ocean following the 2011 Tohoku‐Oki earthquake. We found that the coda energy per unit area (elapsed time of 60–96 hr from the earthquake origin time) does not show a systematic variation with respect to the travel distance at the stations located at sea depths deeper than 2000 m, whereas the maximum amplitude near the source is significantly larger than those of the far‐field stations. This feature is similar to that of a seismic coda in the sense that the coda energy is distributed uniformly in space. The average tsunami coda decays with a decay time of ∼24  hr. When we carefully examined the tsunami waveform near Japan, a large‐amplitude wave was identified at an elapsed time of ∼48  hr, which corresponds to the round‐trip travel time for waves reflected from Chile. To investigate the excitation mechanisms of the tsunami coda, we conducted a tsunami simulation using a global model. Although linear long‐wave tsunami equations were found to overestimate the observed coda amplitude, the equations including an intrinsic energy loss could successfully simulate the observed coda decay if a bottom friction coefficient of 10 −5 was assumed. This indicates that not only wave scattering but also intrinsic energy loss plays an important role in the tsunami coda excitation and decay process.

Tsunami Coda across the Pacific Ocean Following the 2011 Tohoku‐Oki Earthquake

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Tsunami Coda across the Pacific Ocean Following the 2011 Tohoku‐Oki Earthquake