Tsunami source of the 2011 Tohoku-Oki earthquake, Japan: Inversion analysis based on dispersive tsunami simulations

Abstract

[1] The large tsunami of the 2011 Tohoku-Oki earthquake was clearly recorded by the ocean bottom pressure and GPS wave gauges deployed in and around Japan. We estimated the initial tsunami water height distribution by inversion analysis of the waveforms based on dispersive tsunami simulations. The distribution is characterized by a peak height of 8 m located near the trench and the high-water (>2m) region extending landward with a width of ∼100 km. A series of numerical simulations suggests that a relatively steep peak located near the trench is necessary in order to simultaneously reproduce the dispersive wave at a far-field station and the near-field waveforms. Furthermore, we estimated the coseismic slip distribution at the plate boundary, which indicates that large slip (∼30 m) occurred at a depth of 20 km, which corresponds to a large slip deficit area in the interseismic period. Another slip (∼25 m) occurred at the shallower part (<10 km) during the rupture.

Dispersion and nonlinear effects in the 2011 Tohoku‐Oki earthquake tsunami

“…For the 2011 Tohoku-Oki earthquake tsunami, it would be significant to reproduce the tsunami waveform recorded at station 21418, because the record that is located near the source ($500 km) can provide a vast amount of information on the source which is free from distortion caused by the path and site effects. It also shows a clear dispersive wave which can be effectively used for extracting a vast amount of information about the short wavelength component of the source [e.g., Saito et al, 2011;Grilli et al, 2012]. Figure 7 shows the observed and calculated inundation area around the Sendai Plain, which was the widest inundation area for this event.…”

“…This source model was characterized by a steep bump higher than 8 m near the trench and characterized by rich short-wavelength components. MacInnes et al [2013] reported that the source model of Saito et al [2011] reproduced the tsunami waveforms recorded at the deep sea better than other models.…”

“…The bathymetry data used in the simulation were compiled from 1350 m, 450 m, 150 m, and 50 m grid resolution bathymetry data provided by Central Disaster Management Council, Government of Japan. The area is represented by 3200 3 2600 grids with a grid spacing of 500 m. The initial tsunami height distribution was used, which was estimated by the waveform inversion analysis in Saito et al [2011]. This source model was characterized by a steep bump higher than 8 m near the trench and characterized by rich short-wavelength components.…”

“…A gigantic tsunami excited by the earthquake struck the Pacific coast of Japan and more than 15,000 people were killed [e.g., Hayashi et al, 2011]. The ocean-bottom pressure gauges deployed in the focal area recorded the huge tsunami [Saito et al, 2011] produced by the seafloor rise of $ 5 m . The oncoming huge tsunami was recorded from offshore to onshore along the Sanriku coast Maeda et al, 2011].…”

“…Some studies used not only tsunami data but also seismic and geodetic data for the estimation of the earthquake source process [e.g., Yokota et al, 2011;Gusman et al, 2012;Hooper et al, 2012;Yamazaki et al, 2013]. Saito et al [2011] constructed an initial tsunami-height distribution based on the tsunami waveform inversion analysis, in which they used near-field tsunami waveforms that included the records inside the focal area [Hino et al, 2009] and employed the linear Bousinessq equations (linear dispersive equations) to correctly reproduce a short-wavelength tsunami source. Although differences are generally recognized among the source models of those studies, the estimated sources show a common feature in which a steep and high initial-height distribution of more than 8 m formed near the trench.…”