Different depths of near-trench slips of the 1896 Sanriku and 2011 Tohoku earthquakes

Abstract

The 1896 Sanriku earthquake was a typical 'tsunami earthquake' which caused large tsunami despite its weak ground shaking. It occurred along the Japan Trench in the northern tsunami source area of the 2011 Tohoku earthquake where a delayed tsunami generation has been proposed. Hence the relation between the 1896 and 2011 tsunami sources is an important scientific as well as societal issue. The tsunami heights along the northern and central Sanriku coasts from both earthquakes were similar, but the tsunami waveforms at regional distances in Japan were much larger in 2011. Computed tsunamis from the northeastern part of the 2011 tsunami source model roughly reproduced the 1896 tsunami heights on the Sanriku coast, but were much larger than the recorded tsunami waveforms. Both the Sanriku tsunami heights and the waveforms were reproduced by a 200-km × 50-km fault with an average slip of 8 m, with the large (20 m) slip on a 100-km × 25-km asperity. The moment magnitude M w of this model is 8.1. During the 2011 Tohoku earthquake, slip on the 1896 asperity (at a depth of 3.5-7 km) was 3-14 m, while the shallower part (depth 0-3.5 km) slipped 20-36 m. Thus the large slips on the plate interface during the 1896 and 2011 earthquakes were complementary.

Frequency-dependent amplification of the Sanriku tsunamis in Ryori Bay

“…As previously outlined, many source models have been proposed for the 2011 event (e.g., Ammon et al 2011;Koper et al 2011;Fujii et al 2011;Romano et al 2012;Yokota et al 2012;Satake et al 2013); The source model of Satake et al (2013) was adopted in the present study for the simulation of the tsunami because their source model reproduces better offshore wave profiles of the tsunami. The characteristics of the other two sources have also been investigated based on observed earthquake and tsunami records (e.g., Obana et al 2017;Satake et al 2017;Okal et al 2016;Abe 1973Abe , 1978. Kanamori (1971), for example, proposed a source model of the 1933 event based on observed seismic data.…”

“…Tanioka and Seno (2001) discussed the additional sea surface deformation of the 1896 tsunami due to horizontal displacements and bathymetry, using the model proposed by Tanioka and Satake (1996a). Satake et al (2017) re-estimated the source model based on a tsunami waveform inversion technique and compared the estimated slip amounts with that of the 2011 earthquake. Although there are some uncertainties with understanding the two events, many previous studies concluded that the 1933 earthquake was an outer-rise earthquake (e.g., Okal et al 2016;Christensen and Ruff 1988) and that the 1896 earthquake was an earthquake that occurred at (or near) the plate interface of the subducting zone (e.g., Satake et al 2017;Tanioka and Satake 1996a).…”

“…Satake et al (2017) re-estimated the source model based on a tsunami waveform inversion technique and compared the estimated slip amounts with that of the 2011 earthquake. Although there are some uncertainties with understanding the two events, many previous studies concluded that the 1933 earthquake was an outer-rise earthquake (e.g., Okal et al 2016;Christensen and Ruff 1988) and that the 1896 earthquake was an earthquake that occurred at (or near) the plate interface of the subducting zone (e.g., Satake et al 2017;Tanioka and Satake 1996a). In the present study, the source models of Okal et al (2016) and Satake et al (2017) were adopted for the simulations of the 1933 and 1896 tsunamis, respectively.…”

“…The 1933 earthquake was the largest earthquake hitherto ever reported among normal fault earthquakes, with Mw = 8.5 (Okal et al 2016), and it caused a large tsunami that resulted in 3000 deaths (Uchida et al 2016). The 1896 earthquake was an earthquake that generated a relatively larger tsunami, i.e., tsunami earthquake, with Mw = 8.1, and it caused the worst tsunami disaster ever in Japan, resulting in approximately 20,000 causalities (Satake et al 2017;Kanamori 1972). Large run-up heights of 23, 29, and 38 m were observed at the bayhead in Ryori Bay, located on the Sanriku coast ( Fig.…”

“…Suzuki et al (2012) focused on the run-up heights of the Fig. 1 a The rupture areas of the 2011, 1933, and 1896 earthquakes (the squares of black, light blue, and red) based, respectively, on Satake et al (2013), Okal et al (2016), and Satake et al (2017) and the location of Ryori Bay (yellow circle); b the computation domain for the inundation simulation with the control line along the longitudinal direction of the bay. The focal mechanism of the 2011 earthquake displayed in a is based on the Global Centroid-Moment-Tensor Catalogue (Dziewonski and Anderson 1981;Ekström et al 2012).…”