The tsunamicity of the Sanriku Coast has been shown to have an anomalous gap in energy, or tsunami magnitude. Furthermore, this gap in magnitude correlates directly with epicentral distance from shore-there also is a gap in the epicenter distribution versus offshore distance. The large tsunamis are generated on the east side of the trench. The gap is for intermediate tsunamis, of which there are none. These observed features can be explained by considering the spatial distribution of shear stress about a subduction zone. The stress attains maxima at two locations: one is on the upper interface between the mantle and the downgoing slab; the other is within the oceanic lithosphere, at the flexure. The observation rationalizes the observed anomalies of tsunamicity.
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Copyright© The Volcanological Society of Japan