Jeff of PA, if the water were reaching to where it hadn't/wasn't already "acclimated" to, then perhaps you would have a point. But in this case, it came at the low tide time. So even when you add the footage of the surge, to the low-tide height, the resulting height STILL wasn't even above the high water mark, of even a normal high tide time.
Or put another way: There are some storms with their accompanying swells, that we watch and monitor closely for their time of land-fall. And if the "swell train" happens to be short (say.... just a 6 hour bubble of time) and that time happens to occur at a low tide time, we've noticed that as FIERCE as the waves may be, they still do not do the erosion as it would have done, had the swell-train come during the high tide time. Why? Because fierce waves bashing around down there in the normally wet zone, does not do the erosion damage that fierce waves bashing around up in the normally high-dry sand does.
Thus, again I say: this did no erosion (for beach md'ing sakes) to our west coast of the USA. Not sure what it did in Japan, but for us, it occured during the low tide time. Also, unlike storm driven swells, if I'm not mistaken, a tidal wave isn't a continuous multi-hours long event. It's just a single "boom" period, right? Again, un-like the ingredients of normal storm driven erosion, which goes on for an entire day, etc....