Watch this video:
That's not a dyke that the water is overflowing, that's a seawall (you can see here on better days), designed to try and contain a tsunami and is normally back from the canal. This is from a town in northern Japan called Miyako far to the almost due north of the earthquake's epicentre.
At this point, you're probably wondering: "err... what's more interesting about this site than the others?" Well, take a look at a closer view of the area:
That's right: to hit Miyako the Tsunami had to do a 90 to 180 degree wrap around an archipelago and shoot downwards, almost in reverse, and sideways into a bay. When you try to approach this from a layman's idea of what a wave does - spreads consistently outwards from a point of impact - it seems cognitively confounding. At first glance, the area looks like it should avoid damage entirely because there's an entire landmass, including mountains according to the map (which, to be fair, may just be really big hills, but the point stands), that you'd think would act as an active buffer to the wave coming from the south.
The problem is that a Tsunami is not just a "wave", per-se: it's perhaps more accurately defined as water "seeking it's own level" in one of the most violent ways possible. The simplest way to look at what happened here is like this; fill a pot with water. Now, start throwing in potatoes. All of a sudden you've got waves on the surface but you've also got displaced water being carried over the sides by this action as it tries to find someplace else to be. This is what essentially is happening when a Tsunami is created: the Earth's crust is moving violently upwards or downwards, taking on the role of your potatoes, and displacing massive amounts of water by either pushing it towards the surface or sucking it towards the core. Either of these actions imbues the water involved with massive amounts of energy and it responds by trying to immediately move away or gets sucked in and then rebounds from the point of the event, respectively, and floods outwards forcefully to both expend that energy and find its "natural level" again.
Now, to go back to our analogy, if you were to ring that pot with a something to catch that water you'd be able to see just how much more readily it moves into some areas of that ring compared to others as the imperfections in your workmanship - dips, divots, angles - begin to show. Likewise, as Miyako stands as further proof, a Tsunami is going to, quite frighteningly, find its way into every nook and crevice of the Earth that the energy it's been imbued with will allow as it purges that energy and redistributes itself accordingly. That's a realization from this event that exists as a reminder of just how powerful nature is when unleashed.