[iacopo.russo (OP)]

Paul asked:

Is there a way to disrupt tsunamis either just before they reach the shoreline or on reaching the shoreline? I was wondering if there was some way of turning the tsunami against itself so it cancels itself out. Could this be done with a series of walls at different angles?

What do you think?

[Origin]

Is there a way to disrupt tsunamis either just before they reach the shoreline or on reaching the shoreline? I was wondering if there was some way of turning the tsunami against itself so it cancels itself out. Could this be done with a series of walls at different angles?

I would say no.  A tsunamis is not like a normal wave, it is a large 'block' of water that moves onto the shore.  So it is more like an extremely high tide.  A barrier higher that the waves is the only thing that will stop it.  Barriers lower than the waves will simply be submerged as the 'block' of water moves over it.

[Bored chemist]

A mangrove swamp is probably cheaper

[evan_au]

Barriers lower than the waves will simply be submerged as the 'block' of water moves over it.

Generally, I agree with the comment. But there is a tweak:

Let's say the incoming wave has enough kinetic energy to cause an increase of water height of (say) 3 meters in an estuary. The water moves inland, and its kinetic energy is dissipated slowly through friction and turbulence.
However, at a vertical barrier, the incoming wave has kinetic energy turned into potential energy, without being dissipated so much. This means that the peak wave height will not be 3 meters, but more like 4.2 meters = 3√2 (if you want to block the wave entirely). The wave will then reflect back out to sea.
(Similar sorts of wave behaviors happen in electrical transmission lines, only the variables there are current and voltage, and the voltage doubles where the current drops to zero.)

The wall needs to be strong enough to withstand this pressure of water, or the wave will break down the wall.

If you want to be prepared for tsunamis, you need a trained population, with a pack of essentials always close at hand, a network of alerts (eg loudspeakers, or today, a smartphone app), and well-marked tsunami safe zones.

In Hawaii, I saw many signs warning that the area was at risk from tsunamis, and indicating which direction you should run to safety.

Unfortunately, these protections are only as good as the wave height prediction. In the Fukushima earthquake, many tsunami evacuation zones were washed away by the sheer height of the wave, which was driven by a "stuck" fault line which had been accumulating tension for 1200 years.
See: https://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunami

[Petrochemicals]

.

Unfortunately, these protections are only as good as the wave height prediction. In the Fukushima earthquake, many tsunami evacuation zones were washed away by the sheer height of the wave, which was driven by a "stuck" fault line which had been accumulating tension for 1200 years.
See: https://en.wikipedia.org/wiki/2011_T%C5%8Dhoku_earthquake_and_tsunami

Many defences where swept away in Japan, possibly due o the shape of the defence, a wave is a wave so deflecting the energy  is the same. But the question is do you want to build a tsunami barrier strong enough and high enough to block a wave of 15m+ all along your coast for a once in 2000 year event. I can imagine it would really ruin the tourist industry on the south coast of the UK.

Given that even the Japanese earthquake and indonesia in 2004 gave people at least half an hour in between quake and wave and also that concrete structures survived, a nice tall evacuation centre would be the wise thing. Use it as an offce block, no problem.