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I've drawn up a set of landmasses for my story, and now there's a tsunami headed for them. I know where the tsunami is coming from, and I could decide how big it is, or any other characteristics of it.

What parts of the coastline will be devastated and what parts will escape unscathed?

For example, if the landmasses look like this:

caribbean map

and a tsunami emanates from Puerto Lempira (Honduras), does Jamaica protect Guantanamo? Is Maracaibo protected by that thumb of Colombia sticking out into the sea? Is Havana safe because it's on the far side of Cuba?

How can I figure this out for my own fictional setting?

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  • $\begingroup$ Your map is a bit busy with text. Can you please provide a map with either less text or with an arrow or rippling waves showing what you mean about the land masses sheltering each other? $\endgroup$ – Marion Jun 10 '16 at 0:36
  • $\begingroup$ @Marion, I can add a different map. The specifics of the Caribbean aren't important, though, it's just an example. $\endgroup$ – Joe Jun 10 '16 at 0:42
  • $\begingroup$ No worries. My comment was because I'm geographically illiterate and was having a hard time scanning the map for your mentioned islands. $\endgroup$ – Marion Jun 10 '16 at 0:46
  • $\begingroup$ You can get a clearer map by screenshooting Google Maps. $\endgroup$ – Renan Jun 10 '16 at 1:17
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    $\begingroup$ Please take in account that the under water topology may work for or against your islands... and even affect the size of that tsunami. Even the depth of origin and maybe active water streams can affect this. How much detail you are willing to create for this setting? $\endgroup$ – Confused Merlin Jun 10 '16 at 6:46
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All waves, including tsunami waves, follow wave mechanics. Notably here, they follow the rules of diffraction, which you probably learned about in high school physics:

diffraction pattern

Because of this effect, the waves headed for Jamaica will bend around the island, and still strike guantanamo. That being said, the waves will have to travel a greater distance, experience more friction, and be modestly less intense because of that.

However, keep in mind that your coast's topology will usually decide the extent of the damage more so than the strength of the wave. Towns with sheer underwater cliffs at their coastline have been nearly untouched by tsunamis that devastate towns not a hundred miles away with gentle sloping beaches.

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  • $\begingroup$ Don't forget that the wave bending around topology can interfere with the wave that took another path, causing a complex pattern. The speed and diffraction are both dependant on wavelength, so you get a huge amount of dispursion as well. $\endgroup$ – JDługosz Jun 12 '16 at 18:15
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To add to @cinnamon18 answer: do remember that a tsunami seen from the perspective of a human does not at all look like a "wave" as we know them. They are indeed that, but on a huge scale.

To a human, a tsunami instead looks like the sea is just rising, and rising... and rising. As the sea rises it floods over embankments, walls, dunes and other things that normally hold the sea back. It does not look like a wave; it instead seems like a sudden flooding, that happens in just a few minutes instead of days.

Also the coast affects the wave. A shallow coast slows the wave, causing it to "bunch up". Out at deep sea the wave is barely noticeable. But as it slows in shallow waters, it becomes much higher.

So what cinnamon18 said: cities on cliffs faces will see just a mild rise of water, that relatively quickly recedes. But areas on shallow coasts, and that does not rise significantly above the sea level, they will be flooded.

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Here is a link to a tsunami simulator: http://tsunami-maps.com/index.html Allthough it might not look very acurate, it uses data from google maps to deal with the topology. It should give you an idea of which parts of land will get flooded or not in different scenarios.

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