Earthquakes can strike almost anywhere. They can strike on land, beneath cities, in remote mountains, and even deep beneath the ocean floor. When an earthquake happens underwater, it's called an undersea or submarine earthquake, and it can have serious consequences far beyond the shaking itself.

These quakes occur when tectonic plates, which are massive slabs of the Earth's crust, shift along fault lines beneath the seafloor. Just like earthquakes on land, they’re caused by the sudden release of built-up pressure between two moving plates. But in this case, the movement happens beneath the ocean, where it can disturb the seafloor and displace huge volumes of water in an instant.

This sudden shift can trigger a tsunami, sending fast-moving waves across the ocean that can grow dramatically in height as they approach the coast. The stronger the earthquake and the more vertical movement it creates, the more energy is transferred into the water, and the more dangerous the resulting tsunami can be.

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Undersea earthquakes are most common in subduction zones, where one tectonic plate is sliding beneath another. These areas are some of the most geologically active places on Earth, and they’ve been the sites of major historic disasters, like the 2004 Indian Ocean tsunami and the 2011 Japan tsunami.

Although not every undersea earthquake causes a tsunami, they are the most frequent trigger. That’s why monitoring oceanic seismic activity is so critical for tsunami warning systems around the world.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.