A tsunami earthquake begins deep beneath the ocean’s surface — typically in subduction zones, where one tectonic plate is forced under another.

Over time, immense stress builds up as an oceanic plate grinds against a continental plate. When that stress exceeds the friction holding the plates in place, the edge of the overriding plate suddenly snaps and shifts, often with vertical movement of the seafloor.

That sudden lift or drop of the ocean floor displaces a massive amount of seawater, creating a ripple — either a bulge or dip — on the ocean’s surface.

Then gravity kicks in. As the water tries to settle back, it unleashes tsunami waves that race outward from the quake’s epicenter, traveling at jetliner speeds across the ocean.

In deep waters, these waves may look like harmless swells. But as they approach shorelines, the seabed rises, slowing the waves but increasing their height — sometimes transforming them into towering walls of water that devastate coastal communities.

Understanding the mechanics behind tsunami earthquakes is vital to improving early warning systems and minimizing loss of life.