WASHINGTON (AP) — Scientists have discovered a mash-up of two feared disasters — hurricanes and earthquakes — and they’re calling them “stormquakes.”

The shaking of the sea floor during hurricanes and nor’easters can rumble like a magnitude 3.5 earthquake and can last for days, according to a study in this week’s journal Geophysical Research Letters. The quakes are fairly common, but they weren’t noticed before because they were considered seismic background noise.

A stormquake is more an oddity than something that can hurt you, because no one is standing on the sea floor during a hurricane, said Wenyuan Fan, a Florida State University seismologist who was the study’s lead author.

The combination of two frightening natural phenomena might bring to mind “Sharknado,” but stormquakes are real and not dangerous.

“This is the last thing you need to worry about,” Fan told The Associated Press.

Storms trigger giant waves in the sea, which cause another type of wave. These secondary waves then interact with the seafloor — but only in certain places — and that causes the shaking, Fan said. It only happens in places where there’s a large continental shelf and shallow flat land.