"There are some hints that a small number of these reversing earthquake ruptures have appeared on land, but thorough evidence is scant," Hicks said, "so I think our study probably provides the clearest example of one so far."

Double quakes could cause stronger tremors on land

Hicks cautions that because evidence is so sparse, this finding does not mean those living near earthquake hot spots should start prepping for double quakes.

"We're not sure if what we have observed along a specific type of plate boundary may also occur on different fault types on land," he said.

If this type of earthquake were to occur on land, Hicks said, it could cause stronger tremors, as the direction of a quake can impact its strength.

"However, since we have only measured one of these types of earthquake in detail, then it will probably require more scientific analysis of other earthquakes before our result starts to directly impact models of seismic hazard and their mitigation," he said.

Documentation in the recent study of both a change in direction and faster-than-expected rupture speed "challenges our ability to understand how friction operates and also to forecast the shaking expected in future earthquakes," Vidale said.

It is also significant that the study highlights this quake as moving at "supershear" speeds.

A supershear event is an earthquake that moves so quickly that it causes the geologic version of a sonic boom.

Though incredibly rare, these events can cause significant damage.