USGS earthquake study finds we need to redefine aftershock

Big earthquakes can alter seismic patterns in very different ways — including triggering temblors across the globe, the U.S. Geological Survey said today.

It announced two studies that “shed light on more than a decade of debate on the origin and prevalence of remotely triggered earthquakes.”

The conclusions could force scientists to redefine what we know as an aftershock:

While aftershocks have traditionally been defined as those smaller earthquakes that happen after and nearby the main fault rupture, scientists now recognize that this definition is wrong. Instead, aftershocks are simply earthquakes of any size and location that would not have taken place had the main shock not struck.

In one of the studies, USGS seismologists studied the unprecedented increase in seismic activity triggered by the 8.6-magnitude East Indian Ocean quake on April 11. It was the largest strike-slip earthquake ever.

“No other recorded earthquake triggered as many large earthquakes elsewhere around the world as this one,” USGS seismologist Fred Pollitz said.

Read more of the studies’ conclusions, and find links to the papers, here.