More than three dozen smaller earthquakes have been reported around the in Northern California territory where a 6.4 magnitude earthquake struck early Tuesday, the US Geological Survey reported.
These smaller movements are known as aftershocks. Here’s what to know about them as the area continues to assess damage.
What is an aftershock? An aftershock is a smaller earthquake that happens in the same general area as the larger activity, according to the US Geological Survey (UGS). These smaller earthquakes are caused by the fault readjusting from the big earthquake, USGS says on its website.
The seismology lab at UC Berkley puts it like this:
“Imagine you and a friend sliding a large wooden dresser to a new location across a wood or tile floor. After it’s in place, you may hear small popping or squeaking noises coming from it as it settles,” it explains on its website, referring to the way the plates settle into their new positions after they were shaken up by the main earthquake — creating aftershocks.”
USGS says the frequency of these aftershocks decrease with time.
What is the difference between and aftershock and a “swarm?” What is happening in Northern California Tuesday has been defined as an earthquake and aftershocks because there was a main, larger, identifiable “mainshock,” or main earthquake.
“A swarm, on the other hand, is a sequence of mostly small earthquakes with no identifiable mainshock. Swarms are usually short-lived, but they can continue for days, weeks, or sometimes even months. They often recur at the same locations. Most swarms are associated with geothermal activity,” USGS says.
Source: www.cnn.com