Magnitude 5.2 earthquake that shook Southcentral Alaska wasn’t an aftershock

A magnitude 5.2 earthquake with an epicenter west of the Willow area shook Southcentral Alaska just after 5 p.m. Monday.

The quake at 5:09 p.m. was centered near Skwentna, 28 miles west of Willow and about 43 miles deep, according to data from the U.S. Geological Survey and Alaska Earthquake Center. The initial estimates of 5.1 and 5.4 magnitude were revised to 5.2 by the agencies.

earthquake map sept. 16, 2019

One notable fact about Monday’s earthquake: It was not one of the thousands of aftershocks resulting from the Nov. 30 7.1 earthquake that shook Southcentral, but rather an earthquake in its own right. That’s because of where it originated.

The epicenter of Monday’s quake is located about 30 miles west of the Point MacKenzie area, where November’s earthquake and resulting aftershocks originated, said Natalia Ruppert, a seismologist with the Alaska Earthquake Center. (The center says aftershocks from the November quake are likely to continue until around June 2021, and that "people in Southcentral should expect to feel more aftershocks, but only infrequently.”)

Historically, the area west of Wasilla sees "lots of earthquakes, most of them are small of course,” Ruppert said. “Maybe once a year we will see a magnitude 5 north of the Cook Inlet.”

There were several small aftershocks with a magnitude around 2 or 3 following Monday’s earthquake, said Ruppert, but she expected that they were too weak to be felt.

[Related: Why are different quake magnitudes reported, and when do these stop being aftershocks?]