New monitoring allows for recording of smaller earthquakes in northern Alaska

South of the Brooks Range, near the Purcell Mountains, there is an earthquake swarm. Since February 2018, there have been approximately 2,700 earthquakes in that area. Most of them are very small, but there have been 11 that measured between magnitude 4 and 5.3, according the Alaska Earthquake Center.

This series of earthquakes is called a “swarm” because there wasn’t a big earthquake to set it off. Southcentral has experienced thousands of earthquakes since November, but they are aftershocks from that 7.1 quake near Big Lake. Earthquakes in a swarm have no specific trigger. The largest earthquakes in this swarm occurred in the middle of the event. How long the swarm will last is unknown.

“Sometimes a swarm lasts for weeks and months and in extreme cases, for years,” says Natalia Ruppert, seismologist with the Alaska Earthquake Center. “From what we know of Brooks Range seismic activity, these swarms are not really that uncommon.”

There was another swarm near Kobuk in 1989 but the seismic monitoring capabilities then were much different. “In 1989 we only to able to record maybe magnitude 4 and 5 and larger earthquakes in that region,” says Ruppert. “We definitely didn't see all the magnitude 1's and magnitude 2's.” So, Alaska has experienced swarms like this before.

“The intensity of the current swarm may be a little bit deceiving, because we are recording much smaller earthquakes than what we were able to do in the past,” Rupper says. “And this is just because the seismic network is much more comprehensive in the state now couple of decades ago.”

About four years ago, approximately 200 seismic monitors were put in across the state, including the northern areas of Alaska.