Unusual Arctic earthquakes intrigue scientists

 In recent weeks, two powerful earthquakes have rocked the Northwest Arctic, leading some to ask why, and if these two are a sign of things to come.

On April 18, the first quake rang in at a magnitude of 5.6, while on May 3 a second quake shook the region at 5.5.

Before the first one in April, it had been more than 30 years since an earthquake that strong struck the region, said Mike West, a seismologist with the Alaska Earthquake Center.

"This got our attention," West said. "It's not unprecedented, but it is unusual."

As for whether the Big One is imminent, West said there is no evidence to suggest it, but it's not being ruled out.

"It does remain a distant possibility, but we have no reason to believe that there will be a larger earthquake in that area."

The center of both quakes was in nearly the same spot -- about 10 miles outside of Noatak, with the effects being felt all the way to Kotzebue and beyond.

Seismologists from the center are in Kotzebue and Noatak this week to place instruments so they can more closely monitor the area. They will also address the concerns of community members.

Before the most recent events, the last time the region felt a jolt of similar strength was 1981.

The vigorous aftershocks that followed both quakes were in the 4- to 4.5-magnitude range and continued from the time the first quake struck until the second was felt two weeks later.

"Both were essentially the same magnitude and in the same location; that's different for us," said West, who is also the director of the center.

The two quakes were not random occurrences, but were part of the same sequence. Earthquakes happen when pressure builds in the earth and has to be released. A rupture happens and sends seismic waves up through the earth's layers. The first quake in April was not sufficient enough to release all the energy that needed to come out, West said, and thus, there was a second.

The instruments being placed this week will feed live data back to the center and give scientists a better understanding of why this happened. The system will be in place for continuing activity that is expected in the form of more aftershocks over the coming weeks and months.

Magnitude 5 earthquakes happen often in other parts of the state, especially around Anchorage. In fact, West said, four out of five earthquakes that happen in the U.S. happen in Alaska.

No major structural damage or injuries were reported, though some residents did report cracks in various buildings.

An earthquake with that force is enough to cause significant damage depending on where it is in vicinity to a community.

"These earthquakes happened roughly 10 miles out of town and that is very different than if the town was directly on top of the source," West said. "Residents reported very vigorous shaking; they were unnerved and put on edge by the sequence."

These occurrences serve as a good reminder for Alaskans everywhere to prepare their homes. Top-heavy items like full bookcases, heating fuel tanks or water tanks should be secured so they don't tip when the ground starts to shake, said Bob Scher, chair of the Alaska Seismic Hazards Safety Commission.

"The good news is that wood is an excellent building material as far as being resilient to earthquakes, and a lot of the structures (in the region) are made of wood," Scher said. "It might sway or shake and you might see a crack in a window, or Sheetrock, but it takes a lot to actually break."

Scher added that seeing cracks in the ground, ice or snow is normal for that magnitude but does not mean the fault has come to the surface, he said.

"I'm not aware that there is an existing fault in the bedrock in the region that these events are occurring on. These are relatively small (earthquakes) but are certainly disturbing. This is occurring in an area of the state that's not typical so it is alarming for people."

West suggested concerned community members log on to the center's website for more detailed information and ways to prepare homes for quakes.

"Everyone should be prepared," he said. "And this serves as a good reminder that earthquakes occur everywhere in Alaska." ADN