The frigid coastal plain of the Arctic National Wildlife Refuge trembled last week with a series of shallow earthquakes — reminding Alaskans that just about any place in the state can rock any time without warning.
UPDATE: Seismologist Natalia Ruppert has worked up a new map showing the locations of nearly 20 different quakes, strung up and down shallow faults within the Arctic coastal plain.
“The largest earthquake (M4.6, red star) occurred on April 10 at 16:34 UTC (8:34 am ADT),” she wrote. “Due to sparse seismic network coverage in the area (the nearest station is located 152 miles away), accuracy of the earthquake locations is poor, especially for the smaller events recorded by very few stations.”
One of the quakes even triggered a “don’t worry” alert from the West Coast & Alaska Tsunami Warning Center, saying that no wave was expected in the coastal village Kaktovik.
The village’s 288 residents weren’t too anxious, seeing as the frozen Arctic Ocean stretches to the horizon like a great expanse of raggedy white bedrock, according to a story by Alex deMarban in the Anchorage Daily News.
“Everything is too frozen solid to shake,” Kaktovik Mayor Lon Sonsalla told deMarban. “We’re like, ‘Nothing’s shaking.’ ”
The first jolt struck at 8:34 a.m. on April 10 with magnitude 4.5 of force, rupturing faults three miles beneath the ANWR coastal plain about 37 miles southwest of Kaktovik and 100 miles from the oil fields at Prudhoe Bay, according to the Alaska Earthquake Information Center.
At least 11 more shakers followed over the course of the day, including a Magnitude 3.9 quake 10 minutes later and a Magnitude 3.7 some 35 minutes later. What do earthquakes rattling the tundra mean? Not all that much.
“They are part of a diffuse earthquake band that extends from northeast Brooks Range toward the Arctic Ocean,” said Ruppert, with the earthquake center.
Alaska is one of the world’s major earthquake engines, thanks to the titanic collision of the Pacific tectonic plate with the North American plate along the Gulf of Alaska and Aleutian Chain. Three of the 10 largest earthquakes ever recorded occurred in Alaska, including the Magnitude 9.2 quake that ruptured Southcentral Alaska in 1964.
Source: AEIC
With about 10 percent of earthquake energy on the planet rumbling through local bedrock, the entire state had become riddled with faults, cracks and fissures. So earthquakes can strike almost everywhere. One of the largest quakes to hit North America in a century — the Magnitude 7.9 Denali Quake — began its rupture in the Alaska Range hundreds of miles from the ocean.
Although it might seem like the Arctic slope lies too far away from this tectonic action, a Magnitude 5.2 earthquake hit beneath the continental shelf only 18 miles north of Kaktovik in 1968. Over the years, dozens of quakes have rattled the tundra, all reminders of Alaska’s restless turf.
“In 2006, five magnitude 4+ earthquakes (yellow stars on the map at the top of the story) occurred in this general area, with the largest event of M4.6 on February 20, 2006,” Ruppert said.
The center’s catalog for that month located about 12 quakes in the same cluster, about 100 miles southwest of Kaktovik. The whole zone produces strike-slip earthquakes, where one side of a fault moves relative to the other.
Under the relentless, inexorable pressure from tectonic plates and other crustal chunks, the Brooks Range ever presses toward the northwest, while the coastal plain of ANWR wants to go south. Sometimes they jump and give us all a jolt.