On November 3, 2002, just a little after noon, WC was upstairs at his home in Fairbanks, working on his email. Mrs. WC was downstairs doing chores. The whole house gave a very strong, sudden and sharp jerk. There was a pause. And then continuously, for two minutes and 18 seconds, the house thrashed around like a snake with a broken back. Trees outside the windows were flopping around like there was a hurricane. WC struggled to keep computer equipment from falling off desks; Mrs. WC tried to keep the CD collection from falling off its shelves. Neither of us was completely successful.
It was a magnitude 7.9 earthquake. The epicenter was about 90 miles south of Fairbanks, under the Susitna Glacier, on a previously unknown fault. The quake tore east along the Denali Fault, then branched southeast along the Totschunda Fault. There were more than fifty aftershocks of ML 4.0 or greater, some of them much closer to Fairbanks.1
WC mentions the 2002 temblor because his friends and neighbors are making such a fuss about the recent ML 6.7 quake near Salt Lake City, the ML 4.5 quake near Boise and the ML 6.5 quake north of Las Vegas, Nevada. Remember, the earthquake strength scale is logarithmic. The Denali Fault event in November 2002 was more than 100 times stronger than the Salt Lake event. The foreshock and four of the aftershocks were as powerful as the Utah quake.
Alaska’s November 2002 quake shifted the southern third of Alaska between six and twenty-nine feet west. This photo, where the fault trace crossed the Richardson Highway, shows that shift. Imagine the energy required to shift that megatonnage of landscape that distance.
The Black Rapids Glacier lies in the Denali Fault west of the Richardson Highway. The quake fissured the ice and the underlying rock for miles along the glacier. In this photo you can the left side of the fault trace has shifted towards the camera by about twelve feet.
The path of the quake tore down the Totschunda Fault, southeast from the Denali Fault. It crossed the Tok Cutoff, the important highway from Tok to Glenallen, near Mentasta Pass, a swampy area. The underlying soils liquified as a result of the protracted shaking, with this result.
No one likes it when the ground starts shaking. It’s the very opposite of what we expect. “Solid ground” and all that. That makes it deeply unnerving. But the thing about small and moderate earthquakes like the recent three is that, for the most part, they are a good thing. A series of small quakes, dispersing built up tension in rock, is a much better thing than one giant, sudden release. We know pretty well how to build structures that survive most temblors. The November 2002 event caused very, very little serious structural damage to Alaska buildings.2 Encourage your government officials to enact and enforce building codes that require earthquake design standards.
Understand that if you live in the Pacific Rim, or the Intermountain West, there are going to be earthquakes. A glance at the landscape tells you they have happened before; be sure they will happen again. Have an emergency bag at hand. Try to appreciate the experience: it’s geology in real time.
- Of course, the November 2002 was a tiny thing in comparison to the ML9.2 1964 Alaska Earthquake, which was more than ten times as powerful. ↩
- WC’s house sustained a single crack in the sheetrock above the front door; the front porch was built on extensions of the floor joist, set on shallow concrete pads. They stressed the floor joist, and the crack was the result. ↩