Disasters2002 Alaska earthquake helped set standards for buildings, bridges

The Denali 7.9 earthquake that hit Alaska in 2002 was the largest to hit the United States in more than 150 years, and the strongest ever recorded in Alaska. No one was killed and only a few people were injured. The only severe damage the earthquake caused was to a few highways, but the damage was not significant enough to close them

Claims Journal reports that the earthquake set new national standards for building bridges as well as giving seismologists a better understanding of how earthquakes affect frozen ground.

“Really, this last decade has been huge for understanding earthquake hazards in Interior Alaska as a whole, and the Denali Fault in particular,” Peter Haeussler, an Anchorage-based research geologist with the U.S. Geological Survey told the Journal.

The shockwave of the earthquake was so strong it was felt in Louisiana. In Alaska, roads along the fault line were torn up and glaciers were ripped in two.

Natasha Ruppert, the acting seismologist with the Alaska Earthquakes Information Center said the earthquake gave scientists an opportunity to study and get information that had not previously existed.

“If it wasn’t for the 2002 earthquake, if the fault had never ruptured, that research would definitely be a low priority over something else,” Ruppert told the Journal.

During a strike-slip earthquake, an object on one side of a fault could end up as much as fifteen feet to the right of the left of an object that it was previously right next to. According to Haeussler, it was the side-to side action that was interesting to researchers. Only about six earthquakes of can be compared to this one in the last 100 years.

After the Denali earthquake, researchers ran to Alaska to study the fault. The San Andreas Fault in California shares many of the same traits as the Denali fault, but the Denali quake traveled along three separate fault lines.

“I think that grabbed people right away,” Haeussler said.

Originally, researchers thought the earthquake would stop once it hit the intersection of the other fault lines; instead it kept going through each line moving more than 200 miles. According to Haeussler, that has changed what scientists previously thought about earthquakes.

“It just became blatantly obvious that you could have one rupture that goes from the next fault to the next to the next,” he told the Journal.

Scientists were fascinated by Denali fault and earthquake’s effect on cold-weather areas. The way interior bridges responded to the quake gave scientists a new look at how frozen soil reacts to an earthquake. 

For a bridge on unfrozen ground, the risk for structural failure during an earthquake is deep underground, but researchers found out that frozen soil acts like concrete making the point for structural failure just below the surface. 

“I think the engineers knew that frozen layer was different,” Zhaohui “Joey” Yang, associate director at the Alaska University Transportation Center told the Journal. “They didn’t know how different.”

When the Trans-Alaska pipeline was built in the mid-1970s, engineers knew they would have plan for the pipeline to be able to deal with the Denali fault, so the pipeline was built in a zigzag motion along most of the route to give it the ability to stretch and move in the event of a quake.

When the Denali quake hit, the pipeline moved sideways eighteen feet and vertically five feet, but the pipeline held, making it the first structure designed to span a fault line that survived a major earthquake.

“They pretty much nailed it dead on,” Haeussler said of the pipeline engineers.

The pipeline was not realigned after the quake, but horizontal supports were added to make sure the line could take more movement.

“The pipeline performed as designed, so we really didn’t have to change anything,” Sather said. “It did what we wanted it to do,” Alyeska Pipeline Services Company spokeswoman Lynda Sather told the Journal.

According to Haeussler, by examining the sediments along a fault (a process known as paleoseismology) scientists can determine how often quakes have occurred historically. Haussler said the fault had a rupture the size of the 2002 earthquake every 400-600 years, which means that in our lifetime the fault should remain silent, but numerous faults are sprinkled throughout the interior and are mostly unstudied.