Wednesday, May 22, 2013
Alaska's Next Big Earthquake? Part 1
According to geologists, the next big one could be as large or larger than the Good Friday quake in 1964. Worse yet, the earthquake could hit at any time.
According to geologists, the next big earthquake could be as large or larger than the Good Friday quake in 1964. Worse yet, the next one could hit at any time and the Eye Team discovered that Anchorage may not be ready.
The map in the accompanying video was created after the massive quake to indicate which areas of Anchorage are most susceptible to similar ground failure.
Probability of ground failure
Red: very high
Where does the Port of Anchorage fall? Right in the danger zone.
The Port of Anchorage is a piece of critical infrastructure that connects southcentral Alaska to food, supplies and fuel.
But when the next big earthquake hits, officials say the port is headed for disaster.
In 1964, the Port of Anchorage was brand new and survived the massive quake with minor structural damage.
However more than 40 years later, an earthquake in the Port of Anchorage would be quite a different story.
"Over time, the silt builds up under the dock and upland of the dock. If the soils beneath that were to liquefy, all of that weight from that material would come through the facility. Even if the piles were perfect, they are not driven deep enough through that failure plane. It's likely to take the facility with it," said Todd Cowles, Port of Anchorage engineer.
But ground failure susceptibility isn't the only problem.
It's estimated that of the 2,000 piles supporting the port, at least half are corroded and only about 20 percent of those have been repaired with metal sleeves.
Cowles describes the current solution as a band-aid. "We generally repair about 20 pilings a year and it would take us another 10 years to probably fix all of the ones that are suspect," he continued.
According to a 2009 memo, the piles that hold the port above water have well exceeded the design's corrosion allowance.
In a large earthquake the sediment that has built up behind them would liquefy, pushing on the piles, causing them to collapse.
According to the memo there would be little left of the port to repair, which was news to officials at the Municipal Department of Emergency Preparedness.
"I have been here two years, and I have never heard that before... ever," said Dawn Brantley, Municipal Emergency Management.
"If the port goes down, I can tell you there are other methods to get things into and out of Anchorage," said Brantley.
But if the port fails, the secondary method of getting things in and out, air transportation, would be severely impacted.
It supplies two-thirds of the fuel for the Ted Stevens Anchorage International Airport and 100 percent of the fuel for Elmendorf Air Force Base.
Officials agree even if the people working at the port survive, losing the port would be a major economic hit.
As indicated on the map, the port isn't the only area of town that may have big problems when the next big earthquake hits.
The city of Anchorage is built on unique soil: a sensitive layer of bootlegger clay. It's not all composed of bootlegger clay, but certain layers are slick and can lose strength in motion. This means in an earthquake the ground can give way which is exactly what happened in 1964.
"I remember in the '64 quake watching the ground roll, and I was watching the birch trees, the tops hitting the ground even at six years old I remember thinking, that's weird," said Sharen Walsh, a Municipal building official.
Ground failure caused much of the Turnagain neighborhood to fall into Cook Inlet and caused gaping cracks in the streets downtown.
Experts say the same thing could happen again in a similar quake.
The city was so concerned about the affects of another quake shortly after 1964 that city leaders wanted people to relocate out of the dangerous Turnagain and Bootlegger's Cove neighborhoods.
Officials collected the property deeds but then something went wrong.
"Somehow over the course of events, the deeds never got transferred and people ended up retaining ownership and as you know memories got faded and people said 'you know, I would like to build there again,'" said Walsh.
But those neighborhoods aren't the only areas that could see problems in another quake.
Since 1964, municipal code has changed 16 times to require more precautions be taken in the danger zones like downtown.
It has worked well to make sure new buildings could withstand the next big one but not the older buildings.
Ronald Wilde, Municipal structural plan reviewer, said the older structures are "absolutely not" up to current code. "We have a lot of buildings, especially downtown, that were built maybe before these newer requirements came into play.
Officials said the problem with the code is that there are no teeth in the regulations that require existing buildings to come up to current standards.
"Down in California, they are more proactive and for their older building stock, they have laws that require them to go back and retrofit," said Wilde.
"We don't have enough political clout in Alaska to push something like that through," Wilde continued.
Geologists say the next big earthquake could hit southcentral Alaska at any time and how Anchorage fares remains to be seen.
One of the problems with ground failure is it's hard to create building codes to guard against it.
Code officials are working on some possible solutions for 2012.
On the meantime, municipal code officials have set up a special web page to make sure property owners know what kind of ground danger they are in.