Fifty years ago today, on Good Friday in 1964, Alaskans experienced the second-largest earthquake in modern times. One overarching question regarding the 1964 Earthquake is could this kind of earthquake, which killed hundreds, caused millions of dollars in damage, destroyed entire villages, and changed the face of Alaska happen again? The answer is yes, but probably not in our lifetimes or those of the next few generations.
“The repeat of the ’64 earthquake is a very unlikely event in the foreseeable future,” paleoseismologist Gary Carver told the Daily Mirror. “However, regarding the possibility of a destructive earthquake in Kodiak’s future, there are many sources for very powerful earthquakes that could cause great problems and generate large tsunamis.”
In fact, Carver adds, a smaller quake than the magnitude 9.2 Good Friday Quake could be far worse for Kodiak City and adjacent parts of the island. Such an event has a significant probability of occurring in coming decades. In 1964 portions of the Aleutian subduction zone fault from Prince William Sound to Kodiak, a large fault between the Pacific and North American plates ruptured. However, the part of the fault directly under the northeast part of Kodiak Island had minimal slip. A more localized temblor could originate from this low-slip section of the ’64 quake, Carver explained. This section of the fault lies dormant and dangerous like an unexploded landmine. It could generate an earthquake of magnitude 8 or more. Because such an earthquake originating on this part of the subduction zone would happen right under our feet, it could potentially wreak major havoc on Kodiak City and adjacent parts of the Island.
“It would be a minute or more of very strong shaking, as strong or even perhaps stronger than what occurred in 1964. And the reason for that is that in 1964 the energy that generated the shaking here was coming from the sections of the fault that did go off and those were some distance from us,” Carver said.
Strong shaking from this kind of earthquake would not continue as long its 1964 cousin, which lasted six minutes.
“It wouldn’t last six minutes, it would probably last a minute or so, but the shaking would possibly be much stronger because we would be so close to its source, right over the fault rupture,” Carver said.
Carver, 72, a former professor at Humboldt State who moved to Kodiak 15 years ago to study earthquakes and their long-term histories, warns that several sections of the fault including the low-slip section beneath Kodiak City that did not rupture in 1964 is still loaded and could release its long-term accumulated stress at any time.
“In the geologic record we see the heartbeat of the ’64 event, it is recorded in the coastal geological deposits. The heartbeat is one stroke every four or five centuries. For much of the subduction zone fault that stress release just happened. It’s going to be four or five centuries before it happens again. It might be 300 or 400 years for us to get another magnitude 9. But when you dissect that magnitude 9 (from 1964), the whole fault didn’t move uniformly,” Carver said.
“There are some pieces of the fault that moved a lot, up to 25 feet or more, and there are some patches that didn’t move at all. And the piece under Kodiak in 1964 didn’t move at all. So we have this piece under Kodiak that’s still loaded. And that could move by itself, and it isn’t going to generate a 9, but it’s going to generate an 8 or 8.3 and we’re going to be right on top it. From the standpoint of ground shaking, we can have a stronger ground-shaking earthquake tomorrow than happened in ’64. And we expect one in the not so distant future.”
There also are several other active faults near Kodiak City in addition to the subduction zone fault. One of particular concern is the Narrow Cape fault. This fault is in the upper plate of the subduction zone and reaches the earth’s surface on the sea floor just offshore along the eastern side of the island. The fault crosses Narrow Cape on land where it has been studied in detail. Geologic studies of this fault show it is highly active and has generated very large earthquakes in the recent geologic past. This fault also is close to Kodiak City and, when it slips, will generate very extreme ground motions at Narrow Cape and strong shaking in Kodiak City. It also has the potential to generate a destructive tsunami.”
Kodiak Island Borough manager Bud Cassidy has been working with Carver to develop several earthquake scenarios in a report for the Federal Emergency Management Agency (FEMA), the country’s top disaster relief agency.
“The shake could be a lesser magnitude shake but be closer to town and do more damage than the ’64 earthquake,” Cassidy said. “We’ve recognized that and we’ve retrofitted all of our schools. We’ve gone in and made them more earthquake-resistant. Our building codes are improving, so that a lot of the modern houses will be able to withstand, to some degree, some strong shaking.”
In 1964, most of the damage was not caused by the shaking, it was the result of the associated tsunami. Kodiak’s waterfront was destroyed by a series of tsunamis that washed inland in the hour after the shaking ended.
“I think people in town understand what 2 o’clock on Wednesday means, 2 p.m. on Wednesday is the time that Kodiak’s emergency siren test occurs” Cassidy said.
In the event that an actual earthquake happens that could generate a tsunami, don’t wait for the siren. Strong shaking is your warning.
“If strong shaking lasts for 10 or 15 seconds, you go to high ground,” Carver said. “There are evacuation routes — know where to go. You don’t wait, you immediately go to high ground. You want to get 100 feet above sea level immediately, you may only have minutes.”
Before a quake, make preparations beforehand to reduce the impact on you and your home from earthquake damage. “That means you go through and make preparations that will mitigate or reduce the potential for damage. Make sure that objects that could injure aren’t on high shelves. They could fall on you. Ensure that you have strengthened structures.”
Also, make sure everyone in your household knows where to meet on high ground after the quake. Learn the “duck, cover, and hold” concept.
“When the ground starts shaking you get under something or you get away from things that could fall on you,” Carver added.
A good web site for earthquake preparations is http://www.ready.gov/earthquakes.
Cassidy was 10 years old when the ’64 earthquake happened and had just moved to Kodiak with his parents. He recalls “a fair amount of chaos in the city” immediately after the quake.
“I remember the roads being jammed with cars trying to get up to Pillar Mountain, police going around and announcing things from their loudspeakers, but frankly we were up high enough. We went into a back bedroom so I didn’t see a whole lot of it.”
Stories abound from the ’64 wave too.
“That channel between town and near island where the bridge goes across was flowing like a river,” Cassidy said.
Damages to the island by a major earthquake could cause hundreds of millions of dollars in damages, wash away most of the harbor, obliterate the canneries, and cause significant injuries and possibly a death toll.
“Other potential problems are landslides and fires. For example, the Pillar Mountain landslide near the Container Dock, a site of several historical landslides, would likely fail from strong shaking, blocking the highway. In the immediate aftermath of a major earthquake areas south of the slide may be cut off from emergency facilities like the hospital and city fire stations,” Carver said. “Likewise the city would likely not have road access to the airport and the Coast Guard’s rescue and emergency aid assistance.”
“If you do get a shake where do you go?” Cassidy asked. “You don’t run outside, you don’t run to the door, you get under your desk, hang on for dear life, and then come out after the shaking is over. The idea is we live with this threat and hopefully we can respond to it when it does occur.”
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