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Great Alaska Quake shook up science

Posted: March 22, 2014 - 8:17pm

When North America’s largest-known earthquake shook Alaska for all it was worth at 5:36 p.m., on Good Friday, March 27, 1964, George Plafker was in the right place at the very right time.

At 35, Plafker was an up-and-coming geologist with the U.S. Geological Survey in Menlo Park, Calif. Because he had spent the previous three years mapping Southcentral Alaska’s mineral resources, Plafker was one of the few USGS scientists familiar with the infant state and subsequently was sent north.

“I was at a meeting in Seattle so they only had to pay my fare half way,” Plafker said during a February lecture.

The March 28 flight would send Plafker’s career in a new direction.

“I don’t think any of us had any experience working on earthquakes,” he said.

Today, Plafker is scientist emeritus of the Earthquake Hazards Program at the USGS Menlo Park Science Center.

Part of a three-man team of geologists, Plafker was on the ground in Anchorage less than 24 hours after the earthquake struck. His flight was diverted to Elmendorf Air Force Base north of the small city because the air-traffic control tower at the international airport had collapsed. The lone individual in the tower was killed.

The 9.2 magnitude earthquake, with its epicenter 74 miles east of Anchorage on the north edge of Prince William Sound, was felt as far away as Dutch Harbor and Seattle.

The quake and resulting tsunamis took 128 lives from Alaska’s Gulf Coast all the way south to Los Angeles. In Alaska, 15 people are believed to have died during the four-minute quake, while another 113 were killed by the large waves. Damage in the state totaled more than $310 million at the time, roughly $2.3 billion in today’s dollars.

Crescent City, Calif., took the brunt of the damage to the Lower 48. The small town sits about 20 miles south of the Oregon border on the California coast. Its locale on a point in the coastline makes it particularly susceptible to large waves. When the March 27 tsunami hit Northern California, the 21-foot swell of water killed 10 people in the town, according to the University of Southern California Tsunami Research Group.

Of the $17 million worth of damage in California associated with the tsunami, $15 million of it occurred in Crescent City.

Waves as high as 6.5 feet were recorded as far south as San Diego, and one person died when the tsunami surge hit Cerritos Channel in Los Angeles.

Small, “warning waves” along British Columbia gave residents of Vancouver Island notice to the 20-plus foot wall of water that was coming, preventing any loss of life in Canada despite no official warning system.

Plafker said many of the waves that caused damage in Southcentral were “secondary,” localized waves, those caused by coastal landslides and not the direct ground shake. A landslide in Shoup Bay just west of Valdez started a wave that snapped trees 100 feet above the shore, he said.

Southcentral Alaska is particularly prone to earthquake-induced land failures because of the abundance of unstable glacial till soil, above or below the water, that is ready to give way. When added to nearby towns built on the only flat areas near sea level — Valdez, Whittier, Seward — it makes for dangerous sum.

“What we learned is — stay away from these places. If you can’t stay away run like hell to higher ground when it starts shaking,” Plafker said.

During their first 10-day reconnaissance trip to try and draw early conclusions about what had happened during the quake, Plafker said the Army at Fort Richardson made helicopters and housing available to the Outside geology team.

At the time, it wasn’t even known exactly how large of the quake was.

“It was called an 8.5 for 10 to 12 years after the fact,” he said, because that was as high as the Richter scale went in 1964.

The modern theory of plate tectonics was just starting to evolve in 1964 as well, and Plafker’s research would have as much to do as anything with how what happens under our feet is viewed today.

In the early 1960s, evidence began to circulate that what is known as “sea floor spreading” was occurring under the Pacific Ocean, he said. That is, magma erupting and oozing from cracks in mid-ocean ridges cools, hardens and forms new ocean floor.

“About ’64 the idea that the sea floor is spreading out was accepted but all of the people — we called them in those days ‘stabilists’ versus the ‘mobilists’ — the stabilists would say, ‘Oh, well the earth is expanding to accommodate that and there’s nothing happening at the edges,” Plafker said in an interview with the Journal.

The southern coast of Alaska is at one of the edges.

It’s there where the denser, younger sea floor plate is pushed under the lighter, older continental plate, forming a subduction zone. The Pacific plate is sliding under the North American plate at about two to three inches per year, Plafker said.

As the years turn to decades to centuries, that plate relationship is not without stress, however. The edge of the North American plate gradually bunches up and along with it the land behind the edge is pushed upward. When the pressure behind the edge of the plate becomes too great, the land springs forward — generally south — and causes a major earthquake.

Enter Good Friday 1964.

After returning to Alaska in May, Plafker and his team spent the spring and summer of 1964 traveling Prince William Sound by boat, searching for evidence to support the subduction zone theory. Some of the evidence was pushed right out of the ocean for all the world to see.

Parts of Montague Island on the south side of the Sound and Middleton Island farther out in the Gulf of Alaska rose up to 36 feet during the earthquake. Plafker said the movement was obvious where barnacle lines on shore side rocks became exposed.

“These little critters all knew where they belonged in the water and they came up very abruptly and died,” he said.

Dead trees along Kenai Peninsula and Kodiak Island shores evidenced where the ground had sunk into the saltwater zone. As Plafker explained, when the continental plate pushes out it adds mass to its leading edge and stretches and thins the land behind it. He said areas of Anchorage, where sinkholes all but swallowed homes and roads, fell as much as 10 feet.

Plafker’s findings left the stabilists with little solid ground to stand on.

“For 50 years I’ve been telling this stuff to all of the people that would listen,” he said.

After publishing his team’s findings, Plafker said geologists at the California Institute of Technology who had studied the 9.5-magnitude earthquake in Chile in 1960 — still the lone-recorded event larger than the Alaska earthquake — met the results with resistance.

“A friend of mine at Cal Tech said, ‘If that’s what happened (in Alaska), how come it’s the only place in the world it happened?’” Plafker recalled. “I said, ‘Well, I don’t think it’s the only place; it’s the only place we’ve really looked.”

He said the Cal Tech professors had determined the Chile quake was caused by an offshore strike-slip fault where the plates collide and grind sideways, much like the San Andreas fault that bisects California.

When his dissenting friends offered grant money for Plafker to prove them wrong, it was an opportunity he couldn’t turn down.

After chartering a fishing boat for two months in 1969 and studying 600 miles of “inland sea” — an area he said is very similar to Prince William Sound — in Southern Chile, Plafker said the resemblance to what he saw half a world away was undeniable.

“It was a matter of serendipity you can’t believe,” as he described it.

Not coincidentally, the USGS started its formal Earthquake Hazards Program soon after Plafker’s research was publicized.

“I used those two earthquakes and a comparison of the two for my dissertation at Stanford,” Plafker said. “Besides having a hell of a good time in Chile I got a Ph.D. out of it very easily. Those were the two biggest earthquakes in history and they had a very tight story.”

As for when another mega-quake can be expected in Southcentral Alaska, Plafker said, “I’m still working on that.”

He said geologists are studying sediment layers on the Copper River delta to determine if the 1964 quake was the eighth or ninth major event in the last 5,600 years, meaning there should be another one in about 570 to 650 years, he said.

Plafker was scheduled to give a lecture at the Anchorage Museum on March 27 to commemorate the 50th anniversary of the Great Alaska Earthquake, but he is currently recovering from a bike accident and won’t be able to make the trip to Alaska. USGS Research Geologist Peter Haeussler from the Alaska Science Center is expected to take his place.

Alaskans love their state — snow, cold, dark, earthquakes and all. Adapting to most of the challenges Alaska presents means simply having a little thicker skin than Outsiders; living with earthquakes takes a bit more engineering.

Alaska is by far the most seismically active place on Earth. According to the USGS, nearly one in 10 earthquakes in the world happen in the state.

The Municipality of Anchorage adheres to the International Building Code, or IBC. Ron Wilde, a structural plan reviewer with the municipality’s Community Development Department, said IBC standards are then amended to mesh with the local conditions. Areas in West and North Anchorage that have soil layers susceptible to slides and gave way in 1964 call for more particular design requirements, he said.

N. Claiborne Porter, an architect in Anchorage for more than 40 years, said homes in the city mostly survived the large quake unscathed if they didn’t fall into sinkholes or weren’t caught up in landslides.

The 1964 earthquake was not one of terrible motion, rather one of exceptional duration at more than four minutes long, which caused land to give way.

It’s the amount of energy released over such a long period of time that puts it second on the all-time list.

Still, “Post earthquake, there has been a terrific increase in the amount of hardware that goes into a structure,” Porter said.

Almost all wood frame homes in Anchorage today are designed with ultra-sturdy metal plates that fasten the joists together. The idea is that the flexible wood can absorb the energy and motion endured during an earthquake while the strong joints hold the structure together.

“A building is a total system,” Porter said.

Ken Andersen and Mike Fierro, engineers with the structural and civil firm Reid Middleton Inc. in Anchorage, said the modern idea behind designing large commercial buildings is much the same.

Fierro said steel structures are designed so the lateral beams act as a “seismic fuse” and spare the columns — designed heavier for two to three times more load — and thus the entire structure.

“Steel turns into tangy taffy. It can stretch; it can take an enormous amount of deformation but not fail,” he said. “So, we want the (lateral) beam to do that.”

Engineers in Reid Middleton’s Everett, Wash., office have a promising tool to determine the structural integrity of essential facilities immediately after an earthquake; it’s called the Rapid Evaluation and Assessment Program and it’s been installed at the San Diego Naval Medical Center.

Andersen said sensors are installed in key structural areas of the building and after during an earthquake they send signals to a monitoring station where it established whether or not the building exceeded its design acceleration and needs to be evacuated.

While he said it has only been installed in San Diego so far, other military facilities on the West Coast are looking into adopting the REAP technology.

Andersen said nonessential buildings are built to withstand accelerations 25 percent to 30 percent greater than those experienced in 1964. They’re built to stand long enough during design-load events so everyone inside can get out before the building fails, he said.

Essential facilities, such police and fire stations, hospitals and to some extent schools, are designed to levels at least 1.5 times beyond an average office building, Andersen said. Those criteria are likely to change, he added.

“Every time there is a significant earthquake that results in building damage, technical people — scientists, engineers, geologists, FEMA (Federal Emergency Management Agency) — will send out groups to take a look at the site, take a look at the damage and what they see evolves into the code,” he said.

Elwood Brehmer can be reached at elwood.brehmer@alaskajournal.com.

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