How the 1964 Alaska Earthquake Shook Up Science
The
earthquake struck at 5:36 p.m. Alaska Standard Time on Good Friday. For
more than 4 minutes, the earth buckled and lurched all across southern
Alaska. In 50 years, no earthquake since has matched the power of the
March 27, 1964, Great Alaska earthquake.
How the 1964 Alaska Earthquake Shook Up Science
By By Becky Oskin, Senior Writer
3 hours ago
The theory of plate tectonics is a relatively new scientific concept.
In 50 years, no earthquake since has matched the power of the March 27, 1964, Great Alaska earthquake. Now ranked a magnitude 9.2, the second-largest ever recorded, the earthquake radically transformed the young state. Important coastal ports, roads and rail lines were destroyed. The liquefied ground in Anchorage led to the country's strictest seismic building codes (now outpaced by California). President Lyndon Johnson ordered a comprehensive scientific study of the earthquake. [See Photos of the 1964 Great Alaska Earthquake]
The geologic discoveries transformed how we understand the Earth.
"In 1964, earth scientists were swept away by the plate tectonic revolution, which changed everything we know about how the earth works," said Ross Stein, a U.S. Geological Survey geophysicist. "That insight was triggered by the Great Alaska earthquake 50 years ago."
Solving the puzzle
In the 1960s, geologists thought straight up-and-down (vertical) faults bounded the edge of continents, similar to the San Andreas Fault that slices through California. In 1965, Frank Press, who would become science adviser to four presidents and head of Caltech's Seismological Laboratory, said a vertical fault extending from 9 to 125 miles (15 to 200 kilometers) deep caused the Great Alaska earthquake. His model was published May 15, 1965, in the Journal of Geophysical Research. One month later, USGS geologist George Plafker proved him wrong.
As a USGS geologist, Plafker had studied Alaska's geology each summer since 1953. But he was in Seattle when the 1964 earthquake struck. After Plafker heard the Space Needle had swayed as the seismic waves raced past, he called his boss in Menlo Park, Calif., recommending an immediate response. Any earthquake big enough to shake the Space Needle from Alaska must be of interest to the USGS, he said. [Video: The 1964 Great Alaska Earthquake]
"I suggested we get up there fast before everything was bulldozed flat by the engineers," Plafker said.
Plafker's work on the 1964 earthquake solved a key piece of the plate tectonic puzzle: How oceanic plates recycle themselves at collision belts called subduction zones. At a subduction zone, one plate curves beneath another plate and sinks into the mantle, the hotter layer beneath the crust.
"Before the 1964 earthquake, we did not have a unifying theory of how the earth works," said Peter Hauessler, a USGS research geologist. "The 1964 earthquake was the first time people understood that there were places called subduction zones that produce these really enormous earthquakes."
Plate tectonics is now a widely accepted model that explains everything from why earthquakes happen to how mountains grow. The model says that Earth's surface is divided into stiff slabs of crust called plates. The oceanic plates are born and grow at mid-ocean ridges, the long underwater volcanic chains that wind around the Earth like seams on a baseball. Evidence for this growth was first published in 1963 — progressively older magnetic stripes on the seafloor record spreading away from the volcanic ridges.
But in 1964, geologists
believed the Pacific Plate was rotating counter-clockwise. In that
scenario, no new crust was created at underwater volcanic ridges, nor
was old crust shoved under continents at subduction zones. (The
counter-clockwise rotation was a concept created to explain the hundreds
of miles of offset recently discovered along the San Andreas Fault.)
However, this model didn't explain a strange observation: Where some
plates meet, earthquakes deepen, defining a gently-dipping plane.
The careful geologic mapping led by Plafker in the summer of 1964 would
be key to solving the mystery of oceanic plates sliding around Earth's
surface, Stein said."George discovered they were shoved underneath the continents. He solved this incredible puzzle that triggered an understanding of what happens to the Pacific Plate as it subducts."
Grinding plates
Beneath southern Alaska, the Pacific Plate dives underneath the North American plate, grinding northwest at a rate of 2.3 inches (5.8 centimeters)
per year. Friction between the two plates makes them lock together. Even though they're locked, the plates keep moving, compressing the crust like springs. Where the plates lock, they buckle and warp, similar to a piece of carpet wrinkling at one end. Because of this compression, some areas of the Alaska coastline warped downward before the earthquake and others bulged upward.
During the 1964 earthquake, giant sections of coastline rose or fell as each plate relaxed and released the centuries of compression. The rupture was like unpeeling a piece of Velcro, with a segment of the subduction zone 580 miles long (930 km) by 100 miles (160 km) long shuddering apart at more than 100 miles an hour (160 km/h).
Pfalker and his colleagues surveyed the uplift and sinking after the 1964 earthquake. Areas around Montague Island rose 13 to 30 feet (4 to 9 meters) and Portage dropped 8 feet (2 m). Overall, the Pacific Plate slid under North America by about 30 feet (9 m). Like bathtub rings, the boosted-up islands showed the vertical changes. Masses of dead barnacles and starfish proved the land had just been underwater.
Plafker concluded the pattern could only have been caused by a hidden fault, releasing tension about 9 miles (15 km) below the surface. They never found a significant surface break from a vertical fault, just minor cracks from secondary faults. The results were published in the journal Science on June 25, 1965.
"If you do the things right, you can reveal some of nature's secrets," Plafker said.
Aftershocks also confirmed the findings. Following the massive megathrust in March, small earthquakes jangled the sinking plate all along its length. Detecting these quakes with seismometers showed the Pacific Plate bent beneath the North American Plate. (Before March 1964, Alaska had only two of the earthquake-sensing instruments — one in Fairbanks and one in Sitka. A bigger network was installed after the quake.)
And with hindsight, researchers can inspect the seismic record of the 1964 earthquake and see the pattern of a subduction zone earthquake hidden in the needle scratches. The pattern suggests one block thrusting over another, not the up-and-down motion of a vertical fault.
Future hazards
After the coastline sank, trees began dying as saltwater and silt invaded their roots, creating ghost forests still visible today. Decades later, these Alaska ghost forests were the clue to figuring out that the Cascadia subduction zone offshore of Washington also had a magnitude-9 megathrust earthquake in 1700.
"The 1964 earthquake gave birth to modern megathrust earthquake detection," Haussler said. "The patterns have now been recognized in many other regions."
The raised islands and tree graveyards along Alaska's coast suggest that megathrust earthquakes similar to the 1964 temblor happen sometime between every 330 and 900 years. But geologists are more concerned about the hazards Alaskans face from more frequent, smaller quakes along the Aleutian subduction zone, between magnitude 7 and magnitude 8.
State seismologist Michael West thinks Alaskans have grown too lax about earthquake hazards.
"After the 1964 earthquake there was a visceral understanding of the hazards we faced, and I think we've lost a little bit of that edge," he said.
In Anchorage, wet, silty soils liquefied and a massive landslide destroyed 75 homes in 1964. Now known as Earthquake Park, the Turnagain Heights landslide is where children and homes were swallowed in the fissured ground. Some of the city's most expensive houses slid into the ocean atop liquefied soils. Yet people were allowed to rebuild along the bluff.
Saturated
soil can be stiff when it's still, holding up houses and buildings. But
when it shakes, the soil jiggles like gelatin and behaves like a liquid.
Two-thirds of Alaska's population lives on top of these mixes.
Since the 1964 earthquake, geologists have learned that the speed of
earthquake shaking plays an important role in destruction due to liquefaction.
The shaking in 1964 was long and slow, instead of the fast,
high-frequency shaking similar to Christchurch, New Zealand, which
killed 185 people with a magnitude-6.1 quake in 2011. Christchurch and
Alaska share similar mixes of unconsolidated sediments, West said.
Terrible wavesThe earthquake also proved the link between subduction zone earthquakes and tsunamis. The movement of the seafloor during the earthquake shoves the sea, giving it a big slap that translates into a massive tidal wave.
For an earthquake and
tsunami larger than any in the past decade, the death toll was
remarkably low, just 131 people. Throughout the southeast, the worst
damage wasn't from ground shaking, but from soil failure, tsunamis and
landslides. The state had few residents, and they lived in low-rise
wood-frame buildings, the most resistant to shaking. [11 Facts About The 1964 Alaska Earthquake]
Of the 119 deaths attributable to ocean waves, about one-third were due
to the open-ocean tsunami: four at Newport Beach, Ore.; 12 at Crescent
City, Calif.; and about 21 in Alaska. The most terrible damage was from tsunamis
triggered by underwater landslides, as thick piles of sediment slumped
and slid during the earthquake. In some cases, these waves hit before
the earthquake ended, sweeping away entire villages. Eighty-two
people were killed by these "local waves.""The victims in Seward, Chenega, Valdez and Whittier barely had a chance. The tsunami washed over them in a matter of seconds," West said.
In Seward, the tsunami inundation zone, where water destroyed the town
and docks, was turned into a park and public campground. But new
development has crept into the flood zone in recent years, prompting
debate over safety and tsunami hazards.
In the past 50 years, Alaskans have endured scores of powerful
earthquakes that would have devastated other states, such as a magnitude
7.9 earthquake in 2002 and a 7.5 shaker in 2012.
"If you’re not careful, the take-home message is that these big
earthquakes don't hurt anyone in Alaska," West said. "That’s
tremendously naive."
Email Becky Oskin or follow her @beckyoskin. Follow us @OAPlanet, Facebook and Google+. Original article at Live Science's Our Amazing Planet.
- The 10 Biggest Earthquakes in History
- Image Gallery: This Millennium's Destructive Earthquakes
- Get a Rare Glimpse of Remote Alaska
How the 1964 Alaska Earthquake Shook Up Science
1964 Alaska earthquake - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/1964_Alaska_earthquake
The 1964 Alaskan earthquake, also known as the Great Alaskan Earthquake and ... 78 miles (125 km) east of Anchorage and 40 miles (64 km) west of Valdez.
Wikipedia
1964 Alaska earthquake
From Wikipedia, the free encyclopedia
Fourth Avenue in Anchorage, Alaska,
looking east from near Barrow Street. The southern edge of one of
several landslides in Anchorage, this one covered an area of over a
dozen blocks, including 5 blocks along the north side of Fourth Avenue.
Most of the area was razed and made an urban renewal district.
|
|
 |
|
| Date | 27 March 1964 (AKST) |
|---|---|
| Magnitude | 9.2 Mw[1] |
| Depth | 14 miles (23 km) |
| Epicenter | 61°3′0″N 147°28′48″W |
| Countries or regions | United States |
| Total damage | $311 million |
| Max. intensity | XI: Extreme |
| Peak acceleration | 0.18 g |
| Casualties | 139 killed |
Lasting nearly three minutes, it was the most powerful recorded earthquake in U.S. and North American history, and the second most powerful ever measured by seismograph.[4] It had a moment magnitude of 9.2, making it the second largest earthquake in recorded history[2][5]—the largest being the 1960 Valdivia earthquake in Chile.[4]
The powerful earthquake produced earthquake liquefaction in the region. Ground fissures and failures caused major structural damage in several communities, much damage to property and several landslides. Anchorage sustained great destruction or damage to many inadequately earthquake engineered houses, buildings, and infrastructure (paved streets, sidewalks, water and sewer mains, electrical systems, and other man-made equipment), particularly in the several landslide zones along Knik Arm. Two hundred miles southwest, some areas near Kodiak were permanently raised by 30 feet (9.1 m). Southeast of Anchorage, areas around the head of Turnagain Arm near Girdwood and Portage dropped as much as 8 feet (2.4 m), requiring reconstruction and fill to raise the Seward Highway above the new high tide mark.
In Prince William Sound, Port Valdez suffered a massive underwater landslide, resulting in the deaths of 30 people between the collapse of the Valdez city harbor and docks, and inside the ship that was docked there at the time. Nearby, a 27-foot (8.2 m) tsunami destroyed the village of Chenega, killing 23 of the 68 people who lived there; survivors out-ran the wave, climbing to high ground. Post-quake tsunamis severely affected Whittier, Seward, Kodiak, and other Alaskan communities, as well as people and property in British Columbia, Oregon, and California. Tsunamis also caused damage in Hawaii and Japan. Evidence of motion directly related to the earthquake was reported from all over the earth.
Contents
Geology
At 5:36 p.m. Alaska Standard Time (3:36 a.m. March 28, 1964 UTC), a fault between the Pacific and North American plates ruptured near College Fjord in Prince William Sound. The epicenter of the earthquake was 61.05°N 147.48°W, 12.4 mi (20 km) north of Prince William Sound, 78 miles (125 km) east of Anchorage and 40 miles (64 km) west of Valdez. The focus occurred at a depth of approximately 15.5 mi (25 km). Ocean floor shifts created large tsunamis (up to 220 feet (67 m) in height), which resulted in many of the deaths and much of the property damage.[6] Large rockslides were also caused, resulting in great property damage. Vertical displacement of up to 38 feet (11.5 m) occurred, affecting an area of 100,000 miles² (250,000 km²) within Alaska.Studies of ground motion have led to a peak ground acceleration estimate of 0.14 - 0.18 g.[7]
The Alaska Earthquake was a subduction zone earthquake (megathrust earthquake), caused by an oceanic plate sinking under a continental plate. The fault responsible was the Aleutian Megathrust, a reverse fault caused by a compressional force. This caused much of the uneven ground which is the result of ground shifted to the opposite elevation.
Tsunamis
Two types of tsunami were produced by this subduction zone earthquake. There was a tectonic tsunami produced in addition to about 20 smaller and local tsunami. These smaller tsunami were produced by submarine and subaerial landslides and were responsible for the majority of the tsunami damage. Tsunami waves were noted in over 20 countries, including: Peru, New Zealand, Papua New Guinea, Japan, and Antarctica. The largest tsunami wave was recorded in Shoup Bay, Alaska, with a height of about 67 meters.[3]
Red: 1-4 hour arrival times
Yellow: 5-6 hour arrival times
Green: 7-14 hour arrival times
Blue: 15-21 hour arrival times.
Death toll, damage and casualties
 |
This section needs additional citations for verification. (March 2011) |
|
Anchorage area
Most damage occurred in Anchorage, 75 mi (120 km) northwest of the epicenter. Anchorage was not hit by tsunamis, but downtown Anchorage was heavily damaged, and parts of the city built on sandy bluffs overlying "Bootlegger Cove clay" near Cook Inlet, most notably the Turnagain neighborhood, suffered landslide damage. The neighborhood lost 75 houses in the landslide, and the destroyed area has since been turned into Earthquake Park. The Government Hill school suffered from the Government Hill landslide leaving it in two jagged, broken pieces. Land overlooking the Ship Creek valley near the Alaska Railroad yards also slid, destroying many acres of buildings and city blocks in downtown Anchorage. Most other areas of the city were only moderately damaged. The 60-foot concrete control tower at Anchorage International Airport was not engineered to withstand earthquake activity and collapsed, killing one employee.[8]The house at 918 W. 10th Avenue suffered damage peripherally, but one block away the recently completed and still unoccupied Four Seasons Building on Ninth Avenue collapsed completely with the concrete elevator shafts sticking up out of the rubble like a seesaw.
The hamlets of Girdwood and Portage, located 30 and 40 mi (60 km) southeast of central Anchorage on the Turnagain Arm, were destroyed by subsidence and subsequent tidal action. Girdwood was relocated inland and Portage was abandoned. About 20 miles (32 km) of the Seward Highway sank below the high-water mark of Turnagain Arm; the highway and its bridges were raised and rebuilt in 1964-66.
Elsewhere in Alaska
Most coastal towns in the Prince William Sound, Kenai Peninsula, and Kodiak Island areas, especially the major ports of Seward, Whittier and Kodiak were heavily damaged by a combination of seismic activity, subsidence, post-quake tsunamis and/or earthquake-caused fires. Valdez was not totally destroyed, but after three years, the town relocated to higher ground 7 km (4 mi) west of its original site. Some Alaska Native villages, including Chenega and Afognak, were destroyed or damaged. The earthquake caused the Cold-War era ballistic missile detection radar of Clear Air Force Station to go offline for six minutes, the only unscheduled interruption in its operational history. Near Cordova, the Million Dollar Bridge crossing the Copper River also collapsed. The community of Girdwood was also confined to the southern side of the Seward Highway when water rushed into Turnagain Arm arm and flooded or destroyed any buildings left standing to the north of the highway. Interestingly, only the ground immediately along the highway and that on the north side of the road dropped, prompting geologists to speculate that Girdwood may rest upon an ancient cliff face, now covered by countless thousands of years of sediment and glacial deposits.[citation needed]Canada
A 4.5 ft (1.4 m) wave reached Prince Rupert, British Columbia, just south of the Alaska Panhandle, about three hours after the quake. The tsunami then reached Tofino, on the exposed west coast of Vancouver Island, and traveled up a fjord to hit Port Alberni twice, washing away 55 homes and damaging 375 others. The towns of Hot Springs Cove, Zeballos, and Amai also saw damage. The damage in British Columbia was estimated at $10 million Canadian ($65 million in 2006 Canadian dollars, or $56 million in 2006 U.S. dollars).[9]Elsewhere
Aftershocks
There were thousands of aftershocks for three weeks, following the main shock. In the first day alone, eleven major aftershocks were recorded with a magnitude greater than 6.2. Nine more occurred over the next three weeks. It was not until more than a year later that the aftershocks were no longer noticed.[11]See also
References
- U.S. Geological Survey (7 March 2006). Historic Earthquakes - Alaska - 1964 March 28 03:36 UTC - Magnitude 8.5: The Largest Earthquake in the World. Retrieved on 2009-09-02
- US Geological Survey report on the earthquake
- http://www.ngdc.noaa.gov/nndc/struts/results?bt_0=1964&st_0=1964&type_7=Like&query_7=prince&d=7&t=101650&s=7
- "Largest Earthquakes in the World Since 1900". Earthquake Hazards Program. US Geological Survey. 14 May 2009. Retrieved 1 March 2010.
- The Great Alaskan Earthquake & Tsunamis of 1964, by the National Oceanic and Atmospheric Administration. Accessed 2009-06-23. Archived 2009-06-25.
- Historic Earthquakes: Prince William Sound, Alaska
- National Research Council (U.S.). Committee on the Alaska Earthquake, The great Alaska earthquake of 1964, Volume 1, Part 1, National Academies, 1968 p. 285
- Sozen, Mete A. and N. Norby Nielsen, 1973: Analysis of the failure of the Anchorage International Airport control tower. The great Alaska earthquake of 1964, Volume 3, Part 2, National Research Council (U.S.). Committee on the Alaska Earthquake, National Academy of Sciences, ISBN 0-309-01606-1.
- http://www.ngdc.noaa.gov/nndc/struts/results?bt_0=1964&st_0=1964&type_5=EXACT&query_5=CANADA&d=166&query=&dataset=101650&s=166&submit_all=Search+Database 0
- Oregon’s pioneer spirit. Statesman Journal, December 26, 1999.
- USGS Release: 40th Anniversary of "Good Friday" Earthquake Offers New Opportunities for Public and Building Safety Partnerships (3/26/2004)
- http://www.ngdc.noaa.gov/nndc/struts/results?bt_0=1964&st_0=1964&type_4=Like&query_4=freeport&d=166&query=&t=101650&s=167&submit_all=Search+Database
General references
- National Research Council, Committee On The Alaska Earthquake (1971-73). The Great Alaska Earthquake Of 1964. Washington: National Academy of Sciences.
- Geology, Seismology and Geodesy, Hydrology, Biology, Oceanography And Coastal Engineering, Engineering, Human Ecology, Summary and Recommendation
External links
 |
Wikimedia Commons has media related to Good Friday Earthquake. |
- 1964 Good Friday Great Alaskan Earthquake from University of Arizona, Geosciences Department
- USGS report on the earthquake
- Photo library from the U.S. Geological Survey
- The Great Alaskan Earthquake & Tsunamis of 1964: NOAA report
- The Effects of the March 28, 1964 Alaska Tsunami in British Columbia, Canada
- Eyewitness Accounts
- Info on event from Alaska Earthquake Information Center
- The short film ALASKAN EARTHQUAKE (1966) is available for free download at the Internet Archive [more]
- Anchorage, AK Good Friday Earthquake, Mar 1964 at GenDisasters.com
end quote from:
1964 Alaska earthquake - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/1964_Alaska_earthquake
The 1964 Alaskan earthquake, also known as the Great Alaskan Earthquake and ... 78 miles (125 km) east of Anchorage and 40 miles (64 km) west of Valdez.
Wikipedia
In 1964 I was 16 years old (actually when it occurred I was a month or more away from 16) so I didn't get my full driver's license until April or May).
However, this was a very horrific event especially for people in California where we were very used to people dying then in Earthquakes. In fact, I think building codes in California, Oregon and Washington and hopefully in Alaska as well became more stringent after this in order to save more lives in earthquakes in the future. (I don't think anyone has died in an Earthquake in California for at least 10 years now) which is some sort of record since I was born.
The most notable story out of the 1964 earthquake other than pictures of streets in Anchorage chewed up at least 10 feet vertically with cars straight up and down or have crushed under the pieces of pavement or children watching their siblings crushed to death as children there was the following story which is something I like I never heard about again until the 2011 Japanese tsunami by a Japanese man trying to save his ship by heading into the huge set of tsunami waves. He also almost died by somehow saved his boat even though I think he got a slight concussion from being bounced around. He was the only ship on his island to be functional and able to help people on his island survive and get food to his island and people injured to hospitals on the mainland after everything died down once again.
The following story I read about in Reader's Digest then which for me was a rivetting story then of a man and his 10 year old son in a fishing boat that was large enough to have survived what they went through without sinking.
The man saw the tsunami wave coming and it was at least 100 feet high. So, he turned his boat into it and gave the ship full throttle. He said his boat was basically almost straight up into the air with him hanging onto the wheel with his son hanging on nearby him when they crested the 100 foot or more tsunami wave a few miles from the shore of Alaska. As soon as they crested they were okay again and watched as the wave hit the shore and tore out all the trees (thousands of large full grown Alaska trees and rip them back out to sea. At this point he said this was even more dangerous than the 100 foot high wave he had made it over before it broke because now he had to dodge huge trees just ripped out by their roots floating and moving at precarious speeds in the ocean. However, he managed to not let them sink his ship and lived to tell the story along with his son.
I was imagining what a complete mess all these trees made when thousands of trees were eventually washed to shore once again by the waves like they would naturally do. However, some possibly stayed floating out to sea as well as a hazard to shipping.
No comments:
Post a Comment