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Tsunami Advisories Lifted After Alaska Earthquake Earthquake Shakes Alaska and Sends a Shudder of Alarm Along the Coast
(about 4 hours later)
Within four hours of a major earthquake striking off the Alaskan coast early Tuesday, the authorities lifted all tsunami advisories, after initial concerns prompted guidance for coastal areas as far south as the American border with Mexico. ANCHORAGE — The Alaskans, roused by a major earthquake and threatened by the specter of a tsunami, moved in the middle of the night.
“A tsunami was generated by this event, but no longer poses a threat,” a message from the United States National Tsunami Warning Center said just after 4 a.m. in Alaska. They shuffled into schools that had become evacuation centers. They parked their cars on higher ground at Safeway and Walmart stores. They rushed up Pillar Mountain. Then, mercifully, the big waves never came, and within four hours, the authorities lifted the tsunami advisories that had once stretched from Alaska to the American border with Mexico.
The magnitude 7.9 quake was reported at 12:31 a.m. local time in the Gulf of Alaska, about 170 miles off Alaska, according to the United States Geological Survey. There were no immediate reports of damage. “Everybody had to evacuate,” Fran Latham, who runs a bed-and-breakfast in Yakutat, said of her town between Anchorage and Glacier Bay National Park. “It looked like everybody was at the school and the police department.”
The center reported that a small tsunami with a wave height of less than eight inches was observed in the Alaska towns of Old Harbor, Seward and Kodiak. The overnight panic along the Pacific began after a magnitude 7.9 quake was reported at 12:31 a.m. local time in the Gulf of Alaska, according to the United States Geological Survey. There were no immediate reports of damage or fatalities, the authorities said, but the United States National Tsunami Warning Center said a small tsunami, with a wave height of less than eight inches, had been observed in a handful of Alaska cities, including Kodiak and Seward.
Tsunami sirens went off in Kodiak after the earthquake. “Evacuate inland or to higher ground above and beyond designated tsunami hazard zones or move to an upper floor of a multistory building depending on your situation,” the authorities warned on Tsunami.gov. “Move out of the water, off the beach, and away from harbors, marinas, breakwaters, bays and inlets.” “We’re very grateful that there was no major tsunami,” said Mayor Pat Branson of Kodiak, a city of about 6,200 people on an island of about 13,800, at a news conference around 4:30 a.m. local time. “We live in a very prone earthquake and tsunami area, and it’s a beautiful place, but that’s what you have when you live in paradise.”
Stephanie Wyzkoski, 42, who co-owns the Cranky Crow Bed and Breakfast in Kodiak with her husband, John, said emergency workers “told everyone to evacuate in the lower areas of town.” Hawaii, which this month confronted an errant alert of an incoming ballistic missile, was briefly under a tsunami watch, but much of the alarm was concentrated in Alaska, where the earthquake woke people hundreds of miles from its epicenter.
“People are going to the high school and the town pool to evacuate,” she said. Tsunami warning sirens sounded, cellphones pinged with emergency alerts, and in Kodiak, which suffered major damage when an earthquake in 1964 sparked a tsunami, roads filled as residents rushed toward higher ground.
“We are quite high up,” she added. “We are close to the hospital, so we have opened up our house to friends.” “I was at home asleep when I woke up with the shaking,” said Lt. Tim Putney of the Kodiak police after he evacuated his wife and children to a friend’s home that was on higher ground. “It felt like it went on for quite a while: 30 seconds or a minute or so.”
After urging residents to seek higher ground, the police in Kodiak said that one popular area — Pillar Mountain — was at capacity. The police urged people to go instead to the local high school or to the Safeway or Walmart parking lots. At the Hotel Captain Cook in Anchorage, the lobby shook and an urgent alert from the government appeared to unnerve some guests in the 270 or so rooms that were occupied early Tuesday.
The warnings included San Francisco, where the authorities told people living within five blocks of the bay that they might need to evacuate. “It was pretty crazy because for a while I just had to calm the people down,” said Michael Specking, who works at the front desk of the hotel. “Everyone in the hotel called down at once. Everybody kind of freaked out because of that alert.”
The region of the Gulf of Alaska where the quake hit is part of a large subduction zone, where one large piece of the earth’s surface, or plate — in this case the floor of the Pacific Ocean — is slowly sliding under another — the North American continent. The Alaska subduction zone is the source of many earthquakes, including one in 1964 that at magnitude 9.2 was the second largest ever recorded. Even in Anchorage, about 350 miles from the epicenter, Mr. Specking said, “You could look over down the hall and see everything shaking. Our front doors were shaking, you could see the windows moving.”
But in a brief analysis of Tuesday’s quake released several hours afterward, the United States Geological Survey said it occurred not on a sloping thrust fault like the one that moved in 1964, but rather on a near-vertical strike-slip fault. That, the geological survey said, was “consistent with it occurring on a fault system within the Pacific plate before it subducts, rather than on the plate boundary between the Pacific and North America plates further to the northwest.” The earthquake occurred about 175 miles southeast of Kodiak Island. This region is part of a large subduction zone, where one large piece of the earth’s surface, or plate — in this case the floor of the Pacific Ocean — is slowly sliding under another — the North American continent.
Peter J. Haeussler, a research geologist with the survey in Anchorage, said that it appeared likely that the slip occurred at a bulge in the Pacific plate where it bends as it starts to slide under the continent. Such a bulge is referred to as an “outer rise,” he said. The Alaska subduction zone is the source of many earthquakes, including the one in 1964 that, at magnitude 9.2, was the second largest ever recorded.
But Peter Haeussler, a research geologist with the United States Geological Survey in Anchorage, said that the 7.9 quake on Tuesday did not occur directly where the two plates meet. Rather, he said, it appeared that the slip occurred on the Pacific plate only, at a point where it bends as it starts to slide under the continent.
The direction of the fault movement in this case would be horizontal — more like the San Andreas fault in California — and would be less likely to generate large tsunamis, Dr. Haeussler said.The direction of the fault movement in this case would be horizontal — more like the San Andreas fault in California — and would be less likely to generate large tsunamis, Dr. Haeussler said.
He said that tide gauges on Kodiak Island showed a small tsunami, of less than a foot, but the high water arrived more than an hour after it had been expected. It was possible that the wave was created by underwater slumping of sediments during the quake somewhere in the Gulf of Alaska, he said. The Alaska Earthquake Center, which is affiliated with the University of Alaska Fairbanks, reported a series of aftershocks, the largest of which preliminarily registered as a 5.6.
Dr. Haeussler said he had been awakened by the quake at his home north of Anchorage, more than 350 miles from the epicenter, and that the shaking had lasted about a minute. By comparison, ground-shaking lasted about four and a half minutes during the 1964 quake. “Given the location and type of mainshock, we anticipate vigorous aftershocks in the magnitude 4-5 range and can expect aftershocks of magnitude 6 or larger,” the center said in a post on Twitter early on Tuesday. “We have no reason to suspect a follow-on earthquake of comparable, or larger, size than the M7.9 mainshock.”
He said he had spoken to a colleague on Kodiak Island, closer to the epicenter, who had felt a long, gentle rolling from the quake. In a separate post, the earthquake center said the aftershocks suggested “the fault ruptured along a North-South oriented fault.”
Geologists and residents of the West Coast have long been aware of the threat of “the big one.” A 2015 article in The New Yorker described, in occasionally terrifying detail, an expected megaquake in the Cascadia subduction zone, off the coast of the Pacific Northwest. Tuesday’s quake came nearly seven years after Japan was rattled by a magnitude 9.0 earthquake, the strongest ever recorded there. The earthquake set off a powerful tsunami that breached the sea walls of coastal towns, killing at least 15,000 people and sparking a major crisis at the Fukushima Daiichi Nuclear Power Station.
After the quake on Tuesday, Gov. Bill Walker of Alaska urged residents to “heed local warnings to move inland or to higher ground.” A magnitude 9.1 earthquake, one of the most powerful ever recorded, struck off the Indonesian island of Sumatra in December 2004, generating enormous waves that killed more than 230,000 people, mostly in Indonesia but also in India, Sri Lanka, Thailand and as far away as Somalia.
The Alaska Earthquake Center, which is affiliated with the University of Alaska Fairbanks, reported a series of aftershocks, the largest of which registered preliminarily as a 5.3. In Yakutat on Tuesday, Ms. Latham recalled how she had driven, with a 90-year-old neighbor and the neighbor’s dog, through 3 feet of snow to get to safety.
“Given the location and type of mainshock, we anticipate vigorous aftershocks in the magnitude 4-5 range and can expect aftershocks of magnitude 6 or larger,” the center said in a post on Twitter. “We have no reason to suspect a follow-on earthquake of comparable, or larger, size than the M7.9 mainshock.” “The dog thought it was great,” she said. “It was going for a ride at 1:30 in the morning.”
Tuesday’s quake came nearly seven years after Japan was rattled by a 9.0-magnitude earthquake, the strongest ever recorded there. The earthquake set off a powerful tsunami that breached the sea walls of coastal towns, killing at least 15,000 people and sparking a major crisis at the Fukushima Daiichi Nuclear Power Station. She eventually parked her sport-utility vehicle in the parking lot of a Catholic church. She waited. And then word from came over the radio: all clear.
A 9.1-magnitude earthquake, one of the most powerful ever recorded, struck off the Indonesian island of Sumatra in December 2004, generating enormous waves that killed more than 230,000 people, mostly in Indonesia but also in India, Sri Lanka, Thailand and as far away as Somalia.