Residents across parts of southern Alaska were jolted by strong shaking early Friday, prompting tsunami warnings, precautionary evacuations and an immediate response from emergency officials as a powerful earthquake rumbled beneath the Pacific Ocean off the Alaska Peninsula.
The earthquake struck in the early morning hours southeast of Perryville, sending tremors across much of southern Alaska. The quake’s size immediately raised concerns that dangerous tsunami waves could follow, although the epicentre was offshore.
Within minutes, the National Tsunami Warning Center issued tsunami warnings for parts of Alaska’s southern coastline, telling people in vulnerable coastal communities to move to higher ground.
In several towns, warning sirens sounded, emergency alerts were sent to mobile phones, and local authorities put into action evacuation plans that had been rehearsed in previous emergency drills.
As communities including Kodiak, Homer, Sand Point, Chignik Bay and other coastal areas began evacuating residents from beaches, harbours and other low-lying places, officials were monitoring the developing situation.
For many residents, the earthquake was scary enough.
Some people reported being jolted awake by the violent shaking which lasted more than a minute in some places.
Furniture was moved, household items were toppled from shelves and power outages were reported in isolated communities nearest the epicentre.
Emergency managers told residents to stay outside damaged buildings until they could be inspected, although many of them were structurally sound.
The quake occurred in the Aleutian subduction zone, one of the most seismically active areas on the planet, the U.S. Geological Survey said.
This builds up enormous stress over decades that is suddenly released in powerful earthquakes . Here , the Pacific Plate is slowly grinding underneath the North American Plate .
Scientists call these megathrust earthquakes because they occur on massive faults that can generate some of the largest earthquakes ever recorded anywhere on the planet.
The size of the earthquake prompted tsunami warning centers to immediately begin analysing data from deep-ocean sensors, coastal tide gauges and seismic monitoring stations.
Initial computer models suggested tsunami waves were possible, though officials said heights and impact of waves could vary widely depending on local geography and the characteristics of the earthquake itself.
Hours later, tsunami activity was recorded at monitoring stations along portions of Alaska’s coast.
The good news was that the waves were far smaller than many emergency planners feared.
A few ports reported strange currents and minor changes in water level, but there was no serious flooding along the shore.
Warnings were steadily scaled back and called off across many areas as officials confirmed the threat from the tsunami had eased.
Authorities later thanked residents for evacuating quickly.
They said that even if a tsunami turns out to be smaller than feared it is still crucial to follow official advice because the size of a tsunami is not always known straight away after a large earthquake.
Aftershocks continued to shake the region throughout the day.
Small earthquakes continued to rattle the area after the main shock, a reminder to residents that big quakes are often followed by hundreds of aftershocks in the weeks or months to follow.
The smaller quakes are part of the natural process of adjustment as stress is redistributed along the fault, seismologists say.
Also, infrastructure inspections started early in the morning.
Transportation officials checked bridges, highways, airports and port facilities and utility crews checked power lines and communications systems for possible damage.
In some communities, schools and public buildings were temporarily inspected before normal activities resumed.
Authorities reported no widespread structural collapse even though the shaking was strong.
Emergency responders said strict building standards, the offshore location of the earthquake and effective public warning systems helped limit injuries and damage.
Alaska is on the Pacific Ring of Fire and has one of the most extensive earthquake monitoring networks in the world.
Residents are used to earthquake preparedness campaigns, emergency drills, and tsunami evacuation planning.
But those investments in preparedness over the long term, experts say, keep paying off in lives saved every time a big quake hits.
The earthquake also drew international attention because it was among the strongest recorded in the United States in recent decades.
Scientists worldwide began to study the event to gain a better understanding of how stress is transferred along major subduction zones, and how tsunami generation can vary even between earthquakes of similar magnitude.
“Not all magnitude 8-plus earthquakes produce devastating tsunamis,” researchers noted.
The amount of water displaced depends on the amount of vertical displacement of the ocean floor, the depth of the rupture and the exact nature of the fault.
Those factors help explain why the monster quake generated relatively modest tsunami waves, despite its huge magnitude.
For those along the Alaskan coast, however, the event was another reminder that preparation is still the key.
Emergency officials still urge families to keep disaster supply kits, learn local evacuation routes and act immediately whenever tsunami warnings are issued.
While the earthquake caused far less damage than initially feared, experts warn future events may not be so lucky.
The swift response of emergency agencies and the cooperation of the public showed how preparedness and early warning systems can vastly reduce the hazards of some of nature’s most powerful phenomena.
As scientists continue to analyse data collected from the earthquake, the event is likely to become an important case study for future improvements in earthquake monitoring, tsunami forecasting and emergency response planning throughout the Pacific region.