It has been one of the strongest earthquakes ever recorded, yet it has not triggered the catastrophic tsunami that many initially feared.
The 8.8-magnitude quake, which struck eastern Russia at 11:25 local time on Wednesday (00:25 BST), immediately raised concerns for coastal populations across the Pacific.
Millions were evacuated, as memories of the devastating tsunamis of Boxing Day 2004 in the Indian Ocean and Japan 2011, both caused by similarly large earthquakes, resurfaced.
However, the resulting tsunami has been less severe than anticipated, though some damage has been reported.
What caused the earthquake and tsunami, and why was the impact not as drastic as initially feared?
The remote Kamchatka Peninsula lies within the “Pacific Ring of Fire,” an area known for its high frequency of earthquakes and volcanic activity.
The Earth’s upper layers are composed of tectonic plates, which are constantly moving relative to each other.
The “Pacific Ring of Fire” represents an arc of these plates encircling the Pacific Ocean. According to the British Geological Survey, approximately 80% of the world’s earthquakes occur along this ring.
Off the coast of the Peninsula, the Pacific plate is moving northwest at a rate of about 8cm (3in) per year – a relatively rapid pace in tectonic terms, roughly twice the growth rate of fingernails.
Here, it converges with a smaller plate known as the Okhotsk microplate.
The Pacific plate, being oceanic, consists of dense rock and subducts beneath the less dense microplate.
As the Pacific plate descends into the Earth’s mantle, it heats up and melts, effectively disappearing.
This subduction process is often uneven. The plates can become locked as they slide past each other, causing the overriding plate to be dragged downwards.
This friction can accumulate over millennia, only to be released suddenly in a matter of minutes.
This phenomenon is known as a megathrust earthquake.
“When we typically think about earthquakes, we imagine an epicenter as a small point on a map. However, for such large earthquakes, the fault will have ruptured over many hundreds of kilometers,” explained Dr. Stephen Hicks, lecturer in environmental seismology at University College London.
“It is this vast amount of slip and area of the fault that generates such a high earthquake magnitude.”
The largest earthquakes in recorded history, including the three strongest events in Chile, Alaska, and Sumatra, were all megathrust earthquakes.
The Kamchatka Peninsula is particularly susceptible to powerful earthquakes.
Notably, another significant magnitude 9.0 earthquake occurred less than 30km (19mi) from Wednesday’s earthquake in 1952, according to the U.S. Geological Survey.
This abrupt movement can displace the water column above the plates, generating tsunami waves that propagate towards coastlines.
In the deep ocean, tsunamis can travel at speeds exceeding 500mph (800km/h), comparable to a passenger aircraft.
At these depths, the distance between wave crests is considerable, and the wave height is minimal – typically less than a meter.
As a tsunami approaches shallow coastal waters, it decelerates, often to around 20-30mph.
The distance between wave crests decreases, and the wave height increases, potentially creating a substantial wall of water near the shoreline.
However, a high-magnitude earthquake does not automatically guarantee a devastating tsunami with extensive inland inundation.
Authorities reported tsunami waves of up to 4m (13ft) in parts of eastern Russia following Wednesday’s quake.
These waves were significantly smaller than the tens-of-meters-high waves observed during the Boxing Day 2004 Indian Ocean tsunami and the 2011 Japan tsunami.
“The height of the tsunami wave is also affected by local shapes of the seafloor near the coast and the [shape] of the land where it arrives,” said Prof. Lisa McNeill, professor of tectonics at the University of Southampton.
“These factors, along with how populated the coast is, affect how serious the impact is,” she added.
Initial reports from the U.S. Geological Survey indicated that the earthquake’s epicenter was relatively shallow, approximately 20.7km (12.9 miles) below the Earth’s surface.
A shallow depth can result in greater seafloor displacement and a larger tsunami wave, but definitive conclusions are difficult to draw immediately after the event.
“One possibility is that the tsunami models have maybe taken a conservative estimate on the earthquake depth,” Dr. Hicks told BBC News.
“Potentially you could shift that earthquake another 20 kilometers deeper, and that would actually reduce the amplitude of the tsunami waves quite considerably.”
Another crucial factor is the development of early warning systems.
Due to the high frequency of earthquakes in the Pacific region, many countries operate tsunami warning centers that disseminate public alerts and evacuation orders.
No such system was in place during the 2004 Boxing Day tsunami, leaving many without sufficient time to evacuate.
Tragically, more than 230,000 people perished across 14 countries in the Indian Ocean.
Early warning systems are essential because scientists have limited ability to predict the precise timing of earthquakes.
The U.S. Geological Survey recorded an earthquake measuring 7.4 in the same region ten days prior.
While this may have been a foreshock – an early release of energy – it is not a reliable predictor of the exact timing of a future earthquake, explained Prof. McNeill.
“Although we can use how fast the plates are moving, GPS to measure current movements and when previous earthquakes occurred, we can only use this information to make forecasts of probability of an earthquake,” she said.
The Geophysical Survey of the Russian Academy of Sciences (GS RAS) will continue to monitor the region, anticipating that aftershocks could persist for the next month.
The 8.8 magnitude earthquake is believed to be one of the most powerful ever recorded.
Wednesday’s tsunami warning is bringing back memories of one of the world’s worst nuclear disasters.
Tsunami warnings have been issued in Russia, Japan, Ecuador and Hawaii.
The tech giant said only 469 serious warnings were sent out ahead of the 7.8 magnitude quake.
“Everyone’s exhausted. We just want it to stop,” says one resident of the Tokara islands.