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BBC News Climate and Science
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It has been one of the strongest earthquakes ever recorded – but so far has not brought the catastrophic tsunami that many feared.
When the 8.8-magnitude quake struck eastern Russia at 11:25 local time on Wednesday (00:25 BST), it raised concerns for coastal populations across the Pacific.
Millions of people were evacuated, as minds cast back to the devastating tsunami of Boxing Day 2004 in the Indian Ocean and Japan 2011, both triggered by similarly large earthquakes.
But today’s tsunami has been much less severe, even though it’s brought some damage.
So what caused the earthquake and tsunami – and why wasn’t it as bad as initially feared?
What causes a mega earthquake?
The Kamchatka Peninsula is remote but lies in the “Pacific Ring of Fire” – so called because of the high number of earthquakes and volcanoes that occur here.
The upper layers of the Earth are split into sections – tectonic plates – which are all moving relative to one another.
The “Pacific Ring of Fire” is an arc of these plates that extends around the Pacific. Eighty percent of the world’s earthquakes occur along the ring, according to the British Geological Survey.
Just off the coast of the Peninsula, the Pacific plate is moving north-west at about 8cm (3in) per year – only about twice the rate that your fingernails grow, but fast by tectonic standards.
There it comes into contact with another, smaller plate – called the Okhotsk microplate.
The Pacific plate is oceanic, which means it has dense rocks and wants to sink
