Why 8.8 magnitude Kamchatka quake is rare but not unusual

Indian Express

2 days ago

An 8.8 magnitude earthquake, one of the strongest on record, struck the Kamchatka Peninsula, in Russia's far-east, about 6,500 km east of Moscow, on Wednesday morning, triggering a tsunami that struck several countries on both sides of the northern Pacific Ocean.
The tsunami generated waves as high as 3-4 metres in the Kamchatka Peninsula and some other places, about five feet in Hawaii, and about two feet in Japan. Flooding and damage were reported from several places, but no lives were lost.
The earthquake in Kamchatka was the strongest since the 9.1 magnitude quake that had struck Japan in 2011. That quake too had caused a major tsunami which then led to the nuclear disaster at Fukushima.
Wednesday's event was rare — only five earthquakes of magnitude 8.5 and above have occurred in the past 20 years — but it occurred in a region that is one of the most earthquake prone in the world.
Kamchatka Peninsula lies on the Circum-Pacific seismic belt, more popularly known as the 'Ring of Fire', that witnesses the maximum number of earthquakes and volcanic eruptions on Earth.
This seismically active belt encircles almost the entire Pacific Ocean — on its eastern side is the western coast of the Americas, and on its western side lies the Far East and Oceania. It touches countries like the United States, Mexico, Chile, Peru, New Zealand, Australia, Indonesia, the Philippines, Japan and Russia.
According to the United States Geological Survey (USGS), the Ring of Fire accounts for more than 80% of the planet's largest earthquakes. The biggest recorded earthquake, of magnitude 9.5 in Chile in 1960, occurred in this belt, and so did a magnitude 9.2 event in Alaska in 1964. In fact, each of the 23 events of 8-plus magnitude recorded in the last 20 years have happened along this seismic belt.
The nearly 2,000-km long region extending from Kamchatka Peninsula in the north to northern Japan in the south, and including the volcanically-active Kuril Islands of Russia, has witnessed more than 130 earthquake events of 7-plus magnitude since 1900, USGS data show. In 1952, this region even recorded a magnitude 9 earthquake.
The Circum-Pacific seismic belt is home to multiple subduction processes, in which the Pacific tectonic plate is clashing against continental land.
Subduction is a geological process in which one tectonic plate — put simply, a large section of the Earth's crust — presses against another. Usually, the heavier or denser plate, that is, the one with more mass per unit of area, tends to go below the lighter plate. But this process results in deformities and creates a huge stress at the plate boundaries. It is this stress that is released in the form of earthquakes.
The Himalayas were created due to subduction, as a result of the Indian plate pushing against the Eurasian plate. This is also the reason why the Himalayan region is one of the most earthquake-prone in the world.
Vineet Gehlot, director of the Dehradun-based Wadia Institute of Himalayan Geology, says that the region is one of the very few areas where subduction is being observed over land. 'A majority of the subduction zones are under the sea,' he told The Indian Express.
'The Pacific Ocean, particularly the so-called Ring of Fire region, is witnessing several such processes. The Pacific plate is denser, and is subducting under the continental plate at several places on both sides… There is no other place on Earth where so many subduction processes are happening. And this is why the region produces so many earthquakes,' Gehlot said.
The Circum-Pacific seismic belt is one of the three large earthquake zones of the Earth. The Alpide belt — spanning from Indonesia through the Himalayas and further to Afghanistan, Iran, and Turkey — which runs mostly over the land, is the second-most earthquake-prone zone in the world.
But unlike the Ring of Fire, which accounts for around 80% of all big earthquakes, the Alpide belt contributes only 15-17%, according to USGS. However, this belt traverses some of the most heavily populated areas on the planet, which makes earthquakes in the region extremely deadly. In general, while the strongest earthquakes often take place under the ocean, the ones on land, even if they are weaker, are often more deadly due to their proximity to population centres.
The Kamchatka quake stuck off the coast of the peninsula, which is sparsely populated. Official statistics from 2023 put the population density in the Kamchatka Krai of the Russian federation to be roughly 0.62 persons per sq km, which is why the quake did not result in any casualties, even though the much weaker 7.6 magnitude earthquake in Nepal in 2015 killed more than 15,000 people.
The third most prominent seismic belt is what is known as the mid-Atlantic ridge, which runs north-south through the middle of the entire Atlantic Ocean, from the Arctic to the Antarctic region. This subduction zone is in the middle of the ocean, deep underwater, and far away from land. This zone produces relatively moderate earthquakes, and their impact is minimal considering their distance from land.
The strength of an earthquake is, in part, dependent on the length of the faultline, that is, the extent of the plate boundaries that clash against each other. A larger faultline is more likely to produce a stronger earthquake. A 9.5 magnitude earthquake, the largest that has been recorded, is essentially the limit to how strong an earthquake can be. To produce anything stronger, say an event of magnitude 10 or more, a faultline extending to almost the entire Earth would be required. No current faultline is capable of producing a quake that strong.