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RNZ News
31-07-2025
- Science
- RNZ News
Why Russia's megathrust earthquake was among biggest ever recorded, but damage was minimal
By Elissa Steedman , ABC Aerial view of Balneario de Huanchaco in Trujillo, Peru. Photo: AFP / Steffano Palomino Explainer - One of the largest earthquakes in recorded history set off tsunami warnings across the Pacific Ocean on Wednesday. But it has not proved as destructive as experts feared. Here are the factors that contributed to that outcome. It was among the 10 strongest ever recorded. The magnitude-8.8 earthquake was the largest since 2011, when a magnitude-9.1 tremor and subsequent tsunami struck off the coast of Japan and killed more than 15,000 people. Wednesday's earthquake, known as the Kamchatka earthquake, is considered a megathrust earthquake - common to each of the planet's largest recorded quakes. Earth's outer layers are split into 15 slabs known as tectonic plates. These plates slowly shift around - moving a few centimetres every year - and often get stuck against each other due to friction. When that happens, stress builds up over time until the plates suddenly shift and cause seismic waves that shake the ground. Megathrust earthquakes occur when one tectonic plate has been forced underneath another - a phenomenon known as subduction. In this case, it was the Pacific plate beneath the North American plate. Stephen Hicks, an environmental seismology expert at University College London, said megathrust earthquakes "cause some of the world's largest ruptures and trans-ocean tsunamis". Tsunamis occur when earthquakes displace large amounts of ocean water. Megathrust quakes often cause tsunamis because the faults they cause tend to come to, or even directly penetrate, the sea floor, Dr Hicks said. How much of the sea floor moves influences whether a tsunami is formed, and how big it might become, added Lisa McNeill, a tectonics professor at the University of Southampton. "Some fault movements don't move the sea floor much, and so, there is no tsunami," she said. In the case of the Kamchatka earthquake, a large slip occurred and generated a tsunami, Dr McNeill added. Despite the earthquake triggering tsunami warnings across the Pacific Ocean, no deaths were recorded, and minimal structural damage was reported. Maximum wave heights of five metres were observed in Kamchatka yesterday - a tenth of the heights recorded after the Tohoku Earthquake in 2011, which triggered the Fukushima Daiichi nuclear disaster. Waves in Hawaii reached a maximum height of about 1.7 metres. Meghan Miller, a professor of seismology at Australian National University, said where earthquakes strike has a major impact on the severity of subsequent tsunamis. "For the tsunami and earthquake that happened in Japan in 2011, the distances [to land] were much closer," she told ABC Radio National Breakfast. "So the distance for the waves to travel to the coast of Japan was much shorter." Dr McNeill said the height of tsunami waves can also be affected by the shape of the sea floor near the coast. "[The waves] are small at sea but travel fast, and it is when they reach shallow water that they build in height again," she said. " tsunami can have varied heights on one coastline, and it could generate surprisingly large wave heights." She added that wave heights recorded after the Kamchatka earthquake were still "significant", but the potential for destruction was minimised. The tremor triggered tsunami warnings across the Pacific Ocean, as far away as Hawaii, Chile, and Ecuador. "This has been established in the Pacific since the 1960s, and people therefore receive warnings about the tsunami and can evacuate," she said. "It is harder for those living close to the earthquake as they have less time, but the earthquake is their warning of a tsunami and [the] prompt to move to higher ground." Many nations with sea borders have government-run programs to detect and monitor threats caused by earthquakes and tsunamis that may impact the region, and are charged with alerting communities of incoming threats and issuing evacuation orders. There were no warning systems in place in the Indian Ocean when the 2004 Boxing Day tsunami occurred. The enormity of the natural disaster's death toll, estimated to be about 225,000, is attributed to the lack of evacuation alerts. -ABC
IOL News
31-07-2025
- Climate
- IOL News
Millions return home as Pacific tsunami warnings lifted
Aerial view of Balneario de Huanchaco in Trujillo, Peru. Peru closed 65 of its 121 Pacific ports as a tsunami alert was issued following a massive 8.8-magnitude earthquake off the east coast of Russia. Image: Steffano Palomino / AFP Countries across the Pacific rim lifted tsunami warnings on Wednesday, allowing millions of temporary evacuees to return home. After one of the strongest earthquakes ever recorded rattled Russia's sparsely populated Far East, more than a dozen nations -- from Japan to the United States to Ecuador -- warned citizens to stay away from coastal regions. Storm surges of up to four metres (12 feet) were predicted for some parts of the Pacific, after the 8.8 quake struck off Russia's Kamchatka peninsula. The tsunami warnings caused widespread disruption. Peru closed 65 of its 121 Pacific ports and authorities on Maui cancelled flights to and from the Hawaiian island. But fears of a catastrophe were not realised, with country after country lifting or downgrading warnings and telling coastal residents they could return. In Japan, almost two million people had been ordered to higher ground, before the warnings were downgraded to an advisory for large stretches of its Pacific coast, with waves up to 0.7 metres still being observed on Thursday. "We urge the public not to go in coastal waters and please stay away from coasts," a seismologist at Japan's meteorological agency said. The only reported fatality was a woman killed when her car fell off a cliff in Japan as she tried to escape on Wednesday, local media reported. In Chile, authorities conducted what the Interior Ministry said was "perhaps the most massive evacuation ever carried out in our country" -- with 1.4 million people ordered to high ground. Chilean authorities reported no damage or victims and registered waves of just 60 centimeters (two feet) on the country's north coast. In the Galapagos Islands, where waves of up to three meters were expected, there was relief as the Ecuadoran navy's oceanographic institute said the danger had passed. Locals reported the sea level falling and then rising suddenly, a phenomenon which is commonly seen with the arrival of a tsunami. Video Player is loading. Play Video Play Unmute Current Time 0:00 / Duration -:- Loaded : 0% Stream Type LIVE Seek to live, currently behind live LIVE Remaining Time - 0:00 This is a modal window. Beginning of dialog window. Escape will cancel and close the window. Text Color White Black Red Green Blue Yellow Magenta Cyan Transparency Opaque Semi-Transparent Background Color Black White Red Green Blue Yellow Magenta Cyan Transparency Opaque Semi-Transparent Transparent Window Color Black White Red Green Blue Yellow Magenta Cyan Transparency Transparent Semi-Transparent Opaque Font Size 50% 75% 100% 125% 150% 175% 200% 300% 400% Text Edge Style None Raised Depressed Uniform Dropshadow Font Family Proportional Sans-Serif Monospace Sans-Serif Proportional Serif Monospace Serif Casual Script Small Caps Reset restore all settings to the default values Done Close Modal Dialog End of dialog window. Advertisement Next Stay Close ✕ But only a surge of just over a meter was reported, causing no damage. "Everything is calm, I'm going back to work. The restaurants are reopening and the places tourists visit are also open again," said 38-year-old Santa Cruz resident Isabel Grijalva. Earlier, national parks were closed, schools were shuttered, loudspeakers blared warnings and tourists were spirited off sightseeing boats and onto the safety of land. The worst damage was seen in Russia, where a tsunami crashed through the port of Severo-Kurilsk and submerged the local fishing plant, officials said. Russian state television footage showed buildings and debris swept into the sea. The surge of water reached as far as the town's World War II monument about 400 meters from the shoreline, said Mayor Alexander Ovsyannikov. The initial quake also caused limited damage and only light injuries, despite being the strongest since 2011, when 15,000 people were killed in Japan. Russian scientists reported that the Klyuchevskoy volcano erupted shortly after the earthquake. "Red-hot lava is observed flowing down the western slope. There is a powerful glow above the volcano and explosions," said Russia's Geophysical Survey. Pacific alerts Wednesday's quake was the strongest in the Kamchatka region since 1952, the regional seismic monitoring service said, warning of aftershocks of up to 7.5 magnitude. The US Geological Survey said the quake was one of the 10 strongest tremors recorded since 1900. It was followed by dozens of aftershocks that further shook the Russian Far East, including one of 6.9 magnitude. The USGS said there was a 59 percent chance of an aftershock of more than 7.0 magnitude in the next week. AFP
