by By David Stanway
Singapure (Reuters) -The quake of 8.8 magnitude before Russia, which triggered Tsunami warnings over the Pacific, occurred on a so -called “megathust”, in which the denser Pacific plate slides under the lighter North American plate, said scientists.
The Pacific plate was in motion and made the area of the Kamchatka peninsula in front of the Russia’s Far -Ost coast in the Far East, where it was particularly susceptible to such tremors -and larger aftershock cannot be excluded, they said.
With its epicenter near the city of Petropavlovsk-Kamchatsky, it was the largest earthquake since the devastating Tohuku event in 2011, which caused a tsunami that brought Japan’s Fukushima Daiichi atomic work to collapse.
“The Seismian zone of the Kamchatka is one of the most active subduction zones in the Pacific fire ring, and the Pacific plate moves west with around 80 mm (3 inches) per year,” said Roger Musson, honorary researcher at the British Geological Survey.
“Subduction” events in which one plate presses under another can create far stronger earthquakes than “strike slide”, such as those in March, in which the panels brush horizontally against each other at different speeds.
The area of Kamchatka is particularly vulnerable and experienced an event of strength 9 in November 1952. He deletes the city of Severo-Kurilsk and caused extensive damage to Hawaii, Musson told Reuters.
Flat “megathust” events more cause tsunamis because they burst through the sea floor and displace huge amounts of water.
Tsunami risks
With a relatively low depth of 20.7 km (13 miles), the earthquake on Wednesday would always create such tsunami risks, experts said.
“It is an earthquake off the coast, and if you have offshore earthquakes, it is possible to meet tsunamis,” said Adam Pascal, chief scientist at the Australian Seismology Research Center.
“If you have a relatively flat earthquake, it is more likely that it will break the surface of the sea floor,” he told Reuters.
“In some cases, we saw that they have large earthquakes like this and cannot cause a tsunami because they are too deep and that scissors are not expressing themselves on the surface.”
Tsunami waves of around 1.7 meters (5.5 feet) reached Hawaii, less high than originally expected.
Parts of French Polynesia were asked to prepare on waves up to 4 meters (13 ft).
The influence of a tsunami depends on his “apron” when he approaches the coasts, said Pascal.
“If you have a very long, flat climb to the coast, a lot of energy can be solved over this lead, but if it is a very steep shelf before you get to the coast, the shaft height can be higher,” he said.
Preliminary shock and aftershock
The quake on Wednesday has already triggered at least 10 aftershocks above strength 5, and they could continue for months, said Caroline Orchiston, director of the Center for Sustainability at the University of Otago in New Zealand.
“This shows that earthquakes generate subsequent refill sequences with great magazines that start immediately, and some of them can be harmful to themselves,” she said.
The event of 8.8 magnitude on Wednesday was less than two weeks after an earthquake size of 7.4 in the same area, which was now identified as a “advance”.
“Earthquake is naturally unpredictable,” said Pascal. “There are no forerunners who are scientifically consistent in earthquake sequences. Before this morning, these others were the main shocks.”
Larger refilling cannot be completely excluded, he added, but their size and frequency usually decrease over time.
“You can expect great aftershock to be continued for some time, but the frequency of large, harmful events will decrease over time,” he said.
“There is always a chance of a bigger event, but this larger event will usually appear relatively soon within days or weeks.”
(Reporting by David Stanway; Editor from Alison Williams)
