Scientists are struggling to explain the 8.3 magnitude earthquake that struck deep beneath the Sea of Okhotsk on May 24, 2013 happened.
It's been quite a while since the 8.3 magnitude earthquake that struck deep beneath the Sea of Okhotsk on May 24, 2013 took place. The earthquake was deemed the largest deep earthquake ever recorded and even four months after the incident, scientists still don't know what to make of it.
"It's a mystery how these earthquakes happen. How can rock slide against rock so fast while squeezed by the pressure from 610 kilometers of overlying rock?" said Thorne Lay, professor of Earth and planetary sciences at the University of California, Santa Cruz in a press release.
The latest study conducted by researchers from the University of California analyzed the seismic waves from the earthquake and found that the seismic moment was 30 percent larger than that of the next largest deep earthquake recorded, a 1994 earthquake 637 kilometers beneath Bolivia.
Deep earthquakes take place between the upper mantle and lower mantle, 400 to 700 kilometers below the surface and usually occur due to stress in a deep sub-ducted slab where one plate of the Earth's crust dives beneath another plate. They usually occur deep beneath the surface and hence, the surface does not record much disturbance. However, scientists have still been fascinated by them.
According to observations made in this study, researchers found that the Sea of Okhotsk earthquake, off the coast of Russia released three times as much energy as the Bolivia earthquake, which equals to approximately a 35 megaton TNT explosion. The rupture caused by the quake was also the longest rupture and measured up to 180 kilometers.
"It looks very similar to a shallow event, whereas the Bolivia earthquake ruptured very slowly and appears to have involved a different type of faulting, with deformation rather than rapid breaking and slippage of the rock," Lay said.
According to the researcher, age and temperature of the sub-ducted slab could be held accountable for the dramatic difference between the Bolivia earthquake and the Sea of Okhotsk earthquake. Researchers noted that the sub-ducted Pacific plate where the Sea of Okhotsk earthquake took place was much colder than where the Bolivia earthquake occurred.
Researchers also revealed that the Sea of Okhotsk earthquake may have caused a re-rupture owing to a fault that developed when the oceanic plate bent down into the Kuril-Kamchatka sub-duction zone as it began to sink.
"If the fault slips just a little, the friction could melt the rock and that could provide the fluid, so you would get a runaway thermal effect. But you still have to get it to start sliding," Lay concluded. "Some transformation of mineral forms might give the initial kick, but we can't directly detect that. We can only say that it looks a lot like a shallow event."
