Once faults deep in the Earth are shaken by a stress-relieving event, they can be immediately repaired to continue the endless cycle of earthquakes. However, this self-healing ability does not apply to the fast and powerful earthquakes that many people are familiar with; instead, it helps rocks recharge after a slower type of seismic event that we can't even feel.
New research published in Achievements of science discovered a way for faults to self-heal after slow slip, which occurs as accumulated stress is released over days, weeks or months. Although this voltage gradually dissipates, faults can partially regain their power within a few hours and prepare to fail again. Knowing the details of how this process works could help researchers understand how regenerating faults contribute to large earthquakes.
Read more: How worried should we be about earthquakes in the US?
Tectonic stress
Earthquakes typically develop in subduction zones, where dense tectonic plate slips under another, less dense plate. When these plates rub against each other, they sometimes become locked due to friction. The tension then builds until the plates finally fail to break the deadlock, resulting in powerful earthquakes.
This can happen in a number of ways subduction zones around the world, such as the Cascadia subduction zone off the Pacific coast of North America. Here the Juan de Fuca Plate is sliding under the North American Plate.
The movement of these plates could even trigger “megaquakes”, the magnitude of which could exceed magnitude 9.0 on the Richter scale. However, megaquakes are infrequent; According to the data, only 13 of them came from the Cascadia subduction zone in the last 6,000 years, each occurring hundreds of years apart. Earthquakes in Canada.
Recharging Earthquake Energy
According to scientists, slow slip events (SSEs) occur beneath a “transition zone” where tectonic plates become locked, and are characterized by more gradual tectonic movement that occurs over a long period of time. Earth sight.
While the slow sliding motion relieves some of the stress on certain parts of the fault, it also increases stress in the parts where they are locked. So while the SSEs beneath the Cascadia subduction zone, for example, are not powerful enough to be felt by anyone living on the Pacific coast, they still increase the risk of a powerful earthquake as they gradually add stress to the locked plates.
Unlike a typical earthquake, SESs do not deplete all their energy at once before beginning the long process of stress recovery in the first stage. Once energy is released from the SSE, faults can become overstressed in a short period of time, as the researchers behind the new study observed from seismic data in the Cascadia subduction zone.
“We found that deep faults can heal within hours,” said study author Amanda Thomas, a professor of earth and planetary sciences at the University of California, Davis, in her report. statement. “This prompts us to re-evaluate the rheological behavior of faults, and if we have neglected something very important.”
Glued back together
To understand how faults heal themselves, the researchers replicated SSE in experiments where they packed powdered quartz into a silver cylinder, welded it, and placed it under 1 gigapascal pressure (10,000 times atmospheric pressure) at 500 degrees Celsius.
Essentially, the researchers simulated what happens after SSE by “cooking” a quartz sample. After measuring how quickly sound waves could travel through the sample, they opened the cylinders and examined the structure of the sample using electron microscopy. They discovered that when compressed, the mineral grains weld together.
This shows that after SSE the rocks in the faults stick together again. The concept of cohesion may need more attention in earthquake models, the researchers say; this could potentially contribute to stress on smaller faults and other faults that cause strong earthquakes.
Read more: Rising pressure on the Tintin fault could mean dangerous earthquakes
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