There are large earthquakes in southern Japan and an underground mountain-sized chunk of rock may be affecting them.
The Kumano pluton is a dense rock that lies beneath Japan's Kii Peninsula. It is in the middle of the continental plate. Subduction is a process in which the Philippine plate dives toward the Earth's mantle. The Philippine plate may be forced down more steeply by new research that shows the slope of the dive changing.
The epicenters of two large 1940s earthquakes did not cause any damage to the pluton.
"We don't really know why these earthquakes didn't overlap in the region," said study co-author Dan Bassett, a marine seismologist at New Zealand's GNS Science.
The pluton may have an influence on how water moves from the oceans into the mantle. Under the pressure of the pluton, the Philippine plate's subduction is twice as steep. The subducting plate allows it to carry more seawater down toward the deep crust and mantle. volcanic eruptions are caused by water in the mantle.
The Philippine plate is grinding under the Eurasian plate off the coast of Japan at a rate of 1.78 inches per year. Subduction causes earthquakes and volcanism. Scientists use seismic monitors to try to understand the geological structures within subduction zones, but this is often a spotty record, especially in submarine trenches where placing equipment isn't easy.
The coast of Japan is one of the most monitored places in the world. The Japanese Agency for Marine-Earth Science and Technology (JAMSTEC) has blanketed the region with monitors, and Japan has put together the densest array of seismometers.
We knew that we had a huge dataset that would allow us to create a high-resolution three-dimensional model of the entire subduction zone.
The clearest picture of how the subduction zone is influenced by the Kumano pluton was obtained by the team. Most research on subduction zones focuses on the structure of the plate that is diving beneath the surface, but doesn't consider the plate sitting over it. The slab of crust sitting over the subducting plate may be more important than was thought.
We think a lot about the angle of the slab that is going down, but haven't thought about how the upper crust affects it.
There are new questions about the role of the pluton in earthquakes after the findings were published in the journal. A magnitude-8.1 earthquake shook the ground to the northeast in 1944. Two years later, a magnitude-8.6 earthquake started close to the epicenter of the first one but was not as strong.
There are points along the fault that are small rough spots or big rough spots that can stop the earthquake from happening.
There are facts and information related to the Japan earthquake.
It is not clear why the pluton is having this effect. It is possible that the dense volcanic rock is putting so much pressure on the subducting plate that it resists the sort of dramatic rupture needed to continue an earthquake. The shape of the subducting plate below it could be altered by the pluton. The subducting plate doubles the steepness of the downward dive. This means that the ocean's crust drops very quickly. The cool and brittle nature of the crust makes it more likely for earthquakes to happen at shallow depths.
The way that water moves through the subduction zone is impacted by the downward trajectory of the subducting plate. Donna Shillington, an Earth scientist at Northern Arizona University who was not involved in the research, said that the water cycle is important for the creation of magmas and for large-scale mantle processes.
According to Live Science, the pluton seems very important for these processes. The huge structure seems to cause the subducting plate to go into a steep dive. That steep dive causes the subducting plate to warp and crack, which can lead to cracks in the ocean. The trajectory of the dive affects where the water ends up and which minerals it reacts with. The researchers found that the waves in this region were slow and suggested that there was a richly hydrated mineral in the area.
The minerals have to be carried down a way before the plate will heat enough to release water.
When trying to understand the deep-Earth water cycle, scientists focus more on the subducting plate. The study suggests the plate is important.
She said that if we want to understand the water in the plate, we need to think about another variable.
The Hikurangi subduction zone off of New Zealand was the site of the Tohoku earthquake and the research team plans to build three-dimensional models of the subduction zone in northeastern Japan. Those should be ready within a year or two.
Being able to compare high-resolution 3D models of Earth structures across the three subduction zones should allow us to think a little bit more carefully about how the structure of subduction zones is impacting earthquake behavior.
It was originally published on Live Science.
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