Subducted seamountsSubduction zones are some of the most powerful faults in Earth’s crust. The

Subducted seamountsSubduction zones are some of the most powerful faults in Earth’s crust. They store up huge amounts of energy and produce Earth’s most powerful earthquakes. The largest recorded quake in human history happened in 1960 on the subduction zone to the west of Chile, where the Nazca plate sinks beneath South America. That subduction zone regularly produces large earthquakes, including a magnitude 8.1 earthquake in 2014.Generally, the larger the area of the fault that breaks, the more energy is released and the larger the earthquake. The Magnitude 9+ Andaman-Aceh earthquake that triggered the December 26, 2004 tsunami started near the island of Sumatra and broke sections of the fault up to 1000 kilometers to the north.The magnitude 8.1 quake in 2014 ruptured a fairly small portion of the Chilean subduction zone, near where the west coast of South America bends to the west. This quake was still powerful, but nowhere near as powerful as other quakes generated by that fault. For some reason, the quake in this case stopped. It only ruptured a small section.It’s not always understood why some quakes become very large and others stay moderate sized. The most common reason is probably that an area of the fault that recently ruptured hasn’t had time to build stress on it for another quake; when a fault ruptures it releases some stress and may prevent another large quake in that same area.The 2014 quake, however, took place in a large seismic gap. Reportedly that section of the fault, over 550 kilometers long, has not had a major earthquake in nearly 150 years. Once the 2014 quake started, it seems like it should have ripped apart almost this entire seismic gap, but instead only about 100 kilometers broke.This kind of behavior suggested to scientists that something else was happening in this area of the fault. A team from several universities in Germany and Spain investigated this fault by using seismic techniques, bouncing seismic waves off of layers in the subsurface as a way of mapping boundaries. Using this technique, they mapped out the structure of the fault and found something interesting.This area of the subduction zone has recently absorbed several large seamounts. A few can still be seen outboard of the subduction zone, still visible on the ocean floor. The contours in this image show the area that actually broke during the earthquake; it goes right up to several of the green circles that represent thickened crust and subducted seamounts.These scientists believe that subduction of these gigantic submarine mountains has damaged the crust surrounding the fault. Mountains getting pulled down a subduction zone would deform everything around them, breaking rocks and creating a barrier that could block propagation of a new earthquake.This research suggests features on the original seafloor could survive long enough to influence the behavior at megathrust faults. Therefore, similar features in other subduction zones around the world may contribute to the behavior of faults elsewhere, and further characterization of seamounts in subduction zones could help us better understand what segments of faults may break and when.-JBBImage credit and original paper:http://bit.ly/1VrXlcjRead more:http://bit.ly/1JGz9Di -- source link

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