Why are subduction zone earthquakes the biggest in the world? The main reason is size. The size of an earthquake is related to the size of the fault that causes it, and subduction zone faults are the longest and widest in the world. The Cascadia subduction zone offshore of Washington is about miles 1, kilometers long and about 62 miles km wide. Smaller earthquakes also strike all along the descending plate, also called a slab. Seismic waves from these temblors and tremors help scientists "see" inside the Earth , similar to a medical CT scan.
The quakes reveal that the sinking slab tends to bend at an angle between 25 to 45 degrees from Earth's surface, though some are flatter or steeper than this. Sometimes, the slabs may tear, like a gash in wrinkled paper.
Pieces of the sinking plate can also break off and fall into the mantle, or get stuck and founder. Subduction zones are usually along coastlines, so tsunamis will always be generated close to where people live, Titov said.
But the bad news is sometime a tsunami is generated. Thick layers of sediment may accumulate in the trench, and these and the subducting plate rocks contain water that subduction transports to depth, which at higher temperatures and pressures enables melting to occur and 'magmas' to form. The hot buoyant magma rises up to the surface, forming chains of volcanoes.
Onshore, high rates of rainfall on the seaward side of the mountain chains created by the squeezing of the plates makes landslides more probable. Offshore, thick sediments pile up, creating steep unstable slopes. Skip to main content. Search Search. Because the over-riding oceanic plate is relatively thin, the magma burns through it quickly and lavas soon pour out onto the sea bottom. A string of undersea volcanoes begins to rise and some eventually grows above sea level to form a volcanic island arc.
Frequent earthquakes rumble through the islands and all along the subducting plate as well. Life thrives in the warm mineral-rich water rising from the hot crust. The geologic activity at subduction zones is enormously beneficial to all mankind.
Dry land on Earth exists only because continents are born and kept above sea level by the volcanism and mountain building that occurs at subduction zones. Many important natural resources are derived from subduction processes. Oil and natural gas reserves, fresh, highly fertile soils, and gold, silver, uranium, and diamonds are all formed at convergent plate boundaries.
However, the beauty and abundance created by subduction comes at a high price. Powerful earthquakes and violent, unpredictable volcanic eruptions cause great destruction and death near convergent boundaries.
Underwater earth movements and explosions trigger enormous sea waves, called tsunamis, which travel across entire oceans to crash upon the distant shores of unsuspecting lands.
Occasionally, volcanoes and volcanic islands erupt cataclysmically, essentially blowing themselves sky high and pumping great volumes of gas and ash into the upper layers of the atmosphere. Swept around the planet by the jet stream, the volcanic debris blocks incoming sunlight, causes global cooling, and can lead to widespread crop failure and famine. Scientific knowledge of subduction is only a few decades old and still incomplete.
Geologists continue to explore subduction zones, hoping that greater understanding of their complex processes will lead to methods of predicting and minimizing the dangers they pose. Dry land exists only because of subduction. The tectonic plates grate against each other, which often causes earthquakes. The plate that slips under does not stay that way. Due to the heat caused by it rubbing against the other plate as well as the natural heat of the mantle, the plate melts and turns into magma.
The area where subduction occurs is known as the subduction zone. When one plate begins to slip underneath another one a trench is formed. The earthquakes that result due to the plates grinding against each other often cause magma to spill out through the trench in submarine volcanoes. Various formations such as mountain ranges, islands, and trenches are caused by subduction and the volcanoes and earthquakes it triggers.
In addition to causing earthquakes, subduction can also trigger tsunamis. When the older plate is holding a continent however, it does not sink, which is reassuring. Instead, the less dense material slips into a trench behind the denser oceanic crust where it gets stuck.
The pressure continues to build until the trench flips over and the less dense plate slips underneath the one with the continent. It is possible for a whole tectonic plate to disappear.
This happens when the plate goes through subduction faster than new material can be added to the plate through seafloor spreading.
0コメント