Know the scientific reason behind Nepal Earthquake

Nepal Earthquake

Scientists are now analysing seismic data in an effort to understand the strongest earthquake to hit Nepal in more than 80 years, which has left more than 3,000 people dead.
The Earth‘s crust is made of large tectonic plates. These land masses, which sometimes include whole continents, are constantly moving and bumping into each other.
Nepal straddles the fault line between two of these plates; the Indian and the Eurasian plates. These are being forced up against and under each other, at a rate of about 5cm each year.
That may not sound like very much, but there is tremendous force behind them and when this builds up, an earthquake results.
“This is probably the biggest earthquake to hit Nepal since 1934,” Brian Baptie of the British Geological Survey told Al Jazeera.
“Earthquakes of this size are capable of causing an incredible amount of devastation.”
nepal earthquake
Saturday’s earthquake is likely to be especially damaging because it was both strong and shallow.
The depth of a quake frequently determines how much shaking is felt. In this case, the quake occurred just 11km beneath the surface, causing violent tremors in the immediate area. “This is a very large earthquake in a significantly populated region with infrastructure that has been damaged in past earthquakes,” Paul Earle, a US Geological Survey seismologist, said. “Significant fatalities are expected.”
The mountainous terrain is likely to have resulted in even more damage.

Layer of clay

The heavily populated Kathmandu valley has a 300-metre-deep layer of clay beneath it. This reflects and focuses the seismic waves of an earthquake within the valley, resulting in what is known as soil liquefaction. This occurs when vibrations cause solid ground to turn in to something like quicksand. As a result, buildings and roads can be swallowed by the earth. “We know roughly where earthquakes occur, and how often they occur,” Baptie said.
“That helps plan accordingly so it’s possible to construct buildings to minimise the amount of damage. It’s also possible for communities to become more resilient if they are aware.” Nepal is one of the poorest countries in the world and little of this earthquake preparation work had been done. “It was sort of a nightmare waiting to happen,” said seismologist James Jackson, head of the earth sciences department at the University of Cambridge in England, who was attending an earthquake preparedness meeting in Kathmandu last week. “Physically and geologically what happened is exactly what we thought would happen.” Scientists say the area can expect at least 35 5+ magnitude aftershocks over the next few days and weeks. These have the potential to destroy already-damaged buildings. They also warn of the risk of landslides. Some have already been caused by the quakes. Others are likely to happen during the upcoming monsoon season A little before noon Saturday in Nepal, a chunk of rock about 9 miles below the earth’s surface shifted, unleashing a shock wave—described as being as powerful as the explosion of more than 20 thermonuclear weapons—that ripped through the Katmandu Valley.
In geological terms, the tremor occurred like clockwork, 81 years after the region’s last earthquake of such a magnitude, in 1934. Records dating to 1255 indicate the region—known as the Indus-Yarlung suture zone—experiences a magnitude-8 earthquake approximately every 75 years, according to a report by Nepal’s National Society for Earthquake Technology. The reason is the regular movement of the fault line that runs along Nepal’s southern border, where the Indian subcontinent collided with the Eurasia plate 40 million to 50 million years ago. “The collision between India and Eurasia is a showcase for geology,” said Lung S. Chan, a geophysicist at the University of Hong Kong. The so-called India plate is pushing its way north toward Asia at a rate of about 5 centimeters, or 2 inches, a year, he said. “Geologically speaking, that’s very fast.”
As the plates push against each other, friction generates stress and energy that builds until the crust ruptures, said Dr. Chan, who compared the quake to a thermonuclear weapons explosion. In the case of Saturday’s quake, the plate jumped forward about 2 meters, or 6.5 feet, said Hongfeng Yang, an earthquake expert at the Chinese University of Hong Kong. Saturday’s quake was also relatively shallow, according to the U.S. Geological Survey. Such quakes tend to cause more damage and more aftershocks than those that occur deeper below the earth’s surface. After an earthquake, the plates resume moving and the clock resets. “Earthquakes dissipate energy, like lifting the lid off a pot of boiling water,” said Dr. Chan. “But it builds back up after you put the lid back on.”
‘Earthquakes dissipate energy, like lifting the lid off a pot of boiling water. But it builds back up after you put the lid back on.’ —Lung S. Chan, geophysicist at the University of Hong Kong
Nepal is prone to destructive earthquakes, not only because of the massive forces involved in the tectonic collision, but also because of the type of fault line the country sits on. Normal faults create space when the ground cracks and separates. Nepal lies on a so-called thrust fault, where one tectonic plate forces itself on top of another. The most visible result of this is the Himalayan mountain range. The fault runs along the 1,400-mile range, and the constant collision of the India and Eurasia plates pushes up the height of the peaks by about a centimeter each year. Despite the seeming regularity of severe earthquakes in Nepal, it isn’t possible to predict when one will happen. Historic records and modern measurements of tectonic plate movement show that if the pressure builds in the region in a way that is “generally consistent and homogenous,” the region should expect a severe earthquake every four to five decades, Dr. Yang said.
The complexity of the forces applying pressure at the fault means scientists are incapable of predicting more than an average number of earthquakes that a region will experience in a century, experts say. Still, earthquakes in Nepal are more predictable than most, because of the regular movement of the plates. Scientists aren’t sure why this is. The earth’s tectonics plates are constantly in motion. Some faults release built-up stress in the form of earthquakes. Others release that energy quietly. “Some areas, like Nepal, release energy as a large earthquake, once in a while,” said Dr. Chan. “These regions all have different natures for reasons geologists don’t really know.”Read the news of Nepal Earthquake, click here

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