The powerful earthquakes in Nepal on April 25 and on May 12 left about 10,000 dead, hundreds wounded and a trail of devastations. It will take years for the country to recover the losses and rehabilitation of those rendered homeless.
Now it is known that the geologists had warned of the possibility of highly destructive earthquakes in the Himalayas. Ominously, they predict of more earthquakes. The timing is impossible to predict. It may rupture tomorrow, or it can rupture 75 years from now.
The 7.9-magnitude earthquake on April 25 was long overdue, according to Laurent Bollinger, a geologist from the French Alternative Energies and Atomic Energy Commission. This temblor originated 15 kilometers underground, where the Indian plate slides under southern Tibet at a rate of about 20 millimeters per year along the Main Himalayan Thrust fault. The plates snag against each other, building up pressure until the crustal rock gives out. The locked plates under Nepal have been close to the breaking point for centuries, says Vinod Gaur, a geophysicist at Bangalore’s CSIR Fourth Paradigm Institute who co-authored a science article in 2001 warning of the possibility of highly destructive earthquakes in the Himalayas.
More earthquakes predicted
Geologists say the 25 April earthquake was not large enough to release all the pent-up strain, according to Bollinger, Gaur, and other geologists studying the gap, but it did relieve strain at the eastern end. To release more strain, earthquakes are now needed further west of the gap, Bollinger says. The 25 April earthquake may well herald gap-filling quakes. When a portion of a lengthy fault ruptures, it is like making a tiny nick in a piece of cloth and stretching it. This builds pressure along the tear’s edges and makes it susceptible to further rips.
Situated on an ancient lakebed, the Kathmandu Valley’s soil is soft and liquefies easily. The ground motion gets amplified, and people there can feel [earthquakes] very vigorously, says Vineet Kumar Gahalaut, a geologist at the National Geophysical Research Institute in Hyderabad. The two large earthquakes that struck Nepal on Tuesday were likely part of a chain reaction triggered by the magnitude 7.9 temblor that ravaged the country April 25 and weakened other fractures in the earth’s crust, according to seismologists.
While it is impossible to predict the exact timing of an earthquake, the occurrence of another large quake in the region was not a surprise to experts. The movement caused by the first quake added extra stress to other faults in the area, increasing the likelihood of further seismic activity, according to Carmen Solana, a geologist and professor in the School of Earth and Environmental Sciences at the University of Portsmouth in England.
Earthquake overdue in Himalayan region
The experts say Nepal is susceptible to earthquakes because of the regular movement of the fault line along its southern border, where the Indian and Eurasian tectonic plates collide. As the plates push against each other, friction generates stress and energy that builds until the crust ruptures, releasing energy. Scientists had predicted that another earthquake was coming and many more will come in the future in this seismically active region.
The Himalayan region had been overdue an earthquake, since the last one that hit Kathmandu 80 years ago. During the earthquake on April 25, not all of the pent-up seismic pressure was released. This left room for more earthquakes in the near future. That near future could be days or years away. Predicting the precise location and timing of an earthquake is not possible. There are simply no signals from the movement of the Earth’s crust that can definitely point to when a quake is triggered. And that occurred on Tuesday, about 18km below the surface and east of Kathmandu. It is not clear yet if this quake has indeed released all the remaining pent-up pressure.
What happened on April 25 makes things worse for the region. When the fault unloaded its stored energy, it tore through a region underneath Kathmandu that had been previously deemed impervious. We therefore have the potential for bigger earthquakes than we might have otherwise expected, Gavin Hayes of the US Geological Survey said. Roger Bilham, a geologist at the University of Colorado, told the Indian Express: “The Indian government’s attitude to seismic studies is apparently to shoot the messenger.” He claims to have been expelled by the Indian government in 2012 when he ascertained that Nepal is better prepared than India at handling large earthquakes.
Source: Weekly Holiday
