Nepal quake less severe than anticipated? New studies explain.
A series of new studies seeks to 'unravel the scientific lessons' from high-impact earthquakes.
The magnitude-8 earthquake that hit Nepal in April 2015 was deadly – but it could easily have been worse, say experts.
In the aftermath of the earthquake, researchers used a wealth of new data to assess the damage, and according to their results, the effects were actually less catastrophic than initially feared. Findings were published Tuesday in a special issue of Seismological Research Letters.
Seismologist Susan Hough had seen devastation before. When a magnitude-7 quake slammed Port-au-Prince in 2010, she led the US Geological Survey team dispatched to improve seismic monitoring in Haiti. The death toll for that earthquake fell somewhere between 100,000 and 300,000.
By many accounts, the Kathmandu quake should have been even worse. It was more severe, and its epicenter was just below central Nepal. Experts worried that the dense pastiches of construction in the valley would be especially susceptible to high-magnitude earthquakes. But in the end, Nepal’s people (and infrastructure) fared better than Haiti’s – but that doesn't mean they emerged unscathed.
"It's important to remember that 9,000 people were killed, and many more left homeless – in a poor country, where safety nets are few and far between," Dr. Hough says. "People in some of the remote villages are facing enormous hardships. But if the effects had been in keeping with expectations, the numbers could have been magnified by a factor of 10 or more. The difference between Port-au-Prince in 2010 and Kathmandu in 2015 was night and day."
A lack of practical data may have inflated initial damage projections. Large earthquakes are rare, so seismologists must either run computer models or scale up the effects of smaller earthquakes.
"Unfortunately, some of the limited data that do exist are not being made freely available – for example, in neighboring big countries that are not exactly good citizens when it comes to sharing geophysical data," Hough says. "One of the absolute requirements for papers in the special issue was that data sets had to be freely available."
When the quake in Nepal hit, researchers had a rare opportunity to collect real-time information from a wide variety of sources: seismic data, satellite imagery, newspaper accounts, and smartphone apps.
That led to some surprising conclusions. One major finding suggests that an ancient lake bed underneath Kathmandu actually "de-amplified" the more intense shockwaves. Seismologists call this the "nonlinear effect" – where extremely severe earthquakes can actually produce less powerful shaking.
"Imagine trying to shake a sandbox back and forth really hard," Hough says. "If you shook it slowly, the sand would move as a unit, so energy would be transmitted through to the surface. But if you shook it really fast, the sand grains would shift and adjust, and some of the energy would get damped out."
These fundamental revelations are essential to seismological research, says Hough, who is also a contributing editor at Geotimes Magazine.
"People hope earthquake prediction will be possible someday," she says. "To at least provide a heads-up that the ground is going to shake. But early warning doesn't do a building any good. A building is either designed properly or it isn't. The key is building codes, and understanding ground motions is the first key step to developing effective seismic provisions in codes."
Another study highlighted an app called LastQuake, which collects eyewitness accounts and provides hazard updates. It wouldn’t add much value in California and Japan, which are already centers of seismological research, but Hough believes this type of data-centric approach could do real good in poorer nations.
"Imagine a day when every smartphone in the world is able to capture and transmit information about shaking, the second it starts to happen," Hough says. "Imagine being able to warn people about impending earthquakes from a network of smartphone apps. Nobody expects these technologies to ever replace modern [seismometer] networks, but they could be a real boon for countries like Nepal, where modern networks are unaffordable."