December 16, 2015
UW Tacoma geoscientist tracked risks from deadly 2015 Nepal earthquake
When an earthquake struck Nepal in late April 2015, thousands of lives were lost in the initial disaster. But it was hard to assess the scale of the damage to rural areas, and still lurking were threats from unstable slopes and dammed glacier-fed lakes that could dislodge at any time to flood villages below.
A University of Washington Tacoma faculty member was part of an international team of scientists who worked with government agencies and private companies on a massive remote humanitarian effort after the earthquake. The effort is being presented this week in San Francisco at the American Geophysical Union’s Fall Meeting.
“This was one of the most rapid and largest global efforts to study a big disaster,” said co-presenter Dan Shugar, an assistant professor at UW Tacoma. “Within days, satellites had been mobilized to acquire daily imagery of the earthquake-affected region, and provided data quickly to the scientific and citizen science communities. Teams of volunteers worked to map geohazards and damage to buildings and roads. This, to my knowledge, has never been done before at this scale.”
The humanitarian effort led to a larger analysis of the landslides triggered by the Gorkha earthquake which is published today (Dec. 16) in the journal Science.
Lead author Jeffrey Kargel, a research scientist at the University of Arizona, brought his expertise in satellite imaging to help gather information after the Nepal earthquake, especially in remote mountain villages far from population centers.
Kargel called on colleagues in the Global Land Ice Measurements from Space (GLIMS) network he led to help identify affected areas by using satellite images. An international consortium of glaciologists, GLIMS monitors glaciers all over the world. The group’s initial efforts focused on possible earthquake effects on Himalayan glaciers, but quickly expanded to searching for post-earthquake landslides.
“The landslides don’t just happen immediately with the earthquake, they can continue for weeks or months afterward,” Shugar said. “People on the ground don’t necessarily know that a village is at risk of flood if a river is dammed far upstream. But when you have an eye in the sky, the people looking at that imagery might be the first to see it. We were looking for where there might be a risk in the next couple of days.”
Within a day or two, the scientists joined with the NASA Applied Sciences Disasters group to use remote sensing to help document the damage and identify areas of need, and share that information with international emergency-response teams and other groups.
Government space agencies and commercial entities, encompassing more than 10 satellites from four countries, responded to the scientists’ request to provide more data by sharing thousands of images. Kargel’s group selected which ones to analyze, and organized into six teams to scrutinize the vast earthquake-affected region for landslides.
Shugar led the team of volunteers focusing on the Annapurna region, in the westernmost part of the Himalayan region of interest.
“The shaking from an earthquake is like a tuning fork, where the tips of the fork — the mountaintops — vibrate the most strongly,” Shugar said. “This is why landslides tend to develop at the top of mountain ridges.”
Computer models were used to evaluate the likelihood that the downstream edges of glacial lakes would collapse to flood villages and valleys below.
Although the initial research effort was purely humanitarian, the scientists eventually realized they had a huge database that could be analyzed to learn more about geohazards from this and other earthquakes.
To study the Gorkha quake landslides, the scientists used their satellite-based findings plus media reports, eyewitness photography and field assessments from helicopters. The researchers limited their analyses from the day of the earthquake to June 10, 2015, the onset of the monsoon.
In addition to identifying the locations and severity of landslides, which was lower than expected, the researchers found a surprising pattern of where the landslides happened.
Co-author Eric Fielding at NASA’s Jet Propulsion Laboratory used satellite radar imagery to create a map of the terrain that dropped during the earthquake and where land surface had risen. The Earth’s surface dropped almost 5 feet (1.4 m) in some places and rose as much as 5 feet (1.5 meters) in others.
By overlaying Fielding’s map with the landslide map, the scientists could see if there was any correspondence between the number of landslides and the Earth’s displacement. Most of the documented landslides occurred in areas where the ground surface dropped down, rather than in the areas where the ground was uplifted.
“Since this is the first time that this pattern has been observed, it’s tough to explain why it occurred,” Shugar said. “One of the things that we’ll be looking at going forward is seeing if there’s a similar pattern for other large earthquakes.”
Shugar recently joined UW Tacoma from the University of Victoria, Canada. His research focuses on landslide risk and steep slopes, but also includes glaciers, sea-level change and other geophysical phenomena.
“In Western North America we don’t tend to have communities living in steep mountain valleys in the way that they do in the Himalayas or the Andes, so the losses of life here would probably be less,” Shugar said. “But landslides are certainly a problem here, whether triggered by earthquakes or rainfall or some combination of those two elements.”
The Science paper’s three corresponding authors are Kargel, Shugar and Umesh Haritashya of the University of Dayton in Ohio. Other co-authors include some 59 authors from 12 countries.
The research was supported by NASA, Canada’s Hakai Institute, the Japan Aerospace Exploration Agency (JAXA), Colorado-based DigitalGlobe Inc., the Chinese Academy of Sciences and the Nepal-based International Centre for Integrated Mountain Development (ICIMOD).