2015-05-01. Nepal disaster presages a coming megaquake.

posted May 31, 2015, 2:08 PM by Alan Gould   [ updated May 31, 2015, 2:09 PM ]
By Eric Hand and Priyanka Pulla, Science. For GSS Energy Flow chapter 2. Excerpt: ...As rescuers searched for survivors of a devastating earthquake in Nepal on 25 April, geophysicists made a disturbing discovery. An initial assessment suggests that the underground rupture responsible for the magnitude-7.8 quake extended deep below the Himalayas, into a region that many scientists had deemed impervious to tearing. The unexpected extent of the rupture suggests that, as awful as the present disaster is, future earthquakes in the Himalayas could end up being mightier—and more calamitous—than modelers assumed. The discovery “is going to radically change how we predict and interpret future and historic earthquakes,” says Roger Bilham, a geologist at the University of Colorado, Boulder. ...The ultimate driver of Himalayan earthquakes is the slow-motion collision of the Indian subcontinent with mainland Asia, which is also pushing the mountains skyward. Some 15 kilometers below the surface, a nearly horizontal thrust fault marks the plane where the Indian plate is plunging beneath southern Tibet at a rate of about 18 millimeters per year. Microearthquakes—most of them too small to feel at the surface—cluster along a line that trends east to west across this plane. Most of the region's substantial earthquakes have occurred south of the line, where the plates are locked together and strain builds up. North of this “lock line,” however, the Indian plate dives downward and the character of the rock slab changes. Under higher temperatures and rising pressures, the brittle rocks become more plastic, and they creep past the Tibetan crust without rupturing. Or so researchers had thought. The 25 April earthquake followed an ominous new rupture path. ...the temblor ruptured crust well north of the lock line, suggesting the potential for future quakes with a far larger rupture area than seismologists had thought possible.  ...The Nepal disaster “could have been much worse had engineers not sprung into action to retrofit critical facilities in Kathmandu,” says  Bilham, who has long sounded an alarm over the Himalayan earthquake hazard. But with an even greater threat looming, Nepal and its neighbors will have to take a hard look at their earthquake preparedness... http://www.sciencemag.org/content/348/6234/484.summary