The powerful earthquake that devastated Nepal late in the morning on 25 April, causing at least 3200 deaths, could be a fuse that ignites other powerful quakes in a region of the Himalayas that had been seismically quiet for centuries, experts say.
The 7.9-magnitude earthquake was long overdue: The fault segment that ruptured hadn’t seen an earthquake since 1344 C.E., 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.
The Kathmandu temblor seems to have released a portion of the strain building up in the central seismic gap (CSG), a 600-kilometer-long region south of Nepal straddling a major fault that has been eerily quiet for at least 500 years. While the CSG’s earthquake history is disputed—some geologists say a large quake in 1505 C.E. ruptured the gap, while others argue that the 1505 quake wasn’t large enough to do so—specialists concur that the CSG is overdue for a megaquake measuring greater than magnitude 8.