December 31, 2012
Himalayas Will Have More Massive Earthquakes, Warn Scientists
Brett Smith for redOrbit.com - Your Universe Online
An international team of researchers has found that a pair of massive, historical earthquakes ruptured the surface in the central Himalayas–leading them to theorize that similar quakes will threaten the region´s population in the future.
According to the team´s report in Nature Geosciences, the two quakes, in 1255 and 1934, measured between 8 and 8.5 magnitudes on the Richter scale and both left distinct scars in the Earth. While earthquakes on this scale are not without precedent in the Himalayas, most of them are not believed to have broken the earth's surface; these “blind quakes” are much more difficult to track.
Lead researcher, Paul Tapponnier, a preeminent scientist in the field of neotectonics, said that the devastating historical quakes mean that tremors of the same magnitude could happen again in the region in the future, especially in areas of the surface that have not been ruptured.
"The significance of this finding is that earthquakes of magnitude 8 to 8.5 may return at most twice per millennium on this stretch of the fault, which allows for a better assessment of the risk they pose to the surrounding communities," said Tapponnier, a professor at Nanyang Technological University (NTU) in Singapore.
Using new high-res imagery and radioactive dating techniques, the geologists showed that the 1934 earthquake did break the surface over a length of more than 93 miles, just south of the range that includes Mount Everest. The fault line where the break occurred marks the boundary between the Indian and Asian tectonic plates, commonly referred to as the Main Frontal Thrust (MFT) fault.
The team dated offset river sediments and slope deposits, to separate the several episodes of tectonic plate movement along the fault. They were then able to calculate the two distinct ruptures that occurred about 700 years apart.
Despite the relative length of the two events, Tapponnier pointed out that the next event might not occur at the same interval.
"This does not imply that the next mega-earthquake in the Himalayas will occur many centuries from now because we still do not know enough about adjacent segments of the MFT Mega-thrust," he explained.
"But it does suggest that areas west or east of the 1934 Nepal ground rupture are now at greater risk of a major earthquake, since there are little or no records of when last earth shattering temblor happened in those two areas."
The scientists said that future studies will attempt to uncover the extent of these fault ruptures. Once this is accomplished, the team hopes to construct a complete and accurate model of the earthquake zone that lies along the Himalayas.
Unfortunately, the densely populated region is struck by violent quakes with some regularity. Tremors in 1897, 1905, 1934 and 1950 recorded magnitudes between 7.8 and 8.9 on the Richter scale, and each one caused widespread damage. The 2005, 7.6-magnitude earthquake in Kashmir was the most recent example of what a seismic event along these two massive tectonic plates can do to a populated area.