Earthquakes Imminent- Nucleation Point for Massive Earthquakes in the Himalayas.
The Main Central thrust (MCT) is the single largest structure within the Indian plate that has accommodated Indian-Asian convergence. It extends for nearly 2500 km along strike and has been the site of at least 140 and perhaps more than 600 km of displacement (Schelling & Arita 1991; Srivastava & Mitra 1994). Heim & Gansser 1938 defined the MCT in Kumaon based on the difference in metamorphic grade between low to medium-grade rocks of the Lesser Himalaya and higher-grade rocks of the Greater Himalaya. However, the fault originally defined by Heim & Gansser 1938 is not the MCT, but a fault within Lesser Himalaya rocks (Valdiya 1980; Ahmad et al. 2000). This misidentification symbolizes the challenge that workers have faced in locating the MCT. The metamorphic grade within the Lesser Himalaya increases towards the MCT and at higher structural levels.
In central Nepal, the metamorphic grade increases from low (chlorite + biotite) to medium (biotite + garnet + kyanite + staurolite) towards the MCT over a north-south distance. The highest-grade rocks (kyanite and sillimanite gneisses) are found within the MCT shear zone, i.e. upper Lesser Himalaya. Arita (1983) places two thrusts (MCT I and MCT II) on each side of the MCT shear zone.
In a more recent article at indianexpress.com states
Himalayas may experience major earthquakes: study
Scientists studying geologic features and activity in the Himalayas have warned that the mountain range, separating the plains of Indian subcontinent from the Tibetan Plateau, is primed for major earthquakes.
Stanford geophysicists said that The Himalayan range was formed, and remains currently active, due to the collision of the Indian and Asian continental plates.
Scientists have known for some time that India is subducting under Asia, and have recently begun studying the complexity of this volatile collision zone in greater detail, particularly the fault that separates the two plates, the Main Himalayan Thrust (MHT), a Stanford statement said.
Previous observations had indicated a relatively uniform fault plane that dipped a few degrees to the north.
To produce a clearer picture of the fault, Warren Caldwell, a geophysics doctoral researcher at Stanford, has analysed seismic data from 20 seismometers deployed for two years across the Himalayas by the National Geophysical Research Institute of India.
The data imaged a thrust dipping a gentle two to four degrees northward, as has been previously inferred, but also revealed a segment of the thrust that dips more steeply (15 degrees downward) for 20 kilometres.
Such a ramp has been postulated to be a nucleation point for massive earthquakes in the Himalayas.
Although Caldwell emphasised that his research focuses on imaging the fault, not on predicting earthquakes, he noted that the MHT has historically been responsible for a magnitude 8 to 9 earthquake every several hundred years.
"What we're observing doesn't bear on where we are in the earthquake cycle, but it has implications in predicting earthquake magnitude," Caldwell said.
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More on this story at http://www.indianexpress.com/news/himalayas-may-experience-major-earthquakes-study/1040835
Three earthquakes in a time span of 15 hours jolted the Himalayan regions in India
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