Monday, October 17, 2011

Effects on national highway in Jharkhand State of India due to 19th September Earthquake.

The tremor left a 200-foot long/10-foot deep crater on the road.


by


Dr. Nitish Priyadarshi














It is for the first time in earthquake history of Jharkhand that the earthquake, which jolted North and Eastern India on 19th September, left a 200-foot long crack on the NH-75 in Latehar district, disrupting traffic. The tremor left a 200-foot long/10-foot deep crater on the road disrupting traffic near Sikni Colliery. It came as surprise as the area is treated geologically as the most stable cratonic block related to tremors.

According to the local administration it was due to Sikni coal mines near that highway. They said that the mining has created instability of the upper surface of the earth of near by areas and the cracks were the multiple effects of both mining and tremors. If it is true then most of the areas of the Jharkhand State where the coal mining are rampant are under tremendous threat in future.

Geologically Jharkhand state represents a part of the Indian Peninsular shield, which is a stable cratonic block of the earth’s crust. Though it is a part of the stable block it is being rocked by mild to medium tremors. Jharkhand plateau has faced lots of tremors and geological movements in the geological past and now it is assumed that the plateau is free from any type of tremors or cratonic movement. Evidences of the regional tectonic movement in the plateau area are preserved in the form of faulting, folding, joints etc in the rocks.

Earthquakes of Jharkhand may be placed in one broad categories. Earthquakes originate from stress fields built up in the Precambrian shield, supporting the Vindhyan, Gondwana and younger basins.

Several events such as the 1868 Hazaribagh, 1963 Ranchi and 1969 Bankura were generated by release of stress built up in the relatively more stable Jharkhand Plateau region underlain by Precambrian formations. These, by analogy with other Peninsular Shield events such as Latur and Jabalpur earthquakes,may possible belong to the class of Stable Continental Earthquakes.

Possibilities of major earthquake in this stable region cannot be ruled out. Different researches has shown that ancient fault line can be re-activated. Old continental crust contains a billion-year record of past tectonic activity. This area was once a seismically active. "We don't yet understand how faults are reactivated, but it appears that some pre-existing faults are more likely to break than others. Regarding Jharkhand the possibility of reactivation of a pre-existing fault can happen under the influence of the ambient stress field due to the India–Eurasia plate collision forces.










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