Friday, March 27, 2009

Tremor felt in stable parts of Jharkhand State of India.

Tremor in Jamshedpur and Chaibasa
by
Dr. Nitish Priyadarshi

Inspite being a part of the stable block, Jharkhand State of India is being rocked by mild to medium tremors. Fresh incidence of earthquake took place on Thursday morning (26th March,2009) when mild tremor was felt in the area of Jamshedpur and Chaibasa.
The tremor which was measured 3.8 on the Richter scale, hit the region at 10.14 am and lasted about 2 to 3 seconds, said local Meteorological Department in the Ranchi.
According to the Meteorological office the epicenter was recorded at 22.6 degree North latitude and 85.7 degree East latitude. Area is near to Jharkhand and Orissa border.
Five college students and a teacher were injured in Chaibasa town due to “stampede like situation” when they trying to rush out of the college building.
Jamshedpur and its adjoining areas experienced at least four low-intensity tremors in the month of January, 2008.
From last several years many parts of Jharkhand is facing mild to moderate tremors. According to the author there are possibilities that construction of large water dams, water reservoirs, different types of mining and increasing use of groundwater (which is creating vacuum inside the earth) in and around Jharkhand are major reason why these earthquakes are occurring at such frequent intervals.
Present epicenter is very near to mining areas of Iron ore. Though stress and strain developing on the rocks can also be considered as the major cause of the earthquakes.

Jharkhand 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.

Scientists have found evidence that the oldest earthquake followed by tsunami traceable in the earth's history took place more than 1,600 million years ago in what is now Jharkhand. An international team of scientists from India, Japan and Poland has reported the discovery in a paper to appear in the forthcoming issue of the journal 'Sedimentary Geology.' This occurred long before the massive southern land mass called Gondwana land split up and the piece that now forms peninsular India floated north and crashed in the Asian land mass.

Regarding the type of earthquakes occurring in State it may be placed under “Shallow Earthquakes” ("Crustal" quakes) which are caused by faults in the continental plates, as a result from the relative motion of sections of the plates. They are usually 1 to 5 magnitude, less than 15 miles deep, occur random and unpredictable and most of them are not even felt.

Mild tremors struck Jharkhand Plateau on August 1999 for couple of seconds. Few years back too on July and 21st November 1997 Jharkhand Plateau was rocked by the tremors for few seconds. Due to lack of requisite equipment, the Ranchi Meteorological office was not in a position to say something about the intensity. A tremor stronger than these had shaken Chotanagpur Plateau of Jharkhand on August 21, 1988 at 4.40 AM. The epicenters of the Earthquake was 525 km north west of Shillong ( Indo-Nepal border in Bihar state) and was measured 6.6 on the scale. The 1988 quake which lasted for few seconds was reported from Ranchi, Jamshedpur, Dhanbad and Daltongonj. At Ranchi all windows started rattling. Movements of cots was similar to that in a running train.
There was also commotion among birds, and cracks developed in the walls of some houses. Such high intensity earthquake in the Jharkhand State was unnatural. This plateau is peninsular and dead for any crustal adjustment. The high intensity of earthquake in Dharbanga in Bihar State, might have sent tremors to the Jharkhand. One probable cause of the relative strength of shock in Jharkhand, might be transmissibility of the tremors through crystalline rigid and strong crust underlying the Himalayas, the Indo- Gangetic depression, Monghyr region and Jharkhand. The characteristic and consequences of the earthquake of 1988 were similar to those of the shock of January 15, 1934.

Reference:
Rajat Mazumder, A.J. (Tom) van Loon and Makoto Arima (2006)Sedimentary Geology, Volume 186, Issues 1-2, Pages 19-26

Mahadevan, T.M., 2002. Geology of Bihar & Jharkhand. Geological Society of India, Bangalore.

Times of India, March 27, 2009, Ranchi edition.
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