Earthquakes becoming more frequent in Jharkhand State.
Dr. Nitish Priyadarshi
Department of Geology
Ranchi University
Ranchi-834001
Introduction:
PHYSIOGRAPHICALLY and tectonically, India can be divided into three broad ones: Peninsular India, Indo-Gangetic plains and the Extra-peninsular India (Himalayas).
The peninsular India comprises shield elements which are supposed to be geologically stable. But earthquakes of Jabalpur and Latur have shown that the shield areas are also prone to earthquakes.
The Chotanagpur Plateau of 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. 
Chotanagpur 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.
Present topographic features of Chotanagpur are clue to the past, and geographers and geologists think that before Himalayan movement started in Tertiary times Chotanagpur and adjoining areas were a low peneplain. As a side effect of the violent Himalayan movements, parts of Peninsular upland in general and Chotanagpur peneplain in particular began to be successively uplifted. The Himalayan movements occurred three times during Early and Late Tertiary and Pleistocene times and probably the Chotanagpur peneplain was also concurrently subjected to three successive uplifts. The line of this block uplift is marked by
the steep scarps that surround the Ranchi and upper Hazaribagh plateaus and across which streams descend by well-known waterfalls, e.g. Hundru and Hirni waterfalls.
Damodar valley coalfields have been affected by two phases of fold tectonics. It has been suggested that the major faults and joints present in Damodar Valley coalfield, were formed by block-tectonics, possibly during Tertiary period.
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. The scientists analyzed sedimentary rocks deposited in "Chaibasa Formation" in eastern India. "The layers show deformations that have never been described before," Rajat Mazumder, lead author and currently a Humboldt Fellow in the university of Munich told. Mazumder and co-workers show that earthquakes caused the deformations "while the sediments were still being deposited and before their consolidation," they said. The layers containing these deformation structures are termed "seismites" and the scientists could trace the deformed horizons up to a kilometer depth. Considering their occurrence in sediments deposited between 1,600 and 2,100 million years ago, "they are among the earliest records of earthquakes known in the Earth's history," the scientists reported. "One of the strongest arguments for earthquakes as triggers of the deformation is the occurrence of strongly deformed layers (sandwiched) between unaffected layers of similar grain size," they said. Another argument is the finding of "tabular depressions," the formation of which would have required a large block of sediment to move upwards and drift away. According to the scientists a tsunami generated by an earthquake most likely detached a weakly consolidated silt/mud block and lifted and transported it away leaving behind a hole that gradually got filled by laminated sediment observed by them.
It is interesting to note that Chaibasa Formation is underlain by volcanic rocks which have been dated as 2100 million years old. In other words the sediments of Chaibasa Formation were being deposited in a basin affected by active volcanism. In such areas high intensity earthquakes do occur.
Though "deformation structures" in sedimentary rocks have been observed before, the authors say that in their opinion, those found in eastern India "represent the oldest unambiguous "seismites" that are known from the Earth's history."
Fig: Tectonic map of East SinghbhumAccording to GSHAP (Global Seismic Hazard Assessment Program) data, the state of Jharkhand falls in a region of low to high seismic hazard . As per the 2002 Bureau of Indian Standards (BIS) map, this state also falls in Zones II, III & IV. Historically, parts of this state have experienced seismic activity in the M 5.0 range.
Hazard Map of JharkhandSignificant earthquakes in Jharkhand and its possible causes:
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.
The northern Bihar plain falls in the seismic zone of India and is liable to severe earth-quakes as on 15th January 1934.
Due to the devastating Sumatra Earthquake of 26th December 2004 with a magnitude Mw 9.3 Seiches(A seiche is a standing wave in an enclosed or partially enclosed body of water)occurred in the Jharkhand State. Even the Ranchi city felt the tremor.
A mild earthquake struck the adjacent border regions of the districts of Latehar and Lohardagga, Jharkhand, on 21st March 2007 at 22:04 PM local time. It had a magnitude of M?= 3.3 ( M? is magnitude type unknown) and was felt in many parts of the Chota Nagpur Plateau causing minor damage. The earthquake was centred 81.9 kms NW of Ranchi (Jharkhand), India. Tremors were felt strongly at Kuru in Latehar district and woke up many people who were asleep. A few people were reportedly “thrown of” their beds. In parts of Lohardaga district it was experienced for a duration of 5-seconds. Doors and windows rattled under the impact of the tremor and people went outdoors. In Lohardaga cracks developed in the walls of the hostel and other buildings of the Ursuline Woman’s Teacher’s Training College and many windows panes cracked. The strongest tremors were felt in northern parts of Lohardaga town. Houses were shaken at Brahani and Sikni in the Chandwa area of Latehar district. It was also felt for 10-12 seconds at Balumath, Chandwa & Latehar in Latehar district. Here, it was accompanied by the sound of a train and loose objects rattled. A 5-foot crack is thought to have developed outside a house in Chandwa. Elsewhere in the district it was felt at Barwadih, Garu, Mahuadanr and Manika. Many people spent the night outdoors fearing a stronger earthquake would follow. At Chatra, in the district of the same name, people heard doors & windows as well as household articles rattling. Light tremors were felt as far as at Gumla & Sisai in Gumla district, at Bhurkunda (including PTPS), Patratu in Hazaribagh district, Khilari, Mandar & Ranchi in Ranchi district. No damage or injuries have been reported as a result of this earthquake.Rumours of another stronger earthquake at 2 A.M. the following morning resulted in widespread panic in the region. Many people spent the entire night outdoors in the aforementioned areas. In Ranchi
, patients were brought out of the hospitals and elsewhere in the region announcements were made from mosques to alert people. Panic spread in areas of adjoining districts, including those that did not experience such as Bhawanathpur, Bishnupur (Gumla), Daltonganj (Palamau), Jhumri Telaiya (Hazaribagh), Hazaribagh, Ramgarh Cantonment and Simdega.Jamshedpur and its adjoining areas experienced at least four low-intensity tremors in the month of January, 2008. According to the different experts the tremors could well be due to the heavy rainfall that occurred last year 2007. Rain water percolating into the soil may have provided a cushion for the smaller plates to move causing earthquakes.
Huge downpours of rain can trigger earthquakes in landscapes riddled with caves and channels by increasing pressure within underlying rock, suggests a new study.
It was already known that rainfall could cause tremors, but the amount of water needed is much more than previously thought, says Steve Miller, a geologist at the University of Bonn, Germany.
In recent years, geologists have documented small earthquakes that occurred after heavy rainfall in Germany, Switzerland and France. All were low in magnitude – meaning they could be detected by seismographs, but not felt by humans.
Some experts have suggested that although the rainfall was heavy, the fact that rain could trigger an earthquake at all suggests that it takes extremely little to produce a tremor. They concluded that the Earth's crust in a delicate balance, teetering on the edge of a slight shake-up at any moment.
According to me 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.
Severe earthquakes can be triggered by dewatering and flooding of mines, as these activities alter the loading of the Earth’s crust and tectonic stresses in its interior. Worldwide, more than 200 studies have noted sites where human-induced stresses could have reactivated preexisting faults, triggering earthquakes with seismic moment magnitudes of up to M = 7 on the Richter scale. This can only occur where faults are already under high tectonic stresses that have built up over many years. Stable continental regions are seismically less active than unstable regions (e.g. California, Japan, and Turkey). Consequently, faults in stable continental regions can be more earthquake-trigger sensitive, since accumulated stresses have not reached failure conditions.
After becoming the new state there is boom in building industry. Lots of multistoried buildings are being built in the capital city of Jharkhand on the highly metamorphosed rocks filled with numerous joints and fractures. Very few people go for soil or rock testing before constructing huge buildings which is very essential. These constructions may disturb the balance (isostasy) of the local rock types. Stress from the skyscraper may re-open ancient earthquake fault.
Though stress and strain developing on the rocks can also be treated as the major cause of the earthquakes.
From last couple of years Jharkhand has felt few tremors in different parts of the State of low intensity and unfortunately due to its localized occurrence its intensity was not recorded.
Other causes of Earthquakes in Jharkhand:
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. This class of intraplate earthquakes occur in areas characterized by antiquity (2.5-0.5 billion years), much lower deformation rates compared to the more active regions of the intraplate regions and therefore longer periods of recurrence, reduced heat flow, greater average crustal thickness and low elastic attenuation. Several parameters of the earthquakes of the region are still not known and the classification here is, therefore, tentative.
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.
The Tatapani Fault in the western part of the state has been active since the Holocene period and extends across the border into the neighbouring state of Chhattisgarh. The Munger-Saharsa Ridge Marginal Fault runs in a north-south direction through the eastern districts of the state before entering West Bengal. However it must be stated that proximity to faults does not necessarily translate into a higher hazard as compared to areas located further away, as damage from earthquakes depends on numerous factors such as subsurface geology as well as adherence to the building codes.
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.
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.
http://www.boloji.com/environment/58.htm
http://environment.newscientist.com/article/dn13371-heavy-rain-can-trigger-earthquakes.html
http://asc-india.org/maps/hazard/haz-jharkhand.htm
http://www.springerlink.com/content/r0765k18488l23lk/
http://www.scienceblog.com/cms/ancient_fault_lines_may_have_become_re-activated.
N. Purnachandra Rao,T. Tsukuda, M. Kosuga, S. C. Bhatia and G. Suresh, 2002. Deep lower crustal earthquakes in central India: inferences from analysis of regional broadband data of the 1997 May 21, Jabalpur earthquake. Geophysical Journal International Volume 148 Issue 1 Page 132-138.
Dr. Nitish Priyadarshi
76,circular road,
Ranchi-834001
Jharkhand
India
Email: rch_nitishp@sancharnet.in
No comments:
Post a Comment