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Seismology, Seismotectonics and Seismic Microzonation
 
GSI has a legacy of more than 150 years of earth science studies. Along with geological mapping, mineral exploration and number of other earth science research, GSI has always nurtured earthquake related studies. Pioneering work by Thomas Oldham and R.D. Oldham in the 19th Century virtually laid the foundation of modern seismology. The Geological Survey of India has been carrying out macroseismic survey (post-earthquake damage surveys for assessment of intensity) of earthquakes for now over 135 years. The first account of such a study dates back to Cachar earthquake of 1869. Thomas Oldham, who investigated the event, later published a Catalogue of Indian earthquakes dating from historical times to 1869. Jones (1885) conducted studies for the 1885 Kashmir earthquake that took a toll of 3000 human lives and caused widespread destruction in the Kashmir valley. The Great Assam earthquake of 1897, one of the most severe and destructive manifestations of seismic energy release the world has witnessed so far, was investigated in detail by Sir R.D. Oldham. The accounts, observations and analyses of that catastrophe were brought out in the form of a Memoir (Vol. 29) of GSI. The first seismic zoning map of the country was prepared by GSI in 1935. With that beginning and consequent updating with state of the art technology, GSI has been engaged in multifarious earthquake studies including macroseismic survey of every great Indian earthquake, aftershock studies by establishing temporary digital seismic network to interpret causative fault and source mechanism, study of active faults as seismic source, observational seismology with Broad Band observatories at Jabalpur and Nagpur, telemetered seismic network at Khandwa, Madhya Pradesh, tomographic studies, seismotectonic / neotectonic studies and seismic microzonation studies for urban centers etc. Bureau of Indian Standards delineates Seismic Zones of India with inputs from GSI.
 
Indian sub-continent has a diverse tectonic setting. GSI made a neat contribution in bringing out the ‘Seismotectonic Atlas of India and it environs’, which is a comprehensive multi-thematic atlas encompassing integration of geological, geophysical, seismological information up to 1993. This contains 42 maps each depicting seismicity, tectonics, gravity, bathymetry etc as a single source window for primary seismic hazard assessment.
 
Active Fault Studies is a key element of Seismic Hazard Assessment (SHA) to identify and characterize seismic source zone. It includes study of local deformation of ground surface along crustal faults, indicators of sudden uplift or subsidence of large regions and other stratigraphic and/or geomorphic effects of strong ground motion in the Quaternary time. Fault grows by accumulation of displacement that in turn reflects cumulative effect of many earthquakes. As fault grows with time, it has the potential to produce larger earthquakes. GSI has been engaged in such studies in Himalayan frontal belt and in Meghalaya plateau, central Indian tectonic zone, Kutch fault, Suruli Ar lineament (Tamil Nadu), Gunlakamma fault (Andhra Pradesh) etc. The task has been carried out via geomorphological, geological and geochronological inputs.
 
Task of seismic microzonation is a pre-disaster activity to mitigate the effects of an earthquake. Earthquake waves incident at different sites with variable physical properties generate variable site response, which if predicted, could be used for preparation of seismic microzonation maps of relative hazards. A seismic microzone takes into account local site conditions like soil, topography, proximity to faults etc. Primarily it is a geographical delineation of variations in the potential for earthquake hazards. Microzonation is subdivision of a region into zones that have relatively similar exposure to various earthquake-related effects. Geological Survey of India through geological, geotechnical and site response method had already produced microzonation maps for Jabalpur urban area in a multidisciplinary and multi-institutional set up. Microzonation studies in the urban agglomerations of Delhi, Ahmedabad, Dehradun, Guwahati, Siliguri, Vishakhapatnam, Mumbai are in different stages of completion with recent initiation at Pondicherry, Jamnagar and Chandigarh.
 
An all India earthquake database is maintained in Geodata & Database Division, CHq incorporating data from ISC Bulletin. The database has been updated taking stock of 858 events from January to August 2002. Thus a total of 18341 events have been registered so far in the database within the territory covered by latitude 0°-37° N and longitude 68°-98° E.
 
Significance of earthquake related studies in the context of societal safety has been realized in the aftermath of Indian Ocean earthquake and tsunami on 26 December 2004. The unprecedented hazard with a death toll of 10,749 in India alone took everyone by surprise. The knowledge required to combat tsunami was not available with the common people. This again underscores the relevance of earth science in ensuring the safety and prosperity of mankind. Earthquake related studies have already been recognized as a thrust area of activity in GSI. Accordingly focus is on active fault mapping (study of source region of an earthquake) and seismic microzonation of urban agglomerations (sites prone to earthquake risk) in various geological domains of the country. Besides, observational seismology, post-earthquake macroseismic survey for assigning earthquake intensity, microseismic and other geophysical investigations remain additional work areas within the ambit of earthquake related studies in field season programmes.
 
Future programmes on earthquake geology:
 
Active fault mapping and seismic microzonation studies, macro and microseismic investigations in the event of earthquakes, seismotectonic assessment of engineering project sites as per requirement of the sponsoring agencies, MEQ surveys will continue as primary tasks. Further, Continuous operation, monitoring, acquisition and analysis of seismic data will be continued from broadband seismograph observatories at Jabalpur and Nagpur and the data will be contributed to the national netweork.. The DST-sponsored telemetered seismic network at Khandwa will monitor local / regional tremors. Permanent GPS stations at Jabalpur and Lucknow will be engaged in recording and processing of GPS data.
 
In the short term ensuing items, monitoring of GPS stations at Andaman Nicobar Islands, study of 3D seismic structure of Andaman Nicobar Islands, study of palaeo-tsunami deposit / paleoseismology for estimation of recurrence history; monitoring of ground motion across MBT (Mishmi thrust) and MFT in parts of Arunachal Pradesh has been taken up.
 
In the long term, GSI is planning elaborate geodetic survey to constrain active faults and ground deformation, preparation of site condition maps and installation of new seismic observatories in seismically active zones.
 
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Landslides, Landslide Zonation and Avalanches
 
Landslide can be defined as a downward and outward movement of slope forming material in response to gravity. Landslide cause considerable loss of life and property. Globally landslides account for about 1000 deaths annually with property damage of about 4 billion US dollar. Geological Survey of India being the 'Nodal Agency' for landslide related studies is engaged in Landslide Hazard Zonation mapping, Site specific studies of landslides and preparation of Landslide inventory in different parts of the country.
Major types of landslides are as follows:
 
  • Rock Falls
  • Topples
  • Rotational slide
  • Transitional slide
  • Rock creep, soil creep.
  • Debris flow, mud flow
  • Solifluction
  • Subsidence.
 
Factors Triggering Landslide are heavy rainfall, increased pore pressure in the slope forming mass, increased weight of slope forming mass, removal of vegetation cover, Weak rock and soil of the slope forming mass, steep slope, removal of support at the toe and ground vibration during earthquake.
 
Major Landslide prone areas in India are the Himalayas, Indo-Burmese Range, Western Ghats and the Nilgiris. Landslides in these regions causes considerable loss of life, roads, settlements, agricultural fields and forest lands annually.
 
Few major landslides of India are listed below:
 
  • 22 September 1893 -- a huge slide completely blocked the river Birahi Ganga at village Gohna.
  • 11 – 12 July 1996 -- massive landslide in Jaldhaka valley and South Kalimpong hills -- 32 lives lost , damges to huge property
  • 9th June 1997 --Widespread devastation of Gangtok town
  • 7th July 1999 -- Kurseong town devastated
  • 18 August 1998 - major landslide at Malpa, Uttaranchal- 200 people perished.
 
The association of the Geological Survey of India and Landslides studies is more than a century old. As early as 1880, GSI was called upon to study the slope problem in Nainital. In 1893, a mass of rock slide blocked the Birahi Ganga at Gohna. GSI was asked to take up the investigation of the causes and suggest remedies; T.H. Holland surveyed the area and submitted the report. GSI now prepares Landslide Hazard Zonation maps where landslide prone areas are classified as High, Moderate and Low. Apart from these, site specific or incident specific studies are carried out in all critically landslide prone areas. Detailed landslide studies are also carried out in the pre-construction stage of the development of River Valley projects, Communication Routes and Rural and Urban settlements.
 
Under the directives and proposed Action Plan of Ministry of Home Affairs, GSI carried out the following works.
 
  • Formation of a committee on Landslide Macrozonation and preparation of modified BIS guidelines and submission to BIS for its acceptance.
  • Preparation of guidelines on Mesolevel Landslide Hazard Zonation and submission to BIS for its acceptance.
  • Formation of a committee on the development of an Early Warning System by real time monitoring of landslides. Initially six conspicuous landslides have been identified in the North-eastern, Eastern and Western Himalaya for this purpose.
  • Contact programme with the State Governments of Tamil Nadu, Assam, Sikkim and West Bengal, Jammu & Kashmir and Uttaranchal for generation of landslide awareness among local people and state authorities.
 
Future Programme on landslides:
 
  • Land Slide Hazard Zonation in parts of Manipur, Nagaland, Mizoram, Tamil Nadu, Kerala, Uttaranchal, Himachal Pradesh, Sikkim, West Bengal and Maharashtra.
  • Geological and Geotechnical investigation in parts of Uttarkashi district, Uttaranchal and Darjeeling District, West Bengal.
  • Site specific study of Sonapur Landslide and Landslide Inventory of Jaintia Hills, Meghalaya.
  • Landslide Inventory covering 150 L Km. along Western Ghat roads.
 
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Floods and palaeo-floods
Flood as a phenomenon can be defined as inundation of land not usually submerged. Floods are caused by the following factors:
  • over flow of river bank
  • dam failures
  • overflowing of lakes
  • high tides along sea shores
  • cyclone
  • rise of ground water level and manmade causes like
  • Dam construction
  • Channelising of rivers
  • Urban development
  • Deforestation
12.5% of the country’s total area is flood prone. Flood plains and delta of Ravi, Sutlej, Yamuna-Sahibi, Ganga, Gandak, Ghaggar, Teesta, Kosi, Brahmaputra, Mahananda, Mahanadi, Damodar, Mayurakshi, Godavari and Sabarmati and their tributaries and distributaries are the Flood prone areas in India. Flood loss in the country over the period 1953 to 1998 has been estimated at Rs.52,659 crore.
There are two main components of flood related studies
  • Water that inundates
  • Land that is inundated
GSI studies the shape and material of the land getting inundated and generates data on area, shape, slope, infiltration and permeability of soil of the basin, drainage pattern, landform and longitudinal and cross profiles of the channels. On the basis of these studies GSI produces Flood Hazard maps indicating Prohibitive, Restricted, Cautionary and Flood Free Zones.

Significant flood related studies by GSI:
  • Brahmaputra Valley- a comprehensive geo-environmental data base for environmental management and flood control has been generated
  • Lower Banas sub-basin -GSI recommended selective irrigation to prevent rise of groundwater table.
  • Kandi basin in West Bengal- GSI recommended construction of small weirs to reduce impact of flood
  • Mokameh Tal area in the Ganga Flood plain- GSI recommended rejuvenation of existing drainage channels to reduce flood problem
  • Lower Damodar Basin-Diversion along artificial canals and re-excavated old river channel recommended by GSI
Similar studies have been carried out for the Mahanadi basin to provide inputs for flood control measures. One of the objectives of River Valley Projects of Government of India is Flood Control. The Geological Survey of India provides geo-engineering and geo-environmental inputs to all these projects (e. g. Tehri, Bhakra Nangal, RanjitSagar, Pong, Panchet etc)
On recommendation of Rashtriya Barh Ayog (1980) GSI has been continuously carrying out the following studies to generate information base for flood mitigation.
  • Landslide zonation map for Himalayan region
  • The contribution of snow melting to annual flood.
Direct beneficiaries of GSI’s flood related studies are Central Water Commission, Water Resource Development Project Authorities, Urban and Rural Planning Authorities, Ministry of Environment and Forest, Ministry of Agriculture, etc.

Coastal Zone Hazards
The coasts since historical times have been the important interface between land and sea and have had profound bearing on the development of hinterland. The coast also attracts both commercial and recreational ventures and vast populace of India depend on coasts for their livelihood. Accordingly, coastal zone studies aims to construct a evolutionary model, leading to projection of likely future strand line trends so that the economic/commercial activity can be planned in conformity with likely natural changes. Beach Rating hazard map is also prepared for the benefit of users of beaches. Coastal zone studies include geomorphological mapping, beach profiling and mapping, seasonal sediment sampling, etc. As stated above it is of important to have knowledge about beach / coast behavior because of its direct impact on human activity and GSI adopts a uniform approach for entire coast which encompasses studies resulting in understanding of Sea-level rise, strand line changes and wave morphodynamics.

Beside regular projects, Coastal zone studies are also undertaken in the aftermath of natural hazards as in the case of the earthquake and tsunami in Andaman Island to ascertain the extent of subsidence / upliftment and resultant impact.
 
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Studies on Volcanism
Studies on Volcanism in GSI focus on the active volcano, Barren. The objectives of these studies are regular monitoring of the very recently resurrected volcano to record the chronological changes in the nature of eruption (physical and chemical state, morphological changes, nature of lava and ejectas); petrological characterization of the recent volcanic products and comparative studies of the same to that of the earlier ones and study of relationship of volcanism vis-à-vis tectonic framework.
Barren and Narcondam lie on the Neogene inner arc that extends from the extinct volcano like Mt. Popa, Mt Wuntho of central Mynamar up to the Jade mines area in the north through the Barren and Narcondam to the active volcanoes of Sumatra, Java and Bali in the SE. The barren island (12.290N, 93.850E) is located 135km NE of Port Blair with its exposed area of 10 sq.km and height 335 m above the waves, 2250m above the sea floor. Volcanic activity of Barren Island is recorded at different stages as:
  • First cycle: Prehistoric, Late Pleistocene (?). No concrete evidence for Pleistocene.
  • Second cycle: Historic, 1781-1832 AD with intermittent eruptions
  • Third cycle: First phase March-October 1991, second phase December 1994-May 1995, third phase started end –May, 2005.
 
The 1991-eruption was initially of Strombolian type which gradually changed to Plinian style whereas the 1995 eruption althrough Strombolian was interspersed with occasional phreatomagmatic explosions. Significant changes occurred in the morphology of the existing volcanic cone. Geological Survey of India is currently carrying out systematic studies of this active volcano in the following respect
 
  • Chronological account of the state of the volcano.
  • Petrographic characterization of the volcanic products
  • Major, trace (including REE), isotopic studies of the solidified lava samples
 
A team of scientists led by the DG, GSI also made an expedition to Barren Island on 16.2.2005 for on the spot assessment of the volcano. No vigorous fumarolic activity was noticed at that time. Only, intermittent smoke observed at the crater. However, a renewed volcanic activity in Barren Island started on 28 May 2005. A team from GSI inspected the volcano on 13 June 2005, collected pyroclastic materials and reported no pouring of lava flow.
 
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Studies on geological health-hazards (arsenic, fluoride in ground water) and medical geology
 
Millions of people in the deltaic regions of West Bengal, India are exposed to the arsenic hazard. The contamination is chiefly restricted within the shallow aquifers (50-200 ft). Diseases like hypo-pigmentation, keratosis and skin cancer manifest the health hazard. Arsenic contamination in groundwater beyond permissible limit (>50ppb) has also been reported from certain parts of, Bihar, Chhattisgarh and Uttar Pradesh. The problem of arsenic contamination in Bengal basin is geogenic in nature. Late Holocene to Recent floodplain and meander channel deposits of Ganga – Brahmaputra - Meghna river systems supply arsenic. Possible provenance could be Chhotanagpur-Rajmahal hills of eastern Bihar and wide areas of Himalaya. Fluvial depositional processes play a crucial role in concentrating arsenic in aquifer material and it is confined in a specific geomorphic domain.
 
Millions of people in the deltaic regions of West Bengal, India are exposed to the arsenic hazard. The contamination is chiefly restricted within the shallow aquifers (50-200 ft). Diseases like hypo-pigmentation, keratosis and skin cancer manifest the health hazard. Arsenic contamination in groundwater beyond permissible limit (>50ppb) has also been reported from certain parts of, Bihar, Chhattisgarh and Uttar Pradesh. The problem of arsenic contamination in Bengal basin is geogenic in nature. Late Holocene to Recent floodplain and meander channel deposits of Ganga – Brahmaputra - Meghna river systems supply arsenic. Possible provenance could be Chhotanagpur-Rajmahal hills of eastern Bihar and wide areas of Himalaya. Fluvial depositional processes play a crucial role in concentrating arsenic in aquifer material and it is confined in a specific geomorphic domain.
 
Through arsenic mapping programme undertaken by GSI, it has been observed that arsenic contamination is restricted within zones, which are found as narrow, linear, sinuous strips following the geometry of the cut-off / abandoned / palaeo-channels of the river system. It has also been observed that certain minor components of the aquifer sediments contain arsenic. These are clastic, iron bearing silicate and oxide minerals like magnetite / ilmenite, biotite, chlorite, illite, amphibole and iron-hydroxide coated grains of quartz. High values of arsenic is observed when spheroidal, blister like, white colored siderite concretions, grown under microbial influence, are visible on the surface of these minerals. Arsenic is carried in the water/water borne sediments of rivers. During monsoon flooding, arsenic in floodwater percolates subsurface, causing contamination in the abandoned channels. In the flood-plain domains the clay blanket works as a filter and prevents percolation.
 
The phenomenon of release of arsenic in groundwater is a result of complex physico-chemical as well as microbial processes. To properly comprehend these processes an integrated spatial database has been generated. Data driven spatial analysis (Bayesian probability) and fractal analysis carried out has led into developing predictive models that can be used as tools for long term hazard mitigation. The input to this model includes geographical (drainage pattern including surface water bodies); geological (palaeo-geomorphological units) and hydrological (aquifer related) information as well as arsenic concentration data of tubewells.
 
Major Achievements during the Ninth plan period
 
  • Post-earthquake damage survey data of the Jabalpur (1997), Chamoli (1999) and Bhuj (2001) earthquakes have been processed and published.
  • GSI established the Jabalpur Broadband observatory through a DST sponsored Project and regularly contributes data to the National seismological network
  • Published the Seismotectonic Atlas (42 sheets) covering entire India and adjoining areas of bordering countries. This would help in planning and execution of pre-disaster initiatives and strategies for mitigation (including seismic design of major infrastructural facilities).
 
 
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