Seismology research is the scientific study of earthquakes and the propagation of elastic waves through the earth or through other planet-like bodies. The research also includes studies of the environmental effects of earthquakes, such as tsunamis and other seismic phenomena such as volcanic, tectonic, oceanic, and atmospheric explosions. A related field that uses geology to infer information regarding past earthquake is paleo-seismology. Recordings by seismologists of the earth’s movements as a function of time are termed seismograms.
Need for seismology and geo-science research
India has a history of pioneering seismological research in the solid earth sciences that resulted in the discovery of the core of the earth. For the first time, identification of the surface wave and its distinction from the body wave on the recorded seismogram of the June 12, 1897 Shillong earthquake (Mw 8.7) led to several discoveries of the earth’s system in the annals of global seismological research. In recent years (2007-2011), frequent occurrences of macro-and micro-earthquakes in different parts of India and its adjoining regions have posed a challenging task to the Indian seismological community. State-of-the-art techniques in the geosciences have been used to investigate into the principal causes of earthquakes, whose after-affects (tsunamis, landslides, avalanches) have had a major impact on both flora and fauna, in turn causing unprecedented and innumerable earthquake hazards in the region. The Ministry of Earth Sciences (MoES), Government of India has been supporting various research institutions involved in carrying out seismological monitoring and research.
Indian seismological research
The monitoring of earthquake, estimating earthquake parameters, and disseminating this information has been made very efficient. All seismographs, GPS and other related instruments have been networked to provide data in the shortest possible time. During the Sikkim and recent Nepal earthquakes, earthquake information was disseminated within ten minutes to all concerned. The data was used to create damage scenarios which were made available to the crisis management group for rescue and relief. This helped initiate early relief and rescue operations. The density of seismographs, accelerographs, and GPS deployment is being further increased. In the past three years, 25 GPS stations have been added to provide the status of strain accumulation and the mechanism of locking of faults. Strong motion instruments operating all along the Indo-Gangetic plain can estimate accelerations experienced in Uttar Pradesh and Bihar.
Our current knowledge of earthquakes remains as yet insufficient for making reliable predictions regarding magnitude, time and location. Comprehensive long-term assessments need to be made for facilitating probabilistic forecasting.
The continued northward movement of the Indian plate and its under-thrusting beneath the Eurasian plate has resulted in the accumulation of strain energy, which is periodically released during large and great earthquakes in the Himalayan region. It has been observed that during past 200 years, less than 50 per cent of the Himalayan arc has ruptured during major earthquakes. Large earthquakes in these unbroken segments (Uttarakhand, Himachal Pradesh) along the Himalayan belt cannot be ruled out. GPS measurements in the region provide unequivocal evidence of strain accumulation in the region. However, one does not know when the accumulated strain energy will be released through a major earthquake.
National Centre for Seismology and geo-science research
The National Centre for Seismology (NCS) was established by the MoES as an attached office to address all earthquake related matters in the country under the umbrella of the Earth System Science Organisation (ESSO). The Centre has been providing effective linkages/interface amongst various organisations/institutions working in the fields of seismology and allied subjects for the optimal use of infrastructure and resources. The broad and ultimate objective of the NCS is to provide earthquake (M:3.0 and above) related information to all user agencies. This includes information on earthquake hazards and risk related information pertaining to specific regions for mitigative designs and construction of earthquake resistant structures, as also and land use planning towards minimising damage to property and loss of lives. The NCS is also mandated to carry out research in pure and applied seismology and earthquake precursory phenomena, earthquake processes and modelling. The NCS has five divisions:
- Earthquake Monitoring and Services;
- Earthquake Hazard and Risk Assessment;
- Geophysical Observation System;
- Earthquake Process and Modelling; and,
- Programme Planning and Coordination.
The NCS maintains a national seismological network consisting of 82 field observatories, including two telemetry clusters—one each around NCT Delhi (16 stations) and Northeast India (20 stations), for monitoring seismic activities in and around the country on a 24×7 basis.
The NCS has been carrying out active research on the earth’s crust and upper mantle in sections of the Indian Himalayan regions using receiver function techniques and surface wave dispersions, as also estimated expected ground motions for critical areas by carrying out earthquake precursor observations, and comprehensive analysis of the data sets. The NCS is also involved in some ongoing research and development projects such as the National Programme on Earthquake Precursors; Deep drilling investigations in the Koyna-Warna region, Maharashtra; earthquake early warning system in Himalaya; and, study of largest geoid-low volcanological studies in the Andaman islands.
NCS is the nodal agency of the Indian government responsible for monitoring seismic activity in and around the country. Until the establishment of NSC, the India Meteorological Department (IMD) has been rendering seismological services to the nation for more than a century with the first observatory having been set up in Kolkata as far back as 1898.
The operational task of NCS is to quickly estimate the source parameters immediately on occurrence of an earthquake and disseminate the information to all user agencies, particularly the state and central government agencies responsible for carrying out relief and rehabilitation measures. Information relating to under-sea earthquakes leading to tsunamis along the Indian coast is also simultaneously monitored by Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, and disseminated to all concerned user agencies for tsunami-related messages and warnings. NCS also transmits earthquake information to the general public using information channels like the press, media, SMS, fax, besides posting it on its website—imd.gov.in.
National seismological network
IMD maintains a country wide National Seismological Network (NSN), which includes:
- A 16 station V-SAT based digital seismic telemetry system around the national capital territory (NCT) of Delhi;
- 20 station V-SAT based real time seismic monitoring network in North East India;
- A 17 station Real Time Seismic Monitoring Network (RTSMN) to monitor and report large magnitude under-sea earthquakes capable of generating tsunamis that can affect coastal India.
The remaining stations are of stand alone/analog type. A control room is in operation, on a 24×7 basis at NCS, New Delhi, with facilities for data collection, processing and dissemination of information to concerned user agencies.
Real time seismic monitoring for early warning of tsunamis
In the aftermath of the Great Sumatra earthquake of December 26, 2004, the MoES set up an Indian Tsunami Early Warning Center at INCOIS. The Center is mandated to provide advance warnings on tsunamis likely to affect coastal and other regions in India.
A 17 station RTSMN, is capable of monitoring and reporting, in the least possible time, the occurrence of earthquakes capable of generating tsunamis likely to affect Indian coastal regions. Data from the 17 broadband seismic field stations is transmitted simultaneously, real time, through V-SAT communication facilities to the Central Receiving Stations (CRSs) at NCS, and INCOIS, for processing and interpretation.
The CRSs are equipped with state-of-the-art computing hardware, communication, data processing, visualisation and dissemination facilities. For providing better azimuthal coverage towards detecting earthquakes of tsunami-genic potential, the RTSMN system has been configured to include about 100 global IRIS (a consortium of Incorporated Research Institutions in Seismology), stations, whose data is available freely through the internet. The earthquake information is disseminated through various communication channels to all concerned user agencies in a fully automated mode. Based on the information made available by RTSMN and other ocean related observations/analysis, INCOIS evaluates the tsunamigenic potential of undersea earthquakes and issues necessary warnings/alerts, as per the situation.
Seismic hazards and microzonation
Seismic hazard assessment and microzonation studies have emerged as major tools for preparedness, long-range planning and mitigation of losses due to earthquakes. ‘Seismic microzonation’ is a process of classifying a region into zones of relatively similar exposure to various earthquake-related effects .
NCS currently also has a mandate to generate and disseminate user-friendly GIS-based, site-specific hazard and risk related information products to enable appropriate planning of pre- and post-disaster management strategies. The Centre has completed microzonation of the Delhi region on a 1:50,000 scale and played a key role in various studies relating to the seismic microzonation of cities like Jabalpur and Guwahati. NCS is currently engaged in refining the seismic microzonation of NCT, Delhi on a 1:10,000 scale.
The development of seismic microzonation of major urban centres has been recognised as a priority area. Hazard maps for few urban areas such as Delhi, Lucknow, Kolkata, Bangalore, Ahmedabad, Chennai, Dehradun, Jammu, Chandigarh, Sikkim and Guwahati have already been completed. However, they are yet to be integrated with urban planning maps. The identification of active faults, which can generate large earthquakes or which have generated large earthquakes in past few thousand years help to access the risk. A complete inventory of active faults needs to be built.
A new programme on active fault mapping in the Himalayas has been launched, wherein, the target is to identify the faults which can generate large earthquakes or which have generated large earthquakes in the past few thousand years. Several trenches are proposed to be dug to get information on past earthquakes in the region.
Seismic zones of India
The Bureau of Indian Standards (IS-1893-part-1: 2002) has classified the country into four seismic zones viz., zone II, III, IV and V. Of these, zone V is rated as the most seismically prone region, while zone II is the least. The Modified Mercalli (MM) intensity, which measures the impact of earthquakes on the surface of the earth, broadly associated with various zones, is shown in Table 1.
Scientific deep drilling
Scientific drilling, both on continents and oceans, has become an indispensable and unique tool to probe into the geological, geochemical and geophysical processes that shaped the earth. The process is also useful in unravelling the paleo-history of our planet as recorded within sediments and rocks below the land surface and ocean floor. Scientific drilling programmes are coordinated by the International Continental Scientific Drilling Programme (ICDP) and the International Ocean Discovery Programme (IODP). ESSO-MoES represents India in both these institutions and actively participates in their activities.
A field research station for borehole geophysics has been set up with the purpose of undertaking experiments for providing exact, fundamental and globally significant knowledge about the composition, structure and processes in all areas of earth science. The purpose of this station is to build capacity (facilities and trained scientific manpower) to establish world-class facilities for advanced borehole geophysics research and scientific drilling to solve the problems facing earth science. Two problems that are to be pursued through it in the near future are :
- NASA-ISRO Synthetic Aperture Radar (NISAR), a joint venture between National Aeronautics and Space Administration (NASA) and Indian Space Research Organisation (ISRO), to be launched to facilitate measurement of tectonic strain everywhere.
- Study of the tsunamigenic processes operating in the Andaman subduction zone. Research here shall be through the existing GPS stations , with possible Japanese collaboration.
In view of its importance, ESSO-MoES has undertaken two projects, one each under both ICDP and IODP.
The scientific drilling in the Lakshmi basin, in the Arabian Sea in April 2015, was undertaken primarily to understand coupling between climate change and the surface uplift of the mountain ranges. The collision of the Indian plate with the Eurasian plate, saw the lofty Himalayas rise up millions of years ago. Erosion in the Himalayas has resulted in the largest possible sediment accumulations, accounting for the Indus fan in the Arabian Sea and the Bengal fan in the Bay of Bengal. The boreholes drilled here have penetrated the entire sedimentary sequence and reached basement rocks. Sediment cores allow reconstruction of patterns and rates of erosion, as and when continental environmental conditions change. We know that there is strong coupling between climate change and surface uplift of mountain ranges. High-resolution continuous records on millennial scale generated during this drilling show the ~8 Ma climatic transition. This experiment can provide answers to how the Himalayas have evolved and what role they have played in the origin of the Indian monsoon thousands of years ago.
Earthquakes manifest themselves for a few seconds or minutes, but are the result of stress built up over thousands and millions of years deep within the earth. A better characterisation of fault behaviour can therefore provide improved understanding of likely risks. However, triggered earthquakes have garnered a lot of attention of late. The Koyna region is an ideal site to study such triggered earthquakes as the past five decades (since 1967), have seen regular earthquakes here, with the seismicity confined within a very small region.
These earthquakes have typically occurred between 4 and 7 km below the surface, and are hence amenable for drilling and direct observations. The direct measurements of physical and mechanical properties during as well as before and after earthquakes can hence, facilitate modelling.
The pilot borehole will be drilled parallel to the fault zone. Instruments will then be lowered to make varied measurements in the vicinity of the fault zones. It is worthwhile to mention that ICDP has agreed to provide instruments for in-situ stress and other technical support amounting to more than 1 million USD. The instruments will be left with the BGRL for future use. The project aims to address a set of questions that will potentially lead to a major advancement in the understanding of earthquake genesis.
A systematic research plan has been initiated towards generation of long-term, comprehensive multi-parametric geophysical observations in seismically active areas—Ghuttu, Uttarakhand and Shillong, Meghalaya to record precursory signals resulting from stress-induced changes in density, magnetisation, resistivity, seismic wave velocity, fracture propagation, crustal deformation, electromagnetic and radon gas emission as well as fluctuations in hydrological parameters. This can help establish the relationship between various earthquake precursors and processes, and help improve our understanding of earthquakes.
Numerical simulations for earthquake processes to understand the mechanism of earthquake is an urgent requirement. However, modelling earthquakes requires an understanding of the propagation of rupture, which needs to be done at a fine spatial and temporal scale. This is a major challenge, given our limited knowledge about how friction weakens the faults, as also the geometry and nature of fault zones, and how they respond to slips. This is essentially because earthquake processes operate many kilometres deep within the earth. Our data on such processes is limited, since sensors are restricted to the earth’s surface.
Early earthquake warning
The possibility of providing early warning of earthquake occurrence is also being explored. As part of this project, 100 sensors will be (not done yet?) installed in Uttarakhand, which will be connected with a central recording station. These sensors will detect the ground motion radiating from an earthquake rupture and estimate the resulting tremors that occur later in time either at the same location or at some other locations. The warning time will range from a few seconds to a little more than a minute and will primarily be a function of the distance of the user from the epicentre. A successful earthquake early warning system can provide a lead time of about 60-90 seconds to Delhi when a big earthquake occurs in the Himalayas.
It should be remembered, though, that the monitoring and understanding of earthquake is not sufficient to mitigate risk. Unless disaster- related information is disseminated widely and in time through effective communication, the loss of lives cannot be avoided.
Humans too, need to be oriented towards responding to instructions given by local administrators. The response of a community is dependent on the trust built through the social networks and outreach programmes. The Himalayan School Earthquake Learning Programme (HIMSELP) is one such initiative taken to sensitise the general public and school-children about seismic hazards and the steps to be taken during such an event. Mock drills and workshops for communities and neighbourhood populations, could go a long way in preparing people on the do’s and don’ts when confronted by a major disaster.
The NCS has made some major breakthroughs in seismic research since the time it came into being. However, the accurate prediction of an earthquake continues to remain a difficult task, given the gaps in our existing knowledge. Scientific drilling in earthquake and tsunami-prone zones might provide the key to saving populations from seismic and other related disasters.