Informatics Publishing Limited

Harsh Gupta ¹, D. Shashidhar ¹, Metilda Pereira ¹, N. Purnachandh Roa ¹, M. Kousalya ¹, H. V. S. Satyanarayana ¹, Satish Saha ¹, R. T. Babu Naik ¹, V. P. Dimri ¹

Affiliations
1 National Geophysical Research Institute, Uppal Road, Hyderabad -500007, IN

Abstract

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Harsh Gupta ¹, D. Shashidhar ¹, Metilda Pereira ¹, N. Purnachandra Rao ¹, D. Nagesh ¹, H. V. S. Satyanarayana ¹, Satish Saha ¹, R. T. Babu Naik ¹, V. P. Dlmri ¹

Affiliations
1 National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, IN

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Harsh Gupta ¹, D. Shashidhar ¹, Metilda Periera ¹, Prantik Mandal ¹, V. P. Dimri ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

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Kalachand Sain ¹, Harsh Gupta ²

Affiliations
1 National Geophysical Research Institute, Uppal Road, Hyderabad-500007, IN
2 National Geophysical Research Institute, Uppal Road, Hyderabad-500007, IN

Abstract

At present India produces only one-third of her oil requirements. The escalating demand for energy and the rising price of oil are compelling factors to look for an alternate source of energy for sustainable growth. Gas-hydrates, crystalline form of water and methane, seem to be a viable source of energy. Bathymetry, seafloor temperature, sedimentary thicknesses, rate of sedimentation and total organic carbon (TOC) indicate good prospects of gas-hydrates within the vast offshore regions of India. The energy potential of gas-hydrates is estimated to be twice the energy contained in the total fossil fuel reserves. Several oil companies and national institutes are engaged in gas-hydrate investigations making use of geophysical, geochemical, geological and microbiological data. Based on analysis of available seismic data, geological characteristics, geochemical and microbiological proxies, gas-hydrates have been identified in the continental margins of India (the Bay of Bengal and the Arabian Sea). The drilling and coring under the auspices of the Indian National Gas Hydrates Program (NGHP) has validated the ground truth in the Krishna-Godavari (K-G) and Mahanadi basins and in the Andaman region of the eastern offshore. It is necessary to delineate the gas-hydrates and free-gas bearing sediments and evaluate the resource potential in prospective areas. The National Geophysical Research Instimte (NGRI) has built requisite expertise in special processing, modelling and inversion of marine seismic data based on traveltime tomography; waveform inversion; amplitude versus offset (AVO) inversion; AVO attributes and pre-stack depth migration coupled with effective medium theory or rock physics modelling. The blanking, reflection strength, instantaneous frequency and attenuation attributes have been found to be vital for identifying gas-hydrates without BSR and/or ascertaining whether a BSR is related to gas-hydrates. The traveltime tomography of large offset multi-channel or ocean bottom seismic data can be used for demarcating the zone of gas-hydrates and free-gas bearing sediments. The pre-stack depth migration of seismic data using the large wavelength velocity tomograms may help to understand the genesis of gas-hydrates. All these approaches and their application to available marine seismic data are presented here with a view to investigate gas-hydrates along the continental margins of India.

Keywords

Gas-Hydrates, Free-Gas, BSR, Identification, Estimation, Indian Margins.

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Harsh Gupta ¹, N. Purnachandra Rao ¹, D. Shashidhar ¹, K. Mallika ¹

Affiliations
1 National Geophysical Research Institute, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500007, IN

Abstract

On 12 May 2008 an earthquake of magnitude 7.9 devastated the Northwestern Sichuan province of China. This earthquake occurred along the northeast trending Longmenshan fault bordering the Tibetan plateau on the west and the Sichuan Basin on the east. The focal mechanism depicts a thrust fault mechanism with the Northwest dipping fault plane correlating well with the tectonic fault. This plane also hosts a component of right-lateral strike slip consistent with the local tectonics and orients well along the trend of aftershock distribution. Broadly, the Sichuan earthquake is a consequence of the northward convergence of the Indian plate against the Eurasian plate resulting in eastward crustal extrusion of Tibetan plateau accompanied by clockwise rotation of several tectonic blocks of the Eurasian landmass. More specifically, it occurred along the Northeast trending Longmenshan fault, due to over-thrusting of a weak Tibetan crustal block over a mechanically stronger Sichuan Basin. Estimation of p value using about 164 aftershock data provides a value of 0.87, comparable to a value of 1.0 obtained for the Muzaffarabad earthquake in western Himalaya, indicating a normal rate of decay of the aftershocks in the months ahead. We infer that aftershocks of magnitude exceeding 5 may occur for a duration of about 7 months.

Keywords

Earthquake, Seismicity, Tibetan Plateau, Siachun, China.

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Harsh Gupta ¹, D. Shashidhar ², K. Mallika ², N. Purnachandra Rao ², D. Srinagesh ², H. V. S. Satyanarayana ², Satish Saha ², R. T. B. Naik ²

Affiliations
1 National Geophysical Research Institute (Council of Scientific and Industrial Research), Uppal Road, Hyderabad - 500 007, IN
2 National Geophysical Research Institute (CSIR), Uppal Road, Hyderabad - 500 007, IN

Abstract

Earthquake activity is monitored in real time at the Koyna reservoir in western India, beginning from August 2005 and successful short term forecasts have been made of M ∼ 4 earthquakes. The basis of these forecasts is the observation of nucleation that precedes such earthquakes. Here we report that a total of 29 earthquakes in the magnitude range of 3.5 to 5.1 occurred in the region during the period of August 2005 through May 2010. These earthquakes could broadly be put in three zones. Zone-A has been most active accounting for 18 earthquakes, while 5 earthquakes in Zone-B and 6 in Zone-C have occurred. Earthquakes in Zone-A are preceded by well defined nucleation, while it is not the case with zones B and C. This indicates the complexity of the earthquakes processes and the fact that even in a small seismically active area of only 20 km x 30 km earthquake forecast is difficult.

Keywords

Earthquake, Nucleation, Forecast, Koyna Reservoir, Maharashtra.

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Harsh Gupta ¹

Affiliations
1 NGRI, Hyderabad, IN

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Harsh Gupta

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Harsh Gupta

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Harsh Gupta , Shailesh Nayak , Y. J. Bhaskar Rao , R. K. Chadha , B. K. Bansal , D. Srinagesh , N. Purnachandra Rao , Sukanta Roy

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Kalachand Sain ¹, Maheswar Ojha ¹, Nittala Satyavani ¹, G. A. Ramadass ², T. Ramprasad ³, S. K. Das ⁴, Harsh Gupta ¹

Affiliations
1 CSIR - National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, IN
2 National Institute of Ocean Technology, Velachery-Tambaram Main Road, Chennai - 600 100, IN
3 CSIR-National Institute of Oceanography, Dona Paula, Goa - 403 004, IN
4 Ministry of Earth Sciences, Prithvi Bhavan, Lodhi Road, New Delhi - 110 003, IN

Abstract

Gas-hydrates are crystalline substances consisting of mainly methane and water, and occur in shallow sediments of outer continental margins and permafrost regions. They are formed at high pressure and low temperature regime when supply of methane gas exceeds the solubility limit. Unlike natural gas, oil and minerals, gas-hydrates are not stable at standard temperature and pressure (STP). One volume of gas-hydrates, when dissociated, releases 164 volumes of methane at STP. Since methane is the lowest molecular weight hydrocarbon, use of gas-hydrates as fuel will cause less pollution to the environment. These have attracted the global attention due to their natural occurrences in abundance and huge energy potential. The methane locked as gas-hydrates is envisaged as 1-120 x 10¹⁵ m³ (Boswell and Collett, 2011). Only 15% recovery from this gigantic reserve may be sufficient to meet the global energy requirement for about 200 years (Makogon et al. 2007). Thus, gas-hydrates seem to be a viable major energy resource of future, and have been identified globally either by geophysical, geochemical and geological surveys or by drilling and coring (Boswell and Saeki, 2011; Ruppel, 2011; Sain and Gupta, 2012). Besides having the energy potential, the study of gas-hydrates is also important from natural hazards point of view related to seafloor subsidence, slumps and slides (Gupta and Sain, 2011).

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