Current Issue

November, 2018   ||  Volume 22 No.6

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Seismic attenuation in Indian shield and Himalayan regions and its implications

K. S. Reshma* and P. Kumar
CSIR - National Geophysical Research Institute, Uppal Road, Hyderabad-500007, India
*Corresponding author: reshmaks.geo@gmail.com

ABSTRACT
Seismic attenuation is a key parameter to elucidate the properties of the Earth’s internal structure and is defined in terms of Quality factor Q, a dimensionless quantity which is the relative energy loss per oscillation cycle. Various studies have been carried out in the Indian shield and Himalayan regions to understand the risks and hazards due to the earthquake, using attenuation studies. Here, we provide a bird’s eye view on the attenuation studies carried out using Qp, Qs and Qc, which are the attenuation values of P, S and coda wave respectively in the Indian shield and Himalayan regions by combining the available published works by various researchers. Based on the available data set, four broad classifications have been suggested i.e. shield and cratonic regions, rift zones, orogenic belts, and sedimentary basins. Further, an attempt has been made to correlate these values with the geological provinces. It is found that the attenuation value, which has a large variation, agree very well with the geology of the region. The entire Indian shield has in general Qs/Qp > 1, implying that the scattering is a predominant factor which causes the attenuation. Interestingly, in sedimentary basins and rifted regions of India, Q values have been found less, indicating more attenuation of seismic waves. Qs/Qp < 1, would also imply that the underlying rocks are partially fluid-saturated. In addition, we also found that the attenuation values have an anti-correlation with the surface heat flow values, suggesting that the attenuation of seismic waves in the Indian shield and Himalayan region, is not only controlled by the temperature, but also influenced by the other factors such as composition to a large extent.
Keywords: Seismic attenuation, P- wave, S- wave, Coda wave, Indian shield, Himalayan regions, Heat flow, Crustal composition..



Comparing pre- and post- stack seismic inversion methods -
a case study from Scotian Shelf, Canada

S.P. Maurya* and N.P. Singh
1Department of Geophysics, Institute of Science, Banaras Hindu University Varanasi-221005, U.P., India
*Corresponding author: spm.bhu@gmail.com

ABSTRACT
In the present study, pre- and post-stack seismic inversions are performed to estimate subsurface petrophysical properties from the seismic reflection data, obtained over the Penobscot field, Canada. Such methods are routinely used to estimate subsurface property from seismic reflection data but the problem arises in deciding which method will provide more efficient and detailed information of the subsurface structures. Simple procedure is used here at the every step of seismic inversion methods, differences have been taken between pre- and post- stack seismic inversion. It is broadly applied in two steps; first, they are applied to the composite trace near to well location and inverted to obtain petrophysical parameters, which are then compared with the well log data. The analysis shows that both curves (inverted and well log) are in good agreement and display high correlation. The average correlation of post stack inversion (0.92), is higher than the pre-stack seismic inversion method (0.89). In the second step, entire seismic section is inverted and P- impedance, S- impedance, density, P- wave velocity, S- wave velocity and VP/VS ratio are estimated. The post stack inversion methods provide only acoustic impedance which is transformed into the other petrophysical parameters, using relationship derived from the well log data. These parameters are helpful in interpreting seismic sections. The analysis shows that both (pre- and post- stack) methods produces subsurface property in similar way, with high resolution from post-stack inversion, compared to the pre-stack inversion. Although the pre-stack inversion method produces more petrophysical parameters that are sensitive towards fluid and rock property, but the resolution is relatively poorer compared to the post-stack inversion methods. The interpreted inverted section indicates that the studied area does not have any major hydrocarbon accumulation.
Keywords: Pre- and Post- stack seismic inversion, Well log analysis, Amplitude spectrum, Petrophysical properties, Scotian shelf Canada.



Preliminary assessment of seismic hazard in old mining area using surface mounted seismic sensors

K. Goverdhan, V.R. Balasubramaniam*, Praveena Das Jennifer and C. Sivakumar
National Institute of Rock Mechanics, Bengaluru, India 560070
*Corresponding Author: eegd.nirm@gmail.com

ABSTRACT
Seismic monitoring of the old mined-out areas of the Kolar Gold Fields is carried out for the assessment of probable seismic hazard due to the likely change of stress conditions in the underground rocks of the mine. The mining operations in these gold mines had stopped almost two decades ago. However, the occurrence of rockbursts due to failure of rockmass with increase in the depth and their stressed nature, is an inevitable consequence of the deep mining. This is apparently caused by the dynamic stress changes and these changes are always associated with generation of micro tremors, as the rocks under high stress slip, jerk or break suddenly. Monitoring the seismic signals, generated by micro tremors, gives a clue to the changing stress regime in the rock. The seismic monitoring system that is deployed for such monitoring is used to locate the source of seismic events and to demarcate potential zones of occurrence in the mining area and to further understand likely change in the stress regime of the abandoned mines. This paper focuses on preliminary assessment of the probable seismic hazard based on seismic events and their source parameters.
Key words: Seismic monitoring, Seismic events, Seismic hazard, Stress regime, Kolar gold fields.



Morphology, elemental composition and source identification of airborne particles in Delhi, India

Saurabh Sonwani and Umesh Kulshreshtha*
School of Environmental Sciences, Jawaharlal Nehru University, New Delhi-110067
*Corresponding Author: umeshkulshrestha@gmail.com  

ABSTRACT
The present study focused on the morphological and elemental characterisation of PM10 (particulate matter ≤10µm) and total suspended particulate matter present in rainwater (TSPRW) samples at two sites, located in urban background and industrial belt in Delhi region. The scanning electron microscopy, coupled with energy dispersive spectrometer (SEM-EDX), was used to characterise the morphology, elemental composition in PM10 and TSPRW and further link them to the pre-dominant sources. SEM micrographs indicated the predominance of soot aggregates, Fe-rich particles, crystal of sulphate of calcium and potassium (Ca/K) and biological particles in PM10 at Jawaharlal Nehru University site (JNU). Similarly, the Badarpur industrial site (BDP) was found to be predominantly rich in fly ash particles and their aggregates, round/oval aluminosilicate particles, rich in Al, Si and O species. EDX results indicate high carbon contents in the atmosphere at BDP site as compared to the JNU site, suggesting the predominance of the particulates emitted from coal power plants and vehicular emissions in the vicinity of BDP site. Enrichment Factors (EFs) further confirmed the predominance of chlorine and fluorine in the atmosphere at BDP site, which further confirm to the emission from coal based power plants and industries.
Keywords: Atmospheric aerosol, Elemental composition, Morphology, Enrichment factor, Rainwater, Delhi region, Air pollution.



Quaternary carbonate deposits from Katrol Hill Range (KHR), Kachchh, western India: Mode of occurrences and its significance in landscape evolution
 

Rashmikant Talati and Nilesh Bhatt*
Department of Geology, Faculty of Science, The M.S. University of Baroda, Vadodara-390 002
*Corresponding Author: nilesh_geol@yahoo.com

ABSTRACT
Studies on Quaternary geology of Kachchh remained focused on the major structural elements and associated neotectonics that over masked significance of a unique Late Quaternary sedimentary record, popularly known as ‘Miliolite’ or ‘miliolitic limestone’ in Kachchh. In the present study, we investigated mode of deposition, basic sedimentology and stratigraphic associations of miliolite from a part of Katrol Hill Range, situated south of Bhuj. We classified these occurrences into three types viz., (1), obstacle dune deposits, (2) valley fill deposits and (3) fluvial reworked sheet deposits. These represent distinct depositional episodes related to landscape stability, onset of aridity and even onset of humidity, largely controlled by the climate change. However, the substrate landscape and post-depositional modifications were controlled by the episodic tectonic activities, related to the Katrol Hill Fault (KHF). In this paper, we document the sediment body geometry, physical structures, and the field relationships of the Late Quaternary bioclastic deposits, to evaluate overall landscape associated with the KHF. Accordingly, a prominent tectonically active phase caused the pre-miliolite topography, characterized by colluvium deposited either on the moderate slopes or base of the scarp which is overlain by obstacle deposits of miliolite. A later phase of instability must have initiated down slope transport of the miliolitic sand mixed with the local lithoclast that got deposited as valley fills and subsequently as reworked fluvial sheets. The younger phases of increased moisture must have stabilized and lithified the miliolitic sand on the slope and initiated incision of these sediments due to the cutoff of sediment source. Neotectonic activities along the KHF then intensified the incision.
Key words: Quaternary carbonate, Miliolite, Climate change, Neotectonics, Kachchh.



Climatic response of ‘Cedrus deodara’ tree-ring width records from Jangla region of western Himalaya in India: A case study

Somaru Ram1*, H.N. Singh1, Ramesh Kumar Yadav1, and Manoj K. Srivastava2
1Indian Institute of Tropical Meteorology, Pune-411008, India
2Department of Geophysics, Banaras Hindu University, Varanasi-221005, India
*Corresponding author: somaru@tropmet.res.in

ABSTRACT
Cedrus deodara tree ring-width index chronology from Jangla of western Himalaya, showed significant positive relationship with Palmer drought severity Index (PDSI) and cloud cover, and negative relationship with vapor pressure, mean, maximum and minimum temperatures during spring season (March to May). The relationship indicates that rising vapor pressure/temperatures over the region might be linked with low moisture availability due to high transpiration and evaporation which caused insufficient moisture supply at root zone of the trees, thus showing adverse impact on tree growth during growing season. Moreover, the significant positive association of tree growth with the cloud cover and PDSI, showed that increasing/decreasing CLD during growing season, might preserve the high and low moisture availability at trees root, that works as a booster to tree growth and plays the vital role in limiting of tree growth in western Himalaya. The Correlation analysis of CLD with PDSI (moisture availability) for the period 1901-2002 during spring season (March to May) indicates statistically strong correlation (r = 0.30) which is significant at 0.01% level.
Keywords: Tree ring-width, Temperatures, Percentage cloud cover, Vapor pressure, Western Himalaya.


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Delineation of groundwater potential zones in hard rock terrain from magnetic anomalies in Siddipet district (Telangana), India

R. Sandhya, S. Venkata Rama Lingam, B. Madhusudhan Rao* and R. Sudarshan
Centre of Exploration Geophysics, Osmania University, Hyderabad – 500 007, India
*Corresponding author: profmadhurao@gmail.com

ABSTRACT
Systematic and synergistic approaches are required for groundwater prospecting in hard rock areas, where secondary porosity plays a major role. A total field magnetic survey was carried out over a part of the Siddipet District (Telangana) covering an area between 17035’-18018’N and 78025’-79010’E, for identifying structural features and associated dykes apart from marking weathered zones and lithological variations. The magnetic survey consists of about 1000 stations, distributed at an interval of 500 m and covering an approximate area of about 2500 km2. Processing and interpretation of the acquired data resulted in accessing the thickness of weathered layers and the underlying fractured and fissured zones. We discuss these results in the light of groundwater potential in the studied region.
Keywords: Granitic terrain, weathered zone, fractured rocks, Magnetic anomaly, Groundwater potential.


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Satellite derived spatio-temporal characteristics of aerosol optical depths and cloud parameters over tropical Indian region

Adarsh Kumar 
Department of Physics, Amity Institute of Applied Sciences (AIAS), Amity University, Noida (UP) - 201 303, India.
Email: adarsh_phy@yahoo.co.in

ABSTRACT
Moderate Resolution Imaging Spectro radiometer (MODIS) derived Aerosol Optical Depth (AOD) is well suited for the seasonal and inter-annual study of the aerosols distribution and their effects over a long period of time. Daily averaged MODIS retrieved satellite (collection 5 level 3) AOD data has been used to investigate AOD distribution in spatio-temporal domain over Indian subcontinent for the three years period, 2008-2010. In 2008, the average value of AOD over Indian subcontinent was found to be ~0.37±0.088, whereas in 2009 and 2010, the mean values of AOD were estimated as ~0.32±0.075 and ~0.35±0.058 respectively.
The study revealed that during the monsoon season of 2009, the AOD decreased sharply with the increase of days. The highest and lowest values of AOD for the year 2008 were found to be ~1.098 and ~0.219, whereas for the years of 2009 and 2010, these values of AOD over Indian subcontinent were estimated to be ~0.61, ~0.21 and ~0.76, ~0.19 respectively. For these three years period of 2008-2010, the cloud parameters such as cloud fraction (CF), water vapor (WV), cloud optical depth (COD), and cloud top temperature (CTT), were also estimated and spatially correlated with the aerosol optical depths over Indian region. Results have been compared with some of the significant and important investigations made by other workers on AOD and cloud parameter values over entire region of India.
Keywords: Satellite data, TERRA, AOD, Indian region, Cloud parameters, Water vapor.


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Identification of fluvial stratigraphy using shallow subsurface geophysical and field investigations: a case study from Sabarmati River terraces, Mainland Gujarat

Girish Ch Kothyari1*, Raj Sunil Kandregula1, Vasu Pancholi1, and Nirmit Sah2
1Institute of Seismological Research, Raisan, Gandhinagar (Gujarat), India
2Kumaun University, Nainital, Uttarakhand, India
*Corresponding Author: kothyarigirish_k@rediffmail.com  

ABSTRACT
The present investigation is an attempt to understand stratigraphic correlation of fluvial terrace deposits using Ground Penetrating Radar (GPR) and field evidences. The vertical as well as lateral variations in the lithofacies and the continuity of the bounding surfaces are delineated using the conventional geological and high resolution shallow sub-surface GPR profiles. The field investigations revealed presence of three levels of fluvial terraces of 16 m height that are preserved at a section near Gandhinagar along the Sabarmati River. Field examination of these terrace exposures show well developed fluvial facies in the area. The GPR image of lower terraces (T1) indicates depositional minor changes in velocity in the upper two layers giving rise to fining upward planar cross-stratified sand facies, which is typical of a point-bar sequence. The 2D GPR image of upper terraces (T2 and T3) show velocity changes because of high degree lateral and vertical heterogeneity. This heterogeneity in sedimentary facies possibly occurred because of the sediment deposition by high stage flood events.
Key words: Sabarmati River; GPR; Fluvial stratigraphy; Fluvial terraces; Mainland Gujarat..


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