July, 2009

July, 2009   ||  Volume 13 No.3


Anomalous b-value in seismogenic layer of Bhuj Region

Kaushalendra Mangal Bhatt1,2 and Santosh Kumar

1Institute of Seismological Research, Sector 18, Gandhinagar, Gujarat 382018, India
2Institute for Geophysics and Extraterrestrial Physics,
Mendelssohnstr. 3, D-38106, Braunschweig,Germany
E-mail: kmbhatt@rediffmail.com; sundriyal007@gmail.com

The earthquake size distributions follow, in most instances, a power law and slope of this power law, defines the 'b-value'. The parameter b is believed to depend on the stress regime and tectonic character of the region. High and low b-value probably means low and high stressed zone, respectively. Fault/faults has tendency to accumulate the stress. Depth wise, unalike segments of fault act in their own way for stress accumulation, depending on geology and rheology. For study, Bhuj aftershock zone is considered, which chiefly underlies two faults i.e. North-Wagad (NWF) and Bachau fault (BcF). The b-value study of this zone, distinctly demarcates faulted line and its different segment linked b-value are found in correlation with the stress-accumulation. It gives a very clear picture that b-value is not only helpful in demarcation of faulted depth line but also in prediction of segments of stress accumulation. This may help in study of earthquake prediction.
The studies reveal that the b-value more often decreases with depth. This worldwide behavior is found to be valid for about 32% of the entire seismically active crust, at the 99% confidence level. About 2% of the crust only displays the opposite b-gradient. Kachchh is among the rare seismically active crust, which shows negative b-gradient. One plausible explanation for reverse characteristic of b-value could be the styles of faulting.

Equatorial and low latitude geomagnetic field oscillations in the Indian region
Department of Applied Geophysics, Indian School of Mines University, Dhanbad
Jharkhand - 826 004
E-mail: pnsmay1@gmail.com

Monthly mean hourly values of geomagnetic field components D, H and Z for quiet days at equatorial and low latitude stations in the Indian region are analyzed to study the salient features of geomagnetic field oscillations in magnetic elements. The data used in this analysis is from 1958 to 1993 at equatorial electrojet stations: Trivandrum & Annamalainagar, from 1970 to 1993 at Kodaikanal and from 1927 to 1997 at low latitude station Alibag. From this basic data, geomagnetic Sq ranges and summed ranges are computed and subjected to the data adaptive, noise reducing technique of Singular Spectrum Analysis (SSA). The pair of eigen vectors analyzed through SSA up to order 18 represent different oscillations of the field such as; 11-year, annual, semi-annual, 4-month, 14-month (Pole-tide) and a Quasi-Biennial Oscillation (QBO) etc. The Sq ranges, summed ranges at all the stations and monthly mean sunspot numbers for the same period are also analyzed by a band pass digital filter method in order to identify whether QBO signal at these stations is the result of dynamo winds or due to QBO like signature in the Sun’s atmosphere. It is found that, the amplitude of the signal is stronger at equatorial electrojet stations in comparison with low latitude station Alibag and may be due to solar origin.

Crustal Attenuation of Shearwaves in Pithoragarh Region

A.Joshi, M.Mohanty1, S.S. Teotia2, A.R. Bansal3, V.P.Dimri3 and R.K.Chadha3
Indian Institute of Technology, Roorkee, Roorkee 247 667
1Department of Science and Technology, Government of India, New Delhi – 110 016
2 Department of Geophysics, Kurukshetra University, Kurukshetra-136119
3National Geophysical Research Institute, Hyderabad 500 007

The region of Kumaon Himalaya is one of the seismically active regions of Himalaya. Frequent seismic activities in this region demonstrate the seismotectonic nature of the region. In this paper, necessary efforts are being made to study the attenuation properties of shear wave in Pithoragarh region using the data from strong motion network of eight stations installed in Kumaon Himalaya. In the present work, data of eight events recorded at Dharchula station have been utilized for inversion. The input to the algorithm used in the present work is simply the S phase of acceleration record and the hypocentral distance. The raw data have been processed using different steps like instrumental scaling, baseline correction and filtering. In the present work all records have been filtered using band passed Butter worth filter within ranges. Since the strong motion sites are located in weathered rock terrains, necessary efforts have been made to apply site amplification estimated by H/V spectral ratio techniques of Nakamura (1988) to noise data. Site amplification curves have been prepared which show less amplification at low frequencies compared to high frequencies.
Using the inversion algorithm developed by Joshi (2006), the frequency dependent Quality factor(Q) has been calculated which gives Qb(f) = 63 f 1.25 in frequency range. Stress drop for different events has been calculated using corner frequencies obtained from inversion. The stress drop of events ranges from very low to high value indicating highly unstable tectonic activity. Low value of coefficient (< 200) and high frequency dependence (>0. 8) in the Qb(f) relationship suggest that the region is seismically and tectonically active and is characterized by large number of heterogeneities.

Multi Earth Observation data to identify indicators for mineralized zones in parts of Iran
P.Chandrasekhar, K.Vinod Kumar, Tapas Ranjan Martha and S.K.Subramanian
National Remote Sensing Centre (NRSC), Department of Space, Govt. of India, Hyderabad – 500 625
Email: Chandrasekhar_p@nrsc.gov.in

Multi-sensor satellite data such as IRS P6 (RESOURCESAT 1) - LISS IV Mx and LISS III, and IRS P5 (CARTOSAT 1) – PAN A were used for the identification of possible locations of chromite occurrence in a highly inaccessible area having less vegetation cover in the north eastern parts of Iran around Gaft region in the south western portion of Joghatay city. The coarse resolution LISS III data were used mainly for the regional understanding of the geological and geomorphological set up of the area, and the fine resolution PAN A data for delineating the microgeomorphological features. These two data sets were merged and hybrid images were generated in order to obtain the best of spatial and spectral interpretations, particularly for enhancing the minor spectral and spatial components of the lithological units. The existing field data i.e., the coordinates of the mineralized zones, collected using Global Positioning System (GPS) were plotted on the image and studied in conjunction with the multi-sensor data interpretation. The typical spectral signatures observed over known chromite mineralization are correlated with the unknown areas using mainly the lithological controls. The mineralization in this area is mostly controlled by lithology, and wherever these signatures matched, those areas are identified as prospective areas for chromite mineralization.



Investigation of GDOP for Precise user Position Computation with all Satellites in view and Optimum four Satellite Configurations
V.B.S.Srilatha Indira Dutt, G.Sasi Bhushana Rao, S.Swapna Rani,
Swarna Ravindra Babu1, Rajkumar Goswami and Ch.Usha Kumari

Department of Electronics & Communication Engineering
Andhra University College of Engineering, Visakhapatnam -530 003
E-mail: srilatha06.vemuri@gmail.com
1Aerospace Division, WIPRO Technologies, Chennai

The advent of Global Positioning System (GPS) has revolutionized the field of navigation particularly in the field of civil aviation sector. The accuracy of GPS system is affected by several factors. One such factor is satellite Geometry, which represents the geometric locations of the GPS satellites as seen by GPS receiver. This plays a very important role in determining the total positioning accuracy. Better the geometry, better the position accuracy. The Satellite Geometry effect can be measured by a single dimensionless number called Geometric Dilution of Precision (GDOP). Lower the GDOP value, better the satellite Geometry. GPS requires minimum of four satellites to compute user position. When more number of satellites are in view, best four satellites are taken in order to reduce the redundancy. With four satellites, best geometry is obtained when one of the satellites is at the zenith and remaining three forms an equilateral triangle and all the four together forms a tetrahedron structure. The larger the volume of the tetrahedron, the better is the value of GDOP. Similarly, greater the number of satellites, better the value of GDOP. Practically, GDOP ranges from 2 to 6. Monitoring of GDOP is also an important aspect for high-precision applications such as surveying and Integrity monitoring in the GPS receivers. For making use of GPS for en-route and Precision Approach (PA) aircraft landings over the Indian subcontinent, the aspect of best GDOP value to be used in the user position computation is investigated which is obtained due to all the satellites in view or best four satellites in this paper. A new algorithm is proposed to compute various GDOP. Analysis is made by computing the best GDOP due to four optimum satellites as well as for all the satellites in view. The dual frequency GPS receiver data of IISC, Bangalore (13.02o / 77.57o Lat./Long.) is used for investigation of best GDOP configuration to be used in user position determination over the Indian subcontinent.



Geophysical exploration for manganese-some first hand examples from Keonjhar district, Orissa
B.V.S.Murthy, B.Madhusudan Rao, A.K. Dubey and Srinivasulu

Centre of Exploration Geophysics, Osmania University, Hyderabad – 500 007
E-mail: bvs_murthy_2006@yahoo.co.in

Manganese ores in India are being exploited since the past hundred years. Continuous exploitation of shallower and massive deposits led to searching for further occurrences and also necessitated application of geophysical methods. Geological survey of India since 1940s, has been exploring for manganese deposits in various parts of the country employing different geophysical methods (Ganokar, Das & Srirama 2001).
The authors of this paper had opportunity to conduct geophysical surveys comprising gravity, magnetic and electrical resistivity methods in some selected blocks in the JAMDA-KOIRA belt of Keonjhar District, Orissa. Manganese ore, mainly psilomelane and pyrolusite occur in this belt as small lenses/lumps discontinuously and, in general under cover of laterite. These ore occurrences appear to be confined to near NW-SE or N-S belts and associated with shales/phyllitic shales below which are occurring occasionally brecciated conglomerates with chert and cherty quartz. The basement is Banded Iron Formations, mainly BHJ and BHQs.
In the first block, which is about 300mx300m size, magnetic, gravity and electrical resistivity profiling and soundings were conducted. The geophysical signatures, though feeble, showed the trends and alignments of ore bodies and the intervening faults/ fractures associated with iron concentrations. Based on these results two more blocks (Block – II about 89hectares and Block – III about 24 hectares) were covered by magnetic mapping, electrical resistivity profiling and sounding and gravity survey on selected traverses. The geophysical anomalies in these two blocks also are characteristic in delineating the probable alignments of manganese bodies. Critical analysis of, essentially, the magnetic contour maps and resistivity and magnetic profile data helped visualizing pockets of likely occurrence of manganese ore.


Observed local enhancements in Atmospheric Carbon Monoxide during Biomass Burning Events
R.Anjali, G.Mohan Kumar and S.Sampath 1

Centre for Earth Science Studies, PB 7250, Thiruvananthapuram - 695 031
1 D-227, Swathi Nagar, Thiruvananthapuram – 695 023.
E.mail : anjalimeera@gmail.com

An attempt is made to present the observed enhancements in atmospheric carbon monoxide (CO) associated with local biomass burning events at a tropical coastal environment Thiruvananthapuram (8o 29’ N, 76o 57’ E) and with approximations to compare these epochs with empirical estimates. An IR analyzer (Monitor Europe 9830B) was used for the continuous CO monitoring. CO emitted from two massive biomass burning events, including fresh biomass and dry biomass burning near the measurement site, ~200 m were measured and estimated empirically. CO measured using the analyzer showed about 30- fold and 27- fold enhancements compared to normal days. Emperical estimates of CO showed 0.287 kg/m2 CO emission on fresh biomass burning and 0.198 kg/m2 on dry biomass burning. Enhancement in CO during two grassland burning events occurred at a high altitude location about 20 km from the measurement site were studied and about 1.5 fold and 1.4 fold enhancements in CO respectively were observed. Local enhancements in CO during massive biomass burning in open associated with religious festivals were also investigated in the present study.