July, 2013

July, 2013   ||  Volume 17 No.3



Seismic tomographic inversion for rock quality

M.S. Chaudhari, Ch. Subba Rao, V. Chandrashekhar and V. B. Bagade

Central Water and Power Research Station, Khadakwasla, Pune 411024

Assessment of the quality of the rock is important for ensuring stability of an underground power house, especially in the Himalayan region traversed by numerous faults and associated weak zones. The extent of weak zones around such locations can be deciphered from the in situ seismic velocity distribution with depth. A high resolution seismic tomographic study delineating weak zones in an underground power house site is presented. The study was conducted in ten boreholes situated along a line spaced 10 m apart each, taking two boreholes at a time. The rock type available at the power house site was dolomite.
A square grid of 1 m X 1 m was chosen for the tomographic inversion based on the compressional wave velocity of dolomite rock and the dominant frequency in the recorded waveform. The reliability of tomogram construction was ensured by i) comparing the travel time data obtained from field measurements with that generated by the model in the iteration process ii) by checking whether the velocity distribution obtained is consistent with the representative values of velocities of the rock type obtained at the site and iii) by suitably constraining the iteration process through prior knowledge of rock velocities at the site. In all, nine tomograms were obtained. In the combined tomogram, where velocities of individual cells are used, eight isolated weak zones of varying dimensions and orientations were inferred.


Three-way approach to test data homogeneity: An analysis of temperature and precipitation series over southwestern Islamic Republic of Iran

Amit G. Dhorde* and Mohammad Zarenistanak

Department of Geography, University of Pune, Pune – 411 007, India
*Corresponding author e-mail: amitdhorde@unipune.ac.in, amitdhorde@gmail.com

The accuracy and reliability of trend analysis and model results in climate change studies vary according to the quality of data used. Non-climatic factors, such as relocation of station, change of instrument, etc. make data unrepresentative of the actual climate variation. This may influence the outcome of climatic and hydrological studies. Homogenization of climatic data is therefore, of major importance. The objective of the present study was to check the homogeneity of temperature and precipitation data of southwestern Iran to find a break in temperature and precipitation series. Three tests for homogeneity: The standard normal homogeneity test (SNHT), Pettitt’s test, the standard normal homogeneity test by Alexandersson and Moberg were applied to analyse seasonal and annual temperature and precipitation series from 1960-2007 in southwestern part of Iran. Each test was evaluated separately and inhomogeneous stations were determined. The series were then grouped into three classes which were categorized as ‘useful’, ‘doubtful’ and ‘suspect’. It was revealed by the homogeneity analysis that none of the series belonged to the class ‘suspect’, and therefore, it was concluded that the temperature and precipitation series are homogeneous.


Crustal structure along Permanallur-Pallapatti deep seismic reflection/refraction profile and inferred evolutionary history of Palghat-Cauvery Shear System, Southern Granulite Terrain, India
G. Kesava Rao*, B. Rajendra Prasad, A.S.S.S.R.S. Prasad, S. Raju, G.S.P. Rao, M.S. Reddy and Dipankar Sarkar
CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, India
*E-mail: gkrao1950@yahoo.com

Deep seismic studies over Permanallur-Dharapuram-Oddanchatram-Pallapatti profile were conducted for better understanding the structure and tectonic frame work of the northern part of Southern Granulite Terrain (SGT), India. The northwest-southeast trending, 140 km long profile over the SGT depicts the basic nature of crustal-scale shear zones like Palghat-Cauvery Shear Zone (PCSZ), Karur-Kambam-Painavu-Trichur Shear Zone (KKPT) and Karur-Oddanchatram Shear Zone (KOSZ). The seismic evidences in the form of opposing reflectivity trends, horst and graben structure and abrupt south dipping mid-lower crustal reflections along transect indicate episodes of crustal extension and stress accumulation. These episodes might have influenced development of weak zones or faults. Subsequent compressional events might have lead to undulations/ uplifting of crustal columns as indicated by five-layered 2D velocity-depth model (Vp 6.0, 6.6, 6.9, 7.3 and 7.5 km/s). A combined interpretation of long range refraction/ wide angle reflection and the vertical reflection data confirms the basic deep seated nature of the crustal scale shear zones. Presence of diffused reflection Moho is noticed at a depth of ~45 km along the profile. The unusually high velocity of 7.5 km/s in the lower crust, presence of diffused Moho and reflections from upper mantle suggest the magmatic underplating in the lower crust during crust-mantle interactions.  

Relevance of minor irrigation and its restoration to sustain agriculture in Andhra Pradesh – An Overview
P.R. Reddy
Scientist-G (Ret), CSIR-NGRI, Hyderabad-500 007 (A.P)
E-mail: parvatarreddy@gmail.com

Sustainable irrigation, keeping in view all the socio-economic constraints, is vital for overall economic progress of our country. Andhra Pradesh socio-economic structure is linked to agriculture reliant economy. For sustenance of food production, it is essential to strengthen the irrigation potential. It is accepted by both the government , experts and the NGOs that due weightage should be given to minor irrigation as 65% of agriculture is dependent on minor irrigation. For well-being of different types of aquifers (shallow/deeper; soft/hard rock), steps need to be taken to revitalize failed and defunct bore wells through Managed Aquifer Recharge (MAR) technique. An overview of merits and demerits of existing minor irrigation schemes, especially groundwater schemes, and needed steps to ensure better utilization of water resources through Participatory Hydrological Monitoring is presented. A broad exposition of Plan Document released by A.P. State Govt is included, to emphasize the fact that the Govt is well aware of the importance of minor irrigation, but implementation is hampered due to various constraints. From the Plan document it is clear that immediate steps are to be taken to revoke the use of dilapidated tanks/ ponds and put into better use ground water resources by rehabilitating defunct bore-wells and adding new, giving due importance to aquifer management through farmer participatory mechanism.. Importance of conjunctive utilization of surface and sub-surface waters is discussed. Apt steps to identify problems and solving them are detailed. Need for support to field earth scientists and better interaction between lab & theoretical experts and field scientists is stressed, as inputs from all categories of scientists and technical experts are vital for ensuring sustenance of aquifer health.

Comparison of wave equation migration techniques over complex geological structures
Anitha Koduru* and P. R Mohanty*
*Department of Applied Geophysics, Indian School of Mines, Dhanbad -826004
anigeophysics2009@gmail.com, priyamohanty@hotmail.com

Wave-equation migration techniques play an important role in imaging complex geological structures and are becoming more acceptable as data processing tools. Usually, these subsurface geological structures provide complex seismic signature due to their geometrical set up. As a result, it is extremely difficult to interpret these seismic sections in terms of subsurface configuration. In order to image these complex geological features, three wave equation migration schemes such as Phase-Shift (PS), Phase-Shift Plus Interpolation (PSPI) and Stolt migrations schemes are applied to the synthetic time sections generated over the geological models. In addition, we have added Gaussian noise with signal to noise ratio (sn=30) on corresponding sections. On comparison, it is observed that the Stolt migration imaged the subsurface better than Phase-Shift (PS) and Phase-Shift Plus Interpolation (PSPI) migration schemes. Besides, Stolt migration generates minimum noise, in the form of numerical artifacts compared to other two techniques. Even after adding significant noise during migration process, it is observed that the reflectors are clearly delineated.

South Indian Convergence Zone Model: A new approach to seasonal forecasting of summer monsoon rainfall in India Part IV: Intra-seasonal changes and long range forecast of rainfall during 2010 southwest monsoon season
1Onkari Prasad and 2O.P.Singh
143, Ritu Apartments, A-4 Paschim Vihar, New Delhi-110063
2India Meteorological Department, Lodi Road, New Delhi-110003
prasadonkari123@yahoo.in, op_singh54@yahoo.com

While there were no intra-seasonal changes during southwest monsoon-2009, large intra-seasonal changes took place during southwest monsoon-2010: Two intense systems, one each over the Bay of Bengal and the Arabian Sea developed in May, i.e., during the onset phase of monsoon. No depression developed either over the Arabian Sea or the Bay of Bengal during the monsoon season. Though monsoon onset took place over the Bay of Bengal and Kerala coast around its normal date, it was delayed by 1-3 weeks in some parts of East and Central India and still monsoon covered entire country by 6th July, about 9 days earlier to its normal date. Monsoon circulation became weak, particularly from the second half of June till the end of July. It improved thereafter and became weak once again during the second half of September. The combined effect of the features of an active monsoon, as displayed in the activity of South Indian Convergence Zone (SICZ) during the period January to May-2010, and the intra-seasonal changes during the monsoon season resulted in excess rainfall over peninsular India and parts of Northwest India, below normal to deficient over the major parts of monsoon core zone comprising of Gangetic West Bengal, Bihar, Orissa, Jharkhand, Madhya Pradesh and East Uttar Pradesh and normal in the remaining areas. It has been shown that the features in the activity of SICZ as seen during the pre-monsoon months of April and May coupled with the influence of the changes which took place in Equatorial Pacific Ocean (EPO) in association with the demise of El-Nino and development of La Nina resulted in further intensification of SICZ in Southeast Indian Ocean (SEIO) and occurrence of weak cyclo-genesis in it. These factors might have been responsible for the absence of development of any depression in the Bay of Bengal, southward tilt of the eastern portion of monsoon trough and reduction in rainfall, particularly in the monsoon core zone. In spite of such large intra-seasonal changes, Long Range Forecasts (LRF) of seasonal rainfall by SICZ model were found satisfactory.

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