January 2017

January, 2017   ||  Volume 21 No.1


Sparsity- based GPR blind deconvolution and wavelet estimation

Alaeddin Ebrahimi*, Ali Gholami and Majid Nabi-Bidhendi

Institute of Geophysics, university of Tehran, Tehran, Iran
*Corresponding author: ala_ebrahimy@ut.ac.ir

Improving the vertical resolution of Ground Penetrating Radar (GPR) data by blind deconvolution technique is an approach we target here. Sometimes geologic situations such as presence of clay or humidity lead to blurred sections. Advanced processing steps, that are so common in seismic reflection, such as deconvolution are needed. In this approach the sparse deconvolution algorithm on GPR data has been used in a novel way. It is often assumed that reflectivity series are sparse and noise is random. Generalized Cross Validation (GCV) method has been used to estimate the desired wavelet and to find the optimum iteration in the deconvolution algorithm. To examine the efficacy of the method, it is applied to synthetic data. The GCV and MSE curves versus iteration are then plotted in order to determine the optimal point. The final deconvolved section shows a satisfying result for GPR field data and the speed and accuracy of this robust algorithm to reconstruct reflectivity series is considerable.
Key words: Ground Penetrating Radar (GPR), Blind deconvolution, Sparsity, Generalized Cross Validation(GCV) and Reflectivity series.

Edge Detection of Gravity Anomalies with Directional Hyperbolic
Tilt Angles: Application to Synthetic and Field Data

Ahmad Alvandi*1 and Mojtaba Babaei2

1University of Applied Science and Technology, Hamedan Province Branch, Iran
2Department of Physics, Tuyserkan Branch, Islamic Azad University, Tuyserkan, Iran
*Corresponding Author: sim.alvandi@gmail.com

Edge detection is an image processing method for finding the boundaries of anomalies. Local phase filters have been widely used to detect the edges of the anomalies. There are various filters that are employed to attain edge detection, for example, Analytic signal, tilt angle, directional tilt angle and hyperbolic tilt angle. The tilt angle is a widely used edge detection filter. We make some improvement to tilt angle filter, so that it can process the gravity data. We describe a new filter based on the first order directional hyperbolic tilt angle. Directional hyperbolic tilt angle is used for edge detection of the gravity anomalies by a calculation program based on MATLAB. This filter is applied to synthetic data with and without random noise. Finally, the validity of the filter is tested on a real case from Iran.
Key words: Edge Detection, Gravity Anomalies, Hyperbolic Tilt Angle, Salt Dome and Iran.

Gravity Anomalies and Basement Structure below Deccan Traps in Gondwana Basins of Eastern Maharashtra, India

K.V. Swamy1, Neetha Raj1, S. K. G. Krishnamacharyulu*2 and I. V. Radhakrishna Murthy3
1Department of Geology, Adikavi Nannaya University, NH-16, Rajahmahendravaram, Andhra Pradesh
2School of Earth Sciences, SRTM University, Nanded, Maharashtra
3Professor (Retd) of Geophysics, Andhra University, Vishakhapatnam, Andhra Pradesh
*Corresponding Author: skgkchary@gmail.com

The Gondwana basins with their complex tectonics and high hydrocarbon potential have become targets of serious geophysical investigations in the last decade. It is increasingly concluded that the Deccan Syneclise (DS) in the west and central regions of India is underlain by highly prospective hydrocarbon bearing Gondwana basins. However, the nature and thickness of sedimentary basins and the associated basement structure are yet to be geophysically ascertained. In this paper, the Bouguer gravity anomalies of Gondwana basins of Eastern Maharashtra are modelled to infer the thickness and structure of the basins beneath the Deccan trap cover. The modelling studies along six profiles indicate the depth to the basement and thickness of sediments is gradually decreasing from N to S. The study also indicates that the basement undulates with alternative highs and lows with concealed sub-trappean rift basins at the eastern extremity of Deccan Syneclise (DS).
Key words: Deccan Traps, Gondwana basins, Gravity anomalies, Modelling and Basement structure.

Source Characteristics of the 2012 Earthquake Swarm Activity in the Andaman Spreading Ridge

G. Srijayanthi*, M. Ravi Kumar, S. Prasanna, and N. Purnachandra Rao
CSIR-National Geophysical Research Institute, Hyderabad-500007, India
*Corresponding Author email: srijayanthi.india@gmail.com 

Earthquake swarms are a sequence of events clustered in space and time, with no single earthquake dominating in size. Such swarms were observed in the Andaman sea region during the years 1983-1984, 1994, 2005 and 2012. The recent one in 2012 occurred to the north of the Nicobar Islands (9° N, 94° E) within the Andaman spreading ridge, starting on 16 April, 2012. Interestingly, the swarm followed the Mw8.6 Indian Ocean earthquake of 11 April, 2012, the largest strike-slip earthquake ever. This activity lasted for nine days and comprised about 27 earthquakes in the local magnitude (ML) range of 2.2 to 4.4, whose focal depth varied from 4 to 51 km. In the present study, we first analysed the phase data of these earthquakes recorded by a nine station broadband seismological network established by the CSIR-National Geophysical Research Institute (CSIR-NGRI), together with the data from three stations of the India Meteorological Department (IMD), to constrain the hypocentre locations of the swarm events using the double difference method. Further, we determined the moment tensor solutions of the three largest events using the full waveform inversion technique, to understand their source characteristics. Interestingly, all the three mechanisms showed a high non-double-couple component of over 70%, comprising both isotropic and CLVD components. Therefore, it is inferred from the present study that the mechanism of swarm earthquakes can be explained by ascension of magma at the spreading ridge coupled with inflation or deflation of magma chambers in the volcanic source region. In contrast, moment tensor solutions of four tectonic earthquakes that occurred to the north of the Andaman Islands away from the spreading center and the swarm, show a very high double couple percentage as expected for a normal tectonic earthquake, validating our interpretation.
Key words: Andaman Nicobar, Swarm earthquakes, Earthquake relocation and Moment tensor solutions.

Groundwater quality in and around Tuticorin town, Southeast coast of India 

Somvir Singh*1, N.C. Mondal2 and V.S. Singh2
1Central Ground Water Board (MoWR, River Development & Ganga Rejuvenation), Dehradun, India
2CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, India
*Corresponding Author: somvirngri@gmail.com

Rapid urbanization coupled with growth in agriculture and industries has led to deterioration of groundwater quality. The problem is severe in the coastal tracts due to salinity ingression since the last few decades. The present paper deals with a systematic hydrogeochemical study carried out in and around Tuticorin town covering an area of about 120 km2 to assess groundwater quality. A total of 29 groundwater samples were collected and analyzed. Analysis of major ions has shown the anomalous values for total dissolved solids (TDS), sodium (Na+), magnesium (Mg2+), chloride (Cl−), and sulphate (SO42−) resulting in degradation of groundwater quality. Only 21% of samples are potable based on the TDS values. The order of major cations and anions obtained are Na+>Mg2+>Ca2+>K+ and Cl->SO42->HCO3->NO3->F-, respectively. The results of these parameters were interpreted with the help of Piper, Wilcox and Gibbs diagrams apart from correlation matrix analysis. Cross plot of HCO3-/Cl- (molar ratios) versus TDS indicated that about 72% of the analyzed samples are brackish and saline in nature. Out of them, about 42% samples are NaCl-type. On the basis of interpretation of US Salinity diagram, it is found that majority of the samples have very high salinity hazard and sodium hazard, and represent evaporation dominance.
Key words: Hydrochemistry, Drinking and Irrigation, Groundwater salinity, Coastal aquifer, Tuticorin town, Tamil Nadu and India.

Evaluation of shallow aquifers contamination along Cauvery River Basin using Electrical resistivity and hydro chemical investigations 

K.V.Satyanarayana*1, M.Pradeep Kumar1, M.S.Kumar1, B.Balakrishna2 and Dinesh Gupta3
1 Geological Survey of India, Southern Region, Hyderabad – 500 068
2Geological Survey of India, Central Region, Nagpur – 440 006
3Geological Survey of India, Eastern Region, Kolkata, 700 091
*Corresponding Author: satyan0461@gmail.com

The reasons for deterioration of quality of water in coastal aquifers are many. To investigate some of them, electrical resistivity surveys were carried out in the study area namely Cauvery sedimentary basin. A total of about 300 vertical electrical soundings (VES) using Schlumberger array was used for the study. Groundwater samples were also collected from shallow dug wells, hand pumps and ponds at sounding locations for chemical examination of TDS and chloride to correlate with the resistivity data for confirmation of quality of the groundwater. The sources of freshwater in the study area include the shallow unconfined aquifer below the dry unconsolidated layer as well as a series of confined aquifers below it.
The resistivity data was analyzed for true values by inverting the sounding data using partial curve matching as well as software methods. The interpretation of VES data reveal that the low resistivity regions corroborate with higher TDS and Chloride values mostly falling over areas occupied by rivers, canals and inlets which are connected to the sea. The seawater might be flowing into the mainland through these inter connected canals, rivers and inlets due to the action of waves and shore currents resulting in the infiltration of sea water into the shallow aquifers. The permeable zones occurring in proximity to backwater canals are most vulnerable for saline water intrusion and may further damage the deeper aquifers through seepage. The present surveys have clearly established regions of saltwater contamination and causes for deterioration of shallow aquifers. The present surveys helped in the classification of low resistivity regions, corroborating well with the high cut off values of TDS and chloride. This demarcates clearly saltwater contaminated areas. These results may possibly help in taking preventive measures to obstruct backwater flow through rivers and inlets due to tidal action by constructing barriers to safeguard the environmental disorders.
Key words: Coastal aquifers, Saltwater intrusion, Vertical electrical sounding, Water analysis and Cauvery basin.

Co-Seismic Water Level Changes in Koyna – Warna Region - A Wavelet Analysis

D. V. Ramana* and Ch. V. V. Eswari
National Geophysical Research Institute (CSIR), Hyderabad, India
*Corresponding Author: dvr@ngri.res.in

Koyna region in India is known to be the largest case of Reservoir Triggered Seismicity in the world and the region is seismically active till today. As wavelets are mathematical tools they can extract information from different kinds of time series. In this work the wavelet analysis has been used to see the seismic effects on the water level changes in the bore wells of the Koyna-Warna region. The 14th March 2005 earthquake with M5.1 of Koyna-Warna region has been studied for the induced co-seismic changes in bore wells. The Ukalu well has shown the maximum change in the water level since the epicenter is close to the well. The effect of epicenter distance to the wells is also studied. These results are useful in further analyzing the forecasting of the water level changes.
Key words: wavelet analysis, Co-seismic water level changes, Reservoir Triggered Seismicity, Koyna-Warna region.

Simulation Results for Southern Indian Ocean (SIO) Using Ocean Model 

A.P.Mishra1, 2 and A.C.Pandey1 
1Department of Atmospheric and Ocean Studies, Faculty of Science, Nehru Science Centre,
University of Allahabad, Allahabad-211002
2Central Water Commission, Sewa Bhawan, R.K.Puram, New Delhi-110066
*Corresponding Author: anshu_ms@yahoo.com

A z-coordinate Modular Ocean Model (herein after referred as MOM3) has been implemented for global domain forced by NCEP/NCAR wind stress climatologies and executed for twenty five years. Several results of interest were analysed mainly for Southern Indian Ocean (SIO) (60°S-10°N, 30°E-120°E) including Antarctic Circumpolar Current (ACC) region of Southern Ocean (SO) from the output of the above model. The fidelity of the model is examined for varieties of phenomenon viz: surface elevation, horizontal circulations/vertical velocities at sub-surface, property transport including statistical estimation of Sea Surface Temperature (SST). The Results indicate that model produces strong variability of vertical velocity in the deeper ocean showing inability of z level model for bottom boundary layer correctly whereas the strength of the subsurface currents decays in comparison to the preceding depth circulation. It is noticed that in the upper ocean, the zonal transports are eastwards that may directly follow the surface currents. Statistical analyses include the estimation of model Error (ME), Correlation Coefficient (CC) denoted by R and Skill Score (SS) between model & observed SST data and result showing high correlation (R=0.94) with ME between 0 to 10C. CC and SS suggests the success of model up to some extent. As seen from the R values, which are close to 1 over most of the model domain, is thought to be SST is simulated well.
Key words: Wind Stress, ACC, Sub surface horizontal circulation, Sea Surface Temperature, Vertical Velocity and Statistical Analyses.

News at a glance 2

Can we have an organised Sustainable agriculture System that can ensure our food security?

Director Grade Scientist (Retd), CSIR-NGRI, Hyderabad-500 007, Telangana State
E-mail: parvatarreddy@gmail.com

Agriculture practices vary from place to place. Even concepts and methodologies need to be changed, taking in to consideration a region`s ecosystem peculiarities and socio-economic aspects. From time to time decisions are taken by the concerned focusing on the problem on hand, ignoring or not worrying about repercussions of any decisions taken to overcome the problem on hand. At a later stage when setbacks of significant nature crop up critics pounce on the decisions taken earlier, forgetting decisions and execution mechanisms change with time and our focus should be to take steps that can improve the situation, instead of wasting our energies in finding reasons for spilled milk.
Green Revolution was hailed for bailing us out of a tricky situation in 1960s and 1970s.In the process the introduction of chemical fertilizers, chemical pesticides led to deterioration of soil fertility and overall environmental degradation. While there is a definite necessity to improve our soil fertility and proper usage of depleted water resources, it is essential to take up any steps that can help our country as a single entity and not a disjointed forty and odd independent segments.
Key words: Food Security, Green Revolution, Sustainability, chemical fertilizers & pesticides, soil fertility, organic farming.