October, 2004

October, 2004   ||  Volume 8 No.4



Aeromagnetic anomalies, lineaments and seismicity in Koyna-Warna Region
P.K.Agrawal, O.P. Pandey and T.R.K.Chetty
National Geophysical Research Institute, Hyderabad - 500 007

Koyna area, situated near the western margin of India, is well known for its seismic activities for over three decades. In order to understand its seismotectonics, numerous geoscientific investigations in and around this region were conduced, specially after the M = 6.3 disastrous December 10, 1967 earthquake. This included a multi-level aeromagnetic survey around the Koyna-Warna area, which is covered by a suite of thick and randomly magnetized basaltic rocks. Here, we attempt to discern linear magnetic features and prominent lineament patterns from the measured magnetic fields and satellite imagery, and interpret them in the light of available seismological data.
Our study reveals a prominent 300-400 m local Quaternary upliftment over the already uplifting block of western margin. These uplifted regions, situated on either side of the Koyna river faulted/subsided block, appear to be a block-like structure. They are bounded on either side by two faults, one originating in the NNE-SSW and the other in the NNW-SSE direction. The NNE-SSW trending fault falls in the line of Koyna reservoir. These two faults are intersected in the middle by two parallel E-W trending faults, which correspond well to the course of the Koyna River. These intersecting faults result in the formation of two triple junctions, one situated south of the Koyna dam and the other near Urul-Nisre region lying to the east of Koyna. Between the Koyna-Warna reservoirs, several intersecting lineaments are observed. A good correlation between the lineaments derived from the satellite imagery and from aeromagnetics can be seen. The intersection of the magnetic lineaments along Warna region with NNE-SSW trending fault suggests possible development of a new system of faults between Koyna and Warna reservoirs.
It is surmised that the local stress buildup is caused by Quaternary uplifting which, over a period of time, gave rise to the development of several weak zones within the less dense and highly porous vesicular traps into which the Koyna and Warna reservoir waters seem to be percolating through interconnected fault zones. In such a situation, additional stress over and above the one already being generated by localized Quaternary uplifting is likely to be developed due to pore pressure. Slow accumulation of these cumulative stresses may have culminated in generating the recurring seismic activities in the Koyna and Warna region. We infer that the subsurface tectonic features activated with the impounding of water in the reservoirs may have been largely responsible for the recurring seismicity around the Koyna – Warna region.

Analytical computation of Aquifer Potentials in a three- layered Porous Medium
Mathew K. Jose and Rambhatla G. Sastry 1
National Institute of Hydrology, Jalvigyan Bhawan, Roorkee-247667, India
1 Department of Earth Sciences, IIT, Roorkee-247667, India

Layered aquifer systems are common. Seepage from surface water bodies can recharge a layered aquifer system depending upon the hydrogeological set up. In artificial recharge practices, which are on the rise all over the world, it is useful to have a prior understanding of the aquifer system. It may be helpful in planning sustainable watershed development projects in complex terrains. In this context, analytical solutions are presented for steady state hydraulic heads at any point within a three layered aquifer system. The analytical solutions are obtained with a point source of known strength, on the earth’s surface. The recharging due to the point source would result in the build-up of hydraulic potentials in the layers beneath. By considering the analogy between electrical flow and groundwater flow, the geoelectric principles have been suitably invoked in formulating the presented methodology. An algorithm has been designed to compute the hydraulic potentials. The mode requires only recharge rate of the source, (aquifer) grid dimensions, hydraulic parameters for layers and depth to the various layers. Several examples are provided to demonstrate the effectiveness of the analytical solutions. Performance of the analytical model compares well with that of a numerical model, MODFLOW. The algorithm presented is much faster and easy to execute.

Idealized simulation of a thunderstorm over
Kolkata using RAMS

Indian Institute of Tropical Meteorology, 
Dr.Homi Bhabha Road, Pashan Pune – 411 008

An idealized simulation of a thunderstorm is attempted using Regional Atmospheric Modeling System (RAMS). The storm was reported on 1200 UTC of 14 July 1998 over Kolkata station. The upper air sounding data collected over Kolkata station at 0600 UTC under GEWEX Asian Monsoon Experiment is perturbed with a warm bubble to trigger the convection. Subsequently the model is run for 12 hour in forecast mode with two horizontal resolutions namely 5 km and 1 km. Analyzing different forecast fields such as temperature, total cloud condensate, vertical velocity, rainfall, it is found that 5 km grid has produced a strong convection after one hour model run. However it could not generate the convection around 1200 UTC which is the time of actual report of the thunderstorm. On the contrary, the 1 km simulation showed formation of storm after one hour integration and also at 1100 UTC i. e. after five hour of integration. The time of simulated convection by 1 km grid at 1100 UTC is very close to that of actual report. As such this study indicates that cloud resolving grid length of 1 km has better simulated the thunderstorm compared to the 5 km grid resolution.

Ultraviolet Transmission through a few Edible Oils in the context of changing Solar Insolation
Sobhana Teressa, G.Mohan Kumar & S.Sampath
Atmospheric Sciences Division, Centre for Earth Science Studies, Akkulam Thiruvananathapuram - 695 031

Effects of solar ultraviolet (UV) radiation on the biosphere are well known. In an era of atmospheric ozone depletion, there is concern about the solar UV radiation affecting human health. Atmospheric ozone is not uniform over the globe. Less ozone over the tropics makes it receive more UV insolation than higher latitudes. People in the tropics are continuously exposed to high UV dosage, leading to skin reddening known as ‘erythema’. This UV insolation is called erythemal radiation. Its efficacy in inducing erythema is measured in terms of sun burning units, referred to Caucasian skin. UV action spectra of human skin are well documented, but studies on the response of tropical population are few. Skin of tropical population is well pigmented and is not Caucasian. Thus, studies on the effect of erythemal radiation on white skin do not apply to our population. Tropical population in south India is accustomed to using a few vegetable oils as applicant on their skin. This is a study carried out to ascertain qualitatively whether the medium of the applicant has any protection from the UV insolation. The UV transmission characteristics of edible oils were obtained using a dual beam UV -Visible spectrophotometer. UV transmission profiles of these oils smeared on quartz disks were taken. In UV-B (280-320 nm), coconut oil does not absorb much. But, neem-seed oil absorbs heavily in the lower wavelength and its absorption decreases to about 50% at 320 nm. Sesame oil, on an average, has absorption of about 45% in the UV-B. Applying these oils on the skin reduces the UV dose absorbed in the epidermal and subcutatious layers. Results of the study are presented and discussed. To evaluate the efficacy of these oils as UV screens, their Sun Protection Factors are to be estimated involving more quantitative studies.

Role of Heat, Moisture and Momentum Transport across the Air-sea Interface in the Off-shore Trough over the Eastern Arabian Sea during (IOP 22 July - 4 August) ARMEX - 2002.
G.R.Chinthalu, P.Seetaramayya, and S.G.Nagar
Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road,
Pashan, Pune - 411 008.

The day-to-day variability in the synoptic and sub-synoptic weather conditions is responsible for the development, intensification and dissipation of the offshore troughs. The evolutionary processes have been examined using recent surface meteorological data recorded onboard ORV Sagar Kanya, during an intensive observation period (IOP 22 July- 4 August) of ARMEX-2002. Indian daily weather summary (IDWS) have also been consulted. Bulk formulae have been used to compute surface fluxes. The parameter DQ (= difference between saturation specific humidity at sea surface temperature and specific humidity of air at 10m height) is used to assess the moist spells. It is observed that the marine atmosphere near the sea level over the eastern Arabian Sea has become dry (DQ>4 g.kg-1) due to the weakening of the offshore trough and tends to become moist (DQ<4 g.kg-1) due to the intensification of this offshore trough.

Investigation of upper ocean temperature in response to cyclonic circulations over tropical Indian Ocean using satellite winds
D.W.Ganer, A.A.Deo and P.S.Salvekar
Indian Institute of Tropical Meteorology, Dr.Homi Bhabha Road, Pashan, Pune - 411 008

In the present study a 2½-layer thermodynamic ocean model over the region 35°E -115°E, 30 °S - 25 °N is used to simulate the thermal structure during the passage of cyclonic circulations as revealed from daily SSM/I winds. The simulation of Sea Surface Temperature (SST) over the Tropical Indian Ocean with interannually varying daily SSM/I surface winds is in close agreement with observed SST. The daily surface wind data for the year 1994, 1995 and 1996 is examined for the cyclonic vortex during the period of all the cyclonic storms over tropical Indian Ocean. The wind speed however, is less as compared to the real storms. The simulated SST anomalies show cooling of sea surface of the order of 0.5 to 1 oC within a week after the cyclonic circulation has passed over that region. This magnitude of cooling is much smaller due to less wind speed as compared to the earlier model studies and observations reported for cyclone period. The model results for each case are discussed in detail.

Ambient noise levels in Major Cities in Kerala
S.Sampath, S.Murali Das and V.Sasi Kumar
Atmospheric Sciences Division, Centre for Earth Science Studies, Akkulam Trivandrum – 695 031

Acoustic noise beyond a level is harmful. The fact that a regulation to abate noise is in force should remove all doubts about the damaging aspect of noise pollution. The cities being the most polluted, the main thrust is towards estimating the level of pollution in the cities. Of all kinds of noise, traffic noise is known to contribute the maximum. Hence, as a first step towards assessment of noise pollution, measurement was taken up with emphasis on traffic noise. Measurements of noise levels were carried out in the three major cities in Kerala, viz. Thiruvananthapuram, Kochi and Kozhikode to assess noise pollution.
Two types of instruments with a calibration source were used for measurement. One Integrating Precision Sound Level Meter was used for measuring the equivalent continuous level (Leq) and the spectrum of sound. A second instrument, a Noise Dose Meter, was used for continuous monitoring. Both instruments were calibrated before each field session using a secondary standard. All measurements were A weighted.
Measurements of noise levels were carried out in the commercial zones of the three cities. The results indicate that the noise levels are higher than the limits prescribed by the Ministry of Environment & Forests, Government of India. The silence zones in the cities also showed higher levels. The measured sound level inside residential buildings at night during festival time exceeds the prescribed limit by 30 to 40 dB. Announcements from vehicles fitted with public address systems can cause sound levels above 100 dB A at distances of 10 to 15 metres.

Geomagnetic Storm Effects at Equatorial Electrojet Stations
R.G Rastogi1,3, K.Yumoto2, M.E. James3 and K.Kitamura2
1Physical Research Laboratory, Ahmedabad –380 009
2Dept. of Earth and Planetary Sciences, Kyushu University, Hakozaki, Japan
3Physics Dept., Gujarat University, Ahmedabad - 380 009

The studies of the geomagnetic H and D data from the Kyushu University network of stations has confirmed the suggestions made by Rastogi et al (2001) that during the magnetic storms, the deviations of horizontal field (H) and the eastward field (Y) are related by DY/DH = sin (Y-D), where Y is the dipole declination and D is the ground (dip) declination at the station.

Active Seismics – A Comparative Study
P.R.Reddy, G.Kesava Rao, L.Behera, ASSSRS.Prasad and V.Sridher
National Geophysical Research Institute, Uppal Road, Hyderabad – 500007, India


Seismics is the best geophysical technique not only to image shallow structures associated with different sedimentary basins located on the continent and off shore (for oil exploration) but also for imaging of shallower and deeper structures of geodynamic importance.

Basement characteristics of Papaghni Basin of Eastern Dharwar Craton (Inida) - An inference from Aeromagnetic study

R.K.Kishore and Ch.Rama Rao
National Geophysical Research Institute,Hyderabad-500 007, India.

Analysis of the aeromagnetic map of a part of granite-green stone terrain west of the Precambrian Cuddapah Basin (2000-600Ma) has been made to delineate possible lithological variations with in the basement of the oldest Papaghni sub-basin. Three magnetically different zones with in the basement have been inferred where each zone is separated by deep fault/contact. The northern part of the basement (A) is of more felsic nature compared to the middle part (B) which is occupied by older metamorphics. The southern part (C) of the basement is severely affected by mafic intrusions. Analysis of magnetic Profiles yielded a total thickness of 1300mts for the Papaghni rocks and 5.3km for the entire suite of Papaghni & Chitravati group of rocks which is in aggrement with the earlier studies.
Key words: Aeromagnetics, basement characteristics,granite-green stones, Fault/Contact

Ionospheric Time Delay Estimation using IDW Grid Model for GAGAN

Niranjan Prasad1 and A.D. Sarma
R & T Unit for Navigational Electronics, Osmania University, Hyderabad – 500 007
1Defence Electronics Research Laboratory, Hyderabad - 500 005

To facilitate the accuracy required for Category-1 (CAT-1) precision approach landing of aircrafts, augmentation of GPS is planned through regional SBAS called ‘GAGAN’ by Indian Space Research Organization (ISRO) and Airport Authority of India (AAI). In GAGAN, ionospheric time delay is one of the predominant errors that limit the range accuracy of the user. Even though several analytic function based models are available for ionospheric error corrections, grid based models are preferred due to their greater accuracy and less complexity. The accuracy of modeled vertical ionospheric delays at the IGPs, user’s IPPs and GIVE are the functions of IPP density, grid size, input data and measurement update rates. The ionospheric vertical delays and error bound GIVE estimated using Inverse Distance Weighted with Klobuchar model is presented in this paper. The results are encouraging and this model is a good contender for implementation in GAGAN System.