• Volume 92, Issue 3

      November 1983,   pages  217-310

    • Characteristics of Pi2 pulsations at an equatorial station and its occurrence association with the phase of the Moon

      Neeta H Majmudar D R K Rao

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      Diurnal variations of occurrence hours and the period of Pi2 pulsations at Choutuppal (India) for nearly half a solar cycle are presented. Maximum occurrence is noticed to be around local midnight in all the seasons. Shorter periods are observed in the late afternoon hours in E-and J-seasons. Lunar influence on the occurrence of Pi2 pulsations at this station is inferred with the occurrence due to this influence peaking in the vicinity of the lunar phase4.

    • Estimation of the waiting time distributions of earthquakes

      S M J R Goel S K Malasi P S Moharir H R Wason K N Khattri V K Gaur

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      Whether the earthquake occurrences follow a Poisson process model is a widely debated issue. The Poisson process model has great conceptual appeal and those who rejected it under pressure of empirical evidence have tried to restore it by trying to identify main events and suppressing foreshocks and aftershocks. The approach here is to estimate the density functions for the waiting times of the future earthquakes. For this purpose, the notion of Gram-Charlier series which is a standard method for the estimation of density functions has been extended based on the orthogonality properties of certain polynomials such as Laguerre and Legendre. It is argued that it is best to estimate density functions in the context of a particular null hypothesis. Using the results of estimation a simple test has been designed to establish that earthquakes do not occur as independent events, thus violating one of the postulates of a Poisson process model. Both methodological and utilitarian aspects are dealt with.

    • Daily variation of the geomagnetic field near the focus of Sq-current system in Indian longitude

      Asha Patil B R Arora R G Rastogi

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      The paper presents the first results on the behaviour of solar quiet-day variations of the geomagnetic field components at Gulmarg. Combining the data from Russian stations in the same longitude belt, the annual average daily variations are calculated which show, in the horizontal component (H), a reversal of phase between Gulmarg and Tashkent. Studying the Sq-variations at Gulmarg separately for the three seasons, the daily variation of H duringd-months is predominantly diurnal in character with the maximum before noon. Duringe-months, and more so inj-months, daily variation of the H field is predominantly semidiurnal in character with minimum around 08–09 hr LT and maximum around 14 hr LT consistently during 1978, 1979 and 1980. These features of the Sq at Gulmarg are suggested to be due to the deformations of the current loops caused by the changing latitude of focus during the course of the day.

    • Low latitude airglow

      P V Kulkarni

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      Tropical airglow work during the last few years is reviewed. Airglow instrumentation is becoming more complex. Some of these sophisticated airglow experiments giving important information about the upper atmosphere such as ionospheric F region electron density, height of maximum electron density, dynamics of and irregularities in the F region, mesospheric neutral temperature and its variation, dynamics of mesospheric, etc. are mentioned. At the end some problems which could be tackled in near future with airglow techniques have been suggested.

    • Ice accumulation rate in Changme-Khangpu glacier, Sikkim

      P N Shukla N Bhandari V N Nijampurkar D Kameswara Rao V M K Puri Sanjiv Sharma

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      Vertical profiles of137Cs and210Pb have been determined in a 9 m column of ice from accumulation zone of Changme-Khangpu glacier in north Sikkim valley.137Cs activity varies from 4 to 22 dpm/ L. In many samples210Pb occurs at a level of 20 to 65 dpm/ L which is much higher than the expected fallout value.137Cs and210Pb activities correlate well with each other but not with the dust content. Possibility of210Pb production in the nuclear explosions is discussed. Several peaks appear in the depth profile of137Cs and210Pb which can be matched with Chinese atmospheric nuclear explosions with some phase difference if a uniform ice accumulation rate of 0.7 m per year is assumed since 1969.

    • Hypotheses for earthquake occurrences

      Naveen P S Moharir V K Gaur

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      Very little work has been done in generating alternatives to the Poisson process model. The work reported here deals with alternatives to the Poisson process model for the earthquakes and checks them using empirical data and the statistical hypothesis testing apparatus. The strategy used here for generating hypotheses is to compound the Poisson process. The parameter of the Poisson process is replaced by a random variable having prescribed density function. The density functions used are gamma, chi and extended (gamma/chi). The original distribution is then averaged out with respect to these density functions. For the compound Poisson processes the waiting time distributions for the future events are derived. As the parameters for the various statistical models for earthquake occurrences are not known, the problem is basically of composite hypothesis testing. One way of designing a test is to estimate these parameters and use them as true values. Momentmatching is used here to estimate the parameters. The results of hypothesis testing using data from Hindukush and North East India are presented.

    • Electron microscopy of olivine with perfect cleavage

      T R N Kutty G N Subbanna G V Anantha Iyer

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      Electron microscopy (SEM and TEM) of unusual olivine (Fo = 88) crystals, with perfect (010) cleavages, from Chalk Hills, Salem, Tamil Nadu has been carried out. SEM studies reveal the effect of compressive stress. Microstructures by TEM showed the abundance of curved dislocations with jogs, kinks and dipoles, indicative of the dominant climb, characteristic of high temperature deformation. The stacking fault fringes observed in olivine are due to mechanical weakening caused by nonstructural chemical constituents. The evidences for this come from fiuid-microinclusions observed and higher amount of K, Na, Rb and Sr in the olivine. Hydrolytic weakening through dislocation glide motion, assisted by H2O containing incompatible elements, may break the metal-oxygen bonds. This leads to perfect parting of crystallographic planes under deformational stress, during solid emplacement of the dunite. The easily cleavable planes are those with the largest interplanar spacings.

    • Granite-molybdenite association in Kerala in relation to taphrogenic metallogeny

      M Santosh N G K Nair

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      Two molybdenite-bearing granites from the Kerala region, namely, the Chengannoor and the Ambalavayal granites are discussed here in terms of their salient geochemical characters. The geochemistry of the host rocks indicates a peraluminous, calc-alkaline to alkali-calcic nature and the element levels show good fit with the proposed ‘finger-prints’ for granite-molybdenite systems. Fluid inclusion studies suggest that Mo was probably partitioned in vapour phase, which subsequently combined with available sulphur. Regional distribution of molybdenite strongly favours the view of a molybdenum province in the southern part of the Indian shield. Associations of rare metal mineralization with the riftcontrolled acid magmatic phase in the Kerala region are suggestive of a late Precambrian —Early Palaeozoic taphrogenic metallogeny.

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