• SUSHIL KUMAR

      Articles written in Journal of Earth System Science

    • Some results of night-time scintillations at low latitude

      Sushil Kumar S K Vijay A K Gwal

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      Ionospheric scintillation observations of VHF radio signals from FLEETSAT satellite (73°E longitude) at Bhopal from January 1990 to December 1990 have been used to study the characteristic variations of scintillation activity. It is found that scintillation occurrence is essentially a night-time phenomenon and day-time scintillations are very rare. Annual average nocturnal variation of percentage occurrence of scintillations shows maximum at around 2100–2200 hours LT. Seasonally, scintillations are most prominent during equinoxes and least during summer. Geomagnetic disturbances tend to decrease the occurrence of scintillations in the pre-midnight period.

    • Characterization of shear wave attenuation and site eAects in the Garhwal Himalaya, India from inversion of strong motion records

      PARVEEN KUMAR MONIKA SANDEEP SUSHIL KUMAR RICHA KUMARI DINESH KUMAR NARENDRA KUMAR

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      The frequency-dependent shear-wave quality factor (Q_\beta(f )) and site amplification are computed for the seismically and tectonically active Garhwal Himalaya. The inversion technique of strong motion data is applied to obtain Q_\beta(f ) and site effect at each recording station. The strong motion data of 82 earthquakes recorded in the Garhwal region is used for the present inversion algorithm. The comparison of site effects obtained by the present inversion scheme and well developed H/V technique (H/V is the ratio of Fourier spectra horizontal to vertical components) shows that site effects computed through the inversion technique have close resemblance with these estimates from the H/V technique. Both horizontal components are used to establish the frequency-dependent Q_\beta(f ) relations at each station. The values of ‘Q_o’ and ‘n’ at different stations vary from 92 to 112 and 0.9 to 1.1, respectively. The close resemblance of obtained Q_\beta(f ) relations at different stations suggest, the presence of almost similar type of lithology, i.e., hard rock at these stations. A regional quality factor relationship of form, Q_\beta(f ) = (102 ± 3.9)f^(1.0±0.1) is established for the Garhwal Himalaya based on modelled Q_\beta values of each station. This relationship reveals low Q_o value (${\le}$200) and high n value (${\ge}$0.8) for the Garhwal Himalaya, which correspond to tectonically and seismically active region.

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