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81.
Ram Bichar Singh Yadav Jayant Nath Tripathi Bal Krishna Rastogi Mridul Chandra Das Sumer Chopra 《Pure and Applied Geophysics》2010,167(11):1331-1342
Northeast India and adjoining regions (20°–32° N and 87°–100° E) are highly vulnerable to earthquake hazard in the Indian
sub-continent, which fall under seismic zones V, IV and III in the seismic zoning map of India with magnitudes M exceeding 8, 7 and 6, respectively. It has experienced two devastating earthquakes, namely, the Shillong Plateau earthquake
of June 12, 1897 (M
w
8.1) and the Assam earthquake of August 15, 1950 (M
w
8.5) that caused huge loss of lives and property in the Indian sub-continent. In the present study, the probabilities of
the occurrences of earthquakes with magnitude M ≥ 7.0 during a specified interval of time has been estimated on the basis of three probabilistic models, namely, Weibull,
Gamma and Lognormal, with the help of the earthquake catalogue spanning the period 1846 to 1995. The method of maximum likelihood
has been used to estimate the earthquake hazard parameters. The logarithmic probability of likelihood function (ln L) is estimated
and used to compare the suitability of models and it was found that the Gamma model fits best with the actual data. The sample
mean interval of occurrence of such earthquakes is estimated as 7.82 years in the northeast India region and the expected
mean values for Weibull, Gamma and Lognormal distributions are estimated as 7.837, 7.820 and 8.269 years, respectively. The
estimated cumulative probability for an earthquake M ≥ 7.0 reaches 0.8 after about 15–16 (2010–2011) years and 0.9 after about 18–20 (2013–2015) years from the occurrence of
the last earthquake (1995) in the region. The estimated conditional probability also reaches 0.8 to 0.9 after about 13–17
(2008–2012) years in the considered region for an earthquake M ≥ 7.0 when the elapsed time is zero years. However, the conditional probability reaches 0.8 to 0.9 after about 9–13 (2018–2022)
years for earthquake M ≥ 7.0 when the elapsed time is 14 years (i.e. 2009). 相似文献
82.
83.
An analytical study has been performed to examine the characteristics of two-dimensional steady-state advective-diffusive transport of air pollutants emitted from ground-based area sources. The solutions for the concentration of air pollutants are obtained by Integral and Variational Imbedding methods taking chemical reaction process into account. A comparative study of concentration is displayed graphically, followed by a quantitative discussion. 相似文献
84.
We report observations of the dwarf star ε Eri (K2 V) made with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope . The high sensitivity of the STIS instrument has allowed us to detect the magnetic dipole transitions of Fe xii at 1242.00 and 1349.38 Å for the first time in a star other than the Sun. The width of the stronger line at 1242.00 Å has also been measured; such measurements are not possible for the permitted lines of Fe xii in the extreme-ultraviolet. To within the accuracy of the measurements, the N v and the Fe xii lines occur at their rest wavelengths. Electron densities and linewidths have been measured from other transition region lines. Together, these can be used to investigate the non-thermal energy flux in the lower and upper transition regions, which is useful in constraining possible heating processes. The Fe xii lines are also present in archival STIS spectra of other G/K-type dwarfs. 相似文献
85.
Onkar Nath 《Astrophysics and Space Science》1988,146(1):175-182
The self-similar model of propagation of spherical strong shock waves into non-uniform stellar atmosphere under self-gravitation and non-uniform magnetic field is investigated. The disturbances are headed by a shock surface of variable strength. Gas is assumed to be grey and opaque and the shock tobe transparent. 相似文献
86.
Rabindra Nath Das 《Astrophysics and Space Science》1979,60(1):221-232
We have considered six scalar equations which are obtained from the vector transport equation for radiative transfer to the problem of diffuse reflection and transmission in finite plane-parallel Rayleigh scattering atmosphere. By use of the Laplace transform and the theory of linear singular operators these equations have been solved exactly to get the angular distribution of the intensity diffusely reflected from the surface and diffusely transmitted below the surface. 相似文献
87.
The oscillatory nature of wave-particle interaction is proposed to be the source of non-local fluctuations in the electron energy. The energized electron flux when precipitated in the lower ionosphere gives rise to various geophysical phenomena. The time scale of energy oscillation is estimated and its validity is discussed with reference to observed time scales of various geophysical phenomena. 相似文献
88.
Sankar Kumar Nath Kiran Kumar Singh Thingbaijam Abhishek Raj 《Journal of Earth System Science》2008,117(2):809-831
A comprehensive analytical as well as numerical treatment of seismological, geological, geomorphological and geotechnical concepts has been implemented through microzonation projects in the northeast Indian provinces of Sikkim Himalaya and Guwahati city, representing cases of contrasting geological backgrounds — a hilly terrain and a predominantly alluvial basin respectively. The estimated maximum earthquakes in the underlying seismic source zones, demarcated in the broad northeast Indian region, implicates scenario earthquakes of M W 8.3 and 8.7 to the respective study regions for deterministic seismic hazard assessments. The microzonation approach as undertaken in the present analyses involves multi-criteria seismic hazard evaluation through thematic integration of contributing factors. The geomorphological themes for Sikkim Himalaya include surface geology, soil cover, slope, rock outcrop and landslide integrated to achieve geological hazard distribution. Seismological themes, namely surface consistent peak ground acceleration and predominant frequency were, thereafter, overlaid on and added with the geological hazard distribution to obtain the seismic hazard microzonation map of the Sikkim Himalaya. On the other hand, the microzonation study of Guwahati city accounts for eight themes — geological and geomorphological, basement or bedrock, landuse, landslide, factor of safety for soil stability, shear wave velocity, predominant frequency, and surface consistent peak ground acceleration. The five broad qualitative hazard classifications — ‘low’, ‘moderate’, ‘high’, ‘moderate high’ and ‘very high’ could be applied in both the cases, albeit with different implications to peak ground acceleration variations. These developed hazard maps offer better representation of the local specific seismic hazard variation in the terrain. 相似文献
89.
Indrajit Pal Sankar Kumar Nath Khemraj Shukla Dilip Kumar Pal Abhishek Raj K. K. S. Thingbaijam B. K. Bansal 《Natural Hazards》2008,45(3):333-377
An earthquake hazard zonation map of Sikkim Himalaya is prepared using eight thematic layers namely Geology (GE), Soil Site
Class (SO), Slope (SL), Landslide (LS), Rock Outcrop (RO), Frequency–Wavenumber (F–K) simulated Peak Ground Acceleration (PGA),
Predominant Frequency (PF), and Site Response (SR) at predominant frequencies using Geographic Information System (GIS). This
necessitates a large scale seismicity analysis for seismic source zone classification and estimation of maximum earthquake
magnitude or maximum credible earthquake to be used as a scenario earthquake for a deterministic or quasi-probabilistic seismic
scenario generation. The International Seismological Center (ISC) and Global Centroid Moment Tensor (GCMT) catalogues have
been used in the present analysis. Combining b-value, fractal correlation dimension (Dc) of the epicenters and the underlying tectonic framework, four seismic source zones
are classified in the northeast Indian region. Maximum Earthquake of M
W 8.3 is estimated for the Eastern Himalayan Zone (EHZ) and is used to generate the seismic scenario of the region. The Geohazard
map is obtained through the integration of the geological and geomorphological themes namely GE, SO, SL, LS, and RO following
a pair-wise comparison in an Analytical Hierarchy Process (AHP). Detail analysis of SR at all the recording stations by receiver
function technique is performed using 80 significant events recorded by the Sikkim Strong Motion Array (SSMA). The ground
motion synthesis is performed using F–K integration and the corresponding PGA has been estimated using random vibration theory
(RVT). Testing for earthquakes of magnitude greater than M
W 5, a few cases presented here, establishes the efficacy and robustness of the F–K simulation algorithm. The geohazard coverage
is overlaid and sequentially integrated with PGA, PF, and SR vector layers, in order to evolve the ultimate earthquake hazard
microzonation coverage of the territory. Earthquake Hazard Index (EHI) quantitatively classifies the terrain into six hazard
levels, while five classes could be identified following the Bureau of Indian Standards (BIS) PGA nomenclature for the seismic
zonation of India. EHI is found to vary between 0.15 to 0.83 quantitatively classifying the terrain into six hazard levels
as “Low” corresponding to BIS Zone II, “Moderate” corresponding to BIS Zone III, “Moderately High” belonging to BIS Zone IV,
“High” corresponding to BIS Zone V(A), “Very High” and “Severe” with new BIS zones to Zone V(B) and V(C) respectively. 相似文献
90.