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21.
Saurabh Baruah Devajit Hazarika Naba K. Gogoi P. Solomon Raju 《Journal of Earth System Science》2007,116(1):37-47
Microearthquake spectra from Jubilee Hills, Hyderabad are analyzed to observe the effect of attenuation and site on these
spectra. The ratios of spectral amplitudes at lower and higher frequency are measured for three different stations at varying
epicentral distances to estimate Q value for both P-and S-wave in near and sub-surface layer. Average estimates of Qp and
Qs are 235 and 278 respectively. Value of Qs/Qp larger than 1.0 suggests dry crust for most of the Jubilee Hills region. The
near-surface low Qp and Qs for 0 km to 0.9 km depth coincide with the soil layer, top and semi-weathered and highly fractured
zone. In contrast, at a shallower depth beneath the Jubilee Hills area, Hyderabad, we obtain high Qp and Qs zone, which corresponds
to the dense and high velocity rocks of the region. The varying corner frequencies for these spectra are inferred to be characteristics
of site. Comparisons of disparity in spectral content with reference to hard rock site conclude that lithology of the northwest
part of Jubilee Hills area amplify about twice the incoming seismic signal, as compared to the southern part best outlined
at 8 to 10 Hz only. 相似文献
22.
Attenuation of coda waves in the Northeastern Region of India 总被引：1，自引：0，他引：1
Coda wave attenuation quality factor Qc is estimated in the northeastern region of India using 45 local earthquakes recorded
by regional seismic network. The quality factor Qc was estimated using the single backscattering model modified by Sato (J
Phys Earth 25:27–41, 1977), in the frequency range 1–18 Hz. The attenuation and frequency dependence for different paths and the correlation of the
results with geotectonics of the region are described in this paper. A total of 3,890 Qc measurements covering 187 varying
paths are made for different lapse time window of 20, 30, 40, 50, 60, 70, 80, and 90 s in coda wave. The magnitudes of the
analyzed events range from 1.2 to 3.9 and focal depths range between 7 and 38 km. The source–receiver distances of the selected
events range between 16 and 270 km. For 30-s duration, the mean values of the estimated Qc vary from 50 ± 12 (at 1 Hz) to
2,078 ± 211(at 18 Hz) for the Arunachal Himalaya, 49 ± 14 (at 1 Hz) to 2,466 ± 197 (at 18 Hz) for the Indo-Burman, and 45
± 13 (at 1 Hz) to 2,069 ± 198 (at 18 Hz) for Shillong group of earthquakes. It is observed that Qc increases with frequency
portraying an average attenuation relation for the region. Moreover, the pattern of Qc − 1 with frequency is analogous to the estimates obtained in other tectonic areas in the world, except with the observation that
the Qc − 1 is much higher at 1 Hz for the northeastern region. The Qc − 1 is about 10 − 1.8 at 1 Hz and decreases to about 10 − 3.6 at 18 Hz indicating clear frequency dependence. Pertaining to the spatial distribution of Qc values, Mikir Hills and western
part of Shillong Plateau are characterized by lower attenuation. 相似文献
23.
Kumar Naresh Kumar Parveen Chauhan Vishal Hazarika Devajit 《International Journal of Earth Sciences》2017,106(7):2371-2386
International Journal of Earth Sciences - Strong-motion records of recent Gorkha Nepal earthquake (M w 7.8), its strong aftershocks and seismic events of Hindu kush region have been analysed for... 相似文献
24.
Devajit Hazarika Dilip Kumar Yadav V. Sriram Abhishek Rai 《International Journal of Earth Sciences》2013,102(7):2061-2076
Teleseismic earthquake data recorded by 11 broadband digital seismic stations deployed in the India–Asia collision zone in the eastern extremity of the Himalayan orogen (Tidding Suture) are analyzed to investigate the seismic anisotropy in the upper mantle. Shear-wave splitting parameters (Φ and δt) derived from the analysis of core-refracted SKS phases provide first hand information about seismic anisotropy and deformation in the upper mantle beneath the region. The analysis shows considerable strength of anisotropy (delay time ~0.85–1.9 s) with average ENE–WSW-oriented fast polarization direction (FPD) at most of the stations. The FPD observed at stations close to the Tidding Suture aligns parallel to the strike of local geological faults and orthogonal to absolute plate motion direction of the Indian plate. The average trend of FPD at each station indicates that the anisotropy is primarily originated by lithospheric deformation due to India–Asia collision. The splitting data analyzed at closely spaced stations suggest a shallow source of anisotropy originated in the crust and upper mantle. The observed delay times indicate that the primary source of anisotropy is located in the upper mantle. The shear-wave splitting analysis in the Eastern Himalayan syntaxis (EHS) and surrounding regions suggests complex strain partitioning in the mantle which is accountable for evolution of the EHS and complicated syntaxial tectonics. 相似文献
25.
Two pes imprints of a perissodactyl mammal constituting a single step of a trackway have recently been discovered in Oligocene Flysch deposits of the Barail Group in Manipur, India. The tridactyl, mesaxonic imprints (~7 cm in length) show strong similarities to footprints known from the Paleogene of China and can be attributed to a tapiroid, rhinocerotoid or equoid trackmaker. This is the first record of perissodactyl footprints from the Lower Oligocene of India and the first evidence of mammals in the Barail Group of the age. Remarkable is the occurrence in a marginal marine setting, whereas other known perissodactyl footprints from the Eocene–Oligocene in particular from North America, Europe and China come from fluvio-lacustrine strata. 相似文献