On the seismic structure of Indian upper-mantle regions     

Avadh Ram  Om Prakash Singh 《Journal of Earth System Science》1982,91(1):1-13

Several velocity models on upper mantle regions of the world have been postulated during the last two decades. There has been a broad agreement amongst seismologists that upper mantle has got two transition zones, though the models differ in detail. These zones have been found to occur around ‘400 km’ and ‘650 km’ depth ranges with varying thicknesses of the zones. A limited number of such studies have been made on the upper mantle structure of the Indian subcontinent. High positive velocity gradients were reported to exist around the above depth range. Evidence for lateral heterogeneities has also been found. We address some problems like refinement of Indian upper mantle velocity models specially after considering the effect of scattering and attenuation on the short periodP-waves. The study of proper positioning of the cusps of the travel-time branches and their extension is essential as well. In our opinion, analysis of such problems would help in the better understanding of the nature of propagation of seismic waves and mechanism of earthquakes. Complexity of seismic signatures observed is another major problem and may also be taken into consideration.  相似文献   

Equatorial night-time F-region zonal electric fields     

S. S. Hari  B. V. Krishna Murthy 《Annales Geophysicae》1995,13(8):871-878

Night-time F-region vertical electrodynamic drifts at the magnetic equatorial station, Trivandrum are obtained for a period of 2 years, 1989 and 1990 (corresponding to solar cycle maximum epoch), using ionosonde h^‘F data. The seasonal variation of the vertical drift is found to be associated with the longitudinal gradients of the thermospheric zonal wind. Further, the seasonal variation of the prereversal enhancement of the vertical drift is associated with the time difference between the sunset times of the conjugate E-regions (magnetic field line linked to F-region) which is indicative of the longitudinal gradients of the conductivity (of the E-region). The vertical drifts and the causative zonal electric fields at Trivandrum are compared with those at Jicamarca and F-region zonal electric field models. It is seen that the night-time downward drift (as also the causative westward electric field) at Jicamarca is greater than that at Trivandrum. The prereversal enhancement of the drift is greater at Jicamarca than at Trivandrum during the summer and the equinoxes, whereas during the winter the opposite is the case.  相似文献   

Study of P-wave velocities and attenuation coefficients of Gondwana rocks from Chanda-Wardha valley coalfield, Maharashtra, India   总被引：1，自引：0，他引：1  

Ranjit Kumar Sarkar  Om Prakash Singh 《Acta Geophysica》2006,54(3):250-259

This paper describes the findings of the study pertaining to the laboratory measurements of longitudinal wave velocities and attenuation coefficients of various Gondwana rocks of Chikhalgaon, Saoner and Agarjhari areas of Chanda-Wardha valley coalfield. It is found that Barakar sandstones, in general, have higher longitudinal wave velocities than Barakar and Talchir shales and Kamthi sandstones. Of the Barakar sandstones, the fine grained feldspathised variety has the maximum velocity. Attenuation coefficients of coarse-grained rocks are higher than those of fine grained ones. Black carbonaceous shales of Barakar are characterised by moderately high longitudinal wave velocities and attenuation coefficients. Coals are characterized by low longitudinal wave velocities and high attenuation coefficients. Longitudinal wave velocities of the rocks along the bedding plane are always higher than those perpendicular to the bedding plane.  相似文献   

Global volcanism, biological mass extinctions and the galactic vertical motion of the solar system     

Om Prakash Pandey  Janardan G. Negi 《Geophysical Journal International》1987,89(3):857-867

Summary. The recent findings of nearly matching long-term cyclicity in biological mass extinctions, geomagnetic reversals, impact cratering and other terrestrial processes have evoked a major controversy. We report here a compilation and analysis of major global magmatic episodes showing a significant enhancement of volcanic activity with a periodicity of 33 million years for the last 250 million years. These magmatic episodes match extremely well the best available astronomical estimates of the periodic (31 ± 5 Myr) galactic-disc crossing events during vertical motions of the solar system. These events also have a close linkage with the marine biological mass extinctions and other geological rhythms. It is argued that the prolonged volcanic activity, instead of impact cratering, may have been the more immediate primary cause for profound climatic and other environmental deterioration sufficient to create biological crises on a global scale. The volcanic periodicity scheme is well supported by the evidence of recent increases in volcanic activity. However, the alternative hypothesis of the death star 'Nemesis' can be rejected, since it does not explain the recent increase in volcanism and impact cratering during the last 4 ± 3 Myr in view of its quieter apehelion position lying beyond the Oort cloud of comets.  相似文献   

Extreme water levels along the central Red Sea coast of Saudi Arabia: processes and frequency analysis     

Antony  Charls  Langodan  Sabique  Dasari  Hari Prasad  Knio  Omar  Hoteit  Ibrahim 《Natural Hazards》2021,105(2):1797-1814

Natural Hazards - Knowledge about extreme water levels is essential for efficient planning and design of coastal infrastructure. This study uses a high-resolution (~?60 m) coupled...  相似文献   

Multivariate statistical analysis for characterization of sedimentary facies of Tarakan sub-basin,North Kalimantan     

Septriono Hari Nugroho  Purna Sulastya Putra  Eko Yulianto  Dardji Noeradi 《Marine Georesources & Geotechnology》2018,36(8):907-917

A study of sediment dynamics has been conducted on the Tarakan sub-basin, North Kalimantan, Indonesia using multivariate analysis. Multivariate statistical techniques can be used to determine sediment with similar characteristics and be a good proxy to recognize sedimentary facies and depositional environment. These methods have been applied to characterize the sedimentary facies at Tarakan sub-basin. A total of 23 samples were taken from several locations on the different depths of 56–2554?m that represent varieties of environment. The study is interpreted using compositional data analysis associated with a grain size trend analysis (GSTA), principal component analysis (PCA), and cluster analysis (CA). The GSTA value showed the dominance of poorly sorted silt indicating that the sediment is mostly deposited in low-energy depositional. The CA and the PCA determined three distinct sedimentary facies: shelf facies, upper bathyal facies, and lower bathyal facies. The facies were grouped as similar sediment and depositional environment. Sedimentological variables applied in the characterization were described to be an important tool for the interpretation of depositional environments – indirectly showing hydrodynamic energy.  相似文献   

A possible detection of radio pulses from Geminga at 103 MHz     

Hari Om Vats  Ashok K. Singal  M. R. Deshpande  K. N. Iyer  Rupal Oza  Chhaya R. Shah  S. Doshi 《Monthly notices of the Royal Astronomical Society》1999,302(4):L65-L67

  相似文献   

Geo-effectiveness of CMEs     

Ajaysinh K. Jadeja  K. N. Iyer  Hari Om Vats  P. K. Manoharan 《Journal of Astrophysics and Astronomy》2008,29(1-2):287-291

Coronal Mass Ejections (CMEs) are important phenomena in coronal dynamics causing interplanetary signatures (ICMEs). They eject large amounts of mass and magnetic fields into the heliosphere, causing major geomagnetic storms and interplanetary shocks. Geomagnetic storms are often characterized by abrupt increases in the northward component of the earth’s field, called sudden commencements (SSC) followed by large decreases of the magnetic field and slow recovery to normal values. The SSCs are well correlated with IP shocks. Here a case study of 10–15 February 2000 and also the statistical study of CME events observed by IPS array, Rajkot, during the years 2000 to 2003 and Radio Astronomy Center, Ooty are described. The geomagnetic storm index Dst, which is a measure of geo-effectiveness, is shown to be well correlated with normalized scintillation index ‘g’, derived from Ooty Radio Telescope (ORT) observations.  相似文献   

Assessments of Potential Spatial‐temporal Variations in Phosphorus Distribution and Fractionation in River Bed Sediments     

Jingyu Wang  Hari K. Pant 《洁净——土壤、空气、水》2011,39(2):148-156

Sediment characteristics influence the distribution and bioavailability of phosphorus (P) in river sediments. In this study, we analyzed different P fractions in the sediments of the Bronx River, New York City, NY, using sequential extraction. The results showed that the average P pool rank order was HCl?P > NaOH?P > NaHCO₃?P > residue?P, and their relative proportions were 3.7: 2.0: 1.4: 1 in sediments collected in 2006, while HCl?P > NaOH?P > residue?P > NaHCO₃?P, with their relative proportions of 27.8:6.2:2.7:1 in the sediments obtained in 2007. The strong correlation between microbial P and organic P (OP), along with the changes in microbial P over time indicate that most of the OP in the river bed sediments is potentially bioavailable. The sediment transport, deposition, assimilation, the exchange of P between sediments and water columns, the land use changes, raw sewer discharge, gas spill, construction, fertilizer application, etc., as well as the hydro‐climatic changes could result in the spatial and temporal variations in P bioavailability in the river bed sediments. The estimations of P pools and their bioavailability in river bed sediments could help determine the spatial and temporal variations in P transport and impacts of land use on water quality, in turn, help regulate P in the river's watershed.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987113000893   总被引：1，自引：0，他引：1  

K.R. Hari  N.V. Chalapathi Rao  Vikas Swarnkar  Guiting Hou 《地学前缘(英文版)》2014,5(2):261-276

Two petrologically distinct alkali feldspar syenite bodies （AFS-1 and AFS-2） from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidio-morphic texture and consists of feldspar （Or55Ab43 to Or25Ab71）, ferro-pargasite/ferro-pargasite horn-blende, hastingsite, pyroxene （Wo47, En5, Fs46）, magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene （Wo47-50, En22-39, Fs12e31） set in a groundmass matrix of alkali feldspar （Or99Ab0.77 to Or1.33Ab98）, titanite and magnetite. In comparison to AFS-1, higher elemental concentra-tions of Ba, Sr and PREE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is w1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.  相似文献