Effect of Corrugation and Reinforcement on the Dispersion of SH-wave Propagation in Corrugated Poroelastic Layer Lying over a Fibre-reinforced Half-space   总被引：1，自引：1，他引：0  

Abhishek Kumar Singh  Amrita Das  Anirban Lakshman  Amares Chattopadhyay 《Acta Geophysica》2016,64(5):1340-1369

The presence of porosity and reinforcement in a medium is an important factor affecting seismic wave propagation and plays vital role in many geophysical prospects. Also, the presence of salt and ore deposits, mountains, basins, mountain roots, etc. is responsible for the existence of corrugated boundary surfaces of constituent layers. Such facts brought motivation for the present paper which deals with the propagation of SH-wave in a heterogeneous fluid-saturated poroelastic layer with corrugated boundaries lying over an initially stressed fibre-reinforced elastic halfspace. Closed form of dispersion relation has been obtained and is found in well agreement to classical Love wave equation for isotropic case. The effect of corrugation, wave number, undulation, position parameter, horizontal compressive/tensile initial stress and heterogeneity on phase velocity has been analysed through numerical computation and graphical illustration. Moreover, comparative study exploring the effect of presence and absence of reinforcement in half-space on dispersion curve is the major highlight of the current study.  相似文献   

Lithosphere of the Dharwar craton by joint inversion of P and S receiver functions   总被引：1，自引：0，他引：1  

S. Kiselev  L. Vinnik  S. Oreshin  S. Gupta  S. S. Rai  A. Singh  M. R. Kumar  G. Mohan 《Geophysical Journal International》2008,173(3):1106-1118

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A Comparison of Sea Surface Fluxes over Southern Indian Ocean Cruise Expedition Observation and NCEP Reanalysis     

Avinash C. Pandey  Shailendra Rai  Amitabh Mitra 《Marine Geodesy》2013,36(1):82-92

Surface layer atmospheric and ocean observations have been collected along the cruise track from a special scientific expedition to Antarctica. Bulk estimates of surface momentum flux, sensible heat flux and latent heat flux have been computed applying bulk algorithms from the data collected along cruise track during the time period January 27 to March 31, 2006, and compared the results with National Centre for Environmental Prediction (NCEP) reanalysis. Underestimation of surface momentum flux in roaring forties (40°S–50°S) area of Indian Ocean is seen from NCEP reanalysis. Systemic differences in sensible and latent heat fluxes between observed and NCEP reanalysis have been found. Along the cruise track, the average sensible (latent) heat flux was 9.45 Wm^?2 (67.46 Wm^?2) and 3.75 Wm^?2 (64.45 Wm^?2) from the direct measurement and NCEP reanalysis, respectively. The NCEP reanalysis is being widely used in numerical modeling studies, and the discrepancies shown in the NCEP reanalysis in present study will be of immense use to the modeling community of the Indian Ocean in general and Southern Indian Ocean in particular.  相似文献   

On the tidally driven circulation in the South China Sea: modeling and analysis     

Varjola Nelko  Abhishek Saha  Vivien P. Chua 《Ocean Dynamics》2014,64(3):413-428

The South China Sea is a large marginal sea surrounded by land masses and island chains, and characterized by complex bathymetry and irregular coastlines. An unstructured-grid SUNTANS model is employed to perform depth-averaged simulations of the circulation in the South China Sea. The model is tidally forced at the open ocean boundaries using the eight main tidal constituents as derived from the OSU Tidal Prediction Software. The model simulations are performed for the year 2005 using a time step of 60 s. The model reproduces the spring-neap and diurnal and semidiurnal variability in the observed data. Skill assessment of the model is performed by comparing model-predicted surface elevations with observations. For stations located in the central region of the South China Sea, the root mean squared errors (RMSE) are less than 10 % and the Pearson’s correlation coefficient (r) is as high as 0.9. The simulations show that the quality of the model prediction is dependent on the horizontal grid resolution, coastline accuracy, and boundary locations. The maximum RMSE errors and minimum correlation coefficients occur at Kaohsiung (located in northern South China Sea off Taiwan coast) and Tioman (located in southern South China Sea off Malaysia coast). This may be explained with spectral analysis of sea level residuals and winds, which reveal dynamics at Kaohsiung and Tioman are strongly influenced by the seasonal monsoon winds. Our model demonstrates the importance of tidally driven circulation in the central region of the South China Sea.  相似文献   

脉冲星射电轮廓中高斯成分在主脉冲和中间脉冲的不同分布          下载免费PDF全文

韩晓红  YUEN Rai 《天文学报》2022,63(3):29-57

研究了高斯辐射成分在可视点所画出轨迹上的分布,这个可视点因脉冲星的转动而作非匀速度运动.通过假设辐射区域围绕磁轴均匀分布,一个高斯辐射成分便对应于可视轨迹划过的一个辐射区域.因为演示辐射区域在可视轨迹上是不均匀的分布,因此高斯成分沿轨迹也是不均匀的,而高斯成分的密度在磁轴与视线距离最近时为最大.高斯成分的分布取决于脉冲星的两个角度:旋转轴和视线之间的夹角,以及磁轴和旋转轴之间的倾角.基于此模型,一个脉冲星平均轮廓中观察到的多个高斯成分便对应于可视轨迹在特定的转动相位范围内的辐射区域.演示了脉冲星旋转的近侧和远侧的相位,分别对应的主脉冲和中间脉冲,两者高斯成分的数量和分布是不同的.而且还发现,沿可视轨迹上的辐射区域总数与围绕磁轴的辐射区域的总数是不同,并且预测的辐射区域数目会因忽略可见点的运动而明显不同.拟合表明脉冲星轮廓的高斯成分的形状和数量可能与实际构成轮廓的成分的形状和数量不同.以PSR B0826–34的辐射为例,并假设辐射来自单一磁极.  相似文献   

Geochemical studies of granitoids from Shyok tectonic zone of Khardung-Panamik section,Ladakh, India     

D. Rameshwar Rao  Hakim Rai 《Journal of the Geological Society of India》2009,73(4):553-566

The Shyok tectonic zone lies to the north of Ladakh magmatic arc or the Ladakh batholith in the Trans-Himalaya of Ladakh district, J & K. Investigations were carried out on the granitoids exposed along Leh-Siachan highway between Khardung and Panamik villages. The granitoid bodies under study are: Khardung granite (KG), Tirit granite (TG) and Panamik granite (PG) belonging to Ladakh batholith, Shyok ophiolitic mélange and Karakoram batholith respectively. Though the granitoids belong to different litho-tectonic units, yet they have subduction related geochemical characters typical of Andean-type granitoids. Re-melting of crustal rocks of volcanic arc affinity has played an important role for the origin of KG rocks which are more evolved, while the TG and PG rocks represent transitional tectonic environment from primitive to mature arc.  相似文献   

Framboidal — colloform — recrystallised pyrite in the granitoids of Wahkyn area,West Khasi hills,Meghalaya     

N. Ranganath  Ashok Kumar Padhi  Ajoy Kumar Padhi  Ashwini Kumar Rai 《Journal of the Geological Society of India》2009,74(5):591-596

Petrographic studies of Proterozoic pyriteferous granitoids forming basement for upper cretaceous Mahadek sediments from Wahkyn area reveal interesting textural peculiarities of Pyrite. These pyrites also reveal interesting structural peculiarities. The three textural pyrite varieties found in the granitoids are: framboidal, colloform and recrystallised which appear both as composite aggregate as well as independent units. Various textures and variation in reflectivity, microhardness and elemental distribution of the pyrites are described. Average Co/Ni ratio along with the textural manifestation of these pyrites attests their sedimentary origin.  相似文献   

Nonlinear soil response to ground motions during different earthquakes in Nepal,to arrive at surface response spectra     

Abhishek Kumar  N. H. Harinarayan  Olympa Baro 《Natural Hazards》2017,87(1):13-33

Catastrophic damages reported during an earthquake include building damages, excessive ground shaking, uneven settlements and liquefaction. While most of the seismic hazard studies map the probable level of ground shaking at the bedrock level, their use in assessing the above damages is very limited until the response of the local soil is also taken into account. Determination of the local soil response needs regionally recorded ground motions, dynamic soil properties, in situ geotechnical details, etc., which most of the time are not readily available for the region under study. In the present work, the response of local soil for Nepal has been studied indirectly taking into account the surface level of ground shaking during various past as well as recent EQs observed at various locations. Based on the present analysis, a low value of amplification factor for high peak horizontal acceleration and vice versa is observed in central, western as well as southern parts of Nepal. These observations suggest nonlinear soil behavior and are in accordance with the available literature. Further, the ground motion records during 2015 Nepal EQ show maximum soil response at 0.3 s which is exactly matching with the site class C obtained from in situ data for the above locations. Based on the above observations, various correlations between the high peak horizontal acceleration and the surface spectral acceleration are proposed to obtained site specific surface response spectrum for Nepal.  相似文献   

Vulnerability assessment through index modeling: a case study in Muriganga–Saptamukhi estuarine interfluve,Sundarban, India     

Abhishek Ghosh  Sutapa Mukhopadhyay 《Arabian Journal of Geosciences》2017,10(18):408

The coastal regions, deltas, and estuaries are severely affected by the sea level rise and cyclonic activities and climate changes. Sundarban delta is one of the most mysterious landscapes in the world, which has successively evolved due to sediment accumulation by the great Ganga and Brahmaputra river system. The area is characterized by low-lying islands and a flat topography coupled with macro-tidal activities, powerful surges, and seasonal cyclonic events. All these conditions put together this landscape defenseless to frequent flood and erosion. Since the last hundred years, the face of Sundarban has been changed remarkably from wildest to human-occupied territory by protecting this low-lying flat plain from tidal inundation through artificial embankment. In this background, the current study attempts to highlight the spatial extent and magnitudes of internal risk factors of the region using the composite vulnerability index. Coastal vulnerability defines a system’s openness to flood and erosion risk due to hydrogeomorphic exposures and socio-economic susceptibility in conjunction with its capacity/incapacity to be resilient and to cope, recover, or adapt to an extent. Coastal vulnerability assesses the potential risk from erosion and flooding of any low-lying coastal region due to its physiographical and hydrological exposures, socio-economic and political susceptibility, and resilience capacity. A natural system affects the socio-economic scenario of any region. Hence, multidimensional databases can be more effective to understand the extent of exposure, susceptibility, and resilience of any system. To throw some light on the situation of vulnerability of western estuarine Sundarban, between Muriganga and Saptamukhi interfluve, the composite vulnerability index has been carried out to delineate the magnitude and spatial extent of vulnerability with the help of quantitative techniques and geospatial tools. The estuarine tracts and coastal parts of the Ganga delta are two of the most densely populated areas in the world. The study highlights the critical situation of the population under different potential risk classes residing in the study area with the intention of suggesting some proper course of action of planning and management to conserve coastal communities in their original habitat.  相似文献   

Palaeoweathering,composition and tectonics of provenance of the Proterozoic intracratonic Kaladgi–Badami basin,Karnataka, southern India: Evidence from sandstone petrography and geochemistry     

Sukanta Dey  A.K. Rai  Anjan Chaki 《Journal of Asian Earth Sciences》2009,34(6):703-715

Petrographic and geochemical data on the sandstones of the Proterozoic intracratonic Kaladgi–Badami basin, southern India are presented to elucidate the palaeoweathering pattern, and composition and tectonics of their provenance. The Kaladgi–Badami basin, hosting the Kaladgi Supergroup, occupies an E–W trending area. The Supergroup unconformably overlies Archaean basement TTG gneisses, granites and greenstones, comprises a cyclic arenite–pelite–carbonate association and is divided into the Bagalkot and Badami Groups. The immature arkosic character of the basal Saundatti Quartzite Member (Bagalkot Group) containing fresh and angular feldspars, along the northern margin of the basin, suggests that during the initial stage of deposition, this part of the basin received sediments from a restricted, uplifted and less weathered source dominated by K-rich granites occurring to the north. In contrast, the Saundatti Quartzite along the southern margin displays a mostly mature, quartz-rich character with less abundant but severely weathered feldspars, and higher SiO₂ and CIA but lower Al₂O₃, TiO₂, Rb, Sr, Ba, K₂O, K₂O/Na₂O, Zr/Ni and Zr/Cr. This is interpreted in terms of a tectonically stable, considerably weathered mixed source (Archaean gneisses, granites and greenstones) along the southern fringe of the basin. The highly mature (quartz arenite) Muchkundi Quartzite Member (also of the Bagalkot Group), occurring higher up in the succession, exhibits minor but severely altered feldspars, and higher SiO₂, Na₂O, CIA, Cr and Ni with lower K₂O, Al₂O₃, TiO₂ and K₂O/Na₂O. This reflects that with the passage of time the source evolved to a uniform, extensively weathered, tectonically stable peneplained provenance which consisted of less evolved TTG gneisses and greenstones. This was followed by closure, deformation and upliftment of the basin hosting the Bagalkot Group and subsequent deposition of the Badami Group. Sandstone Members of this younger Group (Cave-Temple Arenite and Belikhindi Arenite) range widely in mineralogy (quartz arenite to arkose) and chemistry (including CIA), and point to a source that varied from uplifted, less weathered K-rich granites to less evolved, peneplained TTG gneisses and greenstones or even Bagalkot sediments. Variable alteration of feldspars in the Kaladgi sandstones and severe depletion of Ca, Na and Sr in the associated shales indicate a humid tropical (tropical and subtropical) climate facilitating chemical weathering.  相似文献