Postseismic relaxation due to Bhuj earthquake on January 26, 2001: possible mechanisms and processes     

C. D. Reddy  P. S. Sunil  Roland B��rgmann  D. V. Chandrasekhar  Teruyuki Kato 《Natural Hazards》2013,65(2):1119-1134

Earthquakes cause static stress perturbations in the nearby crust and mantle. Obeying rheological laws, this stress relaxes in a time frame of months to years with the spatial extent of few km to hundreds of km. While postseismic relaxation associated with major inter-plate earthquakes is well established, there have been few opportunities to explore its occurrence following intraplate earthquakes. The M _w 7.6 Bhuj earthquake on January 26, 2001 in western India is considered to be an intraplate event and provided a unique opportunity to examine post-earthquake relaxation processes sufficiently away from plate boundaries. To study the characteristics of transient postseismic deformation, six Global Positioning System campaigns were made at 14 sites. The postseismic transients were delineated after removing plate motions from the position time series. Postseismic deformation has been observed at all the sites in the study area. During 2001?C2007, the site closest to the epicenter exhibited postseismic deformation of about 30 and 25?mm in the north and east components, respectively. Time series of the NS and EW components of the postseismic transients can be fitted to both logarithmic and exponential functions. Close to the epicenter, the logarithmic function fits well to the initial transient, and an exponential function fits well to the later phases. The remaining sites (located east and west of the epicentral region) exhibited significantly diminished north?Csouth relaxation. Rapidly decaying afterslip and poroelastic mechanisms seem to be responsible for postseismic relaxation in the vicinity of epicenter during the initial period subsequent to the Bhuj earthquake. Postseismic relaxation by viscoelastic flow below the seismogenic zone seems to affect displacements across the entire Bhuj region. This paper presents the characteristics of postseismic transients and deformation processes in the scenario of the highly heterogeneous crust in the Bhuj region.  相似文献   

Energy dependence of near-relativistic electron spectrum at geostationary orbit during the SEP events of 2005     

A. Chandrasekhar Reddy  Jatin Rathod  Girija Rajaram  Radharani Alyana  D. S. Misra  C. G. Patil  M. Y. S. Prasad  A. G. Ananth 《Journal of Astrophysics and Astronomy》2008,29(1-2):313-317

In view of the renewed interest in the study of energetic particles in the outer radiation belt of the earth, we feel it will be helpful in looking for the energy dependence of the electron energy spectrum at geostationary orbit. This may give us some insight into how we can safeguard geostationary satellites from functional anomalies of the deep dielectric charging type, which are caused by charge accumulation and subsequent discharge of relativistic electrons. In this study we examine whether there is any energy dependence in relativistic electron enhancements at geosynchronous altitudes during solar energetic proton events of 2005.  相似文献   

Polarized luminescence spectra of kunzite     

B. K. Chandrasekhar  William B. White 《Physics and Chemistry of Minerals》1992,18(7):433-440

Kunzite, the pink, manganese-bearing variety of spodumene, is strongly luminescent under UV or electron beam excitation. Laser excitation of an oriented kunzite single crystal has been used to determine the polarization dependence of the luminescence. The emission spectrum, assigned to an Mn²⁺ center, can be fitted by two Gaussian bands with maxima at 16 568 and 15 679 cm^–1. Analysis of the temperature dependence of emission intensity and band width give estimates of the frequency of the phonons assisting the luminescence transitions. These appear to be bond stretching modes of the octahedral site. Analysis of the polarization dependence of emission intensity allows determination of the orientation of the emission dipole. Comparison of the polarization dependence of excitation and emission radiation shows that coupling between absorption dipole and emission dipole is incoherent.Work supported by the National Science Foundation under Grant No. DMR-74-00340  相似文献   

Tectonics and crustal structures related to Bhuj earthquake of January 26, 2001: based on gravity and magnetic surveys constrained from seismic and seismological studies   总被引：2，自引：0，他引：2  

D.C. Mishra  D.V. Chandrasekhar  B. Singh 《Tectonophysics》2005,396(3-4):195-207

Gravity and magnetic data of the Kachchh basin and surrounding regions have delineated major E–W and NW–SE oriented lineaments and faults, which are even extending up to plate boundaries in the north Arabian Sea and western boundary of the Indian plate, respectively. The epicentral zone of Bhuj earthquake and its aftershocks is located over the junction of Rann of Kachchh and median uplifts viz. Kachchh mainland and Wagad uplifts, which are separated by thrust faults. Gravity data with constraints from the results of the seismic studies along a profile suggest that the basement is uplifted towards the north along thrust faults dipping 40–60° south. Similarly gravity and magnetic modeling along a profile across Wagad uplift suggest south dipping (50–60°) basement contacts separating rocks of high susceptibility and density towards the north. One of these contacts coincides with the fault plane of the Bhuj earthquake as inferred from seismological studies and its projection on the surface coincides with the E–W oriented north Wagad thrust fault. A circular gravity high in contact with the fault in northern part of the Wagad uplift along with high amplitude magnetic anomaly suggests plug type mafic intrusive in this region. Several such gravity anomalies are observed over the island belt in the Rann of Kachchh indicating their association with mafic intrusions. The contact of these intrusives with the country rock demarcates shallow crustal inhomogeneities, which provides excellent sites for the accumulation of regional stress. A regional gravity anomaly map based on the concept of isostasy presents two centers of gravity lows of −11 to −13 mGal (10⁻⁵ m/s²) representing mass deficiency in the epicentral region. Their best-fit model constrained from the receiver function analysis and seismic refraction studies suggest crustal root of 7–8 km (deep crustal inhomogeneity) under them for a standard density contrast of −400 kg/m³. It is, therefore, suggested that significant amount of stress get concentrated in this region due to (a) buoyant crustal root, (b) regional stress due to plate tectonic forces, and (c) mafic intrusives as stress concentrators and the same might be responsible for the frequent and large magnitude earthquakes in this region including the Bhuj earthquake of January 26, 2001.  相似文献   

Angular diameter and effective temperature of a sample of 15 M giants at 2.2 μm from lunar occultation observations     

Anandmayee Tej  T. Chandrasekhar 《Monthly notices of the Royal Astronomical Society》2000,317(3):687-696

High angular resolution measurements of a sample of 15 M giants at 2.2 μm by the technique of lunar occultation are presented in this paper. We obtain angular diameters for 11 sources of which five are the first diameter measurements. For these resolved sources we have estimated the effective temperatures, which are consistent with previous calibrations. For the other four sources we put the first upper limits on their angular sizes to be 2 mas. Two sources, namely IRC+20090 and IRC+20067, yield appreciably low temperatures, which could point to their possible Mira nature. For sources with Hipparcos parallax measurements, we have calculated the linear radii.  相似文献   

Water resource management using geothermal energy: Eritrea     

Dornadula Chandrasekharam  Aref Lashin  Nassir Al Arifi  Abdulaziz Al-Bassam  Varun Chandrasekhar 《Arabian Journal of Geosciences》2018,11(17):523

Eritrea is a country with rich gold, silver and base-metal deposits and geothermal energy resources associated with all the five volcanoes located within the Danakil graben. Due to low rainfall, the country has to depend on imported food and food imports have crossed >?46% in the recent years. Although the cultivable land is about 16,000 km², only 5030 km² land is being cultivated due to insufficient water resources. The per capita water requirement is projected to fall below 1300 m³/year from the present 1470 m³/year. The country’s GDP has fallen from 1.3% in 2013 to 0.3% in 2015. Each geothermal province associated with the active volcanoes can support to generate 445 million m³ of desalinated water from the Red Sea. Providing basic needs like water and energy will boost the country’s economy and lift the socio-economic status of 6 million people in the country.  相似文献   

Direct delivery of remote sensing data to user computer systems using satellite-based data broadcast techniques     

A S Manjunatha  M G Chandrasekhar  A R Virupaksha  S Adiga  P P Nageswara Rao 《Journal of the Indian Society of Remote Sensing》2000,28(2-3):69-78

The remote sensing applications are growing very rapidly with the availability of high-resolution data from the state of the art satellites like IRS-1C/1D/P4. The advancement in computer hardware and software in the area of remote sensing also enhance the growth of remote sensing applications. IRS-1C/1D/P4 provides data with the resolution of 5.6m in panchromatic mode giving more information of the ground area covered. The remote sensing satellites with high-resolution sensors and wide coverage capabilities will provide the data with better resolution, coverage and revisit to meet the growing application needs. Many applications like crop acreage and yield estimation, draught monitoring and assessment, flood mapping, waste land mapping, mineral prospectus, forest resource survey etc., have become an integral part of the resources management system in the developing countries. These resource management systems need the data to be transferred in real time or near real time for processing. The transfer of data in real time or near real time calls for advanced data delivery techniques to deliver the data as quickly as possible. Processing of remote sensing data can be performed even on low cost personal computers, which in turn further increases the remote sensing applications enabling by setting up the processing centers even at grass root level i.e., at district, taluk or village level. Setting up of processing centers at grass root level demands for quick, cost effective and efficient data delivery mechanism to transfer remote sensing data with or without value added services. The digital revolution has reached broadcasting with the introduction of direct broadcasting of digital data. These modify the traditional data transfer techniques by separating the actual service from the transmission system, thus enabling the distribution of any kind of digital data to stationary, portable or mobile terminals. This allows remote sensing data to reach a large number of users simultaneously and independent of their location. This article highlights the concepts, possibilities, and implementation mechanisms to realize the remote sensing data transfer through direct broadcasting technique and enhance remote sensing applications.  相似文献   

The general theory of relativity: Why “It is probably the most beautiful of all existing theories”     

S. Chandrasekhar 《Journal of Astrophysics and Astronomy》1984,5(1):3-11

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Value addition of paper coating grade kaolins by the removal of ultrafine coloring impurities     

P. Raghavan  Sathy Chandrasekhar  A.D. Damodaran 《International Journal of Mineral Processing》1997,50(4):307-316

Two kaolin samples from the southern part of Kerala (A and B) have been characterised. The colouring impurities present were found to be carbonaceous and ferruginous, being also present in ultrafine size ranges. Modern beneficiation techniques such as ultra flotation and high gradient magnetic separation (HGMS) have been carried out to reduce the level of these contaminants and to increase the brightness of the product clays. The results showed that nearly 70% of the ultrafine carbonaceous matter in A, which originally contains 0.13% carbon (as fixed carbon), could be removed by shear floc-flotation. HGMS treatment could remove ∼ 45% of the iron minerals (feed assay 0.58% Fe₂O₃). Sample B contained 0.32% Fe₂O₃ and 0.19% carbon. The shear floc-flotation was found to be the only effective method by which ∼ 75% of the carbon could be floated out. This sample did not respond to HGMS which may be because of the ‘structural’ nature of the iron present. Both the kaolins, after processing, were found suitable for paper coating. Another important aspect of this work is the establishment of maximum permissible level for carbon in paper coating grade clays since the standard specifications do not give any limiting value.  相似文献   

Ground-Water Potential Evaluation of West Godavari District, Andhra Pradesh State, India—A GIS Approach     

M.V.V. Kamaraju  A. Bhattacharya  G. Sreenivasa Reddy  G. Chandrasekhar Rao  G. S. Murthy  T. Ch. Malleswara Rao 《Ground water》1996,34(2):318-325

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