Formation of decollement upwarps during thrusting     

Ashok Kumar Dubey 《地学学报》2004,16(3):91-94

Geometric and kinematic models reveal that rotation of layers during thrusting or development of drag folds produced by movement along listric thrust faults results in the formation of dilation space at the junction of the thrust ramp with the basal decollement. This is accompanied by upwarping of the basement to occupy the available space thereby producing an antiformal structure, which restricts the thrust displacement. The structure is termed a decollement upwarp and examples are cited from the foothill belt of the Himalaya.  相似文献   

Land use/land cover identification in an alpine and arid region (Nubra Valley, Ladakh) using satellite remote sensing     

P. K. Joshi  G. S. Rawat  H. Padaliya  P. S. Roy 《Journal of the Indian Society of Remote Sensing》2005,33(3):371-380

The remote sensing technology has been widely used for mapping the vegetation types in the tropical landscapes. However, in the temperate and alpine arid regions of India very few studies have been conducted using this technique. In the mountainous temperate arid conditions the vegetation is largely confined to marsh meadows, streams courses, river valleys and moist pockets close to snowfields. The ground truth collection in these zones are physically challenging due to tough terrain and restricted mobility. The detailed mapping of vegetation and other land use classes in these areas is therefore, extremely difficult. This paper describes the use of IRS-ID LISS III sensor for deciphering land cover details Nubra Valley, northern portion of Ladakh Autonomous Hill Council, Jammu & Kashmir (India). This analysis essentially emphasizes in bringing out various vegetation classes (speciallyHippophae rhamnoides and other medicinal plant communities) along the narrow river valleys.  相似文献   

Spatial modelling for biological richness analysis in Nokrek biosphere reserve — north-eastern India     

G. Talukdar  N. Lele  M. C. Porwal 《Journal of the Indian Society of Remote Sensing》2005,33(3):435-440

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Estimation of causative fault parameters of the Rudbar earthquake of June 20, 1990 from near field SH-wave data     

I. Sarkar  H. Hamzehloo  K. N. Khattri   《Tectonophysics》2003,364(1-2):55-70

We analyze the strong motion accelerograms recorded for the large (M_S=7.7, M_W=7.3, m_b=6.4) Rudbar earthquake of June 20, 1990. The earthquake had a complex source process. We have identified the imprints of rupture of three localized asperities on the major causative fault on the accelerograms. These asperities are interpreted to correspond to (i) the main shock that initiated the rupture process and was located in the domino block between the Kabateh and Zard Goli faults, (ii) a foreshock that occurred about 10 s earlier in the Kabateh fault and (iii) a later shock, on the western end of the Baklor fault, which terminated the bilateral rupture process at the western end. We estimate the strike, dip and slip of these causative sub-event rupture planes using the SH spectral amplitudes, based on a point source representation of sub-events and a non-linear least square formulation for inversion of the amplitude data. The results of our inversion of the near field data are comparable to other studies based on teleseismic data.  相似文献   

Phases greater than 90° in MT data: Analysis using dimensionality tools     

F.E.M. Lilley  J.T. Weaver 《Journal of Applied Geophysics》2010,70(1):9-16

An example of magnetotelluric data is discussed which has distinctive phase values out of quadrant, and for which the Z_xx element of the measured tensor is greater than the Z_xy element in both real and quadrature parts. Mohr circle plots and principal value decompositions of the real and quadrature parts of the tensor clarify its understanding. An analysis of rotational invariants of the data suggests a case of galvanic distortion of a 2D structure. Results from phase tensor analysis are included, and the example is seen to be a dramatic instance of phase tensor analysis reducing an apparently 3D example to 2D characteristics.The Mohr circles of this example do not capture the axes origin, although there are phases out of quadrant. Extra intrigue is thus added to the question, noted in Lilley, F.E.M., 1998. Magnetotelluric tensor decomposition: part I, theory for a basic procedure. Geophysics 63, 1885–1897 and arising independently in Caldwell, T.G., Bibby, H. M., Brown, C., 2004. The magnetotelluric phase tensor. Geophys. J. Int. 158, 457–469 and Bibby, H.M., Caldwell, T.G., Brown, C., 2005. Determinable and non-determinable parameters of galvanic distortion in magnetotellurics. Geophys. J. Int. 163, 915–930, whether the determinant values taken separately of the real and quadrature parts of a magnetotelluric tensor should both never be negative.For data whose Mohr circles do not capture the axes origin, simple conditions are derived regarding phase. These conditions govern whether or not it is formally possible for observed phases of Z_xy to exceed 90°, for any rotation of the observing axes.  相似文献   

Characterisation of ecological parameters in tropical forest community—A remote sensing approach     

P S Roy  Sarnam Singh  M C Porwal 《Journal of the Indian Society of Remote Sensing》1993,21(3):127-149

Satellite Remote Sensing data has been used for vegetation mapping, initial stratification, distribution of sample plots and for calculating the area under different vegetation types. Primary and secondary analyses of vegetation has been done using phytosociological ground data collected from sample piots to assess the ecological importance of different species. Interrelationships among different communities have been evaluated through various available indices. The spatial distribution and vegetation analysis indicate that commercial extraction of natural forests of Andaman has set in retrogression. The evergreen forests subjected to shorter rotation of commercial exploitation are being invaded with seral deciduous species. The study highlights the status of forests (spatial and community) and stresses the need to conserve germplasm present in the natural evergreen forests.  相似文献   

Land productivity assessment and mapping through integration of satellite and terrain slope data     

M Kudrat  S K Saha 《Journal of the Indian Society of Remote Sensing》1993,21(3):157-166

Evaluation and mapping of spatial variations of land productivity is very important for effective landuse planning. The present study was undertaken in watershed of the Song river (Dehra Dun district, U.P.), for assessing and mapping land productivity using modified Storie Index following integrated approach. This approach utilizes soilscape information (derived from digital IRS-IA LISS-II data), soil characteristics (field observed and laboratory analysed) and terrain slope information (obtained from Survey of India topographical maps). The approach consists of preparation of Storie Index productivity rating factors such as: A (soil profile character), B (soil texture), X (soil physical and fertility conditions), and C (land slope), and computerised integration of these maps to generate land productivity map. The results indicate that in the watershed 30.6%, 19.6%, 12.2%, 11.8% and 18.8% areas have been found to be under good, fair, poor, very poor and not suitable, land productivity classes, respectively.  相似文献   

Evolutionary properties of stochastic models of earthquake accelerograms: Their dependence on magnitude and distance     

J. Alamilla  L. Esteva  J. García-Pérez  O. Díaz-López 《Journal of Seismology》2001,5(1):1-21

An approach to generate artificial earthquakeaccelerograms on hard soil sites is presented. Eachtime-history of accelerations is considered as arealization of a non-stationary gaussian stochasticprocess, with statistical parameters depending onmagnitude and source-to-site distance. In order tolink the values of these parameters for each groundmotion record with the corresponding magnitude andsource-to-site distance, semi-empirical functionalrelations called generalized attenuationfunctions are determined. The set of realground-motion time histories used to obtain thesefunctions correspond to shocks generated at differentsources and recorded at different sites in thevicinity of the southern coast of Mexico. The resultsshow significant dispersion in the parameters of themodel adopted, which reflect that associated with thereal earthquakes included in the sample employed.The problem of conditional simulation of artificialacceleration time histories for prescribed intensitiesis briefly presented, but its detailed study is leftfor a companion paper. The criteria and modelsproposed are applied to generate two families ofartificial acceleration records for recurrenceintervals of 100 and 200 years at a specific sitelocated in the region under study. The results shownin this article correspond to acceleration timehistories recorded on firm ground for earthquakesgenerated at the subduction zone that runs along thesouthern coast of Mexico, and cannot be generalized tocases of earthquakes generated at other sources orrecorded at other types of local conditions. Thismeans that the methods and functional forms presentedhere are applicable to these other cases, but thevalues of the parameters that characterize thosefunctions may differ from those presented here.  相似文献   

Mapping of tropical dry deciduous forest and landuse in part of Vindhyan range using satellite remote sensing     

Pant  D N  Das  K K  Roy  P S 《Journal of the Indian Society of Remote Sensing》1992,20(1):9-20

Forest vegetation of Vindhyan range located in the north of G.B. Pant Sagar (dam) has been subjected to degradation due to high biotic pressure caused by the installation of thermal power plants, coal mining, heavy cattle grazing etc. In the present study Landsat TM FCC of 1∶250,000 scale was visually analysed with respect to forest vegetation types, crown density and structure along with other landuse/land cover classes. ExceptShorea robusta (Sal) andLagerstroemia parviflora (Lendia) all forest vegetation types show higher percentage of degradation and under-stocked condition with respect to their areal extent under study. Overall classification accuracy of the forest types has been found to be 88.94%. This indicates that for obtaining reliable mapping accuracy in dry deciduous areas, satellite remote sensing data of appropriate season is essential.

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Temporal Assessment of Growing Stock, Biomass and Carbon Stock of Indian Forests   总被引：1，自引：0，他引：1  

R. K. Manhas  J. D. S. Negi  Rajesh Kumar  P. S. Chauhan 《Climatic change》2006,74(1-3):191-221

The dynamics of terrestrial ecosystems depends on interactions between carbon, nutrient and hydrological cycles. Terrestrial ecosystems retain carbon in live biomass (aboveground and belowground), decomposing organic matter, and soil. Carbon is exchanged naturally between these systems and the atmosphere through photosynthesis, respiration, decomposition, and combustion. Human activities change carbon stock in these pools and exchanges between them and the atmosphere through land-use, land-use change, and forestry.In the present study we estimated the wood (stem) biomass, growing stock (GS) and carbon stock of Indian forests for 1984 and 1994. The forest area, wood biomass, GS, and carbon stock were 63.86 Mha, 4327.99 Mm³, 2398.19 Mt and 1085.06 Mt respectively in 1984 and with the reduction in forest area, 63.34 Mha, in 1994, wood biomass (2395.12 Mt) and carbon stock (1083.69 Mt) also reduced subsequently. The Conifers, of temperate region, stocked maximum carbon in their woods, 28.88 to 65.21 t C ha⁻¹, followed by Mangrove forests, 28.24 t C ha⁻¹, Dipterocarp forests, 28.00 t C ha⁻¹, and Shorea robusta forests, 24.07 t C ha⁻¹. Boswellia serrata, with 0.22 Mha forest area, stocked only 3.91 t C ha⁻¹. To have an idea of rate of carbon loss the negative changes (loss of forest area) in forest area occurred during 1984–1994 (10yrs) and 1991–1994 (4yrs) were also estimated. In India, land-use changes and fuelwood requirements are the main cause of negative change. Total 24.75 Mt C was lost during 1984–1994 and 21.35 Mt C during 1991–94 at a rate of 2.48 Mt C yr⁻¹ and 5.35 Mt C yr⁻¹ respectively. While in other parts of India negative change is due to multiple reasons like fuelwood, extraction of non-wood forest products (NWFPs), illicit felling etc., but in the northeastern region of the country shifting cultivation is the only reason for deforestation. Decrease in forest area due to shifting cultivation accounts for 23.0% of the total deforestation in India, with an annual loss of 0.93 Mt C yr⁻¹.  相似文献