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71.
72.
The Dharwar craton, Cuddapah basin and the Godavari graben characterise three diverse geological and tectonic settings in
the peninsular shield of India. Owing to their contiguous proximity, they offer a unique opportunity to document differences,
if any, in their seismic wave attenuation characteristics that might have a bearing on the seismogenic nature of the crust
in a craton, basin and a rift-like graben structure. An attempt is made here to bring out these differences using constraints
from coda-Q. We considered local earthquakes with epicentral distances ranging from␣14 to 150 km recorded at the digital broadband stations
at Dharwar (DHD), Cuddapah (CUD) and Kothagudem (KGD) regions to derive the frequency-dependent coda-Q relations. Using the single scattering method, we obtained the frequency-dependent Q
C relationship (Q
C = Q
0
f
n
)for each of the three geological units separately: DHD: Q
C = (730.62 ± 0.09)f
(0.54 ± 0.01); CUD: Q
C = (535.06 ± 0.13)f
(0.59 ± 0.01) and KGD: Q
C = (150.56 ± 0.08)f (0.91 ± 0.01). The Q
C values obtained for all the three sub-regions show moderate to strong frequency dependence and essentially reflect the level
of crustal heterogeneities to varying degrees. 相似文献
73.
In estimating the likelihood of an earthquake hazard for a seismically active region, information on the geometry of the potential
source is important in quantifying the seismic hazard. The damage from an earthquake varies spatially and is governed by the
fault geometry and lithology. As earthquake damage is amplified by guided seismic waves along fault zones, it is important
to delineate the disposition of the fault zones by precisely determined hypocentral parameters. We used the double difference
(DD) algorithm to relocate earthquakes in the Koyna-Warna seismic zone (KWSZ) region, with the P- and S-wave catalog data
from relative arrival time pairs constituting the input. A significant improvement in the hypocentral estimates was achieved,
with the epicentral errors <30 m and focal depth errors <75 m i.e. errors have been significantly reduced by an order of magnitude
from the parameters determined by HYPO71. The earthquake activity defines three different fault segments. The seismogenic volume is shallower in the south by 3 km,
with seismicity in the north extending to a depth of 11 km while in the south the deepest seismicity observed is at a depth
of 8 km. By resolving the structure of seismicity in greater detail, we address the salient issues related to the seismotectonics
of this region. 相似文献
74.
Santanu Banerjee S.K. Bhattacharya Subir Sarkar 《Journal of Asian Earth Sciences》2007,29(5-6):823-831
Variations of carbon and oxygen isotopic ratios in response to cyclical sea level fluctuations have been documented from a Paleoproterozoic peritidal stromatolite succession. The upper division of the Kajrahat Limestone, Vindhyan Supergroup of central India consists of several shallowing upward stromatolite cycles identified by regular and systematic changes in stromatolite size. Normally, larger stromatolites are followed upward in the succession by smaller stromatolites and microbial laminites that occupy the top of the cycle. Desiccation cracks are found in all the facies indicating subaerial exposure. We investigated the stable isotope compositional variations across nine complete stromatolite cycles showing frequent subaerial emergence. Carbon and oxygen isotopic values of the limestones, in general, are comparable to contemporary marine values available from earlier studies but show regular depletion in response to shallowing of the water level. The δ13C and δ18O values of the limestones vary within an individual stromatolite cycle; depleted values characterize the topmost part of the cycles. The isotope pattern is explained by micritic carbonate deposition in different sub environments of the shallow marine domain having different salinity and variable duration of exposure. These variations also probably caused the observed scatter in δ13C and δ18O values of supratidal microbial laminites. 相似文献
75.
The inverse distance weighted model (IDWM) represents a geo-spatial interpolation technique used for estimation of ionospheric
vertical delays at the ionospheric grid points (IGPs) and user ionospheric pierce points (IPPs). The GPS Aided Geo Augmented
Navigation (GAGAN) system is planned for air-navigation over the Indian service region using a space based augmentation. One
of the main needs for GAGAN is to develop a suitable grid-based ionospheric model for estimating the vertical delay and its
error bound, i.e., grid ionospheric vertical error (GIVE) at all the IGPs covering the Indian subcontinent. Dual frequency
GPS receiver data obtained from 17 total electron content (TEC) stations are considered in the analysis. For a typical IGP
(25°N, 75°E), variations in the GIVE for a few days of quiet ionosphere are presented. For a quiet and magnetically moderate
day, the mean and standard deviations of the user IPP (UIPP) estimation error and the mean GIVE are presented using the IDWM
with Klobuchar, Junkins and bilinear models. 相似文献
76.
A Godunov-Type Scheme for Atmospheric Flows on Unstructured Grids: Euler and Navier-Stokes Equations
Nash'at Ahmad Zafer Boybeyi Rainald Löhner Ananthakrishna Sarma 《Pure and Applied Geophysics》2007,164(1):217-244
In recent years there has been a growing interest in using Godunov-type methods for atmospheric flow problems. Godunov's unique
approach to numerical modeling of fluid flow is characterized by introducing physical reasoning in the development of the
numerical scheme (van Leer, 1999). The construction of the scheme itself is based upon the physical phenomenon described by the equation sets. These
finite volume discretizations are conservative and have the ability to resolve regions of steep gradients accurately, thus
avoiding dispersion errors in the solution. Positivity of scalars (an important factor when considering the transport of microphysical
quantities) is also guaranteed by applying the total variation diminishing condition appropriately. This paper describes the implementation of a Godunov-type finite volume scheme based on unstructured
adaptive grids for simulating flows on the meso-, micro- and urban-scales. The Harten-Lax-van Leer-Contact (HLLC) approximate
Riemann solver used to calculate the Godunov fluxes is described in detail. The higher-order spatial accuracy is achieved
via gradient reconstruction techniques after van Leer and the total variation diminishing condition is enforced with the aid of slope-limiters. A multi-stage explicit Runge-Kutta time marching scheme is used for
maintaining higher-order accuracy in time. The scheme is conservative and exhibits minimal numerical dispersion and diffusion.
The subgrid scale diffusion in the model is parameterized via the Smagorinsky-Lilly turbulence closure. The scheme uses a non-staggered mesh arrangement of variables (all quantities are
cell-centered) and requires no explicit filtering for stability. A comparison with exact solutions shows that the scheme can
resolve the different types of wave structures admitted by the atmospheric flow equation set. A qualitative evaluation for
an idealized test case of convection in a neutral atmosphere is also presented. The scheme was able to simulate the onset
of Kelvin-Helmholtz type instability and shows promise in simulating atmospheric flows characterized by sharp gradients without
using explicit filtering for numerical stability. 相似文献
77.
78.
The air-sea exchange is one of the main mechanisms maintaining the abundances of trace gases in the atmosphere. Some of these,
such as carbon dioxide and dimethyl sulphide (DMS), will have a bearing on the atmospheric heat budget. While the former facilitates
the trapping of radiation (greenhouse effect) the latter works in the opposite direction through reflectance of radiation
back into space by sulphate aerosols that form from oxidation of DMS in atmosphere. Here we report on the first measurements
made on DMS in the Bay of Bengal and the factors regulating its abundance in seawater. Phytoplankton alone does not seem to
control the extent of DMS concentrations. We find that changes in salinity could effectively regulate the extent of DMSP production
by marine phytoplankton. In addition, we provide the first ever evidence to the occurrence of DMS precursor, DMSP, in marine
aerosols collected in the boundary layer. This suggests that the marine aerosol transport of DMSP will supplement DMS gaseous
evasion in maintaining the atmospheric non-sea salt sulphur budget. 相似文献
79.
Upendra Baral Ding Lin Tapos Kumar Goswami Mondip Sarma Muhammad Qasim Devojit Bezbaruah 《地学学报》2019,31(1):18-27
Geochronology is useful for understanding provenance, and while it has been applied to the central and western Himalaya, very little data are available in the eastern Himalaya. This study presents detrital zircon U–Pb ages from the late Palaeocene–Eocene Yinkiong Group in NE India. The samples are from the late Palaeocene to early Eocene Lower Yinkiong Formation, and the Upper Yinkiong Formation deposited during the early to mid‐Eocene within the Himalayan foreland basin. The U–Pb ages of the detrital zircon within the Lower Yinkiong Formation are older than late Palaeozoic, with a cratonic and early Himalayan Thrust Belt affinity, whereas the Cenozoic grains in the Upper Yinkiong Formation indicate a Himalayan Thrust Belt source and possibly a granitic body within the Asian plate. The shift of the sources and the changes in the foreland basin system strongly suggest that the India–Asia collision in the Eastern Himalaya began before or immediately after the deposition of the Upper Yinkiong Formation, i.e., within the early Eocene (c. 56 to 50 Ma). 相似文献
80.
Jogendra Nath Sarma Shukla Acharjee Chandraditya Gogoi 《Journal of the Indian Society of Remote Sensing》2011,39(4):507-517
The Dibru river basin of Assam is investigated to examine the influence of active structure by applying an integrated study on geomorphology, morphotectonics, subsurface structure, Digital Elevation Model (DEM) using topographic map, IRS 1D LISS III, IRS P6 LISS III, SRTM, seismic and subsurface data. Seismic data reveals existence of an upwarp and an important fault in the basement around the central and eastern parts of the Dibru basin, respectively. The influence of these structures is well observed on all the younger formations inferring their active nature possibly till the Recent Period. Existence of fluvial anomalies, viz. annular drainage pattern, lineaments, abrupt changes in the direction of river course, beheaded stream and valley incision infer role of structural control on the fluvial features of this basin. Most commonly used indices for morphotectonic analysis, viz. basin elongation ratio (Re), transverse topographic symmetry (T), asymmetric factor (AF), valley floor width to valley height ratio (Vf) have been used to identify the evidences of active structures in the area. The values of Re indicated tectonically active, T indicated an asymmetric nature, AF indicated tilting and Vf indicated active incision in the Dibru basin. The DEM, profiles across the valley and superimposed longitudinal profiles of incised channel bed and valley shoulder of the Dibru clearly reveal valley incision by the river. Three large paleochannels located in different parts of the basin had their headwaters towards east at the common source, i.e. the Diyun river. These paleochannels had been resulted when their headwaters avulsed to create new rivers due to affect of the subsurface structures during Recent (or perhaps Neogene?) Period. 相似文献