Characteristic curves for interpreting the vertical magnetic anomalies of dipping doublets     

B. S. R. Rao  I. V. Radhakrishna Murthy  Y. V. Subra Rao 《Pure and Applied Geophysics》1974,112(2):472-476

Summary Standard charts from which a complete solution of the vertical magnetic anomalies of dipping doublets can be obtained very rapidly are derived and presented. The most important distances to be scaled from the field profile are the distances between the maximum and minimum anomalies, half maximum anomalies and one-third maximum anomalies only. The use of the charts for claculating the various parameters and locating the origin is also incorporated.  相似文献   

On the deformations in a general linear substance of a layered media subjected to a body force and a deforming magnetic field     

Mallik  S. Basu 《Pure and Applied Geophysics》1974,112(1):153-161

Summary The propagation of disturbances has been studied in a layered media, comprising a liquid and a general linear substance, subject to a body force and permeated by an initial magnetic field acting normal to the plane of the contact. The effect of the body force due to some internal source has been considered in the problem and a set of results has been obtained under two possible extreme variants of the boundary conditions in the form of integral forms, which can be computed to visualize the displacement—time and displacement—depth variations, both in the presence and absence of the body force. The effect of body force on the substance has been, as a sample case, illustrated in the graphs. The stress-strain relation of the general linear substance and the electromagnetic equations of Maxwell have been used in working out the problem.  相似文献   

Seismicity, gravity anomalies and lithospheric structure of the Andaman arc, NE Indian Ocean     

M. Radhakrishna  S. Lasitha  Manoj Mukhopadhyay 《Tectonophysics》2008,460(1-4):248-262

The Andaman arc in the northeastern Indian Ocean defines nearly 1100 km long active plate margin between the India and Burma plates where an oblique Benioff zone develops down to 200 km depth. Several east-trending seismologic sections taken across the Andaman Benioff Zone (ABZ) are presented here to detail the subduction zone geometry in a 3-D perspective. The slab gravity anomaly, computed from the 3-D ABZ configuration, is a smooth, long-wavelength and symmetric gravity high of 85 mGal amplitude centering to the immediate east of the Nicobar Island, where, a prominent gravity “high” follows the Nicobar Deep. The Slab-Residual Gravity Anomaly (SRGA) and Mantle Bouguer Anomaly (MBA) maps prepared for the Andaman plate margin bring out a double-peaked SRGA “low” in the range of − 150 to − 240 mGal and a wider-cum-larger MBA “low” having the amplitude of − 280 to − 315 mGal demarcating the Andaman arc–trench system. The gravity models provide evidences for structural control in propagating the rupture within the lithosphere. The plate margin configuration below the Andaman arc is sliced by the West Andaman Fault (WAF) as well as by a set of sympathetic faults of various proportions, often cutting across the fore-arc sediment package. Some of these fore-arc thrust faults clearly give rise to considerably high post-seismic activity, but the seismic incidence along the WAF further east is comparatively much less particularly in the north, although, the lack of depth resolution for many of the events prohibits tracing the downward continuity of these faults. Tectonic correlation of the gravity-derived models presented here tends to favour the presence of oceanic crust below the Andaman–Nicobar Outer Arc Ridge.  相似文献   

Homi Nusserwanji Sethna (1923–2010)     

B. P. Radhakrishna 《Journal of the Geological Society of India》2010,76(5):433-436

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Shelf sediments of the Ganges delta with special emphasis on the mineralogy of the western part,Bay of Bengal,Indian Ocean     

Tapas Kumar Mallik 《Marine Geology》1976,22(1):1-32

Shelf sediments at the mouth of the Hooghly River which forms the western part of the Ganges—Brahmaputra delta consist of sands, silts and clays and their various admixtures. The bulk of the sediments consists of moderately sorted fine sand to very fine sand. There is variation in lithology in the vertical and horizontal directions, as revealed from the study of the grab and core samples collected in this area, suggesting growth of the delta in different stages. In most of the samples three populations have been recognised. The grain-size variation has resulted from mixing of a number of different grain-size populations. A detailed study of the heavy minerals indicates that the suite consists of hornblende, tremolite/actinolite, opaques, zircon, pyroxenes (ortho-and clino-), garnet, sillimanite, chlorite, muscovite, biotite, epidote, monazite, kyanite, staurolite, riebeckite, carbonates and glauconite. The assemblage and the distribution patterns suggest two distinct mixed igneous and metamorphic sources for the sediments—the Himalayas to the north, mainly drained by the Ganges—Brahmaputra and their tributaries, and the peninsular shield drained by the Dhamra and other easterly-flowing rivers debouching into the Bay of Bengal. The mineralogy of the core samples in the top and bottom layers does not differ, indicating that the source area remained the same during the time of deposition of the sediments. The mineralogy of the sediments in this area, when compared with the mineralogy of the Deep-Sea Drilling Project site in the Bengal fan situated very far to the south, shows similarity because the sediments of the Ganges are carried to the deep-sea. Depending on the mineral assemblage, the area has been divided into four distinct zones: (1) Hooghly River province, consisting of hornblende, tremolite/actinolite, epidote and garnet; (2) a mixed province characterised by epidote, monazite, zircon, kyanite, staurolite, hornblende, tremolite/actinolite, biotite; (3) Dhamra River province characterised by opaques, sillimanite and orthopyroxene; (4) an offshore province comprising muscovite, chlorite and pyroxene. ILlite and kaolinite are the principal clay minerals in the sediments. The mineralogical, grain size and the lithologic studies of the sediments from the core samples suggest a southward to south-southwestward direction of dispersals of the sediments in the eastern part of the area.  相似文献   

Surface flux modelling using ARIMA technique in humid subtropical monsoon area     

Manoj Kumar  Anil Kumar  N.C. Mahanti  Chinmay Mallik  Ripunjay K. Shukla 《Journal of Atmospheric and Solar》2009,71(12):1293-1298

In this paper, we attempt to fit sensible heat fluxes obtained by the profile method between 1–2 and 1–4 m height into the autoregressive integrated moving average (ARIMA) family. In both the profiles, fluxes are found to fit into the first-order autoregression [AR (1)] model, which is the continuous analog of the first-order Markov chain. The ARIMA (1, 0, 0) model was able to simulate the heat flux value for 1 h in advance for both the profiles (1–2 and 1–4 m height) generating a prediction error of 18.28% and 4.95%, respectively.  相似文献   

Estimation of sedimentary layer shear wave velocity using micro-tremor H/V ratio measurements for Bangalore city     

B.V. Dinesh  G.J. Nair  A.G.V. Prasad  P.V. Nakkeeran  M.C. Radhakrishna 《Soil Dynamics and Earthquake Engineering》2010

For assessing earthquake hazard of metro cities, knowledge of soil amplification, thickness and properties of sedimentary layer are essential. In order to map the soil thickness using microtremor survey method, in Bangalore city, it is required to calibrate the relation between fundamental resonance frequency of the soil layer and its thickness for the region. For this purpose microtremor survey was carried out at 34 locations in the city where borehole log was available. The resonance frequency of the soil is evaluated from the microtremor recordings using the H/V ratio technique. A nonlinear regression relation between the thickness of sedimentary layer h (m), from the borehole logs, and the resonance frequency f_r (Hz), was derived as h=(58.3±8.8)f_r^{−(0.95)±0.1}. Using the model of shear wave velocity increasing with depth at these locations, the derived average shear wave velocity and the corresponding soil thickness were used, to get an empirical relation between V_S (m/s) and depth z(m), as V_s=(174±28)(1+z)^0.16±0.07. This relation also compares reasonably with the fit obtained between simulated V_S and depth from borehole logs for Bangalore city. The calibrated relations can be used at locations in Bangalore city where borehole logs are not available, for finding the thicknesses and shear wave velocities of the local soil layers at the survey locations.  相似文献   

A Quick appraisal of ground deformation in indian region due to the october 8, 2005 earthquake, Muzaffarabad, Pakistan     

P. K. Champati ray  R. J. G. Perumal  V. C. Thakur  M. I. Bhat  M. A. Mallik  Vivek Kumar Singh  R. C. Lakhera 《Journal of the Indian Society of Remote Sensing》2005,33(4):465-473

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Structure of Charnockitic basement in a part of the Krishna-Godavari basin, Andhra Pradesh     

I. V. Radhakrishna Murthy  S. Bangaru Babu 《Journal of Earth System Science》2006,115(4):387-393

A regional magnetic survey was carried out over an area of 8000 km² in Godavari districts of Andhra Pradesh, India, which is covered by the rocks of Eastern Ghat Mobile Belt (EGMB)viz., the Khondalitic series and Charnockites in the northern half and Permian to Mesozoic and Cenozoic sediments in the southern half, and forms a part of the Krishna-Godavari (K-G) basin. The survey brought out a strong NE-SW trending anomaly in the area covered by the rocks of Eastern Ghat Mobile Belt (EGMB), and a mild ENE-WSW trending anomaly in the area covered by the sediments of the Krishna-Godavari (K-G) basin. The NE-SW trending anomaly in the northern half could be attributed to the exposed/near surface Charnockite basement that has come closer to the surface as a result of Eastern Ghat Mobile Belt (EGMB) tectonics. Explanation of the mild ENE-WSW trending anomaly over the sediments of the Krishna-Godavari (K-G) basin required a faulted magnetic basement at depth downthrown towards the south. It is therefore concluded that the Charnockitic basement together with the Khondalite group of rocks which are folded and faulted during the different phases of tectonics of Eastern Ghat Mobile Belt (EGMB) extend into the Krishna-Godavari (K-G) basin and further, were involved in faulting during the phases of formation and sedimentation in the Krishna-Godavari (K-G) basin.  相似文献   

Land scarcity and land access in a hazard-prone island: Sagar,Indian Sundarbans     

Chinmoyee Mallik  Sunando Bandyopadhyay  Sumana Bandopadhyay 《Singapore journal of tropical geography》2023,44(2):255-276

The analytical inseparability of natural environment and society is reiterated by the findings of this study which contributes to a genre of studies that centre-stages the socio-ecological system. This study seeks to understand the interplay of state-related and other modes of securing property rights in the context of pervasive coastal hazards through a case study from the Indian Sundarbans region (Sagar Island in West Bengal). This paper also contributes to research pertaining to slow-onset disasters and attempts to examine emerging dimensions of land scarcity as well as diverse modes of access to land in the context of progressive ecological vulnerability. The analysis highlights the varying shades of declining land access and investigates how existing land policies and disaster management mechanisms remain far from extending security to communities experiencing environmental crisis. The paper thereby examines how community and state agencies adopting means to allocate property may in fact refute legality and perpetuate informality.  相似文献