Magnitude estimation of Koyna-Warna earthquakes, India     

P. Mandal  B.K. Rastogi  C.S.P. Sarma  P.S. Raju  M. Kousalya 《Journal of Seismology》2002,6(4):447-458

The paper presents the current state of magnitude estimation for Koyna earthquakes exceeding magnitude 3.0. We estimate coda duration magnitude from analogue seismograms recorded on the short period vertical (SPZ) seismometer at Hyderabad seismic observatory HYB and determine moment magnitude using very broad-band (VBB) data from the Geoscope station (HYB)and short period digital data from the local seismic network of NationalGeophysical Research Institute (NGRI) around the Koyna and Warna reservoirs.Firstly, the seismograms of 97 Koyna earthquakes exceeding magnitude 4.0 havebeen used to establish a new empirical coda duration magnitude scale which includes the higher order terms of log₁₀, where is the coda length in seconds. Four background noise levels (1, 2, 6 and 10 mm) areconsidered to estimate the coda duration. We found that the duration magnitudes for 1 mm background level are more stable than those for 2, 6 and 10 mm. The new coda duration magnitude (M_dnew) scale, for 1 mmlevel, is:M_dnew = –0.594 + 2.04 log₁₀ – 0.0435 (log₁₀)²The estimated M_dnew are compatible with the reported M_S values of the NGRI observatory and the m_b values of the United States Geological Survey (USGS). These magnitudes can be obtained within the standard deviation of ± 0.26 units of M_S (NGRI). A new relatively homogeneous catalog for Koyna earthquakes of M_dnew 4.0 is obtained. The momentmagnitudes for 34 Koyna-Warna events of M_dnew ranging from 3.0 to 5.4 have been estimated using two techniques. The first utilizes amplitudes of band-pass filtered (between 15 and 30 sec) velocity traces of moderate Koyna-Warna earthquakes of M_W} 4.4 to 5.4, we abbreviate the magnitude using M_A. The second is based on the S-wave spectrum of short period seismograms of local earthquakes (M_W < 3.8). Moment magnitudes estimated by spectral analysis mainly depend on the estimation of event's long-period spectral level and appears to saturate for moderate Koyna-Warnaearthquakes (M_W > 3.8). We recommend the use of both techniques whenever possible. The estimated moment magnitudes and M_dnew show an almost linear relationship with a standard deviation of ± 0.05.  相似文献   

Delineation of Active Faults, Nucleation Process and Pore Pressure Measurements at Koyna (India)   总被引：1，自引：0，他引：1  

R. K Chadha  H. K Gupta  H. J Kumpel  P. Mandal  A. Nageswara Rao  N. Kumar  I. Radhakrishna  B. K Rastogi  I. P Raju  C. S. P Sarma  C. Satyamurthy  H. V. S Satyanarayana 《Pure and Applied Geophysics》1997,150(3-4):551-562

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Prediction of elastic settlement of rectangular raft foundation — a coupled FE–BE approach     

J. J. Mandal  D. P. Ghosh 《国际地质力学数值与分析法杂志》1999,23(3):263-273

A numerical method of analysis is proposed for computation of the elastic settlement of raft foundations using a FEM–BEM coupling technique. The structural model adopted for the raft is based on an isoparametric plate bending finite element and the raft–soil interface is idealized by boundary elements. Mindlin's half-space solution is used as a fundamental solution to find the soil flexibility matrix and consequently the soil stiffness matrix. Transformation of boundary element matrices are carried out to make it compatible for coupling with plate stiffness matrix obtained from the finite element method. This method is very efficient and attractive in the sense that it can be used for rafts of any geometry in terms of thickness as well as shape and loading. Depth of embedment of the raft can also be considered in the analysis. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Discrimination and classification of mangrove forests using EO-1 Hyperion data: a case study of Indian Sundarbans     

Tanumi Kumar  Abhishek Mandal  Dibyendu Dutta  R. Nagaraja  Vinay Kumar Dadhwal 《国际地球制图》2019,34(4):415-442

In remote sensing the identification accuracy of mangroves is greatly influenced by terrestrial vegetation. This paper deals with the use of specific vegetation indices for extracting mangrove forests using Earth Observing-1 Hyperion image over a portion of Indian Sundarbans, followed by classification of mangroves into floristic composition classes. Five vegetation indices (three new and two published), namely Mangrove Probability Vegetation Index, Normalized Difference Wetland Vegetation Index, Shortwave Infrared Absorption Index, Normalized Difference Infrared Index and Atmospherically Corrected Vegetation Index were used in decision tree algorithm to develop the mangrove mask. Then, three full-pixel classifiers, namely Minimum Distance, Spectral Angle Mapper and Support Vector Machine (SVM) were evaluated on the data within the mask. SVM performed better than the other two classifiers with an overall precision of 99.08%. The methodology presented here may be applied in different mangrove areas for producing community zonation maps at finer levels.  相似文献   

Broad-band spectral evolution and temporal variability of IGR J17091-3624 during its 2016 outburst: <Emphasis Type="Italic">SWIFT</Emphasis> and <Emphasis Type="Italic">NuSTAR</Emphasis> results     

Radhika D.  Sreehari H.  A. Nandi  N. Iyer  S. Mandal 《Astrophysics and Space Science》2018,363(9):189

We report on the 2016 outburst of the transient Galactic Black Hole candidate IGR J17091-3624 based on the observation campaign carried out with SWIFT and NuSTAR. The outburst profile, as observed with SWIFT-XRT, shows a typical ‘q’-shape in the Hardness Intensity Diagram (HID). Based on the spectral and temporal evolution of the different parameters, we are able to identify all the spectral states in the q-profile of HID and the Hardness-RMS diagram (HRD). Both XRT and NuSTAR observations show an evolution of low frequency Quasi periodic oscillations (QPOs) during the low hard and hard intermediate states of the outburst rising phase. We also find mHz QPOs along-with distinct coherent class variabilities (heartbeat oscillations) with different timescales, similar to the \(\rho \)-class (observed in GRS 1915+105). Phenomenological modelling of the broad-band XRT and NuSTAR spectra also reveals the evolution of high energy cut-off and presence of reflection from ionized material during the rising phase of the outburst. Further, we conduct the modelling of X-ray spectra of SWIFT and NuSTAR in 0.5–79 keV to understand the accretion flow dynamics based on two component flow model. From this modelling, we constrain the mass of the source to be in the range of \(10.62\mbox{--}12.33~\mbox{M}_{\odot }\) with 90% confidence, which is consistent with earlier findings.  相似文献   

Observational aspects of outbursting black hole sources: Evolution of spectro-temporal features and X-ray variability     

H. Sreehari  Anuj Nandi  D. Radhika  Nirmal Iyer  Samir Mandal 《Journal of Astrophysics and Astronomy》2018,39(1):5

We report on our attempt to understand the outbursting profile of Galactic Black Hole sources, keeping in mind the evolution of temporal and spectral features during the outburst. We present results of evolution of quasi-periodic oscillations, spectral states and possible connection with jet ejections during the outburst phase. Further, we attempt to connect the observed X-ray variabilities (i.e., ‘class’/‘structured’ variabilities, similar to GRS 1915+105) with spectral states of black hole sources. Towards these studies, we consider three black hole sources that have undergone single (XTE J1859+226), a few (IGR J17091-3624) and many (GX 339-4) outbursts since the start of RXTE era. Finally, we model the broadband energy spectra (3–150 keV) of different spectral states using RXTE and NuSTAR observations. Results are discussed in the context of two-component advective flow model, while constraining the mass of the three black hole sources.  相似文献   

Editorial     

Samir Mandal  Indranil Chattopadhyay  Anuj Nandi  Santabrata Das 《Journal of Astrophysics and Astronomy》2018,39(1):1

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Strong ground motions from two moderate size (Mw5.5) Kachchh intraplate earthquakes,Gujarat, India     

Mandal  Prantik 《Natural Hazards》2020,103(2):2441-2458

Natural Hazards - During 2006–2016, a strong motion seismic network of twenty 3-component accelerogarphs was deployed by the National Geophysical Research Institute, Hyderabad, India, in the...  相似文献   

Relocation of aftershocks of the 2001 Bhuj earthquake: A new insight into seismotectonics of the Kachchh seismic zone,Gujarat, India     

Prantik Mandal  O.P. Pandey 《Journal of Geodynamics》2010,49(5):254-260

In view of an anomalous crust–mantle structure beneath the 2001 Bhuj earthquake region, double-difference relocations of 1402 aftershocks of the 2001 Bhuj earthquake were determined, using an improved 1D velocity model constructed from 3D velocity tomograms based on data from 10 to 58 three-component seismograph stations. This clearly delineated four major tectonic features: (i) south-dipping north Wagad fault (NWF), (ii and iii) south-dipping south Wagad faults 1 and 2 (SWF₁, SWF₂), and (iv) a northeast dipping transverse fault (ITF), which is a new find. The relocated aftershocks correlate satisfactorily with the geologically mapped and inferred faults in the epicentral region. The relocated focal depths delineate a marked variation to the tune of 12 km in the brittle–ductile transition depths beneath the central aftershock zone that could be attributed to a lateral variation in crustal composition (more or less mafic) or in the level of fracturing across the fault zone. A fault intersection between the NWF and ITF has been clearly mapped in the 10–20 km depth range beneath the central aftershock zone. It is inferred that large intraplate stresses associated with the fault intersection, deepening of the brittle–ductile transition to a depth of 34 km due to the presence of mafic/ultramafic material in the crust–mantle transition zone, and the presence of aqueous fluids (released during the metamorphic process of eclogitisation of lower crustal olivine-rich rocks) and volatile CO₂ at the hypocentral depths, might have resulted in generating the 2001 Bhuj earthquake sequence covering the entire lower crust.  相似文献   

Major ion chemistry of two cratonic rivers in the tropics: Weathering rates and their controlling factors     

Anupam Samanta  Gyana Ranjan Tripathy  Aswin T. Pradeep  Anirban Mandal 《水文研究》2021,35(2):e14035

Continental weathering plays a dominant role in regulating the global carbon cycle, soil chemistry and nutrient supply to oceans. The CO₂-mediated silicate weathering acts as a major CO₂ sink, whereas sulphuric acid-mediated carbonate dissolution releases CO₂ to the atmosphere–ocean system. In this study, dissolved major ions and silica concentrations of two tropical (Damodar and Subarnarekha) river systems from India have been measured to constrain the type and rate of chemical weathering for these basins. The total dissolved solids (TDS) of these rivers, a measure of total solute supply from all possible sources, are about 2–3 times higher than that of the global average for rivers. Mass balance calculations involving inverse modelling estimate that 63 ± 11% of total cations are derived from rock weathering, of which 27 ± 7% of cations are supplied through silicate weathering. The sulphide-S concentrations are estimated by comparing the water chemistry of these two rivers with that of a nearby river (Brahmani) with similar lithology but no signatures of sulphide oxidation. The outflows of Damodar and Subarnarekha rivers receive 17% and 55% of SO₄ through sulphide oxidation, respectively. The sulphide oxidation fluxes from the ore mining areas, such as upper Damodar (0.52 × 10⁹ mol/yr) and lower Subarnarekha (0.66 × 10⁹ mol/yr) basins, are disproportionally (~9 times) higher compared to their fractional areal coverage to the global drainage area. The corresponding CO₂ release rate (2.84 × 10⁴ mol/km²/yr) for the Damodar basin is lower by five times than its CO₂ uptake rate (1.38 × 10⁵ mol/km²/yr). The outcomes of this study underscore the dominance of sulphide oxidation in controlling the dissolved chemical (cationic and sulphur) fluxes.  相似文献