Discrimination of explosions and earthquakes: An example based on spectra and source parameters of the 11<Superscript>th</Superscript> May 1998 Pokhran explosion and the 9<Superscript>th</Superscript> April 2009 earthquake

We compare the P-, S- and Lg- spectra of the 11^th May, 1998 Pokhran underground nuclear explosion (NE) with those of an earthquake (EQ) of comparable magnitude that occurred in its vicinity (~100 km west) on 9^th April, 2009, utilizing the waveforms recorded by a Global Seismograph Network station at Nilore (NIL), Pakistan. The contiguous occurrence of these events and the similarity of the travel paths provided a good opportunity to discriminate the nature of the sources. Our results suggest that the Pn/Lg and Pn/Sn amplitude ratios of the explosion and earthquake waveforms exhibit distinct differences in the higher frequency window. Further, since the P-phases have high signal to noise ratio compared to their S counterparts, we utilize their spectra to derive the source parameters of the NE and EQ sources. Our results show that the seismic moment, corner frequency and source dimension of the explosion are ~1.58X10¹⁷ Nm, 1.18 Hz and ~0.793 km respectively. The moment magnitude (M_W) and surface wave magnitude (M_S) for the nuclear explosion are estimated to be ~5.4 and ~3.57 respectively. The values of M_W (5.3) and M_S (4.3) obtained by us for the earthquake are consistent with the estimates in the Harvard catalog and earlier published results. The estimate of M_W for the nuclear explosion was hitherto not available. Lastly, we estimate the yield of the NE to be ~50 kt from the surface wave magnitude and discuss the various limitations related to its estimation.     

Radiation condensation instability in a plasma with ionization and recombination

In this work, we consider radiation (thermal) instability in a weakly ionized plasma with continuous ionization and recombination. The situation can be visualized in the case of envelopes of planetary nebulae, which are envelopes of ionized plasmas surrounding red giant stars. Various observations report continuous photoionization of these plasmas by the highly energetic streams of photons emanating from the parent star. Recently, it has been shown that thermal instability can be a probable candidate in such plasmas for the existence of small scale structures (viz., striations) whose kinematic age is much smaller than that of the parent nebula. We therefore report a systematic study of these plasmas with photoionization and determine the instability domain. We have shown that the continuous ionization and recombination may lead to modification of the underlying instability, which may limit the size of the small structures that are believed to form from these instabilities, and may thus provide an explanation of the physical processes responsible for the existence of these structures. We further show that in many cases the system bifurcates to an ovserstable (growing wave) state from a condensation instability (monotonic) and vice versa.     

The chemical composition of tertiary Indian coal ash and its combustion behaviour – a statistical approach: Part 2

In Part 1 of the present investigation, 37 representative Eocene coal samples of Meghalaya, India were analyzed and their physico-chemical characteristics and the major oxides and minerals present in ash samples were studied for assessing the genesis of these coals. Various statistical tools were also applied to study their genesis. The datasets from Part 1 used in this investigation (Part 2) show the contribution of major oxides towards ash fusion temperatures (AFTs). The regression analysis of high temperature ash (HTA) composition and initial deformation temperature (IDT) show a definite increasing or decreasing trend, which has been used to determine the predictive indices for slagging, fouling, and abrasion propensities during combustion practices. The increase or decrease of IDT is influenced by the increase of Fe₂O₃, Al₂O₃, SiO₂, and CaO, respectively. Detrital-authigenic index (DAI) calculated from the ash composition and its relation with AFT indicates Sialoferric nature of these coals. The correlation analysis, Principal Component Analysis (PCA), and Hierarchical Cluster Analysis (HCA) were used to study the possible fouling, slagging, and abrasion potentials in boilers during the coal combustion processes. A positive relationship between slagging and heating values of the coal has been found in this study.     

Solid state 13C-NMR spectroscopy of some oligocene coals of Assam and Nagaland

Five representative sub-bituminous coals from NE part of India have been analyzed with respect to their distribution of carbon functional groups through ¹³C solid state NMR experiments. The ¹³C Cross Polarised/Magic Angle Spinning NMR spectra of the coal samples were recorded at temperatures of 23°C, 50°C and 70°C respectively and the changes on their structures were interpreted. The NMR spectra of low rank coals were found to exhibit varying degrees of fine structures. The aromaticities of the coal were also determined from the C/H ratios of coal. Some changes in the peak positions along with the formation of simple aromatic units were observed on mild heating.     

Seismic vulnerability assessment of earthquake-prone mega-city Shillong,India using geophysical mapping and remote sensing

ABSTRACT

The concept of seismic vulnerability is a yard-stick of damage estimation from a probable earthquake considering physical cum social dimension and enables a basis for decision-makers to develop preparedness and mitigation strategies. We aim at vulnerability assessment of the typical urban system of capital city Shillong situated on hilly terrain. High-resolution satellite imagery of Shillong facilitates analysis of building footprints, communication network, and open ground. Different building typologies are identified taking into account the building’s structural configuration assessed through a rapid visual survey of more than 15% of total residential households. Slope map demarcates the landslide-prone area through discrete elevation modelling. A methodology incorporating several parameters e.g. building typology, slope angle, shear wave velocity characteristics, geomorphology, and the number of occupants in correlation with a physical measurement of vulnerability is presented and is applied to estimate the dimension of vulnerability. Additionally, MASW survey indicates lithology up to 30?m deep along with the existence of stiff soil and rocks at different depths whereas resonant frequency is identified to be in the range of 6–8?Hz through H/V ratio. Integrating all, it is observed that more than 60% of Shillong city falls under moderate to higher vulnerability and the rest is less vulnerable.     

Multi-Parametric Geophysical Observatory for Earthquake Precursory Research in Assam Valley,Eastern Himalaya (India): Seismotectonic Features of Kopili and Bomdila Faults

Geotectonics - The study of earthquake precursor is being accomplished throughout the world based on observations of ground and ionospheric parameters. The Multiparametric Geophysical Observatory...     

Thermal history of a Late Mesoproterozoic paired metamorphic belt (?) during Rodinia assembly: New insight from medium-pressure granulites from the Aravalli-Delhi Mobile Belt,Northwestern India

In this study, we investigate the possible record of a Late Mesoproterozoic paired metamorphic belt in the Aravalli-Delhi Mobile Belt(ADMB), NW India using a suite of supracrustal and metaigneous granulites from the Pilwa-Chinwali granulite terrain at the north-western margin of the ADMB. Using metamorphic reaction textures, mineral chemistry, metamorphic reaction history, geothermobarometric computations and electron microprobe dating of monazite in 5 samples of pelitic granulite, leptynite gneiss, enderbite and charnockite, we have deduced a medium-pressure granulite facies metamorphism(P between 4.9 and 6.8 kbar, T 760-815℃) along a heating-cooling, counterclockwise P-T path between 1.09 and 1.01 Ga. When collated with published metamorphic and chronological constraints and geological settings of the adjoining crustal domains of the ADMB, these findings provide new insights into the developments of two tectonic domains of contrasting thermal gradients at ca. 1.0 Ga, consistent with metamorphic transformations in tectonically thickened middle-lower crustal sections during continental collision to continental subduction and in the root zones of spatially adjacent island arc, as part of the Rodinia supercontinent assembly event.     

Petro-chemical investigation of some perhydrous Indian coals

An attempt has been made to study the petro-chemical characteristics of some high sulphur sub-bituminous coal samples from Makum coalfield, Assam, India. The proximate and ultimate analyes were carried out and forms of sulphur were determined and their relationships with the Maceral constituents (vitrinite, liptinite, and inertinite) were investigated. The macerals (vitrinite+liptinite+inertinite) have significant relationships (R²>0.500) with volatile matter and carbon, whereas weak correlations were seen with rest of the physico-chemical characteristics of the coals. The study reveals that these coals are rich in vitrinites and sulphur and are aromatic in nature. These coals have good hydrocarbon potential.     

Isotopic r-process abundances produced by supernova explosions

The rapid neutron capture process (r-process) is one of the major nucleosynthesis processes responsible for the synthesis of heavy nuclei beyond iron. Isotopes beyond Fe are most exclusively formed in neutron capture processes and more heavier ones are produced by the r-process. Approximately half of the heavy elements with mass number A>70 and all of the actinides in the solar system are believed to have been produced in the r-process. We have studied the r-process in supernovae for production of heavy elements beyond A=40 with the newest mass values available. The supernovae envelopes at a temperature >10⁹ K and neutron density of 10²⁴ cm⁻³ are considered to be one of the most potential sites for the r-process. We investigate the r-process in a site-independent, classical approach which assumes a chemical equilibrium between neutron captures and photodisintegrations followed by a β-flow equilibrium. We have studied the r-process path corresponding to temperatures ranging from 1.0×10⁹ K to 3.0×10⁹ K and neutron density ranging from 10²⁰ cm⁻³ to 10³⁰ cm⁻³. The primary goal of the r-process calculations is to fit the global abundance curve for solar system r-process isotopes by varying time dependent parameters such as temperature and neutron density. This method aims at comparing the calculated abundances of the stable isotopes with observation. The abundances obtained are compared with supernova explosion condition and found in good agreement. The elements obtained along the r-process path are compared with the observed data at all the above temperature and density range.