Seismicity of the north-eastern region (N.E.R.) of India

Summary The earthquake pattern in the N.E.R. of India is investigated on the background of tectonic conditions. The epicentre maps and the cross-sections indicate some regularities in the spatial distribution of foci, particularly the existence of a Benioff zone, dipping down to 200 km at an angle of 35°–40° to the East between 25° N and 21° N. The shallow and intermediate activities in the Indoburmese zone seem to be mutually related as evidenced by the coincidence of periods of quiescence and activity. The origin of the largest of the whole region (15 Aug. 1950, M=8.6) can be accommodated in the statistics only by assuming a very large preparatory area also encompassing the extended Mishmi region. This event seems to be a rather exceptional event with the return period larger than the sample used for investigation, i.e. 54 years. The problem of a gap in the region of the Upper Assam remains open, the lack of activity also be explained also by pure geological reasons, i.e. by the age of the stable geological formation. The maps and the statistics of extremes provide the estimate of probability of occurrence of large events for practical purpose.     

Petrographical and thermo-chemical investigation of some North East Indian high sulphur coals

The Tertiary North East Indian coals, classified as sub-bituminous rank, have found less industrial application owing to their physico-chemical attributes. These coals are characterized by low ash (<15%), high volatile matter (>35%) and high sulphur (2.9-4.46%). Majority of the sulphur occurs in organic form affixed to the coal matrix owing to marine influence, is difficult to remove. The coal maceral analysis shows the dominance of vitrinite (>75%) with lesser amounts of liptinite and inertinite. Reflectance measurements (Rmax) of these sub-bituminous coals fall in the range of 0.57 to 0.65. In this study, the petrographical (maceral), thermal and other physico-chemical analyses of some low rank Tertiary sub-bituminous coals from north-east India were carried out to assess their potential for combustion, liquefaction and coal bed methane formation. The petrofactor, conversion (%) and oil yield (%), combustion efficiency of the coal samples were determined. The respective linear correlations of conversion (%) of the coals with their vitrinite contents, petrofactor and oil yield values have been discussed. The relative combustion efficiency of the coals was measured from the thermo gravimetric analysis (TGA) of coals. The influence of maceral composition upon gas adsorption characteristics of these high volatile coals showed the increase in methane adsorption with vitrinite enrichment. Both the maceral and mineral matter contents were observed to have important influence on the gas adsorption characteristics.     

Topographic correction of ALOS-PALSAR images using InSAR-derived DEM

Topographic corrections of synthetic aperture radar (SAR) images over hilly regions are vital for retrieval of correct backscatter values associated with natural targets. The coarse resolution external digital elevation models (DEM) available for topographic corrections of high resolution SAR images often result into degradation of spatial resolution or improper estimation of backscatter values in SAR images. Also, many a times the external DEMs do not spatially co-register well with the SAR data. The present study showcases the methodology and results of topographic correction of ALOS-PALSAR image using high resolution DEM generated from the same data. High resolution DEMs of Jaipur region, India were generated using multiple pair SAR images acquired from ALOS-PALSAR using interferometric (InSAR) techniques. The DEMs were validated using differential global positioning system measured elevation values as ground control points and were compared with photogrammetric DEM (advanced spaceborne thermal emission and reflection radiometer – ASTER) and SRTM (Shuttle Radar Topography Mission) DEM. It was observed that ALOS-PALSAR images with optimum baseline parameters produced high resolution DEM with better height accuracy. Finally, the validated DEM was used for topographic correction of ALOS-PALSAR images of the same region and were found to produce better result as compared with ASTER and SRTM-DEM.     

The 2020 Mw 5.5 Mizoram earthquake and associated swarm activity in the junction of the Surma Basin and Indo-Myanmar Subduction Region

Natural Hazards - Two Artificial Intelligence (AI) methods, Fuzzy Inference System (FIS) and Artificial Neural Network (ANN), are applied to Landslide Susceptibility Mapping (LSM), to compare...     

Giant radio sources

We present multifrequency Very Large Array (VLA) observations of two giant quasars, 0437−244 and 1025−229, from the Molonglo Complete Sample. These sources have well-defined FR II radio structure, possible one-sided jets, no significant depolarization between 1365 and 4935 MHz and low rotation measure (|RM|<20 rad m⁻²). The giant sources are defined to be those with overall projected size 1 Mpc. We have compiled a sample of about 50 known giant radio sources from the literature, and have compared some of their properties with a complete sample of 3CR radio sources of smaller sizes to investigate the evolution of giant sources, and test their consistency with the unified scheme for radio galaxies and quasars. We find an inverse correlation between the degree of core prominence and total radio luminosity, and show that the giant radio sources have similar core strengths to smaller sources of similar total luminosity. Hence their large sizes are unlikely to be caused by stronger nuclear activity. The degree of collinearity of the giant sources is also similar to that of the sample of smaller sources. The luminosity–size diagram shows that the giant sources are less luminous than our sample of smaller sized 3CR sources, consistent with evolutionary scenarios in which the giants have evolved from the smaller sources, losing energy as they expand to these large dimensions. For the smaller sources, radiative losses resulting from synchrotron radiation are more significant while for the giant sources the equipartition magnetic fields are smaller and inverse Compton loss owing to microwave background radiation is the dominant process. The radio properties of the giant radio galaxies and quasars are consistent with the unified scheme.     

Nanodiamonds and silicate minerals in ordinary chondrites as determined by micro‐Raman spectroscopy

We present here the Raman spectroscopic study of silicate and carbonaceous minerals in three ordinary chondrites with the aim to improve our understanding the impact process including the peak metamorphic pressures present in carbon‐bearing ordinary chondites. The characteristic Raman vibrational peaks of olivines, pyroxenes, and plagioclase have been determined on three ordinary chondrites from India, Dergaon (H5), Mahadevpur (H4/5), and Kamargaon (L6). The Raman spectra of these meteorite samples show the presence of nanodiamonds at 1334–1345 cm^?1 and 1591–1619 cm^?1. The full‐width at half maximum (FWHM) of Raman peaks for Mahadevpur and Dergaon reflect the nature of shock metamorphism in these meteorites. The frequency shift in Raman spectra might be because of shock effects during the formation of the diamond/graphite grains.     

Simulation of strong ground motion for a potential Mw7.3 earthquake in Kopili fault zone,northeast India

Natural Hazards - The occurrence of major natural disasters in recent years has impacted large cities worldwide and boosted the need of assessing urban resilience. As a key factor of resilience,...     

Seismotectonic study of Kishtwar region of Jammu Province using local broadband seismic data

Two moderate earthquakes of Mw 5.7 on the first of May and Mw 5.2 on the second of August occurred in the Kishtwar region in the year 2013. Our broadband seismic observatories located in the region recorded these events and the aftershocks. We analyzed these data to understand the seismotectonics of this region. Most of the events were located between 33.03° to 33.29° N latitude and 75.40° to 76.07° E longitude. Focal depths of these shallow earthquakes range from 7 to 12 km and are confined between Panjal Thrust (PT) and Kishtwar Window (KW). Spectral analysis of these events reveals that stress drop, source radius, corner frequency, and moment magnitude varied between 3.3 and 70.1 bars, 0.121 and 3.55 km, 0.397 and 6.06 Hz, and Mw 2.2 and Mw 5.7, respectively. The low stress drop of small-magnitude earthquakes reveals the brittle nature of the upper crust which is coincident with the field observations. The variation of stress drop with magnitude shows positive correlation whereas no such relation was observed between stress drop and depth of focus. The b value calculated (0.83) for the area reveals high stress accumulation within the incompetent rock zones in the area.