March, 2026 || Volume 30 No.02
Volume 30(2) March 2026 (2-6)
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1
Seismic quiescence and spatio-temporal b-value variation in the Himalayan region for enhanced hazard analysis
Ashisan Dhodray and S. Lasitha*
Pondicherry University, Puducherry- 605014, India
ABSTRACT
This study presents an integrated spatial–temporal analysis of the Gutenberg–Richter b-value to evaluate the stress distribution and seismic potential along the Himalayan arc using earthquake catalogue spanning 1964–2025. The spatial distribution of b-values (0.5–1.2), exhibits marked heterogeneity, reflecting the complex tectonic architecture and variable stress conditions across the major thrust systems, including the Main Central Thrust (MCT), Main Boundary Thrust (MBT), and Main Frontal Thrust (MFT). Low b-values (<1.0) dominate along the MCT and MBT zones, denoting regions of elevated stress accumulation. In contrast, higher b-values (1.0–1.2) occur north of the MCT and along the MFT, representing relatively relaxed zones. A decreasing trend in b-value from west (0.8–1.0) to east (0.5–0.7), indicates increasing stress concentration in the eastern Himalaya.Temporal b-value variations reveals a cyclic pattern of seismic activity, with alternating phases of quiescence and activation. A recurring sequence of seismic quiescence, followed by a decline in b-value (?b = 0.1–0.4), consistently precedes moderate-to-large earthquakes (Mb ? 6.0) signifying progressive stress build-up prior to rupture. Longer quiescent intervals (?5 years) tend to precede major earthquakes (Mb ? 6.5), while shorter intervals (1–3 years) are associated with moderate events (Mb 5.7–6.1). The observed decline in b-value, following quiescent phases, may serve as a potential short-term precursor to large earthquakes offering valuable insights for seismic hazard assessment and forecasting in the Himalayan region. The increase in frequency of major earthquakes highlights a potential escalation of seismic energy release in the region.
2
Laser Raman characterization and 3D mapping of chromite crystal from Asurabandha mines of Bhuban ultramafic complex, Odisha (India)
Ashish Gupta and Dinesh Pandit*
Department of Geology, Institute of Science, Banaras Hindu University, Varanasi - 221005, India https://doi.org/10.71122/JIGU.30(2)2026.0011
ABSTRACT
The Asurabandha chromite deposits are hosted in the Bhuban Ultramafic Complex (BUC), which is located in the Dhenkanal district of Odisha. The BUC forms part of the transition domain between the Singhbhum Craton and the Eastern Ghats Mobile Belt (EGMB). Highly altered chromitite rocks are found as isolated, irregular and sporadic orebodies located on the southern side of the Sukinda Ultramafic Complex (SUC) accompanied by the granite-charnockite association. Petrographic studies inferred the existence of heteradcumulate texture in the chromitite rock, which indicates early crystallization during the cooling of an ultramafic magma. Chromite begins to crystallize at a high temperature and accumulates to growth of crystal framework, subsequently crystallizing to form silicate minerals (olivine or pyroxene), that later altered to serpentine. Occurrences of euhedral chromite crystal indicates inherent crystal growth during the crystallization of magma. The Laser Raman Micro Spectroscopy (LRMS) analysis, displays four characteristics Raman Shift at 454, 559, 736 and 1437 cm-1 for chromite and five diagnostic Raman Shift at 127, 206, 397, 465 and 1166 cm-1 for serpentine. Laser Raman-SNOM scanning, 2D and 3D mapping of euhedral hexagonal chromite crystal, suggests its heterogenous internal crystal structure in the ultramafic rocks. In the chromite crystal, internal heterogeneity may appear because of trace element substitution during the magmatic crystallization or secondary alteration processes like serpentinization and carbonation. The Asurabandha chromite deposits are characterized by metasomatic alteration, serpentinization and carbonation, where original silicate minerals have been replaced by serpentine, presenting challenges for mineral exploration due to the extent beyond lateritic overburden.
3
Abundance, distribution pattern and health risk assessment of polycyclic aromatic hydrocarbons in size?segregated aerosols during Diwali festival in Delhi (India)
Nisha Rani1,2 and Monika J. Kulshrestha*1,2
1CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi-110012, India
2Academy of Scientific and Innovative Research (AcSIR), Ghaziabad-201002, India
https://doi.org/10.71122/JIGU.30(2)2026.0012
ABSTRACT
Size?segregated aerosol samples were collected in Delhi during the Diwali festival (3-5 November, 2021) to evaluate Polycyclic Aromatic Hydrocarbons (PAHs) concentrations, molecular distribution, sources, and associated health risk. 3 samples (each with nine size ranges) were collected using an eightstage Andersen cascade impactor, i.e., before-Diwali (BD), Diwali day (DD), and after-Diwali (AD). The ?PAHs concentrations across different aerosol size fractions were in the range 1.2-147.4 ng/m³, with a sharp spike on Diwali day, and remained high in the after-Diwali sample. The nine size ranges were classified into submicron (PM<0.43-1.1), fine (PM1.1-2.1), and coarse (PM2.1->9) fractions. Submicron fraction dominated PAHs loading (61.4%), followed by coarse (21.0%) and fine (17.6%) fractions. Naphthalene, benzo[b]fluoranthene, and Chrysene were observed to be the most abundant PAHs. The lognormal size distribution was bimodal, with peaks in the submicron and coarse fractions. Molecular diagnostic ratios indicated firecracker burning, vehicular emissions, coal/biomass burning, and cooking as the dominant PAHs sources. Inhalation cancer risk assessment revealed significantly higher carcinogenic risk in the submicron fraction, with risk exceeding acceptable limits by several orders of magnitude on Diwali day, underscoring the severe health implications of festival-related emissions.
4
A comparative study of stochastic nature of anthropogenic aerosol using SARIMA and LSTM methods
J. Arul Asir1*, H. Johnson Jeyakumar1 and C. P. Anil Kumar2
1P.G and Research Department of Physics, Pope’s College, Manonmaniam Sundaranar University, Abishekapatti, Tirunelveli – 627012, Tamil Nadu, India.
2Equatorial Geophysical Research Laboratory, Indian Institute of Geomagnetism, Tirunelveli- 627011, Tamil Nadu, India.
https://doi.org/10.71122/JIGU.30(2)2026.0013
ABSTRACT
The troposphere is a dynamic region characterized by intricate interactions among natural and anthropogenic processes. Among these, aerosol loading, particularly fine particulate matter (PM2.5), poses significant challenges in understanding the greenhouse effect and complicates air quality assessment due to its spatiotemporal variability. This study presents a comparative stochastic modelling framework for forecasting anthropogenic aerosol concentrations using both parametric and non-parametric approaches over Alandur (13.0° N, 80.10° E), Tamil Nadu, India. Specifically, a Seasonal Autoregressive Integrated Moving Average (SARIMA) model and a Long Short-Term Memory (LSTM) neural network, were employed to forecast PM2.5 levels using observational data from 2023 and 2024. SARIMA, a classical statistical model, effectively captured regular patterns and seasonal trends. In contrast, the LSTM model, a deep learning approach, demonstrated enhanced performance in modelling non-linear dependencies and temporal dynamics. Model evaluations based on Root Mean Square Error (RMSE), indicated that LSTM consistently outperformed SARIMA, underlining its effectiveness in capturing the stochastic and complex behaviour of aerosol concentrations. These findings underscore the potential of integrating advanced machine learning techniques with traditional time series models to enhance the accuracy of air quality forecasting and environmental risk mitigation strategies.
5
Estimation of site response beneath seismic stations in the vicinity of Jaitapur region (Ratnagiri district, Maharashtra), India, using H/V Spectral Ratios
M. Suneetha, H.V.S. Satyanarayana* and P. Pavan Kishore
CSIR-National Geophysical Research Institute, Hyderabad- 500007, India
https://doi.org/10.71122/JIGU.30(2)2026.0014
ABSTRACT
Jaitapur village (16.59°N, 73.35°E) in Ratnagiri district, Maharashtra, India, is the site of a proposed Nuclear Power Plant that lies within the Konkan Plains of the Deccan Volcanic Province. The region has not experienced any moderate to large earthquakes (Mw ? 5.5) during the last five decades, except for a few moderate events (Mw ? 5.0) occurring more than 75 km from the Koyna–Warna seismic zone. At the request of the Nuclear Power Corporation of India Limited (NPCIL), a local seismological network was operated by CSIR–National Geophysical Research Institute (CSIR-NGRI), Hyderabad, from November 2004 to February 2012. In this study, ambient noise data recorded during January 2012 at six seismological stations (Mervy, Madban, Dassure, Mutat, Kharepatan, and Oni), were analysed using the Horizontal-to-Vertical Spectral Ratio (HVSR) technique to estimate the site response characteristics. The predominant resonance frequencies at these sites range from 1.5 to 6.0 Hz, with amplification factors between 0.6 and 9.0. Using an average shear-wave velocity of 350 m/s for the laterite and weathered basalt layer, the thickness of the near-surface geological layer was estimated to vary from approximately 17.5 m to 58.3 m. The results indicate significant spatial variability in site response across the region, reflecting lateral heterogeneity in the near-surface geology. These findings provide preliminary constraints on local site effects, which are important for seismic hazard assessment and infrastructure planning in and around the Jaitapur region.
6
Acanthite (Ag?S) as an indicator of late-stage silver mineralization in the Zawar Pb–Zn system, Rajasthan, India: Insights from Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDS) microtextural studies
Sima Gorai*, Bulusu Sreenivas and T. Vijaya Kumar
CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad 500007, India.
https://doi.org/10.71122/JIGU.30(2)2026.0015
ABSTRACT
This study investigates the occurrence, microtextural characteristics and chemical composition of acanthite (Ag?S) in the Zawar deposit, Rajasthan, India, to understand the conditions and the paragenetic relationship of silver mineralization in this classic carbonate-hosted Mississippi Valley Type (MVT) ore deposit. Silver in Zawar, traditionally considered a by-product of lead (Pb) and zinc (Zn) extraction, is shown here to occur as late-stage acanthite developed as distinctive veins and star-shaped aggregates along the weak zones and micro-fractures within earlier-formed pyrite. Scanning Electron Microscopy (SEM) reveals that these acanthite crystals are confined to structurally controlled micro-openings, indicating precipitation from late stage fluids that exploited preexisting sulfide microstructures. Energy-dispersive X-ray spectroscopy (EDS) confirms a dominantly silver (Ag) and, sulfur (S) composition, and only minor iron (Fe) and calcium (Ca), suggesting limited solid solution or sub-microscopic inclusions of associated sulfides. The dominance of monoclinic acanthite in carbonate-hosted, structurally focused sites, is fully consistent with the deposition from basinal brines at low temperatures. These textural and geochemical observations, collectively indicate that silver enrichment at Zawar is genetically linked to the waning stages of MVT-type hydrothermal activity.