Browsing by Author "A. Akilbasha"

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An insight into seismotectonic scenario of the southwestern part of Delhi-NCR and delineation of new faults: Implications to seismic hazard potential
(Elsevier B.V., 2025) Sudipto Bhattacharjee; Sanjay Kumar Prajapati; A. Akilbasha; Om Prakash Mishra
The southwestern region of the Delhi-National Capital Region (NCR) experiences sporadic micro (M ≤ 3.0) and occasional small (M > 3.0) earthquakes with a seasonal influence. This study integrates remote sensing and seismological data to elucidate the seismotectonic scenario and identify potential unmapped faults. Analysis of DEM data (Cartoset) reveals numerous multidirectional minor faults, some coincident or conjugate to known major faults. Earthquake epicentres spatially correlate with several of these delineated faults. Fault plane solutions suggest a transition from central normal faulting to peripheral thrust faulting. Moment tensor decomposition indicates dominant double-couple mechanisms with significant non-double-couple components for earthquakes ranging from Mw 2.5 to 4.4. A major variation in principal stress orientation is apparent between the eastern and western regions of the study area. Stress inversion reveals a NW-SE shortening direction and unusual principal axis plunges, suggesting a rare “odd” or “unknown” faulting regime. These findings suggest ongoing rifting in the eastern Alwar basin may be inducing thrusting in the surrounding region along pre-existing Aravalli-Delhi fold belt thrusts. Seismogenesis likely results from a complex interplay of faulting, regional tectonics, and fluid interaction. This study highlights the value of a multidisciplinary approach for unravelling the intricacies of seismotectonic in low-to-moderate seismicity regions, with varying strengths due to diverse structural heterogeneity associated with mapped or unmapped (hidden) faults, which have been delineated in this study, as an additional information for assessing seismic hazard potential for Delhi-NCR. © 2024 China University of Geosciences (Beijing) and Peking University.
Geopotential imprints on the tectono-thermal evolution of the northwest Indian Ocean
(Springer Science and Business Media B.V., 2025) Shravan Prasanna Kumar; Korimilli Naga Durga Prasad; Akhil Mishra; A. Akilbasha
The study investigates the tectonic and lithospheric characteristics of the northwestern Indian Ocean, emphasizing tectonothermal parameters: Moho depth, Effective Elastic Thickness (Te), loading ratio (F), Depth to the Bottom of the Magnetic Sources (DBMS), and Geoid-to-Topography Ratio (GTR). Low to moderate Te values, moderate to high F values and low to moderate DBMS over aseismic ridges, such as the Laxmi and Laccadive Ridges, suggest dominant subsurface loading due to underplating and mantle magma intrusion. The Murray Ridge exhibits the DBMS close to the Moho, indicating a relatively warm lithosphere. The Carlsberg Ridge, as expected, shows a thin oceanic crust (~ 8 km Moho depth) and significant variations in Te and DBMS along its length. These reflect mantle upwelling, magmatic processes, and lithospheric stretching. Seamounts in the Arabian Basin likely formed due to ridge spreading and volcanic activity near the Carlsberg Ridge. The seamount chain in the East Somali Basin may have formed from magma rising beneath the moving African plate. The Chain Ridge separates oceanic lithospheres of varying ages, showing strong lithospheric support with localized thermal modifications and high GTR. Variations in GTR values depict compensation mechanisms, transitioning from shallow in the younger crust (< 30 Ma) to deeper in the older crust, driven by mantle dynamics and lithospheric processes. The relationship between crustal age and DBMS reveals two tectono-thermal events: one at 35 Ma, which may be associated with Indian-Eurasian collision processes; the other at 65 Ma, is related to Réunion hotspot activity formed that caused Deccan volcanism and underplating in the adjacent region. © The Author(s), under exclusive licence to Springer Nature B.V. 2025.
Seismic Source Characteristics and Scaling Relations in the Northwest Himalayan Region: Case Study of Himachal Pradesh & Uttarakhand
(Birkhauser, 2025) Shikha Vashisth; Ambikapathy Ammani; Himanshu Mittal; A. Akilbasha; Om Prakash Mishra
The Himachal Pradesh and Uttarakhand areas are known for their high seismic activity in India. According to the Bureau of Indian Standards, the areas are situated in seismic zones IV and V, and have the potential to produce small to large earthquakes. These areas have also seen significant seismic events in the past. To accurately and reliably estimate the seismic hazard and simulate the characteristics of strong ground motion in the region, it is essential to evaluate the source characteristics of earthquakes and their scaling relationships. Our investigation involved the estimation of earthquake source parameters and high-frequency spectrum decay parameters using 1059 seismograms, corresponding to 247 earthquake events with magnitudes ranging from 3.0 to 5.5 that occurred in the Himachal Pradesh and Uttarakhand regions of the Northwest Himalaya between 2010 and 2020. The classic Brune’s model is used to estimate source parameters. The relationship can be expressed as M0=2×1015fc-2.316 for Himachal Pradesh and M0=2×1016fc-3.445 for Uttarakhand region, which agrees with previous studies given for the study region, providing vital insights into tectonics and structural heterogeneity beneath the respective regions of Northwest Himalaya. Our analysis revealed that for earthquakes in Himachal Pradesh, the source radius of circular fault ranges from 42 to 771 m, whereas, for events in the Uttarakhand region, it varies from 48 to 437 m. Additionally, the seismic moment ranged from 2 × 1011 N-m to 9.93 × 1015 N-m for Himachal Pradesh and 1.11 × 1011 N-m to 1.40 × 1016 N-m for Uttarakhand events. An increasing trend in stress drop is observed, varying from 0.0026 MPa to 8.66 MPa for Himachal Pradesh and 0.0014 MPa to 9.51 MPa for Uttarakhand, within the similar range of seismic moment. Moreover, the study highlighted that the estimation of κ and fmax is influenced by both source characteristics and propagation path, with the source exerting a significant impact. A detailed analysis of the data suggests that the differences in how earthquakes start and fade in Himachal Pradesh and Uttarakhand are due to the complex geological structures and the intricate earthquake processes in these regions. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.
Statistical Relationship Between Shear Wave Velocity and Penetration Resistance in Indo-Gangetic Plain, Northern India
(Springer, 2025) Pawan Kumar Yadav; A. Akilbasha; A. P. Singh
Earthquake mitigation and soil investigation for seismic hazard analysis in a potentially active seismic zone around the southern Himalayan region are significant concerns. Since the alluvium soil deposits have a substantial effect on the amplitude of ground motion during earthquake energy transmission. In evaluating the soil stiffness of the layer overlying bedrock; it is necessary to measure the shear wave velocity (SWV) of the soil horizon. To calculate SWV, microtremor array measurements (MAM) were performed nearby borehole locations drilled to a depth of 30 m with standard penetration test blow counts (SPT) N values. This study presents power regression analysis to establish a relationship between SWV and SPT-N values. The laboratory analysis of index properties was conducted concurrently with the collecting of soil samples from boreholes. The lithology extracted from the drilled borehole has shown that the clay is of low plasticity, with dominant silty sand followed by medium to fine-grained sand to a depth of 30 m. The established empirical relationship in this study suggests a correlation coefficient (R2) value of 0.554 for uncorrected N values showing a reasonably strong correlation, and 0.402 for corrected N values (overburden correction), indicating a moderate correlation. Accordingly, uncorrected SPT-N values indicate that shear wave velocity strongly correlates with in-situ conditions with a correlation coefficient (R2) of 0.554 for all types of soil. As per the National Earthquake Hazards Reduction Program (NEHRP) classification, the study area comes under class D soil based on shear wave velocity and N values. In addition, a new empirical relationship was established between SWV and SPT-N values in the Indo-Gangetic Plain (IGP) used for mitigation of seismic hazards and vigilance in geotechnical engineering applications. © The Author(s), under exclusive licence to The National Academy of Sciences, India 2025.