Seismic Zone Research Articles

Steel Structures in Context of Safety, Resilience & Sustainable Construction: Minimizing Environmental Impacts

The study analyzes a G+4 residential building subjected to seismic loads, comparing vertical base shears, material strengths, and foundation design requirements. The results reveal that RCC structures generate significantly higher vertical base shears due to their heavier loads, necessitating larger foundation areas, especially at critical points, and leading to increased construction costs. In contrast, Steel structures, with lower base shears, require smaller foundation areas, reducing both material use and environmental impact. The findings emphasize that Steel structures offer superior seismic performance, cost efficiency, and sustainability by minimizing foundation requirements and associated environmental burdens. This research highlights the importance of material choice in achieving resilient and sustainable construction, particularly in seismic zones, where Steel structures provide a more efficient and environmentally friendly solution compared to RCC structures.

Interparticle friction behaviors of kaolinite: Insights into macroscale friction from nanoscale

The friction behavior of widespread clay minerals is a major concern in many geo-engineering problems, such as the stability of soft soil foundations and the induction of seismic fault zones. The present work aimed to study the friction behaviors of kaolinite at the particle level using the molecular dynamics method. The effects of normal force (Fn), shear velocity (v), and interfacial water film on nanofriction were discussed. The “stick-slip” phenomenon and periodic evolution of friction forces (Ff) were observed in dry friction and became less pronounced with water lubrication. The dry Ff of kaolinite was found to be insensitive to Fn. However, wet Ff exhibited a linear increase with Fn and then transitioned to a non-linear relationship as slip displacement increases due to the continuous loss of water molecules from the interface during friction. Notably, at high loads (Fn ≥ 30 nN), the peak friction of wet kaolinite showed characteristics similar to dry friction. A velocity-strengthening behavior of kaolinite at high velocities was observed in both dry and wet conditions. The macroscale friction coefficients of kaolinite were predicted from nanofriction data and results showed good agreement with experimental values. This study lays the foundation for bridging micro- and macro-mechanical behaviors, suggesting a new pathway for acquiring precise macroscopic friction of minerals through cross-scale studies.

Regional, local and current forecast of the impact hazard of coal seam sites based on seismic monitoring

Relevance. Insufficient validity of the quantitative criteria of the regional, local and current forecast of the impact hazard of the coal seams being developed, the absence of algorithms linking the use of geophysical and direct geomechanical methods in forecasting. Aim. To develop a comprehensive method of geodynamic forecasting, including determining the extent of an impact-prone area identified by the results of a regional forecast based on the registration data of the GITS seismic monitoring system, for conducting local and current forecasts of impact hazard by regulatory methods. Object. An array of rocks of the excavation column 4-1-5-7 of the Osinnikovskaya mine during mining operations in the zone of a group of tectonic disturbances and the intersection of advanced workings. Methods. Regional geomechanical forecast by the geophysical method of seismic activity registration (GITS system), local (current) forecast by natural electromagnetic radiation methods (Angel-M equipment) and the output of drilling fines. Results. The paper introduces the results of complex studies in the excavation column 4 1-5-7 of the Osinnikovskaya mine to establish a correlation between seismic activity and the parameters of the stress-strain state of the array. The authors have introduced the concept of integral indicators of the considered parameters IF and Ikσ. They take into account the area of the zone for the i-th range according to the complex parameter of seismic activity F and the coefficient of vertical stresses in the roof of the formation Kσ. It is established that the informative value of the integral indicators is almost twice as high as the informative value of the initial parameters. Experimental nomograms и are presented to determine the category "DANGEROUS/NON-DANGEROUS" for the regional forecast of impact hazard according to the GITS seismic monitoring system. The authors developed a general algorithm for predicting the impact hazard during clean-up operations. This algorithm uses an integrated approach that includes a regional forecast for recording seismic activity within the mine field and local forecasting methods, both geophysical and direct, to clarify the boundaries of seismic energy release zones and confirm the category of impact hazard. Thу paper introduces the example of determining the width of the zone of increased seismic energy release in the mine closest to the seismically active zone. The dynamics of the occurrence, development and decrease of the seismic energy release zone in the considered areas in the mine workings is shown. The authors give the examples of the implementation of a local forecast of impact hazard in previously established potentially dangerous areas by methods of recording natural electromagnetic radiation of rocks and by the output of drilling fines.

Activity and motion characteristics on the southern segment of the Red River fault zone, Yunnan province, China

The longer time for recording large earthquakes on a plate boundary fault, the better that understanding of large earthquake rupture behavior and seismic hazard on the fault zone. However, large earthquakes (M ≥ 7) are rarely recorded on the boundary fault with slow slipping rate, such as the Red River fault zone (RRFZ), which is an important plate boundary fault that marks the southwestern boundary of the Yangtze platform or south China block. There have been no large earthquake records on the southern segments (including the segment in Vietnam) of the RRFZ since historical earthquake records began in 886 AD, except the 1652 Midu M 7 earthquake and the 1925 Dali M 7 earthquake on the northern segment. The southern segment of the RRFZ will not have a large earthquake in the future or as a large earthquake seismogenic zone with a long period of recurrence, remains controversial, in part because of the absence of constraints from geological evidence. This controversial seriously restricts the risk assessment of future large earthquakes on the southern segment of the RRFZ. By careful interpretations of high resolution remote sensing images, in combination with a detailed field geological and geomorphic survey, we found a series of fault valleys and bedrock outcrops from Gasha toYaojie and Yuangjiang to Hekou on the southern segment of the RRFZ. Multiple trench excavation and radiocarbon dating sample analyses show that the mid valley trace in the southern segment of the RRFZ is an active fault. Geological and geomorphic evidence from Gasha to Yaojie and Yuanjiang to Hekou indicate that the mid valley trace in the southern segment of the RRFZ exhibits dip slip and dextral strike slip motion characteristics. This result is inconsistent with those of previous studies that the mid valley trace is purely strike slip. Furthermore, trenches opened on the range front trace in the southern segment of the RRFZ in Ejia are found to still be active, differing from previous studies. Thus, the seismic hazard on the southern segment of the RRFZ should be reevaluated.

Analisis Deformasi di Lampung dan Selat Sunda berdasarkan Data GNSS tahun 2018 hingga 2021

The Lampung Province and Sunda Strait have a seismic gap zone with the potential for major earthquakes in the future. This study analyzes the deformation occurring in this region using continuous Global Navigation Satellite System (GNSS) station data from Indonesia Continuously Operating Reference Station (InaCORS) and Sumatran GPS Array (SuGAr) from 2018 to 2021.5. The GNSS data was processed using the Bernese 5.2 scientific software, applying least squares for velocity changes and statistical tests to analyze significance. The data processing was carried out in two schemes: the first scheme covering 2018-2020, and the second covering 2019-2021. The results of the deformation analysis from 2018 to 2021, using two continuous GNSS data processing schemes, showed velocity changes relative to the Sundaland Plate ranging from ~2 mm/year to ~20 mm/year. In the eastern region of the Sumatra fault, the velocity changes were smaller, around ~5 mm/year, due to the minimal influence of tectonic activity. However, in the Sunda Strait region, the deformation was influenced by volcanic activity. The deformation occurring in Lampung Province and the Sunda Strait, based on GNSS velocity changes, significantly contributes to tectonic and volcanic activities.

Drivers to seismic hazard curve slope

AbstractThe slope of a linear approximation of a probabilistic seismic hazard curve, when it is represented in the log‐log scale, is a key parameter for seismic risk assessment based on closed‐form solutions, and other applications. On the other hand, it is observed that different hazard models can provide, at the same site, comparable ground shaking, yet appreciably different slopes for the same exceedance return period. Moreover, the slope at a given return period can increase or decrease from low‐ to high‐hazardous sites, depending on the models the probabilistic seismic hazard analysis (PSHA) is based on. In the study, the sensitivity of the slope to the main model components involved in PSHA was explored, that is: the earthquake rate, the magnitude and source‐to‐site distance distributions, and the value of the residual of ground motion models (GMM). With reference to a generic site, affected by an ideal seismic source zone, where magnitude follows the Gutenberg‐Richter (G‐R) relationship, it was found that the local slope of hazard curve increases with the following factors in descending order of importance: (i) increasing distance from the source; (ii) decreasing maximum magnitude and increasing ‐value of the G‐R model; (iii) increasing rate of earthquakes of interest; (iv) increasing residual of the GMM. These results help explain the systematic differences in hazard curve slopes found in three authoritative hazard models for Italy, and the related impact on simplified risk assessment.

Evaluation of priority index for enhancing the seismic resilience of tunnels

Tunnels are essential infrastructure elements, offering significant economic, social, and environmental benefits. However, they are particularly vulnerable to seismic risks, especially in regions with high seismic activity. Given their importance in terms of safety, economy, and social factors, it is crucial for the relevant authorities to prepare for natural and human-made disasters by enhancing the seismic resilience of tunnels. In Algeria, where the number of tunnels is high, this necessity is particularly urgent.This article proposes a prioritization model aimed at improving the seismic resilience of tunnels, based on the expertise of specialists and structured into three main steps. The first step involves identifying key criteria, including the tunnel's condition, design phase, availability of alternative routes, social importance, geometric shape, and seismic zone. The second step applies the Analytic Hierarchy Process (AHP) to calculate the weights of the criteria and incorporates expert opinions through the Euclidean Distance-Based Aggregation Method (EDBAM). Finally, the third step establishes the Priority Index for Tunnel Seismic Resilience Improvement (PIT).The model was tested on five tunnels, and the classification obtained based on the priority index was found to be well aligned with the observed reality on the ground.

Geoelectric studies in earthquake hazard assessment: the case of the Kozlodui nuclear power plant, Bulgaria

AbstractThe study presents the results of geoelectric research for seismic risk assessment on the example of the Kozlodui nuclear power plant in Bulgaria. The image of the geoelectric structure in the study area was obtained using one-dimensional inverse electrical resistivity modeling of the full five-component magnetotelluric data and quasi-three-dimensional inverse conductivity modeling of the geomagnetic responses recorded during the summer 2021 field campaign. According to the presented results, the geoelectrically anomalous structure is divided into two levels. The near-surface anomalous structure in the immediate reach of human geotechnical activity corresponds to the electrically conductive sedimentary fill. The mid-crustal layer is coincident with the low seismic velocity zone at the brittle and ductile crust interface, revealed in previous studies. The presented results imply that the geological environment is not affected by large faults capable of transmitting seismic energy from tectonically active areas, however, in further studies, attention should be paid to the strike-slip fault systems adjacent to the study area.

Can we develop a more targeted approach to mitigating seismic risk?

The recent high death tolls caused by large earthquakes are a further indication that earthquakes remain one of the most destructive natural hazards in the world and can seriously threaten the achievement of disaster reduction goals. To effectively reduce the existing seismic risk, the limited available mitigation resources should be allocated to areas with the most severe potential risk. However, identifying localized concentrations of risk requires detailed studies. Here, we propose a strategy to delineate regional high seismic risk zone at a fine resolution and with high confidence. We demonstrate this strategy by using the seismic hazard and loss estimation results for earthquake scenarios with a magnitude of Mw 7.5 for the Jiaocheng fault of the Shanxi Rift System, China. Our analyses reveal that the delineated zone accounts for only ~7% of the regional land area but for ~85% of the total financial loss. We recommend prioritizing seismic risk mitigation measures in such high-risk zones, especially for densely populated cities in seismically active areas, to better meet the disaster risk reduction targets in the Sendai Framework.

Isotropic High‐Frequency Radiation in Near‐Fault Seismic Data

AbstractWe compare Fourier Amplitude Spectra of Fault Normal (FN) and Fault Parallel (FP) seismograms at near‐fault sites for seven strike‐slip earthquakes with moment magnitudes Mw ≥ 6. For all events we find large FN/FP ratios at low frequencies consistent with near‐fault S‐wave radiation patterns for strike‐slip earthquakes. However, the difference diminishes with increasing frequency and FN/FP is about 1 above a transition frequency. The results may reflect small tensile/isotropic components in the earthquake rupture zones that homogenize the high‐frequency radiation in different directions at near‐fault sites. The FN/FP ratios at low frequencies and transition frequencies above which FN ∼ FP vary among the analyzed earthquakes and have no clear correlation with the magnitudes. The lack of correlation may signify a characteristic scale (e.g., process zone size, duration of source time function) controlling the isotropic radiation, and/or wave propagation and other effects that mask the source effects.

DEVELOPMENT OF PEAK GROUND ACCELERATION USING A NON-LINEAR APPROACH TO EVALUATE LIQUEFACTION POTENTIAL IN SEI WAMPU BRIDGE, LANGKAT, NORTH SUMATRA, INDONESIA

The design of building structures requires compliance with seismic codes and all their consequences. Based on geotechnical investigation reports, the construction of Sei Wampu Bridge in Langkat, North Sumatra, Indonesia, is located in an area where the soil layers are predominantly sand with shallow water levels because of its proximity to a river and is a high earthquake zone due to the Semangko fault. That condition will affect the potential of liquefaction occurring. This study aims to identify the liquefaction potential in the Sei Wampu Bridge. Based on Indonesian National Standard (SNI) 1726-2019, sites prone to liquefaction are categorized as site class-specific soil (F) and requires site-specific response analysis (SSRA) methods. Non-linear analysis 1-D is chosen to propagate earthquake waves with the software DEEPSOIL V7. The input parameter for soil movement utilizes an average spectral matching method with a minimum of 7 pairs of soil movement selected from the earthquake recording website, PEER Ground Motion Database. The selection of earthquake considers a 1000-year earthquake load return period, or a 7% probability exceeded within 75 years. Site-specific response analysis (SSRA) resulted in a peak ground acceleration (PGA) value for each borehole depth used in liquefaction potential analysis. Using a historical earthquake scenario with a 6.3 Mw shows that the research location has liquefaction potential at 0 m-15 m deep with high vulnerability levels, where the LPI value reaches 36.21.

Impact of seismotectonic source zoning and seismic parameter: Sensitivity study on probabilistic seismic hazard assessment

The demarcation of seismic area source zones plays a pivotal role in probabilistic seismic hazard assessment (PSHA). In this study, we developed five distinct seismotectonic area source models, integrating large and small areas based on geological, tectonic, and seismological data. Logic tree methodology is utilized in FRISK88M for PSHA. Analysis revealed higher hazards in models with larger area sources compared to those with smaller ones. Hazard deaggregation of seismotectonic model-5 (SM5) is examined and sensitivity analysis of various logic tree nodes is investigated in terms of percent deviation w.r.t mean hazard at various spectral and return periods. The findings underscore that recurrence methods fall into "insensitive level" (≤5%), source mechanism and a-value distribution belong to "low sensitive level" (>5–15%), magnitude distribution lies in "medium sensitive level" (>15–25%), b-value distribution belongs to "high sensitive level" (>25–35%), and ground motion prediction equations (GMPEs) and depth distribution falls into "very high sensitive level" (>35%) in relation to seismic hazard.

Dynamic rupture modeling in a complex fault zone with distributed and localized damage

Active fault zones have complex structural and geometric features that are expected to affect earthquake nucleation, rupture propagation with shear and volumetric deformation, and arrest. Earthquakes, in turn, dynamically activate co-seismic off-fault damage that may be both distributed and localized, affecting fault zone geometry and rheology, and further influencing post-seismic deformation and subsequent earthquake sequences. Understanding this co-evolution of fault zones and earthquakes is a fundamental challenge in computational rupture dynamics with consequential implications for earthquake physics, seismic hazard and risk. Here, we implement a continuum damage-breakage (CDB) rheology model in our MOOSE-FARMS dynamic rupture simulator to investigate the interplay between bulk damage and fault motion on the evolution of dynamic rupture, energy partitioning, and ground motion characteristics. We demonstrate several effects of damage (accounting for distributed cracking) and breakage (accounting for granulation) on rupture dynamics in the context of two prototype problems addressed currently in the 2D plane-strain setting: (1) a single planar fault and (2) a fracture network. We quantify the spatio-temporal reduction in wave speeds associated with dynamic ruptures in each of these cases and track the evolution of the original fault zone geometry. The results highlight the growth and coalescence of localization bands as well as competition between localized slip on the pre-existing faults vs. inelastic deformation in the bulk. We analyze the differences between off-fault dissipation through damage-breakage vs. plasticity and show that damage-induced softening increases the slip and slip rate, suggesting enhanced energy radiation and reduced energy dissipation. These results have important implications for long-standing problems in earthquake and fault physics as well as near-fault seismic hazard, and they motivate continuing towards 3D simulations and detailed near-fault observations to uncover the processes occurring in earthquake rupture zones.

Assessment of structural performance, materials efficiency, and environmental impact of multi-story hybrid timber structures in high seismic zone

Advancements in wooden manufacture and the inherent sustainable merits of timber have stimulated studies on high-rise wooden structures and their structural performances. Considering the height restrictions of timber structures in Taiwan, two types of hybrid structure systems, reinforced concrete (RC) structure mixed with timber components, were proposed as substitution solutions to explore their feasibility and environmental impact in high seismic zones. A fifteen-story RC structure was adopted as the benchmark building, and building weight, material substitution efficiency, and embodied carbon were thus compared with the proposed hybrid timber structures after determining wind and seismic impacts. The results showed that structure system Type 1, which replaced original RC slabs and RC walls with timber, weighs only 61.3 % of the RC structure, reducing seismic forces by 38.7 % and base shear by 30.6 %, while inter-story drift ratio was smaller than that of RC structure; meanwhile, Type 2, which maintained the original RC service core and replaced timber structure for rest of the area, was only 44.5 % of the structural weight of RC structure, with a reduction of 36.4 % in seismic forces and 21.1 % in base shear. Furthermore, Type 1 featured reduced embodied carbon of 34.8 % and 35.4 % respectively using imported and domestically produced timber, while Type 2 features reductions of 47.4 % and 49.3 % respectively. The study indicated that the RC-timber hybrid structure system not only has significant structural performance in the face of the challenges of high seismic zones but also offers new solutions in terms of environmental sustainability.

Drought-induced seismicity modulation in the New Madrid Seismic Zone, central United States

The New Madrid Seismic Zone (NMSZ) in the central United States is a seismically active intraplate region composed of two fault segments: the Reelfoot and Cottonwood Grove fault segments. It has witnessed several major earthquakes, including a devastating 1811–1812 earthquake sequence of three ~M7 events. Nearly 200 years later, earthquakes still continue today in this complex seismic zone. This seismic zone is located in a domain with higher hydrological load than surrounding regions, which may play a crucial role in seismicity modulation. However, the hydrological unloading or loading-induced seismicity modulation and the underlying earthquake dynamics on this stable plate interior remain equivocal. Our study demonstrates that increased climate variability and drought-induced hydrological unloading can be potential drivers for the crustal stress change in the upper Mississippi embayment and seismicity modulation in the NMSZ. The seismicity rate associated with the Reelfoot fault segment shows ~60% increase during drought-induced prolonged drier periods, linked to La Niña cycles, than during the relatively wetter periods. However, such a feature is lacking for the seismicity associated with the Cottonwood Grove fault segment. We argue that the near-lithostatic pore pressure condition explicitly on the Reelfoot fault segment leads to an increase in the amplitude of the velocity perturbation, making this fault segment more susceptible to seismicity modulation on a multi-annual or annual time scale by the resonance destabilization process.

Propagation buckling failure of a buried offshore pipeline with integral arrestors under external overpressure and strike-slip faulting disturbance

In this study, the propagation buckling failure of a buried offshore pipeline under external overpressure and strike-slip faulting disturbances was investigated numerically. A nonlinear shell model, accounting for geometric, material, self-contact, and pipe-soil interaction nonlinearities, was developed using the vector form intrinsic element method. The arresting performances of the single- and double-integral arrestors were analyzed based on a series of simulations considering various combinations of arrestor diameter-to-thickness ratios, lengths, and sub-arrestor intervals. A comparative analysis was conducted between single- and double-integral arrestors, focusing on their arresting performance, material usage, and manufacturing complexity. The results revealed that pipelines under external overpressure are prone to local collapse and bidirectional buckling propagation under small fault displacements. Reverse ellipticities occur downstream of the buckling propagation and their development leads to flipping propagation. Buckling arrestors function by exhausting the upstream flattening propagation and inhibiting the development of reverse ellipticities downstream. The material consumption of each single-integral arrestor was significantly higher than that of a double-integral arrestor with the same diameter-to-thickness ratio. The weld count of the double-integral arrestors was lower than that of the single scheme, but this difference narrowed as the pipeline mileage increased. These results can serve as valuable guidelines for the design and construction of pipelines crossing seismic zones.

Probability and recurrence interval of large earthquakes (Mw ≥ 6) in the Himalayan seismicity zone

The Himalayan Mountains are one of the world’s most seismically active regions. Due to the active seismic status of the Himalayan belt and ongoing development activities in the region, it is important to keep the seismic hazard estimates updated by incorporating historical and new data. This study uses the Gutenberg-Richter relations for four seismogenic source zones (SSZ) to estimate the probability of earthquakes of a specified magnitude in a given time interval. We used exponential, Weibull, Rayleigh, and log-normal statistical models to assess the probability of earthquakes (Mw ≥ 6). The probable recurrence time of the large earthquake (Mw ≥ 6) can be estimated by maximizing the conditional probability estimates. This recurrence interval is calculated after the elapsed time since the most recent large earthquake in the region. We also apply an autoregressive (AR) forecasting technique to predict earthquake recurrence intervals. The results indicate that the approximate recurrence interval of the large earthquakes (Mw ≥ 6) may be 22.052 ± 5.65 years within the seismicity zones, as per our statistical estimates based on limited and available datasets. The results of this study may be useful for the agencies involved in assessing seismic hazards and developing mitigation and preparedness strategies in the region.

Automatic relocation of intermediate-depth earthquakes using adaptive teleseismic arrays

SUMMARY Intermediate-depth earthquakes, accommodating intraslab deformation, typically occur within subduction zone settings at depths between 60–300 km. These events are in a unique position to inform us about the geodynamics of the subducting slab, specifically the geometry of the slab and the stress state of the host material. Improvements in the density and quality of recorded seismic data enhance our ability to determine precise locations of intermediate-depth earthquakes, in order to establish connections between event nucleation and the tectonic setting. Depth phases (near-source surface reflections, e.g. pP and sP) are crucial for the accurate determination of earthquake source depth using global seismic data. However, they suffer from poor signal-to-noise ratios in the P wave coda. This reduces the ability to systematically measure differential traveltimes to the direct P arrival, particularly for the frequent lower magnitude seismicity which highlights considerable seismogenic regions of the subducted slabs. To address this limitation, we have developed an automated approach to group globally distributed stations at teleseismic distances into ad-hoc arrays with apertures of 2.5$^\circ$, before optimizing and applying phase-weighted beamforming techniques to each array. Resultant vespagrams allow automated picking algorithms to determine differential arrival times between the depth phases and their corresponding direct P arrival. Using these differential times we can then determine the depths of earthquakes, which in turn can be used to create a catalogue of relocated events. This will allow new comparisons and insights into the governing controls on the distribution of earthquakes in subducted slabs. We demonstrate this method by relocating intermediate-depth events associated with northern Chile and the Peruvian flat slab regions of the subducting Nazca plate. The relocated Chilean catalogue contains comparable event depths to an established catalogue, calculated using a semi-automated global methodology, which serves to validate our fully automatic methodology. The new Peruvian catalogue we generate indicates three broad zones of seismicity approximately between latitudes 1–7$^\circ$S, 7–13$^\circ$S and 13–19$^\circ$S. These align with flat to steep slab dip transitions and the previously identified Pucallpa Nest. We also find a regionally deeper slab top than indicated by recent slab models, with intraslab events concentrated at points where the slab bends, suggesting a link between slab flexure and intermediate-depth earthquake nucleation.

Platinum-Group Elements and Nb-Ta geochemistry of the Deccan basalts from Kumbharli and other Ghat sections and the Koyna Seismic Zone, Maharashtra (India): Crustal contamination and implication for sulfide saturation of the magma

The Deccan basalts from Kumbharli, Nadlapur, Bijaynagar, Hazarmacchi, and Surli Ghat sections (surface samples) and the Koyna borehole-7 (KBH-7, sub-surface samples) from Maharashtra (western India) demonstrate a two-stage crystallization process. Olivine and chromite were crystallized earlier in a shallow crustal magma chamber while clinopyroxene and plagioclase phenocrysts were crystallized in the sub-volcanic conduits forming the crystal mush, and carried to the surface by the evolved Fe-Ti-rich ascending basaltic magma. The high modal abundance of plagioclase at the top and clinopyroxene at the bottom part of the Kumbharli Ghat section is responsible for an increase in Sr and a decrease in Sc content towards the upper flows. The surface and sub-surface basalt samples contain Pd = 5–31 ppb, Pt = 4–15 ppb, Ir = 1–4 ppb, Ru = 1–3 ppb, and Rh = 3–5 ppb. Negative relations of Pd/Ir, Pd/Ru, and Pd/Rh with MgO from both sets of samples indicate partitioning of Ir, Ru, and Rh to early fractionated cumulus chromite (or olivine). Magnetite is a late crystallizing phase from the evolved Fe-Ti-rich basaltic magma. With an increasing modal abundance of magnetite, there is an increase of FeO total , TiO 2 , and V with Pd indicating fractionation of Pd by magnetite. Geochemical characters show that the surface basalt samples are less contaminated compared to the sub-surface KBH-7 basalts. High Nb (6.8–13.6 ppm) and low Ta (0.2–0.37 ppm) content and elevated Nb/Ta ratios of the surface samples from the ghat sections indicate the possible interaction of the basaltic magma with the carbonate metasomatized subcontinental lithospheric mantle (SCLM). On the other hand, a high degree of partial melting with limited crustal contamination can also elevate the Nb/Ta ratios of the basalts from the ghat sections. Deccan basalts from the study areas do not bear the signature of sulfide supersaturation and subsequent immiscible sulfide segregation. This is evidenced by their high chalcophile element concentrations (Ni = 79–103 ppm, Cu = 121–259 ppm) and ratios like Cu/Zr (≥ 1), Ni/MgO (13.7–21.8) with low Cu/Pd (2140–29938) compared to other Ni-Cu (PGE) sulfide mineralized continental flood basalts. The lack of crustal sulfur in the various contaminants is perhaps the main reason for this sulfide-undersaturated character of the Deccan basalts of the current study.

Draft Earthquake Zone Map of India

Draft Earthquake Zone Map of India