• Volume 126, Issue 1

      February 2017

    • Editorial

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    • Shear heating by translational brittle reverse faulting along a single, sharp and straight fault plane

      Soumyajit Mukherjee

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      Shear heating by reverse faulting on a sharp straight fault plane is modelled. Increase in temperature (Ti) of faulted hangingwall and footwall blocks by frictional/shear heating for planar rough reverse faults is proportional to the coefficient of friction (μ), density and thickness of the hangingwall block (ρ). Ti increases as movement progresses with time. Thermal conductivity (Ki) and thermal diffusivity (k'i) of faulted blocks govern Ti but they do not bear simple relation. Ti is significant only near the fault plane. If the lithology is dry and faulting brings adjacent hangingwall and footwall blocks of the same lithology in contact, those blocks undergo the same rate of increase in shear heating per unit area per unit time.

    • Optimisation of Hidden Markov Model using Baum–Welch algorithm for prediction of maximum and minimum temperature over Indian Himalaya

      J C Joshi Tankeshwar Kumar Sunita Srivastava Divya Sachdeva

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      Maximum and minimum temperatures are used in avalanche forecasting models for snow avalanche hazard mitigation over Himalaya. The present work is a part of development of Hidden Markov Model (HMM) based avalanche forecasting system for Pir-Panjal and Great Himalayan mountain ranges of the Himalaya. In this work, HMMs have been developed for forecasting of maximum and minimum temperatures for Kanzalwan in Pir-Panjal range and Drass in Great Himalayan range with a lead time of two days. The HMMs have been developed using meteorological variables collected from these stations during the past 20 winters from 1992 to 2012. The meteorological variables have been used to define observations and states of the models and to compute model parameters (initial state, state transition and observation probabilities). The model parameters have been used in the Forward and the Viterbi algorithms to generate temperature forecasts. To improve the model forecasts, the model parameters have been optimised using Baum–Welch algorithm. The models have been compared with persistence forecast by root mean square errors (RMSE) analysis using independent data of two winters (2012–13, 2013–14). The HMM for maximum temperature has shown a 4–12% and 17–19% improvement in the forecast over persistence forecast, for day-1 and day-2, respectively. For minimum temperature, it has shown 6–38% and 5–12% improvement for day-1 and day-2, respectively.

    • 3-D GRACE gravity model for the 2011 Japan earthquake

      Rambhatla G Sastry Mahendra K Sonker

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      The GRACE mission has contributed to the seismic characterization of major earthquakes in offshore regions of the world. Here, we isolate satellite gravity signal (μGal range) for the Japan Earthquake of 2011 using a difference method. Contrary to the existing gravity models, we propose a unit vertical pyramid based five-layer 3-D thrust fault model, which extends to the hypocenter and honors the ocean water layer and sea floor upheaval also. Our model partly uses existing seismological information (hypocenter depth of 32 km, rupture length of 300 km and vertical slip of 4 m), provides a snapshot of episodic subduction of the Pacific Plate below the Atlantic Plate and its gravity response closely matches the observed gravity (RMS error of 3.4012×10−13μGal), fully accounting for co-seismic mass redistribution including sea surface deformation. Our inferred rupture length, rupture velocity, average seismic moment magnitude and momentum, respectively, are 300 km, 4.49 km/s, 1.152×1021 −1.8816×1021 N m and 2.319×106 GNs, which fairly agree with the literature. Further, our model inferred momentum at the sea floor corresponds to an area pulse that led to Tsunami generation.

    • Landforms along transverse faults parallel to axial zone of folded mountain front, north-eastern Kumaun Sub-Himalaya, India

      Khayingshing Luirei S S Bhakuni Sanjay S Negi

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      The shape of the frontal part of the Himalaya around the north-eastern corner of the Kumaun Sub-Himalaya, along the Kali River valley, is defined by folded hanging wall rocks of the Himalayan Frontal Thrust (HFT). Two parallel faults (Kalaunia and Tanakpur faults) trace along the axial zone of the folded HFT. Between these faults, the hinge zone of this transverse fold is relatively straight and along these faults, the beds abruptly change their attitudes and their widths are tectonically attenuated across two hinge lines of fold. The area is constituted of various surfaces of coalescing fans and terraces. Fans comprise predominantly of sandstone clasts laid down by the steep-gradient streams originating from the Siwalik range. The alluvial fans are characterised by compound and superimposed fans with high relief, which are generated by the tectonic activities associated with the thrusting along the HFT. The truncated fan along the HFT has formed a 100 m high-escarpment running E–W for ~5 km. Quaternary terrace deposits suggest two phases of tectonic uplift in the basal part of the hanging wall block of the HFT dipping towards the north. The first phase is represented by tilting of the terrace sediments by ~30° towards the NW; while the second phase is evident from deformed structures in the terrace deposit comprising mainly of reverse faults, fault propagation folds, convolute laminations, flower structures and back thrust faults. The second phase produced ~1.0 m offset of stratification of the terrace along a thrust fault. Tectonic escarpments are recognised across the splay thrust near south of the HFT trace. The south facing hill slopes exhibit numerous landslides along active channels incising the hanging wall rocks of the HFT. The study area shows weak seismicity. The major Moradabad Fault crosses near the study area. This transverse fault may have suppressed the seismicity in the Tanakpur area, and the movement along the Moradabad and Kasganj–Tanakpur faults cause the neotectonic activities as observed. The role of transverse fault tectonics in the formation of the curvature cannot be ruled out.

    • Geochemical characteristics and organic carbon sources within the upper reaches of the Xi River, southwest China during high flow

      Junyu Zou

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      Carbon (POC, DOC) and carbon isotopes (δ13C) within two headwater tributaries to the Xi River Basin, southwest China were analyzed to document the geochemical characteristics and sources of organic carbon (C) within basins characterized by a monsoonal climate and karst landforms. δ¹³CPOC value and C/N ratio data indicate that suspended soil organic carbon (SOC) was an important source of POC in both the Nanpan and Beipan rivers (i.e., the studied tributaries). However, differences in C sources exist between the Nanpan and Beipan River Basins. Higher terrestrial plants supplied a portion of the POC within the Beipan River. In contrast, the Nanpan River was characterized by an inverse correlation between POC and DOC, and a positive relationship between the δ¹³C values. These trends indicate that DOC within the Nanpan River was partly derived from the degradation of soil C within the water column. In addition, the interception of C by hydrological projects (e.g., dams) positioned along the Nanpan River led to higher DOC/POC ratios. In contrast, within the Beipan River δ¹³CDOC values range from −20 to −25.2‰ and are consistent with ratios associated with soil C, suggesting that leaching of C from catchment soil was the dominant source of DOC. Organic C in tributaries to the Beipan River may also have been derived from intense upland soil erosion, a process that resulted in the lowest DOC/POC ratios. The collected data indicate that land-use changes have potentially influenced regionalto local-scale organic C budgets within subtropical basins subjected to karstification.

    • A great volcanic eruption around AD 1300 recorded in lacustrine sediment from Dongdao Island, South China Sea

      Zhongkang Yang Nanye Long Yuhong Wang Xin Zhou Yi Liu Liguang Sun

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      The contents of Ti, Al and Fe₂O₃ in a lacustrine sediment core (DY6) collected from Dongdao Island, South China Sea (SCS), were determined to be much higher than those in the three major sediment endmembers (coral sand, guano and plants), and their likely sources include terrigenous dust and volcanic ash. At 61 cm (~AD 1300), the contents of Ti, Al and Fe₂O₃ have an abnormally high spike, which cannot be explained by terrigenous dust. The Sr and Nd isotope compositions at 61 cm are in excellent agreement with those in volcanic materials, but they are significantly different from those in terrigenous dust, implying a possible material input from historical volcanic eruptions in the lacustrine sediment DY6. The documented great Samalas volcanic eruption at AD 1257 in Indonesia is likely the candidate for this volcanic eruption.

    • Predictive modelling of the spatial pattern of past and future forest cover changes in India

      C Sudhakar Reddy Sonali Singh V K Dadhwal C S Jha N Rama Rao P G Diwakar

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      This study was carried out to simulate the forest cover changes in India using Land Change Modeler. Classified multi-temporal long-term forest cover data was used to generate the forest covers of 1880 and 2025. The spatial data were overlaid with variables such as the proximity to roads, settlements, water bodies, elevation and slope to determine the relationship between forest cover change and explanatory variables. The predicted forest cover in 1880 indicates an area of 10,42,008 km², which represents 31.7% of the geographical area of India. About 40% of the forest cover in India was lost during the time interval of 1880–2013. Ownership of majority of forest lands by non-governmental agencies and large scale shifting cultivation are responsible for higher deforestation rates in the Northeastern states. The six states of the Northeast (Assam, Manipur, Meghalaya, Mizoram, Nagaland, Tripura) and one union territory (Andaman & Nicobar Islands) had shown an annual gross rate of deforestation of >0.3 from 2005 to 2013 and has been considered in the present study for the prediction of future forest cover in 2025. The modelling results predicted widespread deforestation in Northeast India and in Andaman & Nicobar Islands and hence is likely to affect the remaining forests significantly before 2025. The multilayer perceptron neural network has predicted the forest cover for the period of 1880 and 2025 with a Kappa statistic of >0.70. The model predicted a further decrease of 2305 km2 of forest area in the Northeast and Andaman & Nicobar Islands by 2025. The majority of the protected areas are successful in the protection of the forest cover in the Northeast due to management practices, with the exception of Manas, Sonai-Rupai, Nameri and Marat Longri. The predicted forest cover scenario for the year 2025 would provide useful inputs for effective resource management and help in biodiversity conservation and for mitigating climate change.

    • Geology of the Elephanta Island fault zone, western Indian rifted margin, and its significance for understanding the Panvel flexure

      Hrishikesh Samant Ashwin Pundalik Joseph D’souza Hetu Sheth Keegan Carmo Lobo Kyle D’souza Vanit Patel

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      The Panvel flexure is a 150-km long tectonic structure, comprising prominently seaward-dipping Deccan flood basalts, on the western Indian rifted margin. Given the active tectonic faulting beneath the Panvel flexure zone inferred from microseismicity, better structural understanding of the region is needed. The geology of Elephanta Island in the Mumbai harbour, famous for the ca. mid-6th century A.D. Hindu rock-cut caves in Deccan basalt (a UNESCO World Heritage site) is poorly known. We describe a previously unreported but well-exposed fault zone on Elephanta Island, consisting of two large faults dippingsteeply east–southeast and producing easterly downthrows. Well-developed slickensides and structural measurements indicate oblique slip on both faults. The Elephanta Island fault zone may be the northern extension of the Alibag–Uran fault zone previously described. This and two other known regional faults (Nhava–Sheva and Belpada faults) indicate a progressively eastward step-faulted structure of the Panvel flexure, with the important result that the individual movements were not simply downdip but also oblique-slip and locally even rotational (as at Uran). An interesting problem is the normal faulting, block tectonics and rifting of this region of the crust for which seismological data indicate a normal thickness (up to 41.3 km). A model of asymmetric rifting by simple shear may explain this observation and the consistently landward dips of the rifted margin faults.

    • Angle-domain common-image gathers from anisotropic Gaussian beam migration and its application to anisotropy-induced imaging errors analysis

      Jianguang Han Yun Wang Changqing Yu Peng Chen

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      An approach for extracting angle-domain common-image gathers (ADCIGs) from anisotropic Gaussian beam prestack depth migration (GB-PSDM) is presented in this paper. The propagation angle is calculated in the process of migration using the real-value traveltime information of Gaussian beam. Based on the above, we further investigate the effects of anisotropy on GB-PSDM, where the corresponding ADCIGs are extracted to assess the quality of migration images. The test results of the VTI syncline model and the TTI thrust sheet model show that anisotropic parameters ε, δ, and tilt angle θ, have a great influence on the accuracy of the migrated image in anisotropic media, and ignoring any one of them will cause obvious imaging errors. The anisotropic GB-PSDM with the true anisotropic parameters can obtain more accurate seismic images of subsurface structures in anisotropic media.

    • Monitoring of fire incidences in vegetation types and Protected Areas of India: Implications on carbon emissions

      C Sudhakar Reddy V V L Padma Alekhya K R L Saranya K Athira C S Jha P G Diwakar V K Dadhwal

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      Carbon emissions released from forest fires have been identified as an environmental issue in the context of global warming. This study provides data on spatial and temporal patterns of fire incidences, burnt area and carbon emissions covering natural vegetation types (forest, scrub and grassland) and Protected Areas of India. The total area affected by fire in the forest, scrub and grasslands have been estimated as 48765.45, 6540.97 and 1821.33 km², respectively, in 2014 using Resourcesat-2 AWiFS data. The total CO₂ emissions from fires of these vegetation types in India were estimated to be 98.11 Tg during 2014. The highest emissions were caused by dry deciduous forests, followed by moist deciduous forests. The fire season typically occurs in February, March, April and May in different parts of India. Monthly CO₂ emissions from fires for different vegetation types have been calculated for February, March, April and May and estimated as 2.26, 33.53, 32.15 and 30.17 Tg, respectively. Protected Areas represent 11.46% of the total natural vegetation cover of India. Analysis of fire occurrences over a 10-year period with two types of sensor data, i.e., AWiFS and MODIS, have found fires in 281 (out of 614) Protected Areas of India. About 16.78 Tg of CO₂ emissions were estimated in Protected Areas in 2014. The natural vegetation types of Protected Areas have contributed for burnt area of 17.3% and CO₂ emissions of 17.1% as compared to total natural vegetation burnt area and emissions in India in 2014. 9.4% of the total vegetation in the Protected Areas was burnt in 2014. Our results suggest that Protected Areas have to be considered for strict fire management as an effective strategy for mitigating climate change and biodiversity conservation.

    • Region-specific deterministic and probabilistic seismic hazard analysis of Kanpur city

      Anbazhagan P Ketan Bajaj Nairwita Dutta Sayed S R Moustafa Nassir S N Al-Arifi

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      A seismic hazard map of Kanpur city has been developed considering the region-specific seismotectonic parameters within a 500-km radius by deterministic and probabilistic approaches. The maximum probable earthquake magnitude \textit(Mmax) for each seismic source has been estimated by considering the regional rupture characteristics method and has been compared with the maximum magnitude observed \textit(Mobsmax), \textit(Mobsmax) + 0.5 and Kijko method. The best suitable ground motion prediction equations (GMPE) were selected from 27 applicable GMPEs based on the ‘efficacy test’. Furthermore, different weight factors were assigned to different Mmax values and the selected GMPE to calculate the final hazard value. Peak ground acceleration and spectral acceleration at 0.2 and 1 s were estimated and mapped for worstcase scenario and 2 and 10% probability of exceedance for 50 years. Peak ground acceleration (PGA) showed a variation from 0.04 to 0.36 g for DSHA, from 0.02 to 0.32 g and 0.092 to 0.1525 g for 2 and 10% probability in 50 years, respectively. A normalised site-specific design spectrum has been developed considering three vulnerable sources based on deaggregation at the city center and the results are compared with the recent 2011 Sikkim and 2015 Nepal earthquakes, and the Indian seismic code IS 1893.

    • Distribution and sources of carbon, nitrogen, phosphorus and biogenic silica in the sediments of Chilika lagoon

      Sadaf Nazneen N Janardhana Raju

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      The present study investigated the spatial and vertical distribution of organic carbon (OC), total nitrogen (TN), total phosphorus (TP) and biogenic silica (BSi) in the sedimentary environments of Asia’s largest brackish water lagoon. Surface and core sediments were collected from various locations of the Chilika lagoon and were analysed for grain-size distribution and major elements in order to understand their distribution and sources. Sand is the dominant fraction followed by silt+clay. Primary production within the lagoon, terrestrial input from river discharge and anthropogenic activities in the vicinity of the lagoon control the distribution of OC, TN, TP and BSi in the surface as well as in the core sediments. Low C/N ratios in the surface sediments (3.49–3.41) and cores (4–11.86) suggest that phytoplankton and macroalgae may be major contributors of organic matter (OM) in the lagoon. BSi is mainly associated with the mud fraction. Core C5 from Balugaon region shows the highest concentration of OC ranging from 0.58–2.34%, especially in the upper 30 cm, due to direct discharge of large amounts of untreated sewage into the lagoon. The study highlights that Chilika is a dynamic ecosystem with a large contribution of OM by autochthonous sources with some input from anthropogenic sources as well.

    • Geochemistry evidence for depositional settings and provenance of Jurassic argillaceous rocks of Jiyuan Basin, North China

      Yao Meng Deshun Zheng Minglong Li

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      This paper aims to discuss the depositional settings and provenances for the Jurassic in Jiyuan basin, North China, based on the rare earth element (REE) and trace element features of 16 Jurassic argillaceous rock samples from the Anyao, Yangshuzhuang and Ma’ao Formations, respectively. Generally, geochemical analysis results show that chondrite-normalised REE distribution patterns of all the three formations are characterised by light-REE (LREE) enrichment, moderately negative Eu anomalies, slightly negative Ce anomalies, and strong fractionation between LREE and heavy-REE (HREE). Trace element proxies V/(V+Ni), Ceanom index, Ce/La, Sr/Ba, and Sr/Cu indicate a weak oxidation–reduction environment, progressively decreasing reducibility and water depth from the bottom up during Jurassic in Jiyuan basin. Palaeoclimate varied from humid in the Early Jurassic to arid in the Middle Jurassic, corresponding with the variations of palaeoredox and palaeosalinity. The provenances of Jurassic rocks in Jiyuan basin are mainly from felsic sources related to active continental margin and continental island arc. The Early–Middle Jurassic (Anyao and Yangshuzhuang Formations) provenances are mainly derived from North Qinling and partially from the eroded recycled felsic sedimentary covers of Taihang Mountain. In the late stage of Middle Jurassic (Ma’ao Formation), Taihang Mountain has been the primary source to Jiyuan basin. We conclude that the Jurassic rocks of Jiyuan basin reveal the progressive uplift and denudation processes of the Taihang Mountain.

    • Lithostratigraphic contact – a significant site for hydrogeological investigation in crystalline fractured-rock terrains

      Tapas Acharya Rajesh Prasad

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      Estimating the hydrogeologic control of fractured aquifers in hard crystalline and metamorphosed rocks is challenging due to complexity in the development of secondary porosity. The present study in the Precambrian metamorphic terrain in and around the Balarampur of Purulia district, West Bengal, India, aims to estimate the hydrogeologic significance of lithostratigraphic contacts using fracture characteristics obtained from surface bedrock exposures supported by hydrological data from the existing dugwells. This study involves the domain-wise analysis of the frequencies of fractures that control the fractureporosity.The domain-wise study reveals higher fracture-frequencies adjacent to the lithostratigraphic contacts. The concurrence of lithostratigraphic contacts with the occurrences of high-discharging wells and also with the deep weathered zone in low-lying areas is clearly established, thus assigning the lithostratigraphic contact as hydrogeologically significant. An increase in frequencies of the fractures within the ‘influence zone’ of the lithocontact, is clearly visible. Among those fractures, particularly, which make the angle greater than the ‘limiting angle’ with the lithocontact are characterised by increased frequencies. However, brittle rocks like quartz biotite granite gneisses, phyllite and epidiorite show high porosity of fracture, within the ‘influence zone’ of the lithostratigraphic contact. Enhanced deepening of the weathered-zone at lower topographic region may perhaps be a plausible explanation for this increased fracture-porosity at lithocontact to assign it as a hydrogeologically significant transmissive zone within fractured rocks.

    • Effects of climate change on spring wheat phenophase and water requirement in Heihe River basin, China

      Dongmei Han Denghua Yan Xinyi Xu Yu Gao

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      Climate change has significantly altered the temperature rhythm which is a key factor for the growth and phenophase of the crop. And temperature change further affects crop water requirement and irrigation system. In the north-west of China, one of the most important crop production bases is Heihe River basin where the observed phenological data is scarce. This study thus first adopted accumulated temperature threshold (ATT) method to define the phenological stages of the crop, and analysed the effect of climate change on phenological stages and water requirement of the crop during growing season. The results indicated the ATT was available for the determination of spring wheat phenological stages. The start dates of all phenological stages became earlier and the growing season length (days) was reduced by 7 days under climate change. During the growing season, water requirement without consideration of phenophase change has been increased by 26.1 mm, while that with consideration of phenophase change was featured in the decrease of water requirement by 50 mm. When temperature increased by 1°C on average, the changes were featured in the 2 days early start date of growing season, 2 days decrease of growing season length, and the 1.4 mm increase of water requirement, respectively.

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