A Web of Science based bibliometric reconnaissance of the Himalaya-Karakoram-Hindukush-Tibet region with focus on field sciences

A bibliometric survey of the Himalaya-Karakoram-Hindukush-Tibet (HKHT) region, the largest mountain system on Earth, for research publications recorded in the Web of Science (WOS) during 1901-2018 revealed 46,746 citable documents (articles, reviews, letters and notes) showing exponential growth mainly after 1980s. The HKHT publications that cover 244 WOS subject categories (SCs) have been used to determine the relative shares by HKHT units, countries, research organizations and publication sources. Nine WOS SCs related to “earth, environmental and agricultural sciences” exhibit highest shares (22.6% to 3.2% of the total) by the whole counting method. Further analysis of the 1994-2018 subset related to 4 broader disciplinary classes (Geosciences, Environmental Sciences & Technologies, Agricultural Sciences, and Ecological Sciences) attributed to “field sciences” with particular emphasis on the high impact (TOP10% globally by citation) documents enables to capture the most prolific, representative (both in space and time) and impactful research. This study identifies the prolific countries, institutions, journals, etc. characterizing the cross-disciplinary research transcending national boundaries and involving international teams. Science mapping of high impact publications (4,561 documents) using the co-occurrence of keywords restricted to noun phrases reveals six prominent clusters that reflect the prolific and high impact research themes in field science for the whole HKHT region: five of them related to earth and environmental sciences (climate change including monsoon regime, tectonic evolution of the Himalaya-Tibet orogen, India-Asia collision and associated crustal phenomena, activities on major thrusts, channel flows and inverted metamorphism), and one contrasting theme concerning the genetic diversity of plants mainly of medicinal values.

Geology and sedimentary environment of the Surma Group of rocks, Bandarban anticline, Bandarban, Bangladesh

The study illustrates the effect of tectonics, climate, and relative sea-level change on the depositional process of the Miocene Bhuban and Boka Bil Formation of Bengal Basin. Outcrop sediments of five transverse sections exposed along the axial zone of Bandarban anticline were studied. Twelve lithofacies such as Gm, Gms, Sm, ST, Sp, Sr, Sl, Sf, Sll, Fw, Fl and Fm have been identified within the successions and grouped into (i) turbidite generated, (ii) outer fan distal lobe basin plain and (iii) tide-influenced facies association. The analyses reveal that the Bhuban Formation was turbidite- generated that deposited below the continental shelf-slope environment. The Lower Bhuban Member consists of gray to brownish-gray calcareous sandstone with shale deposited under the channelized lobe of submarine fan. The Middle Bhuban Member dominated by black shale-siltstone deposited in distal turbidite lobe due to change the flow regime. The Upper Bhuban Member consists of yellow to yellowish gray, coarse to medium-grained sandstone-siltstone with black shale that deposited under channelized to nonchannelized lobes of submarine fan. The increasing sedimentation during the formation of the Upper Bhuban Member can be caused by increased the intensity of the Asian Monsoon that carried huge sediment from the Himalaya. The Boka Bil Formation was deposited under estuary to tidal flat environment. The area was uplifted during and/or after subduction of the Indian Plate beneath the Burmese Plate. The monsoonal intensity enhances sedimentation that moved prograding delta towards the south. These processes shifted depositional environment from continental shelf-slope to marginal shallow marine during deposition of the Boka Bil Formation. The continental slope aligned east-west direction and sediments likely derived from the Himalaya and Trans-Himalaya in the present geographical setup during deposition of the sediments.

Stability evaluation of hazardous translational slide zones in part of Yamunotri Pilgrimage route, National Highway 507, Uttarakhand, India

Slope failure is a widespread phenomenon in Lesser Himalaya owing to its fragile tectonic settings, rugged topography, high relief, abruptly varying gentle to steep slopes and peculiar climatic conditions. Road development and urban expansion have further deteriorated the slope conditions. National Highway 507, a part of the pilgrimage route to Yamunotri in Uttarakhand, is one such route, experiencing hostility from frequent slope failure episodes that are causing havoc for villagers and pilgrims. In the present study, the four most hazardous translational slide zones in the 22 km stretch from Judo to Kandi village in the Yamunotri pilgrimage route has been identified, for detailed geotechnical investigation and slope stability assessment applying different approaches. The rock masses of this region are inherently weak owing to their closeness to Aglar fault and other joints and fractures. Rock mass classification systems are used to assess the stability and for estimating strength parameters, viz. cohesion and angle of internal friction, essential for the factor of safety determination. They are slightly varying due to the relatively homogeneous grain size distribution and mineralogical composition of rock masses. Kinematic Analysis differentiated the type of failure as planar or wedge and, accordingly, factor of safety is determined by limit equilibrium approach. The factor of safety, computed strength parameters, discontinuity and slope properties, varies from 5.9 to 1.1 in dry conditions while it reduces below unity as the saturation upsurges. It depicts stable conditions in dry conditions but water penetration and saturation along the cracks and discontinuities during rainfall make them unstable. Close vicinity with fault, steep slope, presence of joints and weathered lithology are dominating factors initiating the instability in route with further aggravation by rainfall, road widening and urban expansion.

Geotechnical characterization of Beka-Gotto rock massif (Adamawa Region-Cameroon) for the use in civil engineering

Beka-Gotto is a village of Ngaoundal located in the Adamawa region (Cameroon). The present study is carried out to determine the physical and mechanical characteristics of the local rock massifs, in order to determine their possible uses in various fields of civil engineering. The methodology used consists of petrographic and geotechnical characterization of the different massifs. The rocks crop outas domes or slabs. The rock is light gray. Under the microscope, the rock presents a grainy microstructure composed of plagioclase, potassium feldspar, biotite and quartz. Zircon and opaque minerals represent the accessory phase. With this composition, rock is granodiorite. The geotechnical study, on the other hand, made it possible to understand that, on the physical level, the rock massif has very good properties. In fact, the specific weight on class 6/10 and 10/14 obtained has mean values of ​​2.73 and 2.68 kN/m3 respectively. While the apparent density obtained of the class 6/10 and 10/14 has mean values 1.35 and 1.46 g/cm3 respectively. Mechanically, Los Angeles coefficient is 24-46.3% while the Micro-Deval coefficient is 7-35% and the coefficient of dynamic fragmentation is 18-30%. In accordance with geotechnical standards, with the exception of the Gbago massif, the other massifs have a choc resistance and a wear resistance of satisfactory to limited grade as well as good resistance to dynamic fragmentation and therefore usable in any type of structure.

Hydro-torrential hazard vs. anthropogenic activities along the Seti valley, Kaski, Nepal: Assessment and recommendations from a risk perspective

The Seti River originates from the Annapurna Massif in the Higher Himalaya of Nepal and flows through the Pokhara valley in the Lesser Himalaya. The Seti River witnessed a disastrous flash flood on May 5th, 2012 causing the death of 72 people, obliterating dozens of homes and damaging infrastructures worth millions of dollars. Despite the 2012 flood event and several warnings by scientists for more yet bigger scale future floods in the Seti valley, fluvial risk is being aggravated by anthropogenic activities such as unplanned human settlement, encroachment of riverbanks, haphazard construction of road, drinking water, and hydropower projects in potential flood hazard areas in addition to the increased impacts of climate change on geological and hydro-metrological hazards as in other parts of Hindu Kush Himalayan Range. Covering some 40-km distance from the Seti headwater (Sabche Cirque) down to Pokhara city, the study is carried out based on hydro-geomorphological mapping, analysis of land-use and land-cover change, hydrological analysis including HEC-RAS modelling, historical archives, and interviews with local people. The study shows a significant change on the land use and land cover of the Seti catchment, mainly the urban/built-up area, which is increased by 405% in 24 years period (1996 to 2020) and by 47% in 7 years period (2013 to 2020). Further the study reveals that anthropogenic activities along the Seti valley have increased fluvial risk and are likely to invite more disasters. From the HEC-RAS analysis, two motor bridges built over Seti River were found to have insufficient freeboard to safely pass the highest flood discharge for 100 years return-period. Instead of relocating people to safer places, the government and local authorities rather seem to have encouraged people to live in the floodplain by providing basic amenities such as drinking water, electricity and access road. Given the context of climate change and Pokhara valley and the Seti catchment being in a high-seismic gap zone, there is a strong possibility of similar flood to the scale of 2012 or even greater in Seti River. Though the fluvial risk can be managed in a sustainable way through the application of functional space concept, i.e., by allowing more space (freedom) for rivers, this economic and environment friendly approach of the fluvial risk management has not been implemented yet in the Seti valley nor in Nepal. Rather the encroachment of floodplains by anthropogenic activities along the Seti valley is on an increasing trend. Many settlements and infrastructures along the valley have been identified vulnerable to hydro-torrential hazards, therefore it is utmost necessity to implement functional space river concept, land use and land plan policy, early warning system and public awareness education in order to mitigate and manage the future impact of fluvial hazards along the Seti valley.

Shallow soil effects for contrasting PGAs at nearby strong-motion stations during the 2017, Mj 5.2, southern Akita Prefecture earthquake

On September 8, 2017, an earthquake of Mj 5.2 occurred with the epicenter in southern Akita Prefecture, Japan, at 22:23 local time. According to the Japan Meteorological Agency (JMA), the focal depth was 9 km. Many strong-motion stations of K-NET and KiK-net recorded ground motions from the earthquake. The maximum horizontal vector peak ground acceleration (PGA) of approximately 136 cm/s2 was recorded at one of the KiK-net stations at an epicentral distance of about 8 km. However, despite being 37 km and 53 km far from the epicenter, two stations recorded PGAs of approximately 126 and 113 cm/s2, respectively, similar to that near the epicenter. Even though these PGAs are not rare, we found that the PGAs at the two sites strongly deviated from the median values suggested by a ground motion prediction equation (GMPE), while the nearby sites generally followed the GMPE. Available velocity models showed that shallow shear wave velocities, especially in the top 5 m, were lower (i.e., the soils were softer) at the two sites compared to those at their nearest neighboring sites. We compared the ratios of the PGAs and peak ground velocities (PGVs) at the two sites with respect to their neighboring sites for many earthquakes covering a wide range of magnitudes and azimuths. We found that the PGAs and PGVs at the two sites were systematically larger than those at the adjacent sites. Linear theoretical site amplifications using the available soil models gave peak frequencies around 6-8 Hz at the larger PGA sites. Bandpass-filtered records showed significantly larger PGAs around these frequencies at the larger PGA sites. The above results showed that local site condition is one of the major contributing factors to induce large PGAs. Furthermore, softer sites experience more substantial nonlinear site amplification than the stiffer sites when input motions exceed some threshold PGAs. This latter effect means that the softer sites can produce a variety of ground motion spectra. Nevertheless, the degree of damage to built structures depends on several factors, including the design and quality of construction. We expect that this study contributes to developing improved microzonation maps for earthquake disaster mitigation.

Geometry, kinematics, and magnitude of extension across the Thakkhola Graben, Central Nepal Himalaya

The Thakkhola Graben has been a region of geologic inquiry for many decades. Although it is widely viewed to be in a class of structures that are important in accommodating the three-dimensional strain within the Himalayan thrust wedge, we still lack a detailed understanding of the total finite strain accommodated by graben-bounding faults, as well as their shape and cross-cutting relationships with structures deeper in the thrust wedge. Using geologic mapping and structural analysis, we show that a suite of pre-extensional shortening structures is offset by normal-oblique faults bounding the Thakkhola Graben that we use to define a piercing line. We calculate these faults to have accommodated 8.7 kilometers of vertical thinning, 7.2 kilometers of arc-perpendicular shear, and only 2.2 kilometers of arc-parallel extension. The magnitude of arc-parallel extension is quite low compared to extensional structures to the west in the Gurla Mandhata-Humla region. The cross-cutting relationships established in this study and timing constraints determined by previous works are consistent with a structural history of crustal thickening leading to foreland propagation of the locus of arc-perpendicular shortening contemporaneous with hinterland extension.

Structural and microtectonic analyses of Barpak of Gorkha district, west-central Nepal

Geological mapping was carried out in the Barpak-Bhachchek area of the Daraudi River valley, Gorkha district, West-Central Nepal for structural analysis. The area comprises rocks of the Higher Himalayan Crystalline and the Lesser Himalayan Sequence. Pelitic and psammitic schist, quartzite, calc-quartzite, dolomitic marble, graphitic schist, gneiss are the main rock types within the Lesser Himalayan Sequence, whereas banded gneiss and quartzite form a significant portion of the Higher Himalayan Crystalline in the study area. The area is affected by poly-phase deformation. Lesser Himalayan Sequence has suffered five deformational phases (DL1-DL2, D3-D5) whereas the Higher Himalayan Crystalline has suffered four deformational events (DH1, D3-D5). The Lesser Himalayan Sequence lying to the northern limb of the Gorkha-Kuncha Anticlinorium is contort into doubly plunging to dome-and-basin-like en echelon type of non-cylindrical folds as Baluwa Dome and Pokharatar Basin (DL2 and D4). The direction of shearing as indicated by shear sense indicators (C' Shear band and Mica fish) is top-to-south coinciding with regional sense of shear related to the MCT propagation. The dynamic recrystallization direction, obtained from rock dominant with phyllosilicate minerals is top-to-south and coincides with mineral lineation and indicate the mineral lineation is contemporary with dynamic recrystallization during the MCT propagation.

Balanced cross-section across the Siwaliks of the Trijuga Valley, eastern Nepal

The strata of the Siwalik Group in the Trijuga valley is dissected by two thrusts, repeating the succession three times and forming a longitudinal Dun Valley. The total thickness of the Siwalik strata exceeds 5000 m in the area. A balanced cross-section has been constructed across the Siwalik Range in the Trijuga valley showing that the Main Himalayan Thrust (MHT) lies at the depth of about 5.2 km from the surface. The Main Frontal Thrust (MFT), Kamala Tawa Thrust (KTT), Marine ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­Khola Thrust (MKT) and Main Boundary Thrust (MBT) ramp-up from the MHT. Along with these faults, fault-bend anticlines associated with these thrusts have shortened the Siwalik of the area. The shortening across the area has been calculated to be approximately 33.7 km.

Determination of high-frequency attenuation characteristic of coda waves in the central region of Nepal Himalaya

The high-frequency coda wave attenuation in the central region of Nepal, in and around the Kathmandu valley, is estimated using vertical component seismograms of local earthquakes recorded at 16 different seismic stations of NAMASTE array. The estimated result is expressed in terms of Qc, quality factor (inverse of coda wave attenuation). The value of coda quality factor (Qc) is estimated at eight central frequencies of 1.5, 3.0, 6.0, 9.0, 12.0, 15.0, 18.0, and 21.0 Hz through four different coda window length from 20 to 50 s at 10 s interval by using the single backscattering model. The value of coda Qc obtained from this study, shows a clear dependence on a frequency according to the power relation, Qc (f)= Q0 f n, where Q0 is Qc at 1 Hz, and f is frequency and n represents the degree of frequency dependence. The mean value of Qc of 16 different seismic stations was obtained as (110 ± 10.6) f 1.03±0.03 at 30 s coda window length, which represents the high attenuation characteristics of the study area, and attenuation decreases with increasing central frequency. Qo increases from 73.1 ± 10.1 to 156.1 ± 13.6 and n decreases from 1.12 ± 1.05 to 0.92±0.03 when the coda window length increases from 20 to 50 s. It is concluded that the study area is tectonically very active, highly heterogeneous, and heterogeneity decrease with depth. The coda Q obtained in this study is compatible with the result obtained in the region having a similar tectonic setting.