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An experiment on SKS and SKKS splitting is carried out using teleseismic earthquakes recorded at 10 broadband seismic stations deployed in parts of the NW Himalaya. A total of 47 reliable splitting parameters is estimated using rotation correlation and transverse component minimization methods. A large variation of delay time (δt) of 0.3 to 1.6 s and polarization direction (ϕ) of 42° and 98° of the fast wave is obtained. A strong component of fast axes along the strike of the Delhi–Hardwar Ridge (DHR) near the Himalayan foothills is found to be correlated with the structurally controlled strain-induced shearing. The structural fabrics were likely frozen because of induction of past plate tectonics. The orientations of the fast axes surrounding the Main Central Thrust (MCT) are correlated with the foliation and folding caused by strike-orthogonal compression as well as underthrusting of the Indian plate beneath the Himalaya. A low value of 0.3 s delay time is proposed to be caused by multi-layered anisotropy. A two-layered anisotropy model developed for the stations Adibadri, Gaurikund and Chakrata reveals that the directions of fast axes in the shallow and deeper levels are parallel to the strike of the DHR and to the absolute plate motion (APM) vector of the Indian plate, respectively. We thus propose that the anisotropy observed in the NW Himalaya is a combined effect of the fossil anisotropy preserved in the DHR, the mantle flow and the foliation plane arisen due to collision between the Indian and the Eurasian plates. [ABSTRACT FROM AUTHOR]

Landslides and related mass movement activities along with earthquakes are common in the Himalayan terrain. The distribution of seismic activities in the vicinity of the Main Central Thrust (MCT) is well known. However, in order to assess the relationship between these seismic events and landslides, the spatial distribution of landslides and earthquake events (magnitude >1.5) on either side of the MCT zone was evaluated. It has been observed that seismic events of magnitude <2.1 are clustered around the 1991 Uttarkashi earthquake rupture, 1999 Chamoli earthquake rupture and around Munsiyari. The zone surrounding 1999 Chamoli earthquake rupture indicates the highest earthquake and landslide density of ~75% and 53% respectively. [ABSTRACT FROM AUTHOR]

The Anderson's theory (Anderson, 1951) can be utilized to understand the allocation of principal stresses. For various tectonic regimes, the global seismicity trend for crustal earthquakes of less than 20 km depth suggests that the source fault inclination also plays a critical part in the propagation of the aftershocks in the subsurface rupture with respect to the mainshock earthquake. It has also been observed that majority of the compression earthquakes that display upward seismicity migration typically occur along steep faults. However, in the context of Himalaya seismicity, the opposite migratory behaviour of the aftershock sequence is observed even along the gentle dipping source faulting. The failure envelope Mohr's diagram is used to understand the alteration in the dynamics of the subsurface locked zone of Himalayan Seismic Belt (HSB). This study discusses the alteration in the effective strength of the rock mass which imply the variation in the crustal hydrostatic fluid pressure at shallow depth (0–15 km). Different earthquakes and their aftershocks sequence of Himalayan terrain have been incorporated to corroborate the role of orientation of tectonic principal stresses, subsurface morphology and fluids/partial melts if present. In addition, topography contributes to the vertical loads and development of the subsurface geometry, therefore its role and its influence on seismicity has been discussed. This study highlights the controlling factors and the trend of the principal applied stresses and subsurface fluids in the distribution of aftershock sequences along tectonic regime of the Himalayan arc. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present study, a hypothetical earthquake of magnitude 8.5 has been simulated using the modified hybrid technique. Existing hybrid technique, as the name suggests, is the blend of two already existing simulation techniques, i.e. composite source technique and the envelope technique. In the present modified technique, site response functions and high-frequency decay parameter (kappa factor) have also been introduced in the existing hybrid technique. The waveforms have been simulated at more than 430 points using the calculated site response or transfer function estimated at 50 recording stations situated in the central seismic gap (CSG) region of Himalaya. Peak ground acceleration (PGA) and duration parameters have been estimated. Calculated PGA values helped estimating in the corresponding intensity for those PGA values at various stations. With the help of these PGA and intensity values, the scenario hazard map has been prepared for central seismic gap (CSG) region of Himalaya. It has been found that the stations situated close to rupture initiation point is ≥ 1 g. The estimated PGA values have been compared with the PGA values of other studies. The earthquake has been simulated using three different rupture points The station having highest PGA values changed with rupture initiation point. The intensity values are correlated with the damage pattern of region and therefore relatively more useful for agencies involved in the mitigation of seismic hazard of the region. Accordingly, the synthetic intensity maps have been generated in the present study by converting PGA values into MMI values using an empirical relation. The comparison with the other studies shows an agreement with the other studies. This modified technique is independent aftershocks database and velocity-Q structure. This research work will help bringing light on the effect of site response functions and kappa factor. This kind of study can help in mitigate the earthquake hazard and design an earthquake-resistant structures and building for that particular area. [ABSTRACT FROM AUTHOR]

The historical and the present seismicity catalogues of the Garhwal Himalaya have been studied for their spatio-temporal variations and their implications on the seismotectonics of the region. The Micro-Seismicity, Fractal dimensions (Dc) and Frequency Magnitude Distribution (b-value) coupled with the available literature on geology, geomorphology and geophysics have been used to derive the seismotectonics and stress level changes in the region. The seismic cross sections for the relocated micro-seismicity, focal mechanisms and the swath profiles (for the presence of Physiographic Transition 2 (PT2) at the foothill of the Higher Himalaya) indicate the constant presence of the Mid-Crustal Ramp (MCR) in the detachment plane and its active seismogenic nature. The comparison of this scenario suggests the constant presence of seismogenically active MCR structure throughout the Central Seismic Gap. The seismic cross sections further reveal that the sensu stricto Main Central Thrust (Munsiari Thrust) is also a site of generation of the micro-seismicity in few segments due to its reactivation by thrusting along the MCR. The high fractal dimension value (Dc = 1.47) suggests the heterogeneous nature of the region, owing to the presence of local faults and transverse tectonics. The high stress accumulation in the Garhwal Himalaya with low b value (b = 0.70) suggests the high probability of occurrence of a larger or greater earthquake in the near-future. Further, the study also reveals that the 2011 Chamoli earthquake of M 5.0, preceded by a quiescence period of nearly a year shows different stress levels before and after its occurrence, which is well constrained with the increased moderate earthquake activity around the Chamoli region. This increased seismic activity and stress conditions in the Chamoli region suggest the high possibility of the occurrence of major earthquakes, hence the study recommend for a detailed seismic hazard evaluation of the region. [ABSTRACT FROM AUTHOR]

Source parameters of the small to moderate earthquakes are significant for understanding the dynamic rupture process, the scaling relations of the earthquakes and for assessment of seismic hazard potential of a region. In this study, the source parameters were determined for 58 small to moderate size earthquakes (3.0 ≤ M w  ≤ 5.0) occurred during 2007–2015 in the Garhwal-Kumaun region. The estimated shear wave quality factor (Q β ( f )) values for each station at different frequencies have been applied to eliminate any bias in the determination of source parameters. The Q β ( f ) values have been estimated by using coda wave normalization method in the frequency range 1.5–16 Hz. A frequency-dependent S wave quality factor relation is obtained as Q β ( f ) = (152.9 ± 7) f (0.82±0.005) by fitting a power-law frequency dependence model for the estimated values over the whole study region. The spectral (low-frequency spectral level and corner frequency) and source (static stress drop, seismic moment, apparent stress and radiated energy) parameters are obtained assuming ω −2 source model. The displacement spectra are corrected for estimated frequency-dependent attenuation, site effect using spectral decay parameter “Kappa”. The frequency resolution limit was resolved by quantifying the bias in corner frequencies, stress drop and radiated energy estimates due to finite-bandwidth effect. The data of the region shows shallow focused earthquakes with low stress drop. The estimation of Zúñiga parameter (ε) suggests the partial stress drop mechanism in the region. The observed low stress drop and apparent stress can be explained by partial stress drop and low effective stress model. Presence of subsurface fluid at seismogenic depth certainly manipulates the dynamics of the region. However, the limited event selection may strongly bias the scaling relation even after taking as much as possible precaution in considering effects of finite bandwidth, attenuation and site corrections. Although, the scaling can be improved further with the integration of large dataset of microearthquakes and use of a stable and robust approach. [ABSTRACT FROM AUTHOR]

In order to understand present day earthquake kinematics at the Indian plate boundary, we analyse seismic broadband data recorded between 2007 and 2015 by the regional network in the Garhwal-Kumaun region, northwest Himalaya. We first estimate a local 1-D velocity model for the computation of reliable Green's functions, based on 2837 P-wave and 2680 S-wave arrivals from 251 well located earthquakes. The resulting 1-D crustal structure yields a 4-layer velocity model down to the depths of 20 km. A fifth homogeneous layer extends down to 46 km, constraining the Moho using travel-time distance curve method. We then employ a multistep moment tensor (MT) inversion algorithm to infer seismic moment tensors of 11 moderate earthquakes with M w magnitude in the range 4.0–5.0. The method provides a fast MT inversion for future monitoring of local seismicity, since Green's functions database has been prepared. To further support the moment tensor solutions, we additionally model P phase beams at seismic arrays at teleseismic distances. The MT inversion result reveals the presence of dominant thrust fault kinematics persisting along the Himalayan belt. Shallow low and high angle thrust faulting is the dominating mechanism in the Garhwal-Kumaun Himalaya. The centroid depths for these moderate earthquakes are shallow between 1 and 12 km. The beam modeling result confirm hypocentral depth estimates between 1 and 7 km. The updated seismicity, constrained source mechanism and depth results indicate typical setting of duplexes above the mid crustal ramp where slip is confirmed along out-of-sequence thrusting. The involvement of Tons thrust sheet in out-of-sequence thrusting indicate Tons thrust to be the principal active thrust at shallow depth in the Himalayan region. Our results thus support the critical taper wedge theory, where we infer the microseismicity cluster as a result of intense activity within the Lesser Himalayan Duplex (LHD) system. [ABSTRACT FROM AUTHOR]

Due to the continuous movement of underthrusting Indian plate beneath the Eurasian plate the strain energy accumulates, which is released substantially in the form of great earthquakes. It is yet to be released in the unruptured zone which lies between the two great earthquakes viz. 1934 Bihar-Nepal earthquake and 1905 Kangra earthquake. This zone has been termed as the Central Seismic Gap (CSG). The occurrence of previous great earthquakes and recent Nepal earthquakes, gives a clue to the probable location of future great earthquake. On the basis of analysis of seismicity in the locked portion and the stress drop analysis the CSG has been redefined and location of probable zone of future great earthquake has been demarcated. [ABSTRACT FROM AUTHOR]

Characterizing the stress heterogeneity and crustal complexities are essential to understand the important aspects of rupture development and its propagation in a tectonically active region. We analyze a continuous seismic data (1999–2020) to estimate stress drops, b-value, fractal dimension (D c) and focal mechanisms using a local network of 14 broadband stations. Seismic periodicity on a Himalayan major thrust above locked zone, involves long period of stress accumulation and interseismic strain. There exist a good spatio-temporal-depth correlation between the estimated results which indicates the positive anomaly at 12–14 km (stress transition) beneath the Chamoli region. Interestingly, this region shows maximum geodetic strain rate with comparatively high-stress drop, low coefficient friction value and very low b- (0.583 ± 0.02) and D c - (1.20 ± 0.01) values. Majority of moderate to strong earthquakes and swarms activity have occurred in this region with maximum crustal accommodation. It is also observed that the significant temporal decrease in b-value always followed by moderate earthquakes. Here shallow crustal potential seismogenic asperity controls the earthquake's stress drop and rupture propagation. The observed correlations strongly support the evidence of entrapped fluid-faults interaction which alters pore pressure and generates numerous ruptures. Also, the role of pressurized entrapped fluids and roughness of fault-plane responsible for low friction zone and microseismicity. Continuous stress accumulation along the fault-plane within the asperity could release significant amount of energy in future. • Spatio-temporal depth distribution and correlation of b-value, D c -value, stress drop and focal mechanisms. • Observed depth anomaly at 12–14 km, strongly support evidence of stress transition, structural complexities and fluid-faults interaction. • Fluid-driven shallow crustal layer and fault plane roughness indicates potential asperity nucleation beneath Chamoli region. [ABSTRACT FROM AUTHOR]

The work presents new focal-mechanism data of small-to-moderate (3.0 ⩾ M L ⩽ 5.0) upper crustal earthquakes for the Garhwal Himalaya from a local seismic network installed in July 2007. Majority of the epicenters of these earthquakes are located close to the Main Central Thrust (MCT) zone. We retrieved Moment Tensor (MT) solutions of 26 earthquakes by waveform inversion. The MT results and 11 small-to-moderate earthquakes from the published records are used for stress inversions. The MT solutions reveal dominatingly thrust mechanisms with few strike slip earthquakes near Chamoli. The seismic cross sections illustrate that, these earthquakes are located around the Mid-Crustal-Ramp (MCR) in the detachment. The optimally oriented faults from stress inversions suggest that, the seismogenic fault in this region is similar to a fault plane having dip angle between 12 and 25 degrees, which is compatible with the dip angle of the MCR (∼16°) in this region. P-axes and the maximum horizontal compressive stress are NE-SW oriented; the direction of the relative motion of Indian plate with respect to the Eurasian plate. The Friction Coefficient estimated from stress inversions show that the Chamoli region having low friction in comparison to the overall values. The free fluids trapped beneath the detachment are penetrating into the local faults, hence, decreasing the frictional strength and altering the prevailing stress conditions of the surroundings. The present study reveals that the MCR structure is seismogenically active and producing the small-moderate earthquakes in the region, while the MCT is probably dormant at present. [ABSTRACT FROM AUTHOR]

We estimate frequency-dependent attenuation of P and S waves in Garhwal Himalaya using the extended coda normalization method for the central frequencies 1.5, 2, 3, 4, 6, 8, 10, 12, and 16 Hz, with earthquake hypocentral distance ranging from 27 to 200 km. Forty well-located local earthquake waveforms were used to study the seismic attenuation characteristics of the Garhwal Himalaya, India, as recorded by eight stations operated by Wadia Institute of Himalayan Geology, Dehradun, India, from 2007 to 2012. We find frequency-dependent P and S wave quality factors as defined by the relations Q = 56 ± 8 f and Q = 151 ± 8 f by fitting a power-law frequency dependence model for the estimated values over the whole region. Both the Q and Q values indicate strong attenuation in the crust of Garhwal Himalaya. The ratio of Q/ Q > 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium, playing an important role in seismic wave attenuation in the Himalayan crust. [ABSTRACT FROM AUTHOR]

In the present study, 1991 Uttarkashi (M 7) and 1999 Chamoli (M 6.6) earthquakes that occurred on October 19, 1991, at 21:23:14 h and March 28, 1999, at 19:05:11 h, respectively, have been simulated using the modified hybrid technique. Hybrid technique is the combination of two existing techniques, i.e., envelope technique and composite source model technique. In the present modified technique, site amplification functions and kappa factor have also been incorporated. The simulated waveforms and their corresponding response and Fourier spectra for each site have been generated. In this study, simulation has been done at 11 and 9 recorded stations of Uttarkashi and Chamoli earthquakes, respectively. Important frequency- and time-domain parameters, i.e., Fourier spectra, response spectra, peak ground acceleration (PGA) and duration at stations, have been estimated and compared with the observed accelerograms. It has been observed that the simulated PGA (231 cm/s2) at the closest distance Bhatwari (22 km) matched with the observed one (248 cm/s2) for the Uttarkashi earthquake. The same has been observed at the nearest most station Gopeshwar (19 km) of the Chamoli earthquake. The simulated PGA (347 cm/s2) for this station has been found well matched with the observed PGA value (352 cm/s2). Similar matching has been observed for other stations also. The present technique is independent of velocity-Q structure of earth's layered model and past events data of small earthquakes. This study brings light on the site effect and high-frequency decay parameter. This study can be very helpful in the estimation of seismic hazard in a specific region and designing earthquake-resistant buildings. [ABSTRACT FROM AUTHOR]

In the early morning hours of 23 July 2007 at 04 : 32 : 13.5 (IST), a moderate (ML = 4.9, Mw = 5.0) earthquake occurred in the Garhwal Himalaya near Kharsali, about 50 km northwest of the epicentre of the strong (M 6.4) Uttarkashi earthquake of 20 October 1991. Sourced in the upper crust (15 km focal depth), this earthquake was followed by a series of shallow-focused aftershocks of magnitudes ≤ 3.4. Data from the local broadband seismic network were used for understanding the source characterization. The fault plane solutions of the main shock and the biggest aftershock (M 3.4) are almost similar, suggesting that the deformation occurred by reverse faulting with a significant strike-slip component. For the main shock, the trend/plunge of the major and minor principal axes P/T was 166°/1° and 258°/67° respectively. In these solutions one fault plane is dipping to the NE, and the strike of the fault plane coincides with the major tectonic faults as well as the longest axis of isoseismals. The seismic moment, source radius and stress drop of the main shock are estimated to be 4.15 × 1016 Nm, 1660 m and 4.15 MPa respectively. [ABSTRACT FROM AUTHOR]

Abstract: Himalayas, one of the most seismically active belts, have been formed due to continent–continent collision and are probable locations for future moderate to great earthquakes. It is of paramount importance to recognize precursory swarm activity considered to be long predictors of main events. Recently two earthquake swarms occurred across Main Central Thrust (MCT) in Garhwal Himalayan region in a time interval of nearly one month. The first swarm of April 2009 had epicentral locations lying north of MCT on hanging wall side, which has shown less seismic activity in recent times, while the second swarm occurred in May 2009 near Gopeshwar having epicenters on active seismic zone, located south of MCT. The approximate distance between the two swarms is about 50km. In present study preparation zone of 100×100 km2 has been demarcated recognizing these swarms as precursors to moderate to great earthquake in the Garhwal Himalaya. [Copyright &y& Elsevier]

This paper presents the computation of time series of the 22 July 2007 M 4.9 Kharsali earthquake. It occurred close to the Main Central Thrust (MCT) where seismic gap exists. The main shock and 17 aftershocks were located by closely spaced eleven seismograph stations in a network that involved VSAT based real-time seismic monitoring. The largest aftershock of M 3.5 and other aftershocks occurred within a small volume of 4 × 4 km horizontal extent and between depths of 10 and 14 km. The values of seismic moment ( M) determined using P-wave spectra and Brune's model based on f spectral shape ranges from 10 to 10 dyne-cm. The initial aftershocks occurred at greater depth compared to the later aftershocks. The time series of ground motion have been computed for recording sites using geometric ray theory and Green's function approach. The method for computing time series consists in integrating the far-field contributions of Green's function for a number of distributed point source. The generated waveforms have been compared with the observed ones. It has been inferred that the Kharsali earthquake occurred due to a northerly dipping low angle thrust fault at a depth of 14 km taking strike N279°E, dip 14° and rake 117°. There are two regions on the fault surface which have larger slip amplitudes (asperities) and the rupture which has been considered as circular in nature initiated from the asperity at a greater depth shifting gradually upwards. The two asperities cover only 10% of the total area of the causative fault plane. However, detailed seismic imaging of these two asperities can be corroborated with structural heterogeneities associated with causative fault to understand how seismogenesis is influenced by strong or weak structural barriers in the region. [ABSTRACT FROM AUTHOR]

The Kumaun-Garhwal region of Himalaya falls in the central seismic gap of Himalaya where the probability of occurrence of the great earthquake has been estimated as 31% in a 50-year time window. This underlines the importance of evaluation of seismic hazard in this region. One-dimensional (1D) site response functions provide one-dimensional predictions in a 3D environment and play an important role in assessing the seismic hazard of a region. In the present study, 1D site response functions have been estimated for the Kumaun-Garhwal region using 56 local earthquakes recorded at 14 sites. Ten sites, out of the 14 sites, are situated in Garhwal Himalaya, 3 sites are located in adjacent Kumaun Himalaya and 01 in Indo-Gangetic plain. The widely used horizontal to vertical spectral ratio technique has been adopted here for this purpose. The seismic spectral amplification levels have been obtained at the predominant frequency as well as at five different frequencies corresponding to different types of buildings. The average site spectral amplification levels at the predominant frequency for the sites in higher Himalaya, lesser Himalaya, and in outer Himalaya are found to be 3.94, 4.43, and 5.98 respectively. These estimated values are correlated with rock/soil types in these three sub-divisions of Himalaya. The only site (Deoband) situated in the Indo-Gangetic plain gives the site spectral amplification level of 7.17 at predominant frequency. The seismic hazard to different story buildings in the region based on the estimated site spectral amplification levels is discussed. The computed site spectral amplification functions are useful for estimating the earthquake source parameters and for the simulating techniques for earthquake strong ground motions. [ABSTRACT FROM AUTHOR]

A moderate size earthquake (ML 5.9) occurred near Mechuka in Siang Valley on 23rd April 2019 at 20:15:50.00 UTC in the rupture zone of the great Assam earthquake of 15th August 1950. This shallow-focused earthquake occurred close to NE trending Main Central Thrust has a thrust fault mechanism striking parallel to this major tectonics of the Himalaya. Including this event, a dataset of 46 local, micro and low magnitude earthquakes (1.5 ≤ ML ≤ 5.9) of the Siang Valley of Arunachal Pradesh, NE India, are evaluated for the characteristics of the earthquake source, seismicity, stress drop and tectonic structures. The earthquake events were recorded by a close digital network of eight broadband seismic stations installed in December 2018 in the Siang Valley. The stress drop (Δσ) obtained for the Mechuka earthquake in the Siang Valley is 114.71 bars, the seismic moment (Mo) of 6.86E + 16 Nm and the source radius (r) of 1392.41 m. The seismic moments obtained from the microearthquakes vary between 2.44E + 11 and 6.86E + 16 Nm, and the source radius varies from 172.90 to 1392.41 m based on Brune's circular source model 1970. The corner frequencies (fc) of the events range from 1.03 to 8.04 Hz. Seismically intense clustering of microearthquakes has a low-stress drop below 10 bar except for the Mechuka earthquake, which varies from 0.05 to 114.72. This high-stress drop of moderate earthquake compared to its low values of lower magnitude earthquakes indicates that the earthquake of 23rd April 2019 is associated with high-strength material accumulating high strain during the earthquake-building process. Moment magnitude of whole data set ranges from 1.52 to 5.16. The scaling relationship between Mo and fc is obtained as 9.089E + 16fc–9.52, and for Mo and Δσ are modelled to be related as Mo = 8.96E + 10Δσ2.86. Evaluated low-stress drop for the smaller size of earthquakes shows brittleness of the upper crustal region. Research highlights: Modelling of earthquake source parameters to obtain scaling relations for Siang Valley, Arunachal Pradesh. The estimated Mo, fc, r, ∆σ and Mw are 2.44 × 1011 to 6.86 × 1016 Nm, 1.03–8.04 Hz, 172.90–1392.41 m, 0.05–114.71 bar and 1.52–5.16, respectively. Scaling relation between Mo and fc, Mo and Δσ and Mw and fc is Mo = 9.089E + 16fc−9.52, Mo = 8.96E + 10 Δσ2.86 and Log fc = –0.39Mw + 2.39, respectively. [ABSTRACT FROM AUTHOR]

The seismological data recorded at our four semi-permanent broadband seismographs installed by the CSIR-NGRI, Hyderabad, Telangana in the Aravalli mobile belt (AMB) and Rajasthan craton in the northwest Indian shield during the period 2014–2016 are used in the study. The 16 selected regional Indian earthquakes of Mw 5.5–7.8 that occurred in the North India region recorded at the four seismic stations are used to compute the surface wave (both Rayleigh and Love waves) group velocity dispersion characteristics and average 1-D regional shear wave velocity (Vs) structure beneath the North India which covers the northern part of India between the whole Himalayan region and Rajasthan craton including AMB. First, we compute Rayleigh waves (at 7–87 s) dispersion curves and Love waves (at 7–82 s) group velocity dispersion curves by utilizing the standard frequency time analysis (FTAN) of 3-component broadband data recorded at these four 3-component broadband seismic stations. After that, using the logarithmic stacking technique, we compute the final average stacked fundamental mode dispersion curves of surface waves (both Love and Rayleigh waves) for our study area. Then, we finally invert the final average dispersion curves of surface waves (both Love and Rayleigh waves) to compute the average one-dimensional regional shear velocity structure beneath North India. Our modelling result in North India suggests a two-layered crustal structure with a crustal thickness of 39 km. The thickness of the first crustal layer (upper crust) is 20 km with a shear wave velocity (Vs) of 3.30 km/s. On the other hand, the second crustal layer (lower crust) marks a 19-km thickness with a Vs of 3.70 km/s. Our modelling result suggests that the Vs of the upper mantle is found to be 4.35 km/s below the study region. Research highlights: Modelled average one-dimensional regional Vs structure below northern part of India. A 2-layered crustal velocity model below North India. Upper crust at 20 km thick with Vs of 3.30 km/s. And, lower crust at 19 km thick with Vs of 3.70 km/s. The Moho depth is 39 km and Vs below the Moho depth is found to be 4.35 km. [ABSTRACT FROM AUTHOR]

Labdane diterpene andrographolide ( 1 ) is a major constituent of Andrographis paniculata and known to exhibit wide spectrum of biological activities. In this study, regioselective monoesters of ( 1 ) have been synthesized by using Amano lipase AK ( Pseudomonas fluorescens ) as a biocatalyst. Amano lipase AK was able to execute highly efficient esterification of hydroxyl group attached to C-14 carbon of ( 1 ) in presence of acyl donors. Among the various synthesized derivatives including two novel compounds such as andrographolide-14-propionate ( 3 ) and andrographolide-14-caproate ( 5 ) displayed antimicrobial activity against Staphylococcus aureus with low minimal inhibitory concentration (MIC) 4 µg/mL and 16 µg/mL respectively. Furthermore, they have shown low hemolysis activity at their respective MIC and increase in the permeability of the bacterial cell membrane as delineated by FITC uptake and SEM imaging studies. [ABSTRACT FROM AUTHOR]

Between 2017 and 2019, the CSIR-NGRI, Hyderabad, Telangana, established a broad-band seismic-network with fifty-five 3-component broadband seismometers in the Himalayan region of Uttarakhand, India. Out of 55 three component broadband seismic (BBS) networks, we chose 17 for the present study. Using digital waveform data from twenty-one (21) regional Indian earthquakes of Mw 5.0–6.2 that were recorded in the 17 broadband seismometer, we compute fundamental mode group-velocity dispersion (FMGVD) characteristics of surface waves (Love and Rayleigh waves) and the average one-dimensional regional shear-wave velocity (Vs) structure of the Uttarakhand Himalayan region. First, we compute FMGVD curves for Love waves (6–73 s) and Rayleigh waves (at 6.55–73 s) period, and then, we finally invert these dispersion curves to compute the final average one-dimensional regional crustal & sub-crustal shear-wave velocity (Vs) structure below the Uttarakhand Himalaya. Our best model in Uttarakhand Himalayan region, India, reveals the 8-layered crust with a mid-crustal low velocity layer (MC-LVL) (approximately a drop of 1.5–2.3% in Vs) between 8 and 20 km depth in the proximity of MCT (Main Central Thrust). In the upper crustal part (0–20 km depths), our modelling suggests shear velocities (Vs) varies from 3.1 to 3.9 km/sec while shear velocities (Vs) in the lower crustal part (20–45 km depth) are modelled to be varying from 3.7 to 4.69 km per sec. The Moho-depth is calculated to be 45 km deep below the K-G Himalaya, and the shear-velocity (Vs) in the sub-crustal sector is 4.69 km/sec. Our estimated mid-crustal low-velocity layer (MC-LVL) could be linked to the presence of metamorphic fluids in the fractured Main Himalayan Thrust (MHT), resulting from the weakening of the crustal material at the interface between the overriding Eurasian plate and upper part of the underthrusting Indian plate. [ABSTRACT FROM AUTHOR]

On the 27th of August 2016, a seismic swarm activity consisting of 58 earthquakes (1.5 ≤ M L  ≤ 4.4), which occurred in Rampur area of the Kullu-Rampur Tectonic window of Himachal Pradesh in Northwest Himalaya. The epicenters of these events are located at the northern front of the Berinag Thrust in its hanging wall. To better understand the seismotectonics of this region, we analyzed the spectral source parameters and source mechanism of this swam activity. Spectral analysis shows the low stress drop values (from 0.05 to 28.9 bars), suggesting that the upper crust has low strength to withstand accumulated strain energy in this region. The Moment Tensor solutions of 12 earthquakes (≥2.7M L ) obtained by waveform inversion yield the shallow centroid depths between 5 and 10 km. All these events are of dominantly thrust fault mechanism having an average dip angle of ∼30°. The P-axes and the maximum horizontal compressive stresses are NE-SW oriented; the relative motion of the Indian Plate. The present study reveals that the swarm activity in the Himachal region of NW Himalaya is related to the out-of-sequence thrusting or the Lesser Himalayan Duplex system. [ABSTRACT FROM AUTHOR]

The earthquake Source parameters and scaling relationships derived from our current study could enhance earthquake hazard modelling for the Garhwal Himalayan region, Uttarakhand. [Display omitted] • Modelling of source parameters and scaling relationship of the local earthquakes in the Central Seismic gap (CSG) NW Himalaya, India. • The modelled source parameters, including corner frequency (fc), source- radius (r), stress drop (Δσ), seismic moment (Mo), and moment magnitude (Mw), varied in the ranges of 1.3–11.58 Hz, 117.6–1054.4 m, 0.004–36 bar, 2.83E+11–1.33E+14 N-m, and 1.5–3.3 respectively. • The scaling relation between Corner frequency (fc) and seismic moment (Mo) is obtained as Mo = Afc−2.6 N-m/s3 where, (A = 4 × 1013) N-m/s3, while between Mo and stress drop (Δ σ) the relation is found to be as log (Δσ) = 0.60 log (Mo)-17.34. • It is significant that our modelling indicates a scaling relationship between Mo and fc as Mo fc2.6 ∝ Constant for Garhwal Himalayan local earthquakes of Mw 1.5 to 3.3. In the past decade, the seismicity in the Garhwal Himalayas has been recorded by eight three-component broadband seismographs (BBS) deployed all along the Garhwal Himalayan Seismic Belt (GHSB). In this study, we estimated the source parameters of 52 local earthquakes of M w 1.5–3.3 using a 3-month seismicity catalog and the recordings of the broadband seismographs in a shear wave spectral inversion. This iterative technique is based on Brune's (1970) ω-square circular source spectral model. The modeled source parameters, including corner frequency (fc), source- radius (r), stress drop (Δσ), seismic moment (Mo), and moment magnitude (Mw), varied in the ranges of 1.3–11.58 Hz, 117.6–1054.4 m, 0.004–36 bar, 2.83E+11–1.33E+14 N-m, and 1.5–3.3 respectively. The highest computed stress drop (Δσ max) is 36 bar, while the lowest computed stress drop (Δσ min) is 0.004 bar for events of M w 2.84 and M w 1.81, respectively. The scaling relation between fc and Mo is obtained as Mo = Afc −2.6 N-m/s3 where, (A = 4 × 1013) N-m/s3, while between Mo and Δσ the relation is found to be as log (Δσ) = 0.605 log (Mo)-17.35 and Mo vs. radius, Mo = Br1.24. where (B = 3 × 109). The relation between Mw and Mo is obtained as Mo = C Mw7.51, where (C = 1 × 1010) and other relations are obtained as follows: (Δσ) = D Mw4.7894 where (D = 0.0268), fc = E r −0.948 where (E = 1102.7), Depth (d) = F (Δσ) −0.111. (F = 9.699). The estimation of earthquakes source parameters through waveform spectrum is an important component for the study of seismogenesis and obtaining scaling relations is crucial for understanding the seismic hazard assessment. The scaling relations are used to develop ground motion prediction equations (GMPEs) that relate earthquake source parameters to ground shaking characteristics (e.g., peak ground acceleration, spectral acceleration). The significant result is that our modelling indicates a scaling relationship between Mo and fc suggesting Mo fc2.6 ∝ Constant for Garhwal Himalaya based on local earthquakes of Mw 1.5 to 3.3. These scaling relationships derived from our current study could enhance earthquake hazard modelling for the Garhwal Himalayan region. This, in turn, could allow earthquake engineers to construct more resilient buildings in the area. [ABSTRACT FROM AUTHOR]

The Tehri Dam is located in a seismotectonically active region in the Indian Himalayan belt. This 260.5 m high dam has a live water storage of 2615 × 10 m and is capable of generating crustal deformation corresponding to water fluctuation. Filling of the reservoir started in October 2005. Seismic data around the dam between 2000 and 2010 shows that seismicity is corresponding to drawdown levels of the reservoir rather than to higher water levels. GPS data at twelve local benchmarks were collected from 2006 to 2008 during filling and drawdown reservoir levels. The velocity vectors show ground motion to be between ∼0.69-1.50 mm in the different filling-drawdown cycles with reference to the permanent station at Ghuttu. The motion appears to be inwards into the reservoir when the reservoir is filled and outwards when the reservoir is drained. This ground motion corresponds to elastic deformation and rebound due to effect of the oscillating water levels. [ABSTRACT FROM AUTHOR]

On 7 February 2021, Chamoli district (Uttarakhand, India) was devastated by a deadly rock-ice avalanche that led to a large causality of more than 200 people and a huge economic loss. We found noteworthy sequence of precursory signals of main failure/detachment preceded by a dynamic nucleation phase. The rock-ice avalanche appears to have been initiated by seismic precursors which were continuously active for 2:30 h prior to main detachment. The seismic amplitude, frequency characteristics and signal-to-noise ratio variation of detected tremors indicate static to dynamic changes in nucleation phase located at the source of detached wedge. The characteristics of seismic data distinguished debris flow and hitting obstacles from other seismic sources and allowed the estimations of debris flow speed. We analyzed and verified the seismic signals with field evidences to estimate the associated impacts and velocity of dynamic flow. The proximal high-quality seismic data allowed us to reconstruct the complete chronological sequence and evaluate impacts since the initiation of nucleation phase to its advancement. Furthermore, we suggest that real-time seismic monitoring with existing network and future deployment of integrated dense network can be used for forecasting of flow events and hazard mitigation in the downstream. [ABSTRACT FROM AUTHOR]

The tectonics of the Garwal-Kumaon Himalaya is characterized by thrusts, tectonic windows, and klippen. We investigate crustal shear wave velocity variations using ambient noise cross-correlation tomography. The studied region encompasses the Kali River valley in the east to Satluj valley in the west, with the adjoining Indo-Gangetic Plain in the south covering the northern part of the Delhi-Haridwar ridge. The fundamental mode group velocities of Rayleigh waves are extracted from cross-correlation data of 33 broadband seismological stations from a regional seismic network. A total of 374 dispersion curves with a period range of 4–29 s show a group velocity variation between ∼2.3 and ∼ 3.4 km/s. The shear wave velocity structure of the uppermost lithosphere down to ∼50 km obtained by non-linear inversion of the Rayleigh wave dispersion data provides new insight into the geometry of the crust. A large variation in Vs in the range of ∼2.8 to ∼4.7 km/s corresponds to a variety of changes in the tectonic deformation, structure, and crustal thickness of the Himalayan wedge. Thick low-velocity sedimentary formations are identified beneath the Indo-Gangetic Plain and the frontal Himalaya. Anomalous low Vs zones are also observed in the mid-crust beneath the higher Himalaya and southern Tibet, indicating partial melting or the presence of aqueous fluid zones. The high-velocity anomalies may be correlated with duplex structures beneath the Lesser Himalaya and with lithospheric flexure. [Display omitted] • Very low Vs in the uppermost crust beneath IGP indictes upto 10 km thick sediments. • Contrast of Vs in different depths in western and eastern parts of Central Himalaya. • Low Vs around MCT with high seismicity close and above Main Himalayan Thrust. • Possibility of flexure in the mantle below ramp structure. • Moho depth is between 40 and 47 km depth or deeper beneath study region of NW Himalaya. [ABSTRACT FROM AUTHOR]

Achieving selective and sensitive carbohydrate–protein interactions (CPIs) using nanotechnology is an intriguing area of research. Here we demonstrate that the different shapes of gold nanoparticles (AuNPs) functionalized with monosaccharides tune the bacterial aggregations. The mechanism of aggregation revealed that the large number of surface interactions of rod shaped mannose-AuNPs with E. coli ORN 178 compared with spherical and star-shaped AuNPs exhibited higher avidity and sensitivity. Moreover, such sensitive binding can be used for effective inhibition of bacterial infection of cells. [ABSTRACT FROM AUTHOR]

We describe here the sugar functionalized β-cyclodextrin–ferrocene glass slides as fully reversible bacterial biosensors under the influence of external adamantane carboxylic acid. The prototype d-mannose –E. coli ORN 178 and l-fucose –P. aeruginosa interactions serve as a model to illustrate the new approach. [ABSTRACT FROM AUTHOR]