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Parwan Gravity Dam is under construction stage in the Jhalawar district of Rajasthan, India. A thin sub-vertical surficial fracture trending N 75°W to S 75°E has been observed in the foundation area of the dam. Geophysical techniques such as electrical resistivity tomography (ERT), seismic refraction tomography (SRT), and multichannel analysis of surface waves (MASW) are utilized extensively in the field of civil engineering, exploration geophysics for the assessment and construction of large-scale infrastructures such as dams. These methods provide critical information about the subsurface conditions without the need of extensive drilling and excavation. The combination of electrical resistivity tomography (ERT), seismic refraction (SR), and multichannel analysis of surface waves (MASW) techniques with the different acquisition parameters have been used to image the extent of shallow subsurface geological structures. Various geophysical Surveys have been carried out along several profiles in the longitudinal direction and along the transverse direction to the fault axis. A total of 13 refraction and resistivity profiles were conducted of which 9 were transverse profiles and 4 were longitudinal profiles. A total of nine MASW profiles were conducted of which 8 are transverse profiles and 1 is a longitudinal profile. In this paper, the subsurface distribution of seismic wave velocity and electrical resistivity have been studied to identify any possible anomalous zone in bedrock and to detect the downward extension of surface fracture of brittle fault using the afore mentioned methods. The vertical and lateral extent of the surface fracture of the fault has been investigated by the analysis of these survey results. The analysis of the results indicates that a very tight and narrow fracture is present in the shallow subsurface. [ABSTRACT FROM AUTHOR]

Landslides are one of the prevailing threats to life that cause huge loss to the environment. Around 3.7 million km2 of the area is exposed to landslides globally, and 820,000 km2 is at high risk for landslides in India. Rainfall and earthquakes are the two primary landslide-causing variables in India. The Nilgiris district which is in the south-western part of India is more prone to rainfall-induced landslides. This study intends to calculate the depth of the slip surface on a slope (Lovedale area, the Nilgiris) in the event of a future landslide using Multichannel Analysis of Surface Waves (MASW) and validate using bore log data. During November 2009 rainfall, a shallow landslide occurred at the toe of this slope. There is a greater chance that a landslide will occur again in the event of rainfall in the future. To comprehend how the sub-strata vary, and to forecast the depth of a prospective failure surface, the shear wave velocity (Vs) obtained from MASW proved beneficial. Slip surfaces, one at a shallow depth and another at a deeper depth, were found based on the shear wave velocity and bore log data. The importance of the MASW output in the engineering properties of soil was also studied. The compressional velocity (Vp) and shear wave velocity obtained from MASW were evaluated for their applicability in calculating the elastic moduli of soil. It was established that shear wave velocity was of greater significance than compressional velocity. The MASW results can be further used as a preliminary data for analysing the stability of the slope, reactivation of landslides, and landslide early warning system. [ABSTRACT FROM AUTHOR]

Even after a century, the site-specific seismic parameters are unidentified for seismically vulnerable Kangra city, which has witnessed a disastrous effect from the 4th April 1905 Kangra earthquake (Ms 7.8). This earthquake resulted in a varied damage distribution from the unconsolidated Quaternary sediments (alluvial fans to boulders conglomerates). The site-specific response analysis was carried out with multi-geophysical approach. The seismic methods, viz., ambient noise measurement and multichannel analysis of surface waves (MASW), were employed to understand local site conditions. horizontal to vertical spectral ratio (HVSR) peaks and their corresponding frequencies are interpreted for subsurface characterization. The fundamental frequency ranged from 4.23 to >20 Hz and the amplification factor varied from 1.5 to 6.67. The vulnerability analysis was carried out to identify the weak zone on the surface. The HVSR analysis shows that dominance of high fundamental frequency (f0 > 10 Hz) component also brings possibility of heavy damage from a near-source earthquake. While the results from MASW provide two-dimensional (2D) shear wave velocity (Vs), which are used for comparison and validation. These results provide important input for earthquake-resilient planning with resilient structures as per local site conditions. Research highlights: Multi-geophysical seismic methods were tested in the complex geologically sedimentary environment of Kangra city, NW Himalaya, India. Estimation of predominant frequency and amplification from ambient noise records. Active seismic data acquisition of Multichannel Analysis of Surface Waves (MASW) for comparison and validation. Evaluation of site-specific characteristics for vulnerability analysis and earthquake risk management. [ABSTRACT FROM AUTHOR]

The unusually intense precipitations of the 2018 monsoon triggered numerous landslides in the Western Ghats region, southwest of India. Although the landslides caused no casualties, significant damage to property and infrastructure was observed. We present, as a case study, the results of active and passive seismic prospecting at two of those landslides with the goal of characterizing them, in a first application of shallow seismic exploration to landslides in the region. Our deployments included both sites perturbed by the landslides and unperturbed slopes adjacent to them with the purpose of identifying possible structural differences between slopes that underwent landsliding from slopes that were not affected. We analyze seismic sections obtained using the multi-channel analysis of surface waves technique and compare the results with seismic noise analyzed using seismic interferometry. We show that different analyses give similar results. The lateral variations observed in the shear-wave velocity distribution below the different profiles are well correlated with dominant frequency determined from seismic noise horizontal-to-vertical spectral ratios. Our measurements were taken after the landslides occurred. In hindsight, our results suggest that soil thickness played a major role in the triggering of landslides. [ABSTRACT FROM AUTHOR]

In India, many regions under high seismic risk are located on deep soil deposits extending up to several hundred meters of depth. Deep sedimentary deposits are more prone to earthquake hazard. The Indo-Gangetic Basin (IGB) is located in the vicinity of Himalayan Frontal Fault (HFT) and the presence of thick alluvium makes it more vulnerable to seismogenic sources and hence, its characterization is required. In the present study, six sites in Uttarakhand are characterized by using the joint fit Inversion method from the data obtained from Multi Channel Analysis of Surface Waves (MASW) technique with a combination of Horizontal-to-Vertical Curve (H/V) from microtremor studies. Further, seismic hazard assessment for a scenario earthquake (Mw= 8.0) is performed to study the behavior of IGB. There is an increase in spectral acceleration at sites with deep soil profiles and amplification also increases due to the presence of deep soil deposits in this region. This indicates that these sites suffer from high liquefaction potential as compared to shallow soil profiles. Moreover, peak ground horizontal accelerations at bedrock level are computed by dividing the study area into seven seismogenic source zones. On a regional scale, the b value is relatively high for seismic zone VI indicating high locally concentrated stress and fracturing. Also, the value of l is highest in seismic zone IV and lowest in seismic zone II. The estimated return periods for R6.0, R7.0 and R8.0, represents the seismic zone IV as the most active in the whole region. The estimated hazard parameters are possibly in agreement with the reported hazard parameters in the literature. Seismic characteristics of seismogenic source zones may be used for earthquake engineering purposes, e.g. assigning the severity of input motions for earthquake resistant construction. [ABSTRACT FROM AUTHOR]

We carried out shallow subsurface investigations at 600 sites covering all types of geological units in the Northwestern Deccan Volcanic Province of India, using the multichannel analysis of surface waves and suspension PS‐logging methods. The results reveal that VS30 values are in the range of 760–1500 m/s for granites and Deccan traps, thus enabling their classification as B‐class, as per the National Earthquake Hazard Reduction Program recommendations. The Tertiary, Cretaceous, Jurassic and Paleoproterozoic sediments show VS30 values between 360 and 760 m/s, and hence, are assigned C‐class. Further, the Quaternary soils are categorized as D‐class, since they show VS30 in the range of 180–360 m/s. Also, the Holocene tidal flat and Rann sediments are classified as E‐class, since the VS30 values are less than 180 m/s. The observed site response reveals that the D‐ and E‐type soils have significantly higher seismic amplification than that in the B‐ and C‐category soils. We noticed that the buildings on D‐ and E‐classes soils experienced higher damage than those on the B‐ and C‐classes, during the past large earthquakes in the Northwestern Deccan Volcanic Province. Our study suggests that VS30 is a good proxy for soil classifications in the Northwestern Deccan Volcanic Province. We validated our results using available geological, geophysical and geotechnical data. For the first time, a regional site characterization map for the Northwestern Deccan Volcanic Province of India is prepared based on geology and VS30. [ABSTRACT FROM AUTHOR]

We study strong ground motion characteristics and ground response analysis of different sites in Nanded City, India. Synthetic strong ground motion records are obtained for two scenario earthquakes of magnitude M 5.2 and M 6.8 in southern Peninsular India using the finite fault model. Shear-wave velocity averaged over top 30 m of the soil is obtained from multichannel analysis of surface wave survey at 60 sites at depths of 20-50 m below the ground surface. The sites in different parts of the city are characterized by peak ground acceleration (PGA) at the surface and bedrock level, 5 % damped response spectra at the ground surface and the amplification factor defined as the ratio of ground motion at the surface to that at the bedrock. The area east to the lineament is characterized by low V values (<200 m/s), probably associated with Godavari River basin sediments with alluvial deposits, composed of brown clay with intercalated bands of sand and gravel. A relatively high PGA value at the surface of about 0.24 g for the M 5.2 target event and hence high ground motion amplification indicative of major damage are observed at sites E-NE to the lineament in the area that are associated with the top soil column consisting of unconsolidated river basin sediments with very low V values (<200 m/s). The amplification factor for the city ranges from 3 to 8 for the highest target event of magnitude M 6.8. There is a strong lateral variation in PGA values at the surface for the part of the city lying to the east of the lineament and parallel to its trend, where a relatively high amplification factor of 6-8 is found at a dominant frequency of 1.5-2.5 Hz, which can be considered as a significant zone of amplification and hence areas with high seismic hazard. The site-specific response spectra show that the peak of spectral acceleration for different sites occurs around 3 Hz. There is a large spatial variation of spectral acceleration at any given frequency for the city. For example, site nos. 9 and 50 are characterized by a peak in spectral acceleration of 0.55 and 0.9 g, respectively, at 3 Hz frequency. [ABSTRACT FROM AUTHOR]

The dispersive characteristics of Rayleigh type surface waves were utilized to estimate shear wave velocity (Vs) profile followed by imaging the shallow subsurface granitic layers in the heart of Hyderabad. The reliability of Multichannel Analysis of Surface Waves (MASW) depends on the accurate determination of phase velocities for horizontally traveling fundamental mode Rayleigh waves. Multichannel recording leads to effective identification and isolation of various factors of noise. Calculating the 1-D shear wave velocity (Vs) field from surface waves ensures high degree of accuracy irrespective of cultural noise. The main advantage of mapping the bed rock surface with shear wave velocity (Vs) is the insensitivity of MASW to velocity inversion besides being free from many constraints such as contrast in physical properties etc. Modeling of surface waves data results a shear wave velocity (Vs) of 250-750 m/s covering the top soil to weathering and up to bedrock corresponding to a depth range of 10-30 m. Further, the computed N values (which is an indicator of site characteristic) based on the harmonic shear wave velocity up to a depth of 5 m is found to be quite high (> 25-30) well above 5 indicating the site to be safe and strong enough and not prone to liquefaction. A pair of selected set of results over granites are presented here as a case study highlighting the salient features of MASW. [ABSTRACT FROM AUTHOR]

In this study, a shallow region of engineering bedrock in Bangalore, India, was chosen to investigate the application of 30 m based site classification scheme. About 370 bore logs previously drilled up to the bedrock were selected from a geotechnical database. Equivalent N values for 30 m were estimated using measured standard penetration test (SPT) N values, which mean that the study area may be classified as site class C and D. In the study area, a geophysical test and a multi-channel analysis of the surface wave (MASW) were conducted at 58 locations. The shear wave velocities were measured and then used to estimate the equivalent 30 m shear wave velocities (Vs30), upon the results of which the study area was then classified as class B, C, and D sites. The average 30 m SPT N and Vs values were included rock N and Vs values when the depth of the rock is less than 25 m. Therefore, an attempt was made to estimate the equivalent SPT N values and shear wave velocity of the thickness of the overburden soil up to the engineering bedrock and compared with 30 m values. This study shows that, by excluding the N and Vs values of the bedrock, this area can be classified as site class D. There were large spatial site class variations between the site classifications based on the 30 m and engineering bedrock. If the area had clearly defined engineering bedrock within 30 m, then average 30 m SPT N values and the shear wave velocity would mean a higher classification. Site response analysis carried out considering selected SPT N and Vs profiles by giving regional synthetic ground motion at 30 m and engineering bedrock. Response spectrum and amplification values are much higher than 30 m based spectrum and amplifications. Separate site classification scheme needs to be developed for the shallow bedrock region with response spectrum and amplification values. [ABSTRACT FROM AUTHOR]

Abstract: Multichannel analysis of surface waves (MASW) technique was employed for site characterization studies at the identified lineament locations along coastal regions of Andhra Pradesh covering ~600km to measure the shear wave velocity. The shear (S)-wave velocity of near surface materials (such as soil, rocks and pavement) and its effect on seismic wave propagation are of fundamental interest in many groundwater, engineering and environmental studies. Geologically, the study area comprises of Precambrian basement over which younger rocks commencing with Jurassic, Cretaceous, Tertiary and Quaternary have given rise to varying sequences in different parts. The study has been conducted along the lineaments and these were selected based on the analysis of IRS-1D LISS-IV satellite images and the field geological investigation. The average shear wave velocity, stiffness and the liquefaction potential were evaluated by using the obtained shear wave velocities. Soils are classified into four categories as soft soils, stiff soils, dense soils/soft rock and hard rock based on the obtained shear wave velocities. The factor of safety (FS) against liquefaction is determined and it is found that the sites with low shear wave velocity have FS <1 and these are possible liquefiable zones. The results of this study are useful to study the earthquake hazard assessment, and also taking the necessary precautions in the vicinity of the faults/lineaments for the construction of engineering projects such as pipelines, dams, bridges, canal alignments, and cross-drainage structures. [Copyright &y& Elsevier]

Abstract: 1-D shear wave velocity structure is important for site effect studies and geotechnical engineering, but it is quite difficult and expensive to derive from the conventional geophysical techniques. Active (MASW) and passive (microtremors, HVSR) methods were conducted at 30 sites in the frontal part of the Himalaya which is characterized by soft sediments and strong seismological effects. Shear wave velocity (Vs) in the range of ~238m/s to ~450m/s has been obtained from 30m thick layer of quaternary sediments overlying Lower Miocene bed rock (Upper Siwalik Conglomerate) in Jammu city, NW Himalaya. The shear wave velocity (Vs) along with seismic input motion of Chamoli earthquake (mb 6.8) has been used to obtain site response spectrum. The response spectrum suggests five to seven times increase in peak ground acceleration for single or two storey buildings and by eight to twelve times increase in amplification ratio with respect to input ground motion. The amplification spectrum shows peak amplification of ~2Hz–~3Hz in the central part and ~1.75Hz–2Hz in the northern, southwestern and southeastern parts of the city. The advantage of microtremor HVSR is that it yields direct estimate of the fundamental frequency which is found to vary from ~1Hz to ~3Hz for same sites. Further, the 1-D velocity models obtained from ModelHVSR Matlab routine have been compared with the soil models prepared by derived using MASW. The comparison shows correlation between soil models for sites having high shallow impedance contrast between the overlying sediments and very stiff material (bedrock) underneath as than sites having less impedance contrast. [Copyright &y& Elsevier]

Abstract: Site amplifications at over 100 sites in the frequency range of 0.1–10Hz were investigated in and around Jabalpur city of central India using the conventional Nakamura technique of computing H/V spectral ratios, to estimate the predominant frequencies and corresponding amplifications at each site. To validate these results, Multichannel Analysis of Surface Waves (MASW) technique was adopted, coupled with refraction measurements over short profiles (∼100m) resulting in detailed images of shear wave and primary wave velocity structure of the shallow subsurface as well as the depth to basement, which are crucial for estimation of the amplification of seismic signals propagating through the medium. Synthetic seismograms generated based on these detailed structural models using a hybrid method comprising normal mode summation for the regional 1D structure and finite difference approach for site specific 2D structure of the medium are used to compare with site response results from the Nakamura approach. The local site amplifications expressed as the response spectral ratios – the ratio of 2D to 1D ground acceleration response-compare fairly well with the H/V results enabling proper interpretation of the composition and thickness of the upper soil cover and its hazard potential. The most significant amplification values are seen over the alluvial filled region in the north-western part of Jabalpur having soil thickness up to 30–50m, with amplifications ranging from 4.0 to 6.0, predominantly in the frequency range of 4–5Hz. Also, the areas covered with Lameta sediments in the west and northeast have thicker soil cover and indicate amplifications twice that of the adjoining Deccan trap areas. The Gondwana sediments are an exception where, in spite of thick soil covers, lower amplification values are observed which are about half of that in the alluvial regions with similar thicknesses. This is probably due to the compactness of the sedimentary formations in the former as compared to the loose, low velocity and low density alluvium in the latter. The study indicates the importance of a multi-disciplinary approach for better understanding the site amplification characteristics in any seismically active region. [Copyright &y& Elsevier]

Foundation floor mapping is essential for very important structures to provide permanent data set for geological interpretations. Prototype fast breeder reactor (PFBR) is being constructing at Kalpakkam, India. Nuclear Island Connected Building (NICB) is the main nuclear safety related structure of (PFBR), and is resting on a raft of 101.5 m × 93 m size at about 20 m below the existing ground level. Geological floor mapping was prepared after the excavation. 2 m × 2 m grids were used for sampling study and mapping of the walls and floor. The floor region of this raft foundation was seen to contain certain weathered zone with fractures of thickness of in the order of 2 m. No evidences of faulting/shearing were observed on the surface of the floor area. The entire floor area was made up of compact and sound rock mass. However, there were some isolated patches of soft weathered/altered rock and small fractures in the rock. The structural features observed during the mapping exercise indicated the need for consolidation grouting so that the entire floor area function as single rock mass. This foundation geological map will assist in making better interpretation of post-construction foundation instrumentation data. [ABSTRACT FROM AUTHOR]

In the present study, an attempt has been made to evaluate the seismic hazard considering local site effects by carrying out detailed geotechnical and geophysical site characterization in Bangalore, India to develop microzonation maps. An area of 220 km2, encompassing Bangalore Mahanagara Palike (BMP) has been chosen as the study area. Seismic hazard analysis and microzonation of Bangalore are addressed in three parts: in the first part, estimation of seismic hazard is done using seismotectonic and geological information. Second part deals with site characterization using geotechnical and shallow geophysical techniques. In the last part, local site effects are assessed by carrying out one-dimensional (1-D) ground response analysis (using the program SHAKE2000) using both standard penetration test (SPT) data and shear wave velocity data from multichannel analysis of surface wave (MASW) survey. Further, field experiments using microtremor studies have also been carried out for evaluation of predominant frequency of the soil columns. The same has been assessed using 1-D ground response analysis and compared with microtremor results. Further, the Seed and Idriss simplified approach has been adopted to evaluate the soil liquefaction susceptibility and liquefaction resistance assessment. Microzonation maps have been prepared with a scale of 1:20,000. The detailed methodology, along with experimental details, collated data, results and maps are presented in this paper. [ABSTRACT FROM AUTHOR]