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Earthquakes, when it comes to natural calamities, are characteristically devastating and pose serious threats to buildings in urban areas. Out of multiple seismic regions in the Himalayas, Bhutan Himalaya is one that reigns prominent. Bhutan has seen several moderate-sized earthquakes in the past century and various recent works show that a major e...
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... objective of such extension of the city involves the construction of buildings and facilities (public, commercial or private) and the PCC intends to develop all kinds of modern amenities in the LAP. A general plot of earthquake data for the period 1937-2000 procured from the National Earthquake Information Center (NEIC) catalog covering the Bhutan region is depicted in Figure 2. As mentioned earlier, though Bhutan has not faced any major earthquake in recent times, the neighbouring regions of two countries India and Nepal have faced few considerable magnitude earthquakes. ...
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... objective of such extension of the city involves the construction of buildings and facilities (public, commercial or private) and the PCC intends to develop all kinds of modern amenities in the LAP. A general plot of earthquake data for the period 1937-2000 procured from the National Earthquake Information Center (NEIC) catalog covering the Bhutan region is depicted in Figure 2. As mentioned earlier, though Bhutan has not faced any major earthquake in recent times, the neighbouring regions of two countries India and Nepal have faced few considerable magnitude earthquakes. ...
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... objective of such extension of the city involves the construction of buildings and facilities (public, commercial or private) and the PCC intends to develop all kinds of modern amenities in the LAP. A general plot of earthquake data for the period 1937-2000 procured from the National Earthquake Information Center (NEIC) catalog covering the Bhutan region is depicted in Figure 2. As mentioned earlier, though Bhutan has not faced any major earthquake in recent times, the neighbouring regions of two countries India and Nepal have faced few considerable magnitude earthquakes. ...
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A strong earthquake (Mw=7.3) hit the Darbandikhan dam on November 12, 2017. According to its magnitude and effect classifications, the earthquake was classified as a major earthquake with serious damage effects. Consequently, the earthquake caused deformation (cracks and settlement) in the dam body. The dam could not store water during 2018. Theref...
Citations
... Remote Sensing (RS) and GIS-based applications are still rare, Tempa and Yuden Geoenvironmental Disasters (2023) 10:7 which is one of the powerful tools to perform multitemporal hazard assessment (Fernández et al. 2021). Some of the recent single hazard studies carried out in Bhutan include earthquakes (Tempa et al. 2020;Stevens et al. 2020;Chettri et al. 2021;Tempa et al. 2021a, b) and landslides (Dikshit et al. 2019Sarkar and Dorji 2019). The history of hazard cascades (hazard inventories) and impacts on populations, settlements, and infrastructures are directly linked to hazard risk, which typically results in fatalities, damages, and losses. ...
... The history of earthquake impacts in Bhutan dates back to the eighteenth century Great 1987 Assam earthquake 8.15 < Mw < 8.358 which struck on a south-dipping fault near the northern edge of the Shillong Plateau, India (England and Bilham 2015). Bhutan Himalaya is considered one of the most seismically active regions in the world due to active seismic-tectonic activities, however, in particular, Bhutan has not faced an extreme earthquake (Mw > 6.5) for the past 6 decades (Tempa et al. 2020). In most of the cases, the earthquake impacts were felt due to earthquakes in the neighboring regions. ...
Landslides, floods, fires, windstorms, hailstorms, and earthquakes are major dangers in Bhutan due to historical events and their potential damage. At present, systematic collection of data is scarce and no multi-hazard zoning is reported in the existing literature for Bhutan. In addition, for proper disaster management, recognizing the existence of the hazards and identifying the vulnerable areas are the first important tasks for any multi-hazard risk studies. To fill the gap, the main objective of this study is to prepare the multi-hazard zoning and assess the multi-hazard population risk for Bhutan on seven historical hazard events. To achieve this, we first collected data on the historical events of different periods based on the data availability and created a district-level database. A total of 1224 hazard events were retrieved. We then calculated the weighted score for individual hazards based on the number of occurrences and the degree of impact through a multi-criteria decision analysis model (MCDA) using the analytic hierarchy process (AHP). The district-wise individual hazard scores are then obtained using the weighted scores. The total hazard score (THS) was aggregated and normalized to obtain the district-wise multi-hazard scores. A multi-hazard zoning map was created in the open-source software QGIS, highlighting 70% of districts with moderate to severe multi-hazard vulnerability. Considering the population distribution in each district at the local levels, the multi-hazard score is integrated and the multi-hazard population risk is mapped.
... Some other studies have also shown that equivalent linear, and nonlinear methods work well for earthquake records with a maximum PGA of 0.2 g [9][10][11]. There are also other studies that have been done in this field indicating that the use of one-dimensional profiles for soil modeling has a good performance in predicting the effect of the site on the earthquake wave [3,[12][13][14][15][16][17][18][19][20][21]. Some studies have compared the performance of the equivalent linear and nonlinear methods together. ...
In this paper, the wavelet transform is used for the first time to reduce the cost of site response analysis calculations for different soil profiles in Isfahan city. This downsampling method was used up to three levels to generate approximate waves from the ground motion records. Site response analysis was done using the one-dimensional equivalent linear and nonlinear method. Down-hole seismic tests of 71 boreholes in Isfahan city were used to make different soil profiles. In addition, 30 ground motions compatible with seismic hazard analysis of this city were selected. Due to the lack of comprehensiveness in previous studies, none of them has definitively indicated which level of wave decomposition is the last reliable wavelet filter. But in this article, for the first time, by performing a data reliability review, it is shown that the last reliable filter for the site response is related to the second level of decomposition. Comparison of the site response analysis using approximate waves and the main records, by performing more than 2100 analyses, showed that wavelet transform could be used up to two levels with the maximum error of 8% in predicting amplification factors. In addition, approximate waves were used for the nonlinear dynamic analysis of structures with different heights located at different soil profiles, and results showed that wavelet transform decreases the cost of calculations up to 50% with a 5% error.
... A parametric investigation was done for the same region as this study, by Tempa et al. [53] and Sarkar et al. [43]. The soil was characterized as medium dense to very dense sands and of type B as per the V s30 range classification of Eurocode 8. ...
... Map Shear modulus decay and damping curves, respectively, as reported by Tempa et al.[53] ...
Phuentsholing is a thriving border town in the southwestern part of Bhutan. With the development of infrastructure over time, the safety of the residence and lifeline buildings becomes a matter of concern. Bhutan lies in the Himalayan mountain ranges, which is considered one of the most active regions for seismic events. The Indian seismic code, IS 1893-2016, has assigned Zone IV for the region, which signifies the large risk that exists for all the structures. Therefore, conducting a seismic hazard assessment for the site becomes extremely necessary before any major construction. The present study focusses to perform the deterministic seismic hazard analysis (DSHA) around certain points of interest in the town of Phuentsholing, in Bhutan. Furthermore, site-specific response spectra for Pipaldhara-1, Pipaldhara-2, Kabreytar-1, Kabreytar-2 and Phuentsholing town were plotted from the results of the DSHA. It is estimated that a peak ground acceleration ranging from 0.11 to 0.14 g can be anticipated at the level of bedrock in the study region. Response spectra were plotted for the ground level using appropriate soil-amplification coefficients, derived from the analyses in the DEEPSOIL program.
... The majority of the landslides in the Bhutan Himalayas are mainly rainfall-induced phenomena [37] with consequences similar to flooding every monsoon. Geologically, Bhutan Himalayas is characterized by fragile geological settings over complex topographical features [38]. The study area falls within the Phuentsholing Formation under the Buxa Group of the Lesser Himalayas [39]. ...
The study of land use land cover has become increasingly significant with the availability of remote sensing data. The main objective of this study is to delineate geohazard-prone areas using semi-automatic classification technique and Sentinel-2 satellite imagery in Bhutan. An open-source, semi-automatic classification plugin tools in QGIS software enabled efficient and rapid conduct of land cover classification. Band sets 2-8, 8A, and 11-12 are utilized and the virtual colour composites have been used for the clustering and creation of training samples or regions of interest. An iterative self-organizing data analysis technique is used for clustering and the image is classified by a minimum distance algorithm in the unsupervised classification. The Random Forest (RF) classifier is used for the supervised classification. The unsupervised classification shows an overall accuracy of 85.47% (Kappa coefficient = 0.71) and the RF classifier resulted in an accuracy of 92.62% (Kappa coefficient = 0.86). A comparison of the classification shows a higher overall accuracy of the RF classifier with an improvement of 7.15%. The study highlights 35.59% (512,100 m²) of the study area under the geohazard-prone area. The study also overlaid the major landslide polygons to roughly validate the landslide hazards.
Article highlights
Semi-automatic classification technique was applied to delineate the geohazard-prone area in the heterogeneous region of Bhutan Himalaya.
Unsupervised and supervised classification technique were used to perform land cover classification using the semi-automatic classification plugin (SCP).
The Random Forest classifier predicted higher accuracy and the application is rapid and efficient compared to the unsupervised classification.
... Local site characterization is inevitable procedure for sustainability against the natural disasters which results in huge number of mortalities and infrastructure destruction. Site characterization can be achieved systematically by evaluating the response of soil layers to earthquake vibrations (Nejad et al., 2018;Tempa et al., 2020). Soil layers under the effect of dynamic forces can act quite contrarily as compared to static conditions. ...
The soil conditions variability at site strongly influence ground motions during earthquakes. The disastrous earthquakes have shown that the local site conditions are the essential factors that impact lsurficial ground motions. In present study, local site effects are evaluated for ground motion acceleration and amplification at Bahrah. The town is situated on which is covered by quaternary alluvial wadi deposits. The ground motion time series are obtained through Spectral matching technique. is utilized to generate well matched ground motion time series based on the results of the PSHA and the deaggregation process. The ground motion time series and shallow Geophysical data are utilized to carry out One-dimensional simulation is carried out for equivalent linear seismic response analyses for soil layers. Results of One-dimensional site response analysis are interpolated to generate maps that account for ground motion accelerations and amplifications at top of the soil for selected spectral periods (PGA, 0.1, 0.2 and 2) for 475 years return period. The maps show the ground shaking rather than the probability of damage to buildings. The maximum values of amplification ranges upto 3.46 and acceleration upto 0.86 g. The undulation of bed rock topography and existence of deep soft sediments are reflected considerably on the results of the study area. The surface ground motion maps show that the seismic hazard level in Bahrah is moderate.
... It is observed from Figures 10-12 that for all 3 RQDs, a peak is observed in the non-linear relation between F(0.01 s) and Vs30 when Vs30 is in the range of 360-550 m/s. Tempa et al. [49] conducted a parametric study with 1-D EL method to investigate how the bedrock characteristics influence the surface ground motions for various depths of soil profiles in Bhutan. The PGA values near ground surface are in the range between 0.191 and 0.221 g for 30 m thick soil profiles [49]. ...
... It is observed from Figures 10-12 that for all 3 RQDs, a peak is observed in the non-linear relation between F(0.01 s) and V s30 when V s30 is in the range of 360-550 m/s. Tempa et al. [49] conducted a parametric study with 1-D EL method to investigate how the bedrock characteristics influence the surface ground motions for various depths of soil profiles in Bhutan. The PGA values near ground surface are in the range between 0.191 and 0.221 g for 30 m thick soil profiles [49]. ...
... Tempa et al. [49] conducted a parametric study with 1-D EL method to investigate how the bedrock characteristics influence the surface ground motions for various depths of soil profiles in Bhutan. The PGA values near ground surface are in the range between 0.191 and 0.221 g for 30 m thick soil profiles [49]. To identify the amplification characteristics due to geotechnical uncertainty in site classification for South Korean sites, Sun et al. [50] proposed a dual framework: firstly, a site classification method by using depth to bedrock, V s30 and site period, secondly, a site classification method by using digital elevation, SPT-N values and slope of surface soil (topography). ...
Site amplification factors in National Building Codes are typically specified as a function of the average shear wave velocity over the first 30 m (Vs30) or site class (A, B, C, D and E) for defined ranges of Vs30 and/or ranges of depth to bedrock. However, a single set of amplification factors may not be representative of site conditions across the country, introducing a bias in seismic hazard and seismic risk analyses. This is exemplified by significant differences in geological settings between East and West coast locations in North America. Western sites are typically characterized by lower impedance contrasts between recent surface deposits and bedrock in comparison to Eastern sites. In North America, site amplification factors have been derived from a combination of field data on ground motions recorded during West Coast earthquakes and numerical models of site responses that are meant to be representative of a wide variety of soil profiles and ground motions. The bias on amplifications and their impact on seismic hazards is investigated for the Montreal area, which ranks second for seismic risks in Canada in terms of population and hazard (PGA of 0.25 g for a 2475 years return period). Representative soil profiles at several locations in Montreal are analyzed with 1-D site response models for natural and synthetic ground motions scaled between 0.1 to 0.5 g. Since bedrock depths are typically shallow ( 0.3 g). In this study, all simulations with input motion PGA >0.3 g have been performed by using the EL method instead of the NL method considering that cohesive soils (clay and silt) at Montreal sites are stiff and cohesionless soils (sand and gravel) are considerably dense. In addition, the field and laboratory data required to perform NL analyses are not currently available and may be investigated in future works.
... Despite the achieved success of intelligence computational techniques in solving the demerits of DTB models [17,38,39], no distinguished work using GEP for the purpose of subsurface DTB modeling has been reported. Moreover, variability of DTB due to great influence on the stability of dam in high seismic zone such as northern Iran is preferred to be estimated as accurately as possible [40][41][42][43]. This gap motives dedicating an appropriate alternative with supreme predictability levels by introducing a predictive 3D spatial DTB using the GEP. ...
Infrastructures play an important role in urbanization and economic activities but are vulnerable. Due to unavailability of accurate subsurface infrastructure maps, ensuring the sustainability and resilience often are poorly recognized. In the current paper a 3D topographical predictive model using distributed geospatial data incorporated with evolutionary gene expression programming (GEP) was developed and applied on a concrete-face rockfill dam (CFRD) in Guilan province- northern to generate spatial variation of the subsurface bedrock topography. The compared proficiency of the GEP model with geostatistical ordinary kriging (OK) using different analytical indexes showed 82.53% accuracy performance and 9.61% improvement in precisely labeled data. The achievements imply that the retrieved GEP model efficiently can provide accurate enough prediction and consequently meliorate the visualization insights linking the natural and engineering concerns. Accordingly, the generated subsurface bedrock model dedicates great information on stability of structures and hydrogeological properties, thus adopting appropriate foundations.
... These features span the entire Himalayan arc including the Bhutan Himalaya [1,2]. Due to high seismicity in the region and in absence of national seismic code [2,3], the height of the buildings is regulated to eight story. With recent progression in engineering trends in infrastructure development projects, Detail Project Report (DPR) is required to signify project time 376 Comprehension of Conventional Methods for Ultimate Bearing Capacity of Shallow Foundation by PLT and SPT in Southern Bhutan frame, planning strategy and cost estimate [4]. ...
Shallow foundations are very distinctive in Bhutan since construction of buildings are regulated to 7-8 story and the superstructure loads are not very high compared to high-rise buildings elsewhere. However, the safety of the buildings depends primarily on the stability of the subsoil. This can be evaluated by estimating Ultimate Bearing Capacity (UBC) and it is the measure of the subsoil strength. In the current study, field test such as Plate Load Test (PLT) and Standard Penetration Test (SPT) are conducted in the study area which are most common conventional methods adopted in Bhutan given the typology of infrastructures. Detail analysis is performed for PLT and SPT data collected from southern parts of Bhutan to assess the shear stability characteristics of the subsoil. The field exploration was carried out at embedment depth of 1.5 m in both the tests. PLT directly provides UBC through load and settlement plot. With SPT N-values, UBC are estimated for square footing using empirical correlations proposed by Terzaghi 1943 and Meyerhof 1963. The results are compared to comprehend the design parameters. Both in-situ test resulted close estimation of UBC. In SPT, analysis results indicate Meyerhof's correlation more conservative suggesting safe and economical foundation design. The parametric analysis was performed to deduce and validate correlations among the parameters used. The subsoil lithology was reviewed to validate the subsoil characteristics for the southern belt of Bhutan to which resistivity profiles of the underlying strata of the subsoil in the region have been reported similar to the investigation conducted in this study.
... We selected eight locations in Dhamdhara, Toorsa and Rinchending regions in Phuentsholing, Bhutan, as shown in Fig. 1. In the study area, MASW measurements were conducted by the Norwegian Geotechnical Institute (NGI) [31] that indicated the majority of shear wave velocity (V s ) ranging between 380 and 470 m/s [32]. Phuentsholing city is located in the southern foothills of the country and shares international border with India (Fig. 1). ...
... For seismic site characterization, mean value of surface wave velocity of 30 m (V s, 30 ) soil column is considered as one of the most important parameters. The V s,30 ranging between 300 and 600 m/s has been reported in all the sites which corresponds to ground type B as per Eurocode EC-08 [32]. However, soil classification exclusively based in terms of V s,30 assumptions is a rather simplified hypothesis, which can potentially lead to erroneous results, especially in the case of deep soil formations or abrupt changes in stiffness between the soil layers at 30 m depth and the bedrock lying deeper down. ...
... Using the correlation proposed by Ohta and Goto [28,41], the effect of overburden pressure due to depth is accounted. Several studies conducted in the same study area have pointed out bulk unit weight variation between 12 and 21.5 KN/m 3 (e.g., [5,31,32,35,37,42]). Furthermore, based on the V s,30 site characterization, an average unit weight of 18 KN/m 3 for the soil deposit was considered in the analysis. ...
Shear wave velocity is directly related to earthquake energy characteristics and is a useful parameter in estimating the surface motion parameters. Shear wave velocities can be obtained from geophysical investigation or by empirical correlations. In the present paper, combinations of both approaches are used to estimate shear wave velocity for some locations in Bhutan. Although some measurements based on the Multispectral Analysis of Surface Waves (MASW) are available for the depth up to 22 m, the deep subsoil geology is still unknown in Bhutan. This study estimates the shear wave velocity for the depth until elastic rock (VS > 800 m/s) is found. The results highlight that the elastic rock is found at the depth between 150 to 400 m in Phuentsholing region of Bhutan. Furthermore, one-dimensional equivalent-linear ground response analysis is conducted using Equivalent-linear Earthquake site Response Analyses (EERA) program to estimate shear wave profile and surface ground motion parameters are obtained.
... The study location was explored through geophysical survey to determine geological stratigraphy using Electrical Resistivity Tomography (ERT, Electrical Imaging) technique ( Figure 6(a,b)). There are several geophysical investigation methods available based on different equipment and working principles to assess various physical properties (Tempa et al., 2020). For this study, the surface electrical resistivity method was used. ...
... Geological setting of study region(Tempa et al., 2020). ...
The research area falls at the downstream level of Bhalujhora landslide area in Alay which is located in Pasakha, Bhutan. Local Government authority proposed for construction of custom station between the commercial town Phuentsholing and Pasakha Industrial estate. However, downstream region which connects the core town to industrial estate are severely affected by the flash floods every year and the runoff causes huge sediment deposits leading risk for community and substantial damages to the infrastructures. The site is seasonally eroded and subsequently deposited by the sediments from upstream. Although, the formation level for infrastructure are proposed on the deposit layer, the assessment of soil parameters is necessary for design and planning to ensure the overall safety and long-term economic benefits. Through this study, the subsurface soil parameters are assessed by in-situ open pit investigation, geophysical survey and Standard Penetration Test (SPT), while the engineering properties of the sediment deposits were determined from laboratory tests. The field investigation was important to decide the suitability of foundation type and depth. Further, soil parameters were determined to classify the soil type, understand permeability characteristics, and predict shear strength parameters and compaction behaviour. The result shows that the sediments consist of mixture of natural aggregates and sand mixed with silt and clay. An estimate of sediment accumulation was carried out to determine the volume of the sediment deposited. The outcome will allow the relevant stakeholders to decide the management of the risk from this future disaster and propose alternative use of the sediment materials in road works.
