Estimation of the shallow velocity structure using surface wave method in the Kathmandu Valley, Nepal

Shigefuji, Michiko; Takai, Nobuo; Bijukchhen, Subeg; Timisina, Chintan; Mori, Takuho; Bhattarai, Madhusudan

doi:10.1190/segj2018-117.1

Cited by 3 publications

(1 citation statement)

References 6 publications

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“…History shows that the devastating earthquake occur in Nepal in every 80 to 100 years (Chaulagain et al, 2018). Researchers like Mori et al, 2020;Shigefuji et al, 2019 have used strong motion data for calculating ground motion prediction equations and estimation of shear wave velocities. However, we lack enough instruments and strong motion data in Nepal.…”

Section: Introductionmentioning

confidence: 99%

Estimation of Vs30 and site classification of Bhaktapur District using Microtremor Array Measurement

Prajapati,

Dhonju,

Bijukchhen

et al. 2024

Preprint

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The past earthquakes have depicted the strong need for the study of seismic behavior of sediments. Shear wave velocity directly relates to elastic shear modulus of the material and helps to incorporate the behavior of the soil in a design of structure which can be determined invasively as well as non-invasively. Multi-sensory Microtremor Array Measurement (MAM) is one of the non-intrusive methods of determining a subsurface soil characteristic by analyzing ambient vibration of the ground. In this method several geophones either in a linear or grid configuration are deployed on a firm ground surface for recording the ambient vibration. The ambient vibration data obtained by employing seismometer array of different sizes can then be jointly processed to obtain the single combined dispersion curve for a site. We determined averaged shear wave velocity (Vs30) of Bhaktapur district by two ways using non-invasive method of MAM using dispersion curve. The first method lies in obtaining Vs30 from dispersion curve directly and the second method extracts Vs30 from the inversion process using Genetic Algorithm. The first approach is direct and doesn’t require any prior knowledge of geology of site while the later one gives the velocity structure for the study area. The Vs30 thus obtained was tallied with previous works which illustrated a good correlation. The Vs30 at the south eastern part of the study area is higher than in other parts of the study area. Similarly, Vs30 at the western part of the study area is lower. The soil of the study area is found to be composed of both hard and soft soil but it is categorized as type D soil (i.e. very soft soil sites) in the new building code of Nepal. Also, the Vs30 from first method had high correlation so was used for the classification of soil of the study area based on NEHRP site classification system. As per this classification system, the study area lies in a site class C, D and E respectively.

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Section: Introductionmentioning

confidence: 99%

Estimation of Vs30 and site classification of Bhaktapur District using Microtremor Array Measurement

Prajapati,

Dhonju,

Bijukchhen

et al. 2024

Preprint

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Examination of shallow and deep S-wave velocity structures from microtremor array measurements and receiver function analysis at strong-motion stations in Kathmandu basin, Nepal

Shigefuji,

Takai,

Bijukchhen

et al. 2024

Earth Planets Space

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The Himalayan collision zone, where the Indian Plate subducts beneath the Eurasian Plate at a low angle, has caused many devastating earthquakes. The Kathmandu basin, situated in this region, is surrounded by mountains on all sides and is filled with distinct soft lake sediments with a highly undulating bedrock topography. The basin has been experiencing rapid urbanization, and the growing population in its major cities has increased the vulnerability to seismic risk during future earthquakes. Several strong-motion stations have recently been deployed in the Kathmandu basin. It is expected that the data captured by this strong-motion station array will further enhance our understanding of site amplification in sedimentary basins. Clear P-to-S converted waves have been observed in the strong-motion records. In this study, we investigate the medium boundary that generated these converted waves. First, we estimate the shallow velocity structures, which correspond to the topographic slopes or surface geology, beneath the strong-motion stations. We then apply a receiver function analysis to the strong-motion records. The receiver function indicates that the interface between the soft sediment and seismic bedrock serves as a boundary that generates converted waves. The obtained results can be used for tuning three-dimensional velocity structures. Graphical Abstract

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Estimation of Vs30 and site classification of Bhaktapur district, Nepal using microtremor array measurement

Prajapati,

Dhonju,

Bijukchhen

et al. 2024

Earth Planets Space

View full text Add to dashboard Cite

The severe damage observed in the Kathmandu Basin, Nepal, during past earthquakes necessitates a thorough study of the seismic behavior of the basin sediments. As the shear-wave velocity is directly related to the elastic shear modulus of the material, it is essential to determine it to incorporate the behavior of the soil in the design of the structure. Hence, we determined average shear-wave velocity in upper 30 m (Vs30) of soil in Bhaktapur district in the eastern part of the Kathmandu Basin at 73 observation points, employing two methods involving the use of non-invasive microtremor array measurements (MAMs). These MAMs are widely used for determining subsurface soil characteristics by analyzing the ambient vibrations of the ground. The first method involves inversion using a genetic algorithm, and the second is a method for obtaining Vs30 directly from the dispersion curve. We found that Vs30 in the southeastern part of the study area was higher than that in other parts. Conversely, Vs30 in the western region was lower. The calculated Vs30 values were used to classify the sites. The elevated eastern and southeastern areas with high Vs30 were categorized as dense soil or soft rock, whereas the areas with low Vs30 that had suffered significant damage during the 2015 Gorkha earthquake were classified as soft soil sites. Graphical Abstract

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Estimation of the shallow velocity structure using surface wave method in the Kathmandu Valley, Nepal

Cited by 3 publications

References 6 publications

Estimation of Vs30 and site classification of Bhaktapur District using Microtremor Array Measurement

Estimation of Vs30 and site classification of Bhaktapur District using Microtremor Array Measurement

Examination of shallow and deep S-wave velocity structures from microtremor array measurements and receiver function analysis at strong-motion stations in Kathmandu basin, Nepal

Estimation of Vs30 and site classification of Bhaktapur district, Nepal using microtremor array measurement

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