Site Characteristics of Kathmandu Valley from Array Microtremor Observations

Array microtremor observations were conducted in Kathmandu Valley close to six seismic stations. Sedimentary layers from surface to deep basement rock were modeled according to the derived velocity structures for site response analysis. The records in horizontal component from the 2015 Gorkha earthquake main shock at deep sedimentary sites were compared with the predictions from analysis using the records from a shallow sedimentary site as input motions. Generally, the comparisons are in good agreement where spectral amplification at long periods and suppression at short periods could be justified by the velocity models.

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Contribution of Fault Geometry on Probabilistic Seismic Hazard Assessment in Intermontane Basin: An example from Kathmandu Valley

Journal of Nepal Geological Society ◽

10.3126/jngs.v60i0.31257 ◽

2020 ◽

Vol 60 ◽

pp. 21-36

Author(s):

Deepak Chamlagain ◽

Govinda Prasad Niroula

Keyword(s):

Seismic Hazard ◽

Hazard Assessment ◽

Main Shock ◽

Seismic Hazard Assessment ◽

Probabilistic Seismic Hazard Assessment ◽

Kathmandu Valley ◽

Probabilistic Seismic Hazard ◽

Gorkha Earthquake ◽

2015 Gorkha Earthquake ◽

The Himalaya

The intermontane basins of the Himalaya are prone to damaging earthquakes as they are located roughly 10-15 km above the Main Himalayan Thrust (MHT), a major seismogenic thrust fault in the Himalaya. After the Mw 7.8 2015 Gorkha earthquake, the geometry of the MHT has been investigated using different approaches. Two contrasting models with a single ramp and double ramp geometries are proposed. However, the contribution of these geometries on seismic hazard has not been investigated yet. In this contribution, therefore, a probabilistic seismic hazard assessment is carried out using both models for Kathmandu valley and the obtained results are compared with the measured strong ground motion data of main shock of the 2015 Gorkha seismic sequence at Kirtipur, Kathmandu (rock site). It is found that the areal sources have the least contribution indicating sole contribution of MHT to relatively higher level of seismic hazard in the valley located on the up-dip locked portion of the MHT. The Peak Ground Acceleration (PGA) of the main shock of the 2015 Gorkha earthquake and PGA for 760 yr (exposure period of 50 yr and probability of exceedance 6.36%) of return period adopting both single and double ramp models are approximately same with error level of ± 3.84%. The results indicate that the adopted seismic model fairly represents the seismo-tectonic of the region, particularly of MHT. Considering this as the best fit results, the spatial distribution of the seismic hazard is analysed using double ramp model. It is found that the PGA values in the valley for 760 yr return period vary from 0.24 g to 0.28 g. The PGA values are higher in the southern part and gradually decrease towards north. Such decrease in PGA is consistent with the decrease in locking level of the MHT towards north. The study, therefore, emphasizes detailed geometrical characterization of the MHT while carrying out the seismic hazard assessment in the Himalaya.

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The Influence of Surface Topography on the Weak Ground Shaking in Kathmandu Valley during the 2015 Gorkha Earthquake, Nepal

Sensors ◽

10.3390/s20030678 ◽

2020 ◽

Vol 20 (3) ◽

pp. 678

Author(s):

Mark van der Meijde ◽

Md Ashrafuzzaman ◽

Norman Kerle ◽

Saad Khan ◽

Harald van der Werff

Keyword(s):

Numerical Simulations ◽

Surface Topography ◽

Seismic Energy ◽

Spectral Element ◽

Kathmandu Valley ◽

Ground Displacement ◽

Gorkha Earthquake ◽

Ground Shaking ◽

Earthquake Scenarios ◽

2015 Gorkha Earthquake

It remains elusive why there was only weak and limited ground shaking in Kathmandu valley during the 25 April 2015 Mw 7.8 Gorkha, Nepal, earthquake. Our spectral element numerical simulations show that, during this earthquake, surface topography restricted the propagation of seismic energy into the valley. The mountains diverted the incoming seismic wave mostly to the eastern and western margins of the valley. As a result, we find de-amplification of peak ground displacement in most of the valley interior. Modeling of alternative earthquake scenarios of the same magnitude occurring at different locations shows that these will affect the Kathmandu valley much more strongly, up to 2–3 times more, than the 2015 Gorkha earthquake did. This indicates that surface topography contributed to the reduced seismic shaking for this specific earthquake and lessened the earthquake impact within the valley.

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Characterizing the Kathmandu Valley sediment response through strong motion recordings of the 2015 Gorkha earthquake sequence

Tectonophysics ◽

10.1016/j.tecto.2016.09.030 ◽

2017 ◽

Vol 714-715 ◽

pp. 146-157 ◽

Cited By ~ 18

Author(s):

S. Rajaure ◽

D. Asimaki ◽

E.M. Thompson ◽

S. Hough ◽

S. Martin ◽

...

Keyword(s):

Strong Motion ◽

Earthquake Sequence ◽

Kathmandu Valley ◽

Gorkha Earthquake ◽

2015 Gorkha Earthquake

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Liquefaction hazard assessment and ground failure probability analysis in the Kathmandu Valley of Nepal

Geoenvironmental Disasters ◽

10.1186/s40677-021-00203-0 ◽

2022 ◽

Vol 9 (1) ◽

Author(s):

Mandip Subedi ◽

Indra Prasad Acharya

Keyword(s):

Soil Liquefaction ◽

Kathmandu Valley ◽

Borehole Data ◽

Gorkha Earthquake ◽

Engineering Structures ◽

Liquefaction Potential ◽

Ground Failure ◽

2015 Gorkha Earthquake ◽

Scenario Earthquakes ◽

Liquefaction Hazard

AbstractDuring the 2015 Gorkha Earthquake (Mw7.8), extensive soil liquefaction was observed across the Kathmandu Valley. As a densely populated urban settlement, the assessment of liquefaction potential of the valley is crucial especially for ensuring the safety of engineering structures. In this study, we use borehole data including SPT-N values of 410 locations in the valley to assess the susceptibility, hazard, and risk of liquefaction of the valley soil considering three likely-to-recur scenario earthquakes. Some of the existing and frequently used analysis and computation methods are employed for the assessments, and the obtained results are presented in the form of liquefaction hazard maps indicating factor of safety, liquefaction potential index, and probability of ground failure (PG). The assessment results reveal that most of the areas have medium to very high liquefaction susceptibility, and that the central and southern parts of the valley are more susceptible to liquefaction and are at greater risk of liquefaction damage than the northern parts. The assessment outcomes are validated with the field manifestations during the 2015 Gorkha Earthquake. The target SPT-N values (Nimproved) at potentially liquefiable areas are determined using back analysis to ascertain no liquefaction during the aforesaid three scenario earthquakes.

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The 2015 Gorkha Earthquake and response of the Kathmandu Valley sediments

Journal of Nepal Geological Society ◽

10.3126/jngs.v49i1.23136 ◽

2015 ◽

Vol 49 (1) ◽

pp. 1-5

Author(s):

Sudhir Rajaure ◽

Megh Raj Dhital ◽

Lalu Prasad Paudel

Keyword(s):

Source Zone ◽

Great Earthquake ◽

Kathmandu Valley ◽

Main Central Thrust ◽

Gorkha Earthquake ◽

Ground Acceleration ◽

Low Frequencies ◽

High Frequencies ◽

Nepal Earthquake ◽

2015 Gorkha Earthquake

The Gorkha Earthquake occurred on the gently dipping part of the Main Himalayan Thrust (MHT), close to the Main Central Thrust (MCT). This earthquake possibly occurred in the source zone of the 1833 Nepal Earthquake (Mw 7.6), which occurred after 182 years. The region between the 1905 Kangra Earthquake and 1934 Bihar-Nepal Earthquake has not produced any great earthquake since the last 500 years and still remains a potential site for great earthquake(s) in future. The Kathmandu Valley witnessed moderate ground acceleration and comparatively large velocity as recorded at Kantipath during the Mw 7.8, Gorkha Earthquake. The analysis of the records show that high frequencies were damped and low frequencies were dominant over the sedimentary basin, which can be attributed to the response of the sediments underneath. Because of damping of high frequencies, the engineered, low storey buildings were less damaged and resisted the ground shaking comparatively well. However, on the other hand, the historical monument 'Dharahara' collapsed completely and the high rise apartment buildings suffered more because of the dominance of low frequencies.

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The Performance of Slender Monuments during the 2015 Gorkha, Nepal, Earthquake

Earthquake Spectra ◽

10.1193/120616eqs223m ◽

2017 ◽

Vol 33 (1_suppl) ◽

pp. 321-343 ◽

Cited By ~ 1

Author(s):

Anjali Mehrotra ◽

Matthew DeJong

Keyword(s):

Ground Motion ◽

Low Frequency ◽

Kathmandu Valley ◽

Discrete Element Modeling ◽

Frequency Content ◽

Gorkha Earthquake ◽

Long Period ◽

2015 Gorkha Earthquake ◽

Long Period Ground Motion ◽

2015 Gorkha Nepal Earthquake

This paper studies damage to a few specific monuments in the Kathmandu Valley that were either partially or completely destroyed during the 2015 Gorkha earthquake. Three of these structures—namely, the Basantapur Column, the Dharahara Tower, and the Narayan Temple—were modeled both analytically using rocking dynamics and computationally using discrete element modeling (DEM). The results emphasize the importance of large low frequency content within the ground motion, demonstrating that the Dharahara Tower could have collapsed due to the primary long-period ground motion pulse alone. In addition, comparison of analytical and computational modeling to the observed response enables evaluation of structural behavior, including discussion of the importance of elastic amplification and column embedment on performance during the earthquake.

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Identifying archaeological evidence of past earthquakes in a contemporary disaster scenario: case studies of damage, resilience and risk reduction from the 2015 Gorkha Earthquake and past seismic events within the Kathmandu Valley UNESCO World Heritage Property (Nepal)

Journal of Seismology ◽

10.1007/s10950-019-09890-7 ◽

2019 ◽

Vol 24 (4) ◽

pp. 729-751 ◽

Cited By ~ 2

Author(s):

Christopher Davis ◽

Robin Coningham ◽

Kosh Prasad Acharya ◽

Ram Bahadur Kunwar ◽

Paolo Forlin ◽

...

Keyword(s):

Risk Reduction ◽

World Heritage ◽

Lessons Learned ◽

Kathmandu Valley ◽

Gorkha Earthquake ◽

Unesco World Heritage ◽

2015 Gorkha Earthquake ◽

Reduction Strategies ◽

The Face ◽

Disaster Scenario

AbstractThe 2015 Gorkha Earthquake was a humanitarian disaster but also a cultural catastrophe that damaged and destroyed historic monuments across Nepal, including those within the Kathmandu Valley UNESCO World Heritage Property. In the rush to rebuild, traditionally constructed foundations are being removed and replaced with modern materials without assessments of whether these contributed to the collapse of a monument. Generally undertaken without scientific recording, these interventions have led to the irreversible destruction of earlier subsurface phases of cultural activity and the potential loss of evidence for successful traditional seismic adaptations and risk reduction strategies, with no research into whether modern materials, such as concrete and steel, would offer enhanced resilience. In response to this context, multidisciplinary post-disaster investigations were undertaken between 2015 and 2018, including archaeological excavation, geophysical survey, geoarchaeological analysis, linked to architectural and engineering studies, to begin to evaluate and assess the damage to, and seismic adaptations of, historic structures within Nepal’s Kathmandu Valley. Where possible, we draw on archaeoseismological approaches for the identification and classification of Earthquake Archaeological Effects (EAEs) at selected monuments damaged by the 2015 Gorkha Earthquake. Lessons learned from evidence of potential weaknesses, as well as historic ‘risk-sensitive tactics’ of hazard reduction within monuments, are now being incorporated into reconstruction and rehabilitation initiatives alongside the development of methods for the protection of heritage in the face of future earthquakes.

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Estimating shear wave velocity using acceleration data in Antakya (Turkey)

Earth Sciences Research Journal ◽

10.15446/esrj.v18n2.41810 ◽

2015 ◽

Vol 18 (2) ◽

pp. 99-105 ◽

Cited By ~ 2

Author(s):

Aydın Buyuksarac ◽

Semir Over ◽

Mehmet Cemal Genes ◽

Murat Bikce ◽

Selcuk Kacin ◽

...

Keyword(s):

Wave Velocity ◽

Site Response ◽

Free Field ◽

Soil Conditions ◽

Response Analysis ◽

Seismic Velocities ◽

Seismic Wave Velocity ◽

Velocity Models ◽

Acceleration Data ◽

Joint Research Project

This manuscript presents a site response analysis and an estimation of S-wave velocity that are dependent on acceleration data. First, existing data, such as density, seismic wave velocity, and soil cross-sections, are obtained from previous seismic microzonation studies and used to prepare input data for a suite of MATLAB routines, which are referred to as SUA software. Acceleration data are obtained from four free-field strong-motion stations of the SERAMAR project, which was conducted between 2006 and 2009 in conjunction with a Turkish-German joint research project, and inputted into the software as basic data. The results include a 1D velocity cross-section versus depth and an amplification model of the site. Three different depth levels can be determined for the ranges of 0-5 m, 5-15 m and 15-25 m. The seismic velocities vary between 380 and 470 m s-1 for the first 5 m; 320 and 480 m s-1 for 5-15 m; and 470 and 750 m s-1 for 15-25 m. These results are comparable with the amplification values from the microtremor data from previous studies. The 1D velocity models are appropriate for the soil conditions. ResumenEste trabajo presenta el análisis a una respuesta de sitio y una estimación de la velocidad de la onda de corte que son dependientes de la información de aceleración. Los datos adicionales como la densidad, la velocidad de onda sísmica y los cortes transversales de suelo, se obtuvieron de estudios previos de microzonificación sísmica y se utilizaron para preparar el registro de datos en una plataforma de rutinas MATLAB, que se refieren al software SUA. Los datos de información de la aceleración se tomaron de cuatro estaciones de monitoreo de movimientos fuertes a campo abierto del proyecto SERAMAR, que se realizó entre 2006 y 2009 en una investigación conjunta turco-alemana, y se ingresaron en el programa como la información básica. Los resultados incluyen una sección cruzada de velocidad 1D versus profundidad y el modelo amplificado del sitio. Se pudieron determinar tres niveles diferentes a partir de los rangos de 0-5 m, 5-15 m y 15-25 m. Las velocidades sísmicas pueden variar entre 380 y 470 m s-1 para los primeros 5 metros; 320 y 480 m s-1 para el rango 5-15 m, y 450 y 750 m s-1 para el rango 15-25 m. Estos resultados son comparables con los valores de amplificación del perfil Microtemor de estudios previos. Los modelos de velocidad 1D son apropiados para las condiciones del suelo.

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