Stratigraphic Response Analyses of Kathmandu Valley

STRATIGRAPHIC RESPONSE ANALYSES OF

KATHMANDU VALLEY

Dipendra Gautam

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OUTLINESIntroductionGeology of NepalGeology of Kathmandu ValleySeismicityResearch ObjectivesMethodologyResultsDiscussionsConclusionResearch HorizonAcknowledgements

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INTRODUCTION

Effects of Earthquakes:

Ground Shaking

Structural Hazards

Liquefaction

Landslides

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INTRODUCTION

Ground Shaking

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Source: www.google.com

INTRODUCTION

Structural hazard

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Source: www.google.com

INTRODUCTION

Liquefaction

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Source: www.google.com

INTRODUCTION

Landslide

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Source: www.google.com

INTRODUCTION

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Site Effects

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Amplitude r(t)= source signal e(t)* distance from source p(t)* local site effects s(t)

INTRODUCTION

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Seismic Hazard Map of Nepal ( After DMG)

Kathmandu

INTRODUCTION

Site Effects are important

1985 Mexico City earthquake (Mw=8.1) 1989 Loma Prieta earthquake (Mw=7.1)

NEPAL: An earthquake prone area…!

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GEOLOGY OF NEPAL

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Kathmandu

After Uprety and Le Fort, 1999

GEOLOGY OF KATHMANDU VALLEY

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GEOLOGICAL CROSS SECTION OF KATHMANDU VALLEY

04/28/2023 13After Sakai, 2001

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SEISMICITY

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Rupture zones of large Himalayan earthquakes since 1800 (After Bilham et. al., 2001, modified by Feldl, 2005)

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SEISMICITY

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Intense micro-seismicity monitored between 1994 and 2005 ( after DMG, 2006)

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RESEARCH OBJECTIVES

Work out equivalent linear site response

analyses of soft sediment deposit of Kathmandu

valley

Comparison of computed parameters with the

damage pattern of 1934 Bihar-Nepal earthquake

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METHODOLOGY

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BOREHOLE LOCATIONS

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INPUT MOTION

(Uttarkashi earthquake) Time History

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Response spectra

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DATA ANALYSIS

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Boreholes: 53

Spatial variation

Depth of boring : 20 m to 30 m

Sediment deposit sites of

Kathmandu, Lalitpur and

Bhaktapur

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RESULTS

PEAK HORIZONTAL ACCELERATION

PEAK SPECTRAL ACCELERATION

AMPLIFICATION FACTOR

PREDOMINANT PERIOD

PEAK SPECTRAL VELOCITY

AVERAGE SHEAR WAVE VELOCITY

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RESPONSE OF SOIL

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Filling materials

Sandy silt

Medium to stiff clayey silt of low plasticity

30 m

Input motion: 6.9 Magnitude earthquake with epicentral distance of 34 km, PHA = 0.32 g

Surface: Amplified 7.788 times

Peak Horizontal Acceleration (g)

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BKTPATAN

THAMEL

Peak Spectral Acceleration (g)

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BKT

THAMEL

PATAN

Amplification factor

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PATAN

Predominant period (s)

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THAMEL

BKTPATAN

Peak Spectral Velocity (cm/s)

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BKTPATAN

Avg. Shear Wave Velocity (m/s)

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DISCUSSION

Consistent results with the damage

pattern of 1934 Bihar-Nepal earthquake,

and the hazard map of JICA

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CONCLUSIONS

Results are consistent with the damage patterns of 1934 Bihar-Nepal earthquake

Higher amplification, higher peak spectral acceleration: Gokarna, and Kalimati Formation

Lower the shear wave velocity, lower is the amplification

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RESEARCH HORIZON

Development of Vs-N relationship for Kathmandu

valley

Assessment of signal attenuated at local site

Development of site specific design spectra using

‘NONLIN’

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ACKNOWLEDGEMENTS

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Thank you for your kind presence !!!

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