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Impact of regolith thickness on regional seismic amplification

Ellahi, Hafiz Imtenan (2009) Impact of regolith thickness on regional seismic amplification.

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Abstract:Influence of regolith thickness on the variance of seismic ground shaking is widely accepted. However most of the studies assume it constant for simplicity. Regolith thickness can be modelled by integrating field observations, geology and topography using GIS and geostatistical tools. A predicted thickness of regolith map can be used for assessing seismic amplification. The present study was conducted in the seismically active area of Balakot and Muzaffarabad in Pakistan administered Kashmir region. Regolith thickness was determined by field measurements carried out on the exposed outcrops and modelled by integrating with geology, slope and elevation using GIS and geostatistical tools. ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) and SRTM (Shuttle Radar Topography Mission) digital elevation models (DEMs) were used for deriving slope and elevation and modelling regolith thickness. A site condition map based on geology and shear wave velocity was prepared for the assessment of seismic amplification. The predicted regolith thickness in the study area varies from 1 to 10 meters. Slope, geology, and elevation have influence on regolith thickness and their correlation coefficients with regolith thickness are -0.43, 0.36 and -0.28 respectively with slope and elevation derived from ASTER DEM. Correlation coefficients of regolith thickness with slope and elevation derived from SRTM DEM are -0.48 and -0.27 respectively. The adjusted R-square and p-values of model derived from ASTER DEM are 0.20 and 5.7e-08 respectively, whereas that derived from SRTM DEM are 0.14 and 1.6e-05 respectively. The study concluded that regolith thickness is more in the centre of the valleys, flatter slopes and the areas where soft rocks are exposed. The model derived from ASTER DEM explains more variation and is more significant then that of SRTM DEM. More observations for the regolith thickness can be useful for further study. Keywords: Regolith thickness, slope, elevation, geology, seismic ground shaking, Balakot, Muzaffarabad.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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