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Probabilistic seismic hazard analysis with nonlinear site response and liquefaction potential evaluation for deep sedimentary deposits

University of British Columbia

Seismic hazard analysis includes deterministic or probabilistic seismic hazard analysis (DSHA or PSHA), site response analysis, and liquefaction potential evaluation. In the present study, probabilistic ground motion maps were prepared at bedrock condition for Bangladesh by using ground motion prediction equations (GMPEs) as a function of earthquake magnitudes and distances from the sources. The seismic sources have been modeled as background seismicity, crustal fault, and subduction zone. The uncertainties in the source parameters and GMPEs were accounted for using the logic tree approach. The activity rates of the background and regional seismicity sources were estimated using a declustered and complete earthquake catalog. The activity rates of the crustal fault and subduction zone sources were predicted from the geodetic strain rates using the well-accepted relationships. The Vs30 (time-averaged shear wave velocity in the top 30 m) map for Dhaka City was prepared using the relationship between the Vs30 and Holocene soil thickness to estimate site coefficients. The Vs30-based site coefficients and one-dimensional linear, equivalent-linear, and nonlinear site response analysis approaches have been used to evaluate the site effects of the deep sedimentary deposits in Dhaka City. The one-dimensional nonlinear site response analysis improves the accuracy of the ground motion. The site response analysis has to be performed using the soil profile down to the depth of the bedrock. In areas of thick and soft Holocene deposits, the long period seismic waves of the far-field earthquakes will amplify and the resonance will occur with the natural periods of the high-rise buildings, and consequently, the damage to high-rise buildings will be increased in these areas. The short period seismic waves of the near-field earthquakes will amplify in the artificially filled shallow valleys of the Pleistocene Terrace and the resonance will occur with the natural periods of the low-rise buildings, and consequently, the damage to the low-rise buildings will be increased in these areas. In this study, liquefaction hazard map for Dhaka City was prepared using liquefaction potential index (LPI) and cumulative frequency distribution of LPI of different surface geological units, which is an excellent approach to evaluate the liquefaction hazard quantitatively and spatially. The LPI values were calculated using the results of liquefaction potential evaluation that were estimated using Simplified Procedure from standard penetration test blow count (SPT-N).

Text

2019-01-28

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/68289

Civil Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/