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Seismic Hazard Assessment Scenario of Metropolitan City of Karachi

Seismic Hazard Assessment Scenario of Metropolitan City of Karachi. Presented By: Dr. Sarosh. H. Lodi Department of Civil Engineering NED University of Eng & Tech, Karachi. 30th International Nathiagali Summer College on Physics and Contemporary Needs, 2005. Presentation Layout.

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Seismic Hazard Assessment Scenario of Metropolitan City of Karachi

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  1. Seismic Hazard Assessment Scenario of Metropolitan City of Karachi Presented By: Dr. Sarosh. H. Lodi Department of Civil Engineering NED University of Eng & Tech, Karachi 30th International Nathiagali Summer College on Physics and Contemporary Needs, 2005

  2. Presentation Layout • Aims and Objectives • Methodology • Seismotectonic History of Earthquakes around Karachi.   • Probable and Active Faults in the vicinity of region. • Existing seismic design practices. • Component Attenuation Modeling Technique • Estimating Ad-hoc design response spectra on the basis of available faults   • Comparison with the UBC code based Response Spectra   • Conclusion & Recommendations.

  3. Aims and Objectives • To develop an ad-hoc Design Response Spectra using Maximum Considered Earthquake Scenarios • To perform a comparative study between currently adopted Design Response Spectra with that predicted with Component Attenuation Modeling Technique.

  4. Methodology • Active and Probable Active Earthquake source surrounding the city of Karachi have been calibrated using Magnitude of 7.5. • Component Attenuation Modeling Technique (CAM) developed by Chandler et al., have been implemented to predict frequency characteristics of earthquake ground motion. • Comparative Analysis is performed

  5. Seismotectonic History of Earthquakes around Karachi. • History reveals that Karachi was completed annihilated during earthquake of Diul (also known as Debal Earthquake) in 893 A.D. • Seismotectonic settings surrounding the Karachi can be divided into two regions • On the South-East of Karachi, Rann of Kutch has exhibited a recurring history of earthquake for the last two decades. • On the West in Baluchistan Province, it is endangered by complex faults, including subduction boundary of Indian and Eurasian plates

  6. History of Seismicity in Rann of Kutch region

  7. History of Seismicity in Kutch region (Contd)

  8. Seismotectonic settings on the South-East of Karachi Karachi 1819 Allah Band Fault Nagar-Parkar Fault 2001 Bhuj Earthquake Kutch Mainland Fault 1956 Anjar Earthquake

  9. Active and Probable Active Faults on the West of Karachi • Ornach-Nal Fault • The Pab Fault • The Sonmiani Fault

  10. Seismotectonic settings on the West of Karachi Ornach Nal Fault Pab Fault Surjan Fault Sonmiani Fault Karachi Karachi

  11. Existing Seismic Design Practices • Currently UBC-97 is used as seismic design code. • Karachi is taken into zone 2B i.e. peak ground acceleration is taken to be 0.2g.

  12. UBC-97 Design Response Spectra at Rock and Soft Rock Sites for Zone 2-B Soft Rock Rock

  13. Component Attenuation Modeling Technique (CAM) • CAM is the modified version of stochastic simulation method using wave attenuation model, developed by Boore (1983). • It is a technique proposed by Lam et al., to predict response spectral parameters of an earthquake for regions with scarcity of earthquake ground motion data. • The idea is based on the finding of Atkinson and Boore, that the source models for interplate and intraplate regions exhibit similar frequency content properties.

  14. Component Attenuation Modeling Technique Response spectral parameter of interest (SDmax, SVmax and SAmax) Constant pertaining to spectral parameter of interest Source factor Geometric factor Anelastic attenuation factor Upper crust factor, product of Cm and Cu for mid-crust amplification and combined upper crust amplification and attenuation

  15. Calibrated Faults and Respective Parameters • Maximum Magnitude =7.5 • Mid-crust exhibits Pre-Cambrian Crystalline basement and upper crust consists of Phanerozoic sedimentary sequence (Lozios et al.) Hence an amplification of 30% in response spectral ordinates is predicted, due to hard mid-crust and relatively soft upper crust. • The thickness of the crust is taken to be 40 km. • Nagar-Parkar Fault • Distance = 225 Km • Ornach-Nal Fault • Distance = 150 Km • Pab Fault • Distance = 100 Km • Sonmiani Fault • Distance = 50 Km

  16. Calibration Results

  17. Calibration Results (Contd)

  18. Comparative Analysis UBC-97 Nagar-Parkar Fault Ornach-Nal Fault

  19. Comparative Analysis (Contd) UBC-97 Pab Fault Sonmiani Fault

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