Seismic Hazard Assessment Scenario of Metropolitan City of Karachi 30th International Nathiagali Summer College on Physics and Contemporary Needs, 2005.

Seismic Hazard Assessment Scenario of

Metropolitan City of Karachi

30th International Nathiagali Summer College on Physics and Contemporary Needs, 2005

Presented By:Dr. Sarosh. H. Lodi

Department of Civil EngineeringNED University of Eng & Tech,

Karachi

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.

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.

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

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

History of Seismicity in Rann of Kutch region

Date Latitude Longitude Magnitude

00-05-1668 24 68 Moderate

16-06-1819* 24 70 8

13-08-1821 23 70 5

19-06-1845 24 69 >6

29-04-1864 24 70 6

14-01-1903 24 70 6

History of Seismicity in Kutch region (Contd)

Date Latitude Longitude Magnitude

31-10-1940 24 68 Moderate

21-07-1956 24 70 8

18-07-1982 23 70 5

17-02-1996 24 69 >6

26-01-2001* 24 70 7.7

Seismotectonic settings on the South-East of Karachi

Allah Band Fault

Karachi

1819

Nagar-Parkar Fault

Kutch Mainland Fault

1956 Anjar Earthquake

2001 Bhuj Earthquake

Active and Probable Active Faults on the West of Karachi

Ornach-Nal Fault

The Pab Fault

The Sonmiani Fault

KarachiKarachi

Ornach Nal Fault

Pab Fault

Sonmiani Fault

Surjan Fault

Seismotectonic settings on the West of Karachi

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.

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

Soft Rock

Rock

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.

Component Attenuation Modeling Technique

)()()()(*78.0 crustRRGM

*

)(M

)(RG

)(R

)(crust

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

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

Calibration Results

FOR NAGAR PARKAR FAULT

M 7.5 R 225

SAmax(g)SVmax (mm/s)

SDmax (mm)

T1 T2

0.234 72.42 26.65 0.198 2.312

Ornach Nal Fault

M 7.5 R 150

SAmax(g)SVmax (mm/s)

SDmax (mm)

T1 T2

0.409 88.725 33.297 0.138 2.358

Calibration Results (Contd)

PAB FAULT

M 7.5 R 100

SAmax(g)SVmax (mm/s)

SDmax (mm)

T1 T2

0.657 108.732 41.607 0.106 2.404

SONMIANI FAULT

M 7.5 R 50

SAmax(g)SVmax (mm/s)

SDmax (mm)

T1 T2

1.082 130.478 51.617 0.077 2.485

Comparative Analysis

UBC-97Nagar-Parkar FaultOrnach-Nal Fault

Comparative Analysis (Contd)

UBC-97Pab Fault

Sonmiani Fault