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CE-312

Engineering Geology and Seismology

Instructor:

Dr Amjad Naseer

Lecture#17

Department of Civil Engineering

N-W.F.P University of Engineering and Technology, Peshawar

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• Seismic Risk

• Seismic Hazard Assessment• Deterministic Seismic Hazard Assessment (DSHA)

• Probablistic Seismic Hazard Assessment (PSHA)

Outlines of the PresentationOutlines of the Presentation

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Seismic RiskSeismic RiskSEISMIC RISK refers to the amount of damage to be expected with a certain probability in a fixed period time. It is the composition of

RISK =HAZARD * EXPOSURE * VULNERABILITY

The hazard is controlled by Nature.

Vulnerability and Exposure are controlled by humans.

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Seismic RiskSeismic Risk

• Seismic hazard is the probability of observing a certain ground shaking (e.g., PGA, macro-seismic intensity, etc.) in a fixed time period.

• Vulnerability is the tendency of a structure to suffer damage.• Exposed value is an economic, but also social, quantification

of the object exposed to earthquakes.

Nature Engineers Planners

7Seismic Hazard Zoning Map

“Natural” Disasters and Casualties

Economic Impact of Earthquakes

The Gross National Product (GNP) is the total dollar value of all final goods and services produced for consumption in society during a particular time period.

HAZARD * EXPOSURE * VULNERABILITY * COST

Assess

ReduceBalance

Seismic Risk Mitigation

Control

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• The different sources of seismicity around a site are

identified and an earthquake scenario is fixed for each of

source. The location of the scenario is usually taken to be at

the least favourable location, in other words at the closest

approach to the site, possibly such that the site will also

experience forward directivity effects. The magnitude of

each scenario is a more difficult subject to select.

• However, the results of a deterministic analysis are far

more sensitive to the choice of upper-bound magnitude

than a probabilistic analysis. The term generally used to

define the size of the controlling event is the Maximum

Credible Earthquake (MCE), although there are many who

argue for this term to be abandoned.

Deterministic Seismic Hazard Assessment (DSHA)Deterministic Seismic Hazard Assessment (DSHA)

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• Once the design scenarios are fixed in terms of magnitude

and distance from the site, it is a very straightforward

operation to estimate the resulting levels of ground motion

using attenuation relationships. The most onerous ground

motion can then be taken as the basis for design, although

in some cases it may be necessary to consider more than

one scenario if the ground motions do not show a single

clearly dominant case.

Deterministic Seismic Hazard Assessment (DSHA)Deterministic Seismic Hazard Assessment (DSHA)

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Deterministic Seismic Hazard Assessment (DSHA)Deterministic Seismic Hazard Assessment (DSHA)

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• Once the design scenarios are fixed in terms of magnitude

and distance from the site, it is a very straightforward

operation to estimate the resulting levels of ground motion

using attenuation relationships. The most onerous ground

motion can then be taken as the basis for design, although

in some cases it may be necessary to consider more than

one scenario if the ground motions do not show a single

clearly dominant case.

Deterministic Seismic Hazard Assessment (DSHA)Deterministic Seismic Hazard Assessment (DSHA)