Lecture 4 Aleatory Worst Case

7/26/2019 Lecture 4 Aleatory Worst Case

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CE 5603 SEISMIC HAZARD ASSESSMENT

LECTURE 4

ALEATORY vs. EPISTEMIC UNCERTAINTY

DETERMINISTIC vs. WORST CASE

By : Prof. Dr. K. nder etin

Middle East Technical University

Civil Engineering Department


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Aleatory

Variability and Epistemic

Uncertainty

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Aleatory variability is defined as the randomness in the phenomena itself. There's

no control of uncertainty in the phenomenon and the process is purely random.

Aleatory variability can not be reduced with more or better observations. One

solution to decrease aleatory variability inherent in the model may be to completely

change the model (i.e. switch from empirical observations to a physical model).

Natural randomness is modeled as a probability density function for the specificproblem being handled.

Epistemic uncertainty is due to lack of information in how the properties of the

process changes. With more data and enhanced models, epistemic uncertainty

can be reduced. Attenuations by proposed by different researchers using the same

raw sample set, and different best function fits to sample points with small numberof samples will vary the epistemic uncertainty for the problem. Figures 8-10 show

the seismic source characterizations used by various researchers in nationwide

seismic hazard mapping studies, forming a typical example for epistemic

uncertainty definition.


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Aleatory


Uncertainty

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Aleatory


Uncertainty

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Aleatory


Uncertainty

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Seismic Hazard Framework

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Worst Case Approach

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Mmax: Maximum Earthquake Magnitude

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Closest Distance and Maximum Ground

Motions

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Notes on Worst Case Ground Motions

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Example on Worst Case Ground Motions

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Lecture 4 Aleatory Worst Case