Implementing the use of Conditional Mean Spectrum (CMS) in the Zagros Region

Document Type : Research Article


1 PhD. Student, International Institute of Earthquake Engineering and seismology (IIEES)

2 Assistant Professor, Seismological Research Center, International Institute of Seismology and Earthquake Engineering (IIEES), Tehran, Iran

3 Professor, Seismological Research Center, International Institute of Seismology and Earthquake Engineering (IIEES), Tehran, Iran


This paper aims at implementing and introducing the use of conditional mean spectrum (CMS) as the main input parameters in the practice of seismic safety evaluation in Zagros, instead of the used uniform hazard spectrum (UHS). The CMS has been proposed as an alternative to the UHS to be employed as a target spectrum in ground motion record selection. The CMS provides the expected response spectrum, conditioned on occurrence of a target spectral acceleration value at the period of interest.

For this purpose, a procedure for M-R-epsilon seismic hazard deaggregation in Zagros was first developed.

The results indicate that by selecting high periods as the target period, the difference between the uniform risk spectrum and the conditional mean spectrum increases. So the shape of the conditional mean spectrum is more sensitive to tall structures. In fact, the shape of these spectra is highly dependent on the target period. This point is more important in the dynamic analysis of structures with several degrees of freedom. Because in these structures, considering only one period of target rotation, results in downstream results. In the conditional mean spectrum, the closer the two cycles are to each other, the higher the correlation of the epsilon values and the less scatter. This means that the farther apart the two rotations are, the less similar the spectral acceleration values are to each other.


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