Uniform Hazard Spectra and Design Spectra in Northern Algeria

Abstract eng:
A new probabilistic seismic hazard assessment for Northern Algeria has been carried out. To do it, the used seismic catalog mainly consists of those published by the Spanish IGN, supplemented for the Algeria zone with data published by the CRAAG, and initially updated to 2002. Taking into account the particularity of the seismicity in northern Algeria, the spatially smoothed seismicity approach was used to the computation of seismic hazard. Seismic hazard map in term of PGA with 10% probability of exceedance in 50 years are obtained for rock, which correspond with a seismic hazard map for a return period of 475 years. Afterward, we have derived SA values for rock (VS > 750 m/s), corresponding to soil types A in the Eurocode 8 and S1 in the Algerian building code, damped at 5%, for different periods. The obtained results were plotted as contour maps as well. In addition to the seismic hazard assessment at different periods, we have computed the UHS at different locations. The used attenuation model allows us a high definition in the computation of the spectra. Finally, from the computed uniform hazard spectra for different type of soils, and estimated specifically for the most important cities, those obtained for a return period of 475 years and a 5% of damping are proposed as design spectra. We have used the Newmark-Hall (1982) approach with certain modifications. The spectral acceleration for 0.2-sec is used to establish the spectral region for lower periods (region controlled by the acceleration), while spectral acceleration value for 1.0-sec is used to establish the spectral region for intermediate periods (region controlled by the velocity), as such it is proposed in the most recent International Building Code.

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