Determination of a unique aftershock spectra

Abstract

Aftershock seismic hazard analysis depends on both mainshock magnitude and elapsed time after the main earthquake. Aftershocks can result in an increment in the seismic demand of the structures. The objective of the current study is to determine a final aftershock spectrum as an applicable outcome in seismic design and assessment of buildings. As a numerical example, aftershock probabilistic hazard analysis (APSHA) was calculated at a location in southern California. The proposed method was applied for four different periods. Furthermore, a three-story existing concrete building was selected and analyzed regarding aftershock spectrum. It was shown that the amount of spectrum follows an upward trend by increasing the amount of main shock magnitude. The second finding was that the spectral value decreases with growth in elapsed time after the mainshock. While both beams and columns did not have enough strength, by applying aftershock to the building, 20% of the columns were required to be retrofitted again, and the figure for strengthened column experienced a rise of about 38%. However, the number of retrofitted beams did not change considerably.