An improved approach for aftershock hazard assessment

Estimation of aftershock hazard is one of the most critical issues in evaluation of the post-earthquake safety of damaged structures. Unfortunately, misevaluation of this risk has claimed many lives in the past. In this proceeding, an improved probabilistic aftershock hazard analysis (IPAHA) approach is presented. Proposed method has two contributions to existing approaches that are aimed at achieving more reliable estimation of aftershock hazard. First contribution is related to the spatial distribution model for aftershock clusters. In order to develop a reliable model, spatial distribution of aftershock focal points is investigated statistically for set of earthquake sequences. Specifically, positions of aftershock focal points relative to the mainshock rupture plane are investigated. Second contribution of the proposed method is related to quantification of the correlation of "epsilon" values for pairs of mainshock-aftershock ground motion intensities. Epsilon refers to the standard random error parameter that is defined as the difference between the actual and the estimated median ground motion intensity divided by standard deviation representing the total variability. Using the correlation between mainshock-aftershock epsilons, an improved aftershock hazard estimation model has been established. These developed models establish the basis of the proposed IPAHA procedure. As an example application of proposed method, the aftershock hazard is assessed for a site in Istanbul, Turkey that is assumed to be affected by a scenario mainshock earthquake.