Forecasting aftershock activity: 2. Estimating the area prone to strong aftershocks

The technique for forecasting the spatial domain where fairly intense aftershocks should be expected after a strong earthquake is considered. The paper presents the task of estimating the area prone to the strong future aftershocks using the data for the first 12 h after the main shock. The existing aftershock identification techniques are inapplicable to this task because they either analyze the distributions of the epicenters of the aftershock process that has been already completed or only consider the parameters of the main shock and only provide rough estimates. Using the developed criteria of estimating the quality of the prediction, we quantitatively compared quite a few different candidates. The latter included the main known techniques and their modifications suggested by us. In these modifications, we took into account the results of the recent studies on the dynamics of the aftershock process. This enabled us to select the optimal procedure which demonstrated the best results of the quantitative tests for more than 120 aftershock sequences with the magnitudes starting from 6.5 all over the world. This procedure can be used in the seismological monitoring centers for forecasting the area prone to the aftershock activity after a strong earthquake based on the data of operative processing.