Statistical Features of Foreshocks in Instrumental and ETAS Catalogs

We study the spatial distribution of earthquakes in temporal intervals before and after the occurrence of large shocks (mainshocks) in the magnitude range m ∈ [ 2 , 5 ] for four different regional catalogs. We find that the spatial organization of pre-shock seismicity depends on the mainshock magnitude and is independent of the lower magnitude threshold. These properties are found to be a stable feature of regional catalogs and cannot be reproduced by Epidemic Type Aftershock Sequence models. Our findings suggest that the area fractured during the mainshock is encoded in the foreshock spatial organization and, therefore, enhance the prognostic value of foreshocks.