We calculated the Coulomb failure stress change generated by the 1976 Tangshan earthquake that is projected onto the fault planes and slip directions of large subsequent aftershocks.Results of previous studies on the seismic fail-ure distribution,crustal velocity and viscosity structures of the Tangshan earthquake are used as model constraints.Effects of the local pore fluid pressure and impact of soft medium near the fault are also considered.Our result shows that the subsequent Luanxian and Ninghe earthquakes occurred in the regions with a positive Coulomb fail-ure stress produced by the Tangshan earthquake.To study the triggering effect of the Tangshan,Luanxian,and Ninghe earthquakes on the follow-up small earthquakes,we first evaluate the possible focal mechanisms of small earthquakes according to the regional stress field and co-seismic slip distributions derived from previous studies,assuming the amplitude of regional tectonic stress as 10 MPa.By projecting the stress changes generated by the above three earthquakes onto the possible fault planes and slip directions of small earthquakes,we find that the “butterfly” distribution pattern of increased Coulomb failure stress is consistent with the spatial distribution of follow-up earthquakes,and 95% of the aftershocks occurred in regions where Coulomb failure stresses increase,indicating that the former large earthquakes modulated occurrences of follow-up earthquakes in the Tangshan earthquake sequence.This result has some significance in rapid assessment of aftershock hazard after a large earthquake.If detailed failure distribution,seismogenic fault in the focal area and their slip features can be rapidly determined after a large earthquake,our algorithm can be used to predict the locations of large aftershocks. We calculated the Coulomb failure stress change generated by the 1976 Tangshan earthquake that projected onto the fault planes and slip directions of large subsequent aftershocks.Results of previous studies on the seismic fail-ure distribution, crustal velocity and viscosity structures of the Tangshan earthquake are used as model constraints.Effects of the local pore fluid pressure and impact of soft medium near the fault are also considered. Our result shows that the subsequent Luanxian and Ninghe earthquakes occurred in the regions with a positive Coulomb fail-ure stress produced by the Tangshan earthquake.To study the triggering effect of the Tangshan, Luanxian, and Ninghe earthquakes on the follow-up small earthquakes, we first evaluate the possible focal mechanisms of small earthquakes according to the regional stress field and co-seismic slip distributions derived from previous studies , assuming the amplitude of regional tectonic stress as 10 MPa. By projecting the stress changes gen erated by the above three earthquakes onto the possible fault planes and slip directions of small earthquakes, we find that the “butterfly ” distribution pattern of increased Coulomb failure stress is consistent with the spatial distribution of follow-up earthquakes, and 95% of the aftershocks occurred in regions where Coulomb failure stresses increase, indicating that the former large earthquakes took occurreds of follow-up earthquakes in the Tangshan earthquake sequence. This result has some significance in rapid assessment of aftershock hazard after a large earthquake. If detailed failure distribution , seismogenic fault in the focal area and their slip features can be rapidly determined after a large earthquake, our algorithm can be used to predict the locations of large aftershocks.