We have studied the static stress interactions between two mainshock subevents and the two largest aftershocks of the Tangshan, China, earthquake, Ms 7.8, 1976. Fault parameters were taken from previous studies based on inversion of geodetic and teleseismic waveform data. For each event in the sequence we calculated the static change in Coulomb failure stress (cfs), including changes in pore pressure, due to all preceding events. In all cases, for the preferred mechanical parameters, we found increased cfs over nearly the entire fault plane of concern. We think that stress interactions were important in determining where large aftershocks, away from the mainshock, might occur. Rapid determination of a mainshock’s location and mechanism, together with knowledge of nearby major faults, may be useful in postevent hazard estimates.

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