Unconstrained Rupture Length of the 1668 M8.5 Tancheng Earthquake: Insights from dynamic rupture simulation

The 1668 M8.5 Tancheng earthquake is one of the largest historical intraplate earthquakes in eastern China, yet its rupture length, particularly the southward extent across the Yaoshang area, remains debated. We investigate the dynamic rupture process of this event using four fault geometry models and compare the simulated seismic intensity with field observations, constraining the rupture length of the 1668 M8.5 Tancheng earthquake. The models consist of six near‐parallel fault segments with rupture nucleation on the central segment near Tancheng. Yaoshang is located near the southern end of this segment and is separated from the adjacent southern fault by a ~13 km gap, which is a strong barrier to the rupture based on our simulations. With a linking fault, rupture can cross this gap and extend southward to the adjacent segment but terminates there. Further southward propagation requires enhanced weakening such as the thermal pressurization effect. However, models involving rupture of the southernmost segments generate a seismic intensity X zone southeast of Bengbu, which is inconsistent with historical intensity records. The preferred model suggests that the 1668 Tancheng earthquake was dominated by northward rupture propagation, including supershear rupture on northern segments, with limited southward extension beyond Yaoshang. Thermal pressurization played a minor role in the overall rupture process. These results provide new constraints on the rupture extent of large intraplate earthquakes and highlight the complexity of cascading rupture dynamics.