Recurrence of paleoearthquakes on the southeastern segment of the Ganzi-Yushu Fault, central Tibetan Plateau

Although there are many earthquake relics preserved in the southeast segment of the Ganzi-Yushu Fault in the central Tibetan Plateau, the recurrence regularity of paleoearthquakes is not yet clear. This work studies paleoearthquakes on this fault segment since the Holocene through geomorphic investigation and trench excavation. The results show that sinistral dislocation of the T3/T2 terrace boundary is up to 80 m at the Cuoa Township. A 1.5 m-high fault scarp extends 3 km near the Renguo Township. A number of paleoearthquakes are exposed in trenches at two places, respectively. In combination with historical records, our work has identified 5 or 6 paleoearthquakes on this fault segment since last 5600 years. The occurrence times and recurrence intervals of these paleoearthquakes are estimated by 14C dating on strata in the trenches. Our analysis shows that these paleoearthquakes do not exhibit evident periodicity, but instead show a clustering characteristic. From 5600 a to present, seismicity of the southeastern segment of the Ganzi-Yushu Fault has two active periods and one quiet period, and the present-day time is just in the second active epoch. The recurrence intervals of each active epoch are different: 1000–1300 a in the first one, 534 a in the second one.