Research on Paleoearthquake and Recurrence Characteristics of Strong Earthquakes in Active Faults of Mainland China

Paleoearthquake research represents an essential method for determining recurrence intervals of large earthquakes. Reasonable determination of the average recurrence interval and coefficient of variation provides a crucial basis for the analysis of the recurrence characteristics of strong earthquakes on intraplate faults in Mainland China. Paleoearthquake data from 145 fault segments of 93 well-studied faults in Mainland China were collected, organized, and analyzed to discuss the rational estimation of the average recurrence interval and coefficient of variation of a strong earthquake occurrence probability model. First, differences in structural environments were used as a basis to investigate the spatial distribution characteristics of the average recurrence intervals of strong earthquakes. The results indicate significant variations in the recurrence periods of strong earthquakes in the Sichuan-Yunnan, Xinjiang, North China, and northeastern Tibetan Plateau structure zones. The Sichuan-Yunnan structure zone exhibited the shortest average recurrence interval for strong earthquakes, which was mainly distributed between 100 and 2000 years, and a relatively high slip rate. The Xinjiang structure zone attained a relatively balanced recurrence interval frequency distribution of 1000-4500 years and a moderate slip rate. The North China structure zone showed the lowest slip rate, with the strong earthquake recurrence interval mainly concentrated between 1000 and 4000 years. The northeastern Tibetan Plateau structure zone presented two main frequency peaks in the strong earthquake recurrence intervals between 1000-3000 years and 3000-5000 years and a relatively high slip rate. The slip rate is a key factor influencing the recurrence interval of strong earthquakes, and active faults with high slip rates show short recurrence intervals. Furthermore, the relationship between fault slip rate, fault type, and the average recurrence interval of strong earthquakes was examined. The results indicate a good logarithmic linear relationship between the fault slip rate and the average recurrence interval of large earthquakes-the higher the slip rate, the shorter the recurrence interval of strong earthquakes. Fault type also showed a relation to the average recurrence interval, with the intervals for various types of active faults gradually increasing in the order of strike-slip, normal, reverse strike-slip, reverse, and normal strike-slip faults. Second, we calculated the proportions of active faults and various fault types in each structure zone that had a coefficient of variation in recurrence intervals less than 0.4. The findings reveal that the occurrence of strong earthquakes on most active faults in Mainland China satisfies a quasiperiodic model. The general coefficient of variation across different structure zones and fault types ranges between 0.36 and 0.44, which indicates the nonsignificant difference in the degree of variability in the periodicity of strong earthquake occurrence across various structural zones and fault types.