NONLINEAR CHARACTERISTICS OF PALEOSEISMICITY IN CHINA

Detailed studies of historical seismicity and paleoseismological data for major late Quaternary faults in China reveal spatial and temporal patterns in paleoseismic activity associated with these faults. Analys is of space-time distributions of late Quaternary faults and considera tion of new models for deformation of the Asian continent provide a ba sis for proposing a division of China and surrounding areas into five active tectonic provinces. Slip rates for active faults are highest in the Himalayan collision zone between the Indian and Eurasian plates a nd gradually decrease away from the collision zone into the adjacent a ctive tectonic provinces. Paleoearthquake recurrence intervals in the active tectonic provinces of China reflect seismogenic properties that are closely related to the position of these provinces relative to th e converging Indian and Eurasian plates. Average recurrence intervals are <2000 years to as little as 310-900 years for active faults in the Qinghai-Tibetan active tectonic province, whereas recurrence interval s are 2000-4500 years in the Xinjiang active tectonic province and lon ger than 2000 years to as much as 7250 years in the North China active tectonic province. Although average recurrence intervals are closely related to the slip rates of late Quaternary faults, no simple linear relationship exists between recurrence interval and slip rate. Further , analysis of paleoseismicity on major active faults shows that there are temporal variations in recurrence intervals. The case studies also indicate that for some provinces, faults, or fault segments there are three paleoseismic patterns: linear, logarithmic, and stepped. In the logarithmic and stepped patterns, the earthquake temporal sequence is characterized by active periods (earthquake clusters with relatively short recurrence intervals) and quiet periods (lack of clustering and relatively long recurrence intervals).