关键词: 历史地震, 破裂区, 烈度-破裂区关系, 准则与方法, 华北

Abstract: An earthquake rupture zone is defined as the vertical projection area on the ground surface of the plane(s) on which coseismic slip(s)/rupture(s) occurred along a seismogenic fault zone, and indicates both the position and the extension of a seismic source fault zone/rupture zone. Determination of rupture zones of strong and major earthquakes occurring in the long-past history is an important foundation for identifying seismic gaps, studying and forecasting seismic potentials. Several modern techniques and methods are available to determine rupture zones of modern strong and major earthquakes. However, the relevant methods need to be developed if we hope to determine the rupture zones of the historical events. Taking North China(108°～124°E, 32°～42°N)as a research region, this paper tries to establish the empirical criterion that can be used to determine both positions and extensions of the rupture zones of strong and major earthquakes using data of modern seismic intensities/coseismals and seismotectonics and surficial geologic environments of seismogenic regions, and then makes case studies applying the method developed in this paper. To establish the regional empirical criterion, we systematically collect and analyze the relational material and the research results of the modern earthquakes whose maximum intensities are equal or greater than Ⅶ occurring in North China since 1966, including the surficial geologic-environments, the seismogenic faults and their movement styles, intensity distributions, the inversion of seismic fracture process, the aftershock distributions and the coseismic deformation. Based on those data, we determine the rupture positions and extensions among the seismic intensity spans of eight modern strong and major earthquakes occurring in North China. To compare with the other regional empirical criterions and making up for the inadequacy of the data in North China, we also determine the rupture zones and their extensions among the seismic intensity spans of the 2008 Wenchuan earthquake, Sichuan and the 2010 Yushu earthquake, Qinghai. Our researches show that a close correlation exists among the seismic intensity spans in which the rupture zones extend, with respect to the highest seismic intensities and the surficial geologic-environments of seismogenic regions. Based on the correlations, we establish two empirical criterions that can be used to determine both positions and extensions of rupture zones of historical strong and major earthquakes in two kinds of surficial geologic-environments, regions of basement rocks and regions covered by thick loose sediments of the Quaternary, respectively, in North China, from seismic intensity distributions. In this paper, we also put forward relevant thinking and methods for determining the widths of rupture zones of historical events by combining information from seismotectonics and distributions of modern small earthquakes/aftershocks. As an application test, we use the method presented in this study to determine rupture zones of five historical events, and the results prove that the empirical criterions and the corresponding methods developed in this study are effective to determine rupture zones of historical strong and major earthquakes in North China.

Key words: historical earthquakes, earthquake rupture zones, seismic intensity-rupture zone relation, criterions and method, North China