根据烈度分布确定华北历史地震破裂区的经验准则及其应用

EMPIRICAL CRITERIONS AND THEIR PRELIMINARY APPLICATION TO DETERMINE RUPTURE ZONES OF HISTORICAL EARTHQUAKES IN NORTH CHINA FROM SEISMIC INTENSITY DISTRIBUTIONS

地震破裂区是地震时沿发震断裂带的同震错动面或破裂面在地表的垂直投影区域,指示了震源断层/破裂的位置与尺度。确定过去长期的强震/大地震破裂区是鉴别地震空区、研究与预测强震危险性的重要基础。对于现代强震,破裂区可运用多种现代技术方法确定,但对于历史强震,破裂区确定的方法需要探索与发展。以华北地区为例,研究利用烈度/等震线资料、结合地震构造与震区地表地质环境等信息确定历史强震破裂区的方法,并开展应用试验。结果表明:研究区现代地震破裂区延伸的烈度区间与极震区烈度、震区环境之间存在密切关系,基于这种关系建立了2条经验准则,可分别用于根据烈度分布确定华北2类震区环境(基岩区和厚层第四纪松散堆积覆盖区)历史强震破裂区的位置与延伸。文中还提出通过综合地震构造、现代小震/余震分布等信息,辅助确定历史强震破裂区横向宽度的思路与途径。作为应用试验,文中确定了5次历史地震的破裂区,结果表明本文发展的经验准则及相应方法适用于华北地区历史强震破裂区的确定。

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/eoseismals and seismotectonies and surficial geologic environments of seismogenic regions, and then makes ease 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 coseismie 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.