摘要
研究断层活动性的主要目的之一是了解地震危险性,与地震危险性最直接相关的是现今的断层活动情况。如果对当地断层分布和性质有比较清楚的了解,那么就可以根据位错理论用钻孔应变仪观测资料反演断层活动。用遗传算法进行这种反演可以在进行全局搜索的同时大大提高计算效率。北京地区的活断层研究程度比较高,同时有比较密集的钻孔应变观测台站。利用2003—2005年钻孔应变观测资料对北京地区活断层活动的初步尝试性反演表明,在此期间顺义-良乡断层北段和南口-孙河断层东南段的活动可能起主导作用,活动程度与小震活动有关系。
One of the principal goals of studying active faults is to understand the possibility of earthquakes. Contemporary faults＇ activities are most important from this point of view.
When a fault slips, the surrounding strain field changes. The linear elastic dislocation theory provides a powerful tool to solve problems associated with strain field changes due to fault slip. In some widely acknowledged studies in fields such as interpreting InSAR pattern of seismic fault slip and analyzing stress transfer or stress trigger of earthquakes, dislocation theory is always the first selection of researchers.
Inversion with data from observatory stations is a common method in geophysical research. It can be used with recordings by borehole strainmeters as well as by seismometers. We introduce in this paper an approach of inverting contemporary fault slip with continuous data recorded by borehole strainmeters. Since relatively more stations are located in Beijing area and more and better studies about active faults here are documented,we have,as an attempt,carried out a practical inversion over this region of the faults＇ possible slips.
In our problem here, known conditions include observations from several stations and distribution as well as senses of the faults. We calculated the slips of the faults. Apart from contributions of the local faults ,the strain field is also affected by background tectonic deformation ,whose influence is assumed to be evenly distributed over the study area.
We examined influences of errors in Poisson ratio and fault parameters such as dip,strike,length and depth. The result shows that Poisson ratio＇s error can be ignored; while,within the searching extent ,changes in fault parameters only affect adjacent areas of the faults significantly. In contrast, fault slip plays an overwhelmingly important role in determining amplitudes of strains at all the points.
Since there are numerous faults of various sizes and shapes,and with inhomogeneous dislocation distributions,in the earth＇s crust,one may take our results of inversion as a predominant effect of the faults. We pointed out that only 9 stations are referred to and many parameters are involved in our study. Therefore, the result is with remarkable uncertainty. We can improve the inversion when there is a denser borehole strainmeter network.
出处
《地震地质》
EI
CSCD
北大核心
2007年第4期716-728,共13页
Seismology and Geology
基金
国家发展和改革委员会发改投资"城市活断层试验探测"项目(20041138)资助
关键词
钻孔应变观测
断层活动
反演
位错
遗传算法
borehole strain observation, fault activity, inversion, dislocation, Genetic Algorithm （GA）
