河北平原地震带b值时空变化特征

Spatial and Temporal Variations of b-value in the Hebei Plain Seismic Belt

利用华北地区近44年地震资料,在区域地震序列完整性分析的基础上,用最小二乘法进行b值时间扫描计算,用最大似然法进行b值空间扫描计算。时间扫描中的b值为研究区内每个扫描窗口的平均b值,因此其变化幅度不大,基本保持在0.62~1.05之间。研究区b值空间分布范围基本维系在0.5~1.4,低b值区域为昌平—宝坻断裂段和唐山—迁安断裂段,变化范围为0.5~0.7,表明该区域地壳介质正处于相对高应力或闭锁状态,存在未来可能发生中强以上地震的潜在危险。

b-value is the basic parameter of seismic risk analysis and seismic prediction,describing the distribution characteristics of the magnitude frequency relation of earthquakes of study region.Actually it is a symbol that measures the seismicity levels in a certain region,and it is widely used in seismic prediction research and seismic risk analysis both at home and abroad.In this article,several important aspects of the influence of b value statistical are discussed.We draw some conclusions and hope to facilitate seismic prediction research.First of all,we studied the influence on the b-value by calculating seismic data integrity.Based on the observation bulletins and earthquake catalogues in the north China area,we analyzed temporal and spatial variations in seismic network monitoring capability.The effect of the bvalue curve to inspect network monitoring ability is discussed,and the results prove that the effect with regional b value curve fitting to ensure the network monitoring ability is not reliable.As the Hebei plain seismic belt is one of main activity areas of the strong earthquakes that occurred at the third and fourth activity times in North China,and it has complicated geological structure with relatively dynamic moderate-strong earthquakes in history and modern times.So according to seismic data records in the last 44 years,based on the complete analysis of seismic sequence in the district,least square method is used to conduct time-scanning calculations of b-value,and the maximum likelihood method is used to conduct space-scanning calculations of b-value.During the scanning time,b-value is the mean b-value of research zone in every scanning window,its amplitude of variation is not quite great,with a variation range of 0.62~1.05.Space-scanning results indicate that the space distribution range of bvalues basically stays within 0.5~1.4.The lowb-value zone is in the Tangshan-Qian＇an section and the Changping-Baodi section,consequently,b-value range 0.5~0.7,which indicates that the earth crust medium of this region is in a state of high horizontal stress accumulation and it there is aprobability of a moderate strong earthquake in future.