首都圈地区地震视应力的计算及空间分布  

Computation of Apparent Stress and its Spatial Distribution in the Capital Region of China

作　　者：杨志高[1] 张晓东[2] 

机构地区：[1]中国地震局地震预测研究所,北京100036 [2]中国地震台网中心,北京100045

出　　处：《地震》2009年第4期32-43,共12页Earthquake

基　　金：中国地震局行业专项(200808036);国家科技支撑计划(2008BAC38B03-021)

摘　　要：本文计算了首都圈地区2003年9月到2007年12月117个ML>2.5地震的视应力,计算视应力的两个参数地震矩(M0)和地震辐射能量(Es)都是通过分析地震波形得到。首先用多重窗FFT获得观测谱,在扣除仪器响应后对其进行几何扩散和非弹性衰减校正。几何扩散使用Gail提出的三分段几何模型,非弹性衰减用随频率变化的Q值来表征。之后通过遗传算法找到一组Brune圆盘模型下的低频水平(Ω0)和拐角频率(fc),使得它们的理论震源谱和校正过的观测谱残差最小。通过Ω0可以得到M0,通过对校正过的观测谱求积分再加上有限仪器响应带宽补偿可以得到Es,最后就能通过M0和Es获得视应力。计算结果与先前的一些研究比较符合:视应力随地震矩不存在系统变化;fc随着M0变化和定标率M0∝fc-3符合较好;M0和ML的关系与定标率lg(M0)=1.20ML+10.0符合较好。最后给出了视应力的空间分布,结果显示视应力在邢台、唐山和晋冀蒙交界处的空间分布有不同的特征。还显示在2006年7月发生M5.1地震的文安北东方向有一个较大的视应力值,唐山地区视应力从南西到北东方向大体是增加的。In this paper, we calculate seismic apparent stresses for 117 earthquakes occurred from September 2003 to December 2007 in the capital region of China, with the minimum magnitude limit of ME2. 5. The spectral technique was used to estimate the low frequency flat level （120） and the corner frequency （fc） of Brune ω^2 model and radiated energy （Es）. We first use the multi-window FFT to obtain the observed spectrum, and then after extracting the instrument response it is corrected for geometry spreading and attenuation. For geometry spreading correction, Gailrs three section geometry spreading model was used. The frequency-dependent Q value was used for inelastic attenuation correction. The genetic algorithm was applied to determine a pair of fc and Ω0 of Brune ω^2 model, which yields the least deviation between theoretical ω^2 model and corrected spectra. Seismic moment （M0） was calculated from Ω0, and Es was obtained by integrating corrected spectral with limited bandwidth compensation. Apparent stress can be calculated from M0 and Es. The results turn out to fit well with some previous work, the apparent stress does not vary with earthquake size; fc decreases with Mo following the scaling law Mo ∝fc^-3; M0 and ML follows the scaling low lg（M0）-1. 20ME-F10.0. In the end, we give the spatial distribution of the calculated apparent stress. The result indicates that the value of earthquake apparent stress concentrated in three zones of the capital region and their spatial distribution characteristics are different. There is a high value in 2004 northeast of Wen＇an region where Ms5. 1 earthquake occurred in Jul 2006, and apparent stress in the Tangshan region on the whole increases from southwest to northeast.

关 键 词：视应力 地震矩 拐角频率 辐射能量 首都圈 

分 类 号：P315.7[天文地球—地震学]