京西北延庆-怀来盆地的Q_(SH)值和小震震源参数的测定  

Q SH in the Yanqing Huailai basin, NW of Beijing and determination of source parameters of small earthquakes

作　　者：于湘伟[1] 陈运泰[1] 王培德[1] 李春来[1] 

机构地区：[1]国家地震局地球物理研究所

出　　处：《地震地磁观测与研究》1997年第5期6-18,共13页Seismological and Geomagnetic Observation and Research

摘　　要：用在一个地震台接收到的同一个震源区内的较小地震的振幅谱去除较大地震的振幅谱，求得较大地震震源谱高频趋势的斜率。利用Ｑ值在０．０００１～１００Ｈｚ之间几乎是常数的特性，用网格搜寻法对较大地震的振幅谱因衰减造成的损耗进行补偿，同时确定自震源至地震台传播途径上的介质的品质因数、拐角频率和补偿后的频谱的零频极限。用这种方法，利用中－欧合作北京西北怀来数字地震台网的记录，确定了延庆－怀来盆地的品质因数ＱＳＨ值并测定了４个小地震的震源参数。延庆－怀来盆地的ＱＳＨ值很低，在１４０～３６０之间，平均为２３０±６６。在靠近震源的地区，ＱＳＨ最低，只有１４０。怀来地震的震源谱可以用一个简单的ω２模式来表示。所研究的４个震级ＭＬ＝１．０～３．４的小地震，地震矩Ｍ０＝（１．７～３４）×１０１４Ｎｍ，震源半径ａ＝０．１４～０．２２ｋｍ，平均位错Ｄ＝０．１７～０．８２ｍ，应力降Δσ＝２．６～１８．７ＭＰａ。The slop of the high frequency asymptote for the seismic source spectra of the larger earthquake is obtained by using direct division of the amplitude spectra of the larger and smaller earthquakes with identical hypercenter location and focal mechanism, recorded by the same instrument in the same recording site. In considering the property that the quality factor is almost constant in the frequency band of 0.0001～100 Hz, the quality factor, corner frequency and zero frequency limit of the compensated spectra are determined simultaneouly by a grid search procedure, in which the observed displacement spectrum is compensated by the attenuation factor. The quality factor for the SH waves Q SH in the Yanqing Huailai basin and the source parameters of 4 small earthquakes are determined by using the recordings of the Huailai Digital Seismograph Network, northwest of Beijing. It is found that in the basin the Q SH values, ranging from 140 to 360, are very low. The average Q SH is 230±66. It is also found that in the near source region the Q SH ,equals to 140, is the lowest. The scaling relationship of the source spectra for the SH waves of the Huailai earthquakes can be expressed by a simple ω 2 model. For the 4 earthquakes of M L=1.0～3.4, studied in this paper, the seismic moment ranges from 1.7×10 14 Nm to 3.4×10 15 Nm, the radius of the source, from 0.14 km to 0.22 km, the average final dislocation, from 0.17 m to 0.82 m, and the stress drop, from 2.6 MPa to 18.7 MPa.

关 键 词：地震 盆地 震源谱 拐角频率 震源参数 Q值 

分 类 号：P315.3[天文地球—地震学]