小浪底水库区域尾波Qc值研究初探

根据Aki的单次散射尾波理论,利用小浪底水库地震台网短周期仪器记录的地震波形资料,估测了小浪底水库地区的尾波Qc值,Qc=(89.2±28.78)f0.913 1±0.154 3。结果表明,小浪底库区Qc值与频率有很强的依赖关系,尾波Qc值较小。参照国内相关研究成果,结合本区区域尾波Qc值数值特征认为:本研究区构造活动复杂,地震活动水平高,应加强地震监测工作。     

利用天然地震研究蒙城地震台区域范围内介质的品质因子Q值

基于单次散射模型的尾波功率谱分析法,利用安徽省蒙城区域数字地震台1999年12月30日记录震中距35 km,M_S 4.1地震波形资料计算蒙城地震台周边半径约55 km范围内区域地球介质不同频率的Q值,发现0.5—20 Hz频率范围内,Q值随频率的变化关系近似服从幂函数关系Q_c=Q_0f~η,Q_0为1 Hz时的Q值,即Q_c=27.04f~(0.9952±0.0004),其中Q值在13—533范围内,平均值为273,η值在0.9952±0.004。结果表明,蒙城地震台附近范围内Q值具有较强的频域依赖性,与他人研究求得的Q作比较,平均值结果接近该Q值可以较好反映当地地球介质的品质因子;给出当地地震波传播介质的平均自由程为15 km,探讨介质的品质因子Q(Q_c)值的物理意义及应用,对研究本地区的地震活动习性及震后趋势预测具有重要意义。     

基于单次散射模型的近震尾波Q值计算软件的研制

介绍了一套基于Aki单次散射模型在Visual C++6.0平台上开发的近震尾波Q值计算程序,并应用于2005年11月26日九江—瑞昌5.7级地震余震序列的分析。本软件的研制成功,使地震近震尾波Q值计算常规化成为可能。     

Distribution of Lg coda Q in Xinjiang and its adjacent regions

In this study, we collected 1 156 broadband vertical components records at 22 digital seismic stations in Xinjiang region, ürümqi station, and 7 stations in the adjacent regions during the period of 1999–2003. The records were firstly processed by the stacked spectral ratio method to obtain Q ₀ (Q at 1 Hz) and the frequency correlation factor η corresponding to each path. Based on the results, the distribution images of Q ₀ and η in 1°×1° grids for Xinjiang region were gained by the back-projection technique. The results indicate that Q ₀ is high (300–450) in the Tarim platform and marginal Siberian platform, while Q ₀ is low (150–250) in the southern regions as west Kunlun fold system and Songpan-Ganzi fold system. In the northern regions as Junggar fold system and Tianshan fold system, Q ₀ is also low (250–300) and η varies between 0.5 and 0.9. Foundation item: National Natural Science Foundation of China (49974012) and Joint Seismological Science Foundation of China (604004).     

Scattering attenuation and intrinsic absorption using uniform and depth dependent model – Application to full seismogram envelope recorded in Northern Chile

Two seismic wave attenuation factors, scatteringattenuation Q _s ^-1 and intrinsicabsorption Q _i ^-1 are measured using theMultiple Lapse Time Window (MLTW) analysis method forthree different frequency bands, 1–2, 2–4, and 4–8 Hz.Data from 54 temporally deployed seismic stationslocated in northern Chile are used. This methodcompares time integrated seismic wave energies withsynthetic coda wave envelopes for a multiple isotropicscattering model. In the present analysis, the waveenergy is assumed to decay with distance in proportionto1/GSF·exp(- (Q _s ^-1+Q _i ^-1)· r/v), where r, and v are the propagationdistance, angular frequency and S wave velocity,respectively, and GSF is the geometricalspreading factor. When spatial uniformity of Q _s ^-1, Q _i ^-1 and v isassumed, i.e. GSF = 4r ², theestimates of the reciprocal of the extinction length,L _e ^-1 (= (Q _s ^-1+Q _i ^-1)·/v), are 0.017,0.012 and 0.010 km^-1, and those of the seismicalbedo, B ₀ (= Q _s ^-1/ (Q _s ^-1+Q _i ^-1)), are 0.48, 0.40and 0.34 for 1–2, 2–4 and 4–8 Hz, respectively, whichindicates that scattering attenuation is comparable toor smaller than intrinsic absorption. When we assumea depth dependent velocity structure, we also findthat scattering attenuation is comparable to orsmaller than intrinsic absorption. However, since thequantitative estimates of scattering attenuationdepend on the assumed velocity structure (strength ofvelocity discontinuity and/or Moho depth), it isimportant to consider differences in velocitystructure models when comparing attenuation estimates.     

2005年云南文山地震余震序列尾波Qc值研究

基于Aki等（1975）的地方震尾波单次散射模型,利用文山地震台记录到2005年8月13日在云南文山县发生的5.3级地震余震序列的数字化波形观测资料,测量了震源区尾波Q（f）值。测量结果表明,当中心频率为1．5Hz时,文山地区的尾波Q值在52～155之间,平均值为91,尾波的振幅衰减率β（f）在0.013～0．039之间,平均值为0．024;测量得到该区尾波Qc值与频率f的关系为Qc（f）=62f^“0.87;尾波波源因子A0与震级ML成正比关系,满足关系lgA0=1．02ML-0．73。此次地震的发震构造为文山断裂带,地震波受到破碎带强烈的非弹性吸收,尾波Qc值明显降低。