2017年8月8日九寨沟MS7.0地震震源谱及震中区域品质因子

2017年8月8日四川省九寨沟县发生M_S7.0地震，国家强震动台网中心正式发布了此次地震中收集的66组强震动记录，采用其中震源距不超过150 km且台站场地反应已确定的8组记录，基于S波傅氏谱反演方法确定了此次地震的震源谱及震中区域的地壳介质品质因子.结果为：品质因子Q（f）=84.9f^0.71，说明该区域的S波非弹性衰减较为强烈；根据ω^-2震源谱模型，确定该地震的地震矩为9.42×10¹⁸Nm，其对数标准差为0.12，相应的矩震级M_W=6.616±0.079，拐角频率为0.131±0.011 Hz，应力降为3.854 MPa，该值明显低于全球板内地震的应力降平均水平（4.89 MPa），但高于2013年芦山M_W6.6地震的应力降.

Source spectra of the 8 August 2017 Jiuzhaigou MS7.0 earthquake and the quality factor of the epicenter area

On August 8, 2017 an M_S7.0 earthquake rocked Jiuzhaigou, Sichuan Province. The China Strong-Motion Networks Center (CSMNC) officially released 66 strong-motion recordings collected during this event. Eight of them obtained at stations up to 150 km from the hypocenter, of which the site responses are available, were used to retrieve the source spectra of this earthquake and the frequency-dependent quality factor in the vicinity of the epicenter. The resultant quality factor is Q(f)=84.9f ^0.71, indicating the strong non-elastic attenuation of S-waves. Based on the commonly used ω^-2 source model, the grid-searching technique was used to determine the optimum source parameters for this earthquake. The results show that the seismic moment is 9.42×10¹⁸ Nm with the standard deviation 0.12 on the log₁₀ scale, corresponding to the moment magnitude M_W=6.616±0.079, and the corner frequency f_c is 0.131±0.011 Hz. Based on these values of M_W and f_c, the Brune-type stress drop was estimated as 3.854 MPa, significantly lower than the average of the global intraplate earthquakes (4.89 MPa) but higher than that of the M_W6.6 Lushan earthquake in 2013.