Abstract: We analyzed the variation characteristics of Poisson's ratio in crustal media from January 2009 to December 2012 at 11 fixed seismic stations(for station SCH, it is from January 2006 to December 2012)within an epicenter distance of 200km of the Xinyuan-Hejing M_S6.6 earthquake in Xinjiang on June 30, 2012 using the methods of P wave receiver functions, H-κ stacking of receiver functions, and time sliding window, and obtained the following conclusions:
(1)The crustal media's Poisson ratio of five stations in an epicenter distance less than 130km showed a significant and long-lasting decline about 2~3 years before Xinyuan-Hejing M_S6.6 earthquake. Taking the crustal Poisson ratio mean value as reference, the decrease ranges between 0.003 and 0.014, the decrease in 4 stations are more than twice the mean error. The variations of the Poisson's ratio in crust are characterized by "V" shape or "double V" shape. Earthquakes occur at the end of the formation of "V" shape. After the occurrence of earthquakes, the Poisson's ratio continues to rise. The earliest initial fall appeared in July 2009 at WUS station which has the minimum epicentral distance(77km). The Poisson ratio of the crustal media of 6 stations with epicentral distance more than 150km fluctuated up and down around the mean value, and there is no significant decline or persistent low value.
(2)We analyzed the arrival-time variations of the quasi-repetitive receiver functions Ps converted wave(t_Ps)of the 3 stations WUS, SCH and XNY and found that the travel times of Ps converted waves became smaller in the crust before the earthquake and increased after the earthquake.
(3)Through the comprehensive analysis on the descending process, decline ranges, variations process, duration of Poisson' ratio, the Ps converted waves arrival time variations, the original time of earthquake, and the number of stations, it is inferred that the cause for Poisson's ratio anomalous variations is the change of physical properties of crustal media in the process of earthquake preparation and occurrence. Since the variation characteristics of crustal media may be related to the earthquake magnitude, the size of seismogenic area, the medium properties under stations, and the focal distance, whether the medium variation characteristics exist before and after Xinyuan-Hejing M_S6.6 earthquake will need more earthquake cases analyses.
(4)The H-κ stacking of receiver functions is used to calculate the velocity ratio. Because P-wave velocity is given, this method can only be applied when the Ps converted wave velocity of Moho surface of receiver functions changes before an earthquake. With the application of receiver functions to the analysis of more earthquake cases, we can gain more insights into the variation of crustal medium parameters during the seismogenic process. This observation indicates that the receiver function method may become a new approach to detect the Poisson's ratio change of the crustal media before strong earthquake under the condition of high seismic network density.

Key words: receiver function, Poisson ratio variation of the crustal media, the arrival-time variation of Ps converted wave, before and after Xinyuan-Hejing M_S6.6 earthquake

摘要： 文中利用远震P波接收函数，联合接收函数H-κ叠加方法和时间窗滑动方法，分析了2012年6月30日新疆新源-和静M_S6.6地震震中距200km内11个固定地震台2009年1月-2012年12月（石场台为2006年1月-2012年12月）的地壳介质泊松比的变化特征，分析了乌苏、石场和新源3个台站准重复接收函数的莫霍面Ps转换波到时（t_Ps）变化，获得了以下认识：1）在新源-和静M_S6.6地震前2~3a的不同时段，5个震中距<130km的台站的地壳介质泊松比相继出现了较为明显的持续下降过程，与台站平均地壳泊松比相比，下降幅度为0.003~0.014，4个台站的下降幅度大于均值误差，乌苏台（震中距最小，为77km）的下降起始时间（2009年7月）最早；6个震中距>150km的台站的地壳介质泊松比在均值上下波动，没有出现明显的下降和持续低值现象；2）出现泊松比低值异常的台站，其接收函数t_Ps在震前变小（Ps转换波在地壳内的走时变小），在震后变大（Ps转换波在地壳内的走时变大）；3）综合分析泊松比下降的幅度、持续时间、后续变化过程及接收函数t_Ps的变化，推测这种异常变化的原因是地震孕育、发生过程中出现的地壳介质物性变化，这一观测结果表明，在高密度台网的支撑下，接收函数方法可能成为探测强地震前地壳介质泊松比变化的一种新的技术途径。

关键词: 接收函数, 地壳介质泊松比变化, Ps转换波到时变化, 新源和静M_S6.6地震前后