接收函数分析中强地震前后地壳泊松比变化在新疆地区的初步应用

Preliminary Application of Crustal Poisson's Ratio Variations of Crustal Media before and after the Moderate-strong Earthquakes in Xinjiang by Using P Receiver Function

摘要:

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，分析了新疆31次中强地震前后地壳介质泊松比随时间的变化。结果显示，5次M_S6地震中有4次地震、17次5.0≤M_S≤5.8地震中有4次地震、9次4.6 ≤ M_S ≤ 4.9地震中有1次地震观测到震前泊松比出现低值异常，变化形态特征呈“V”字型（乌苏台呈双“V”字型），地震发生在“V”字型的尾端，地震发生后，泊松比继续回升。根据地壳泊松比的下降幅度、后续变化过程、发震时间以及出现这些变化的地震震级和震中距，认为在新疆地区现有的台网密度下，利用远震P波接收函数可以对重点监视防御区的地下介质泊松比变化进行动态监测。6级以上地震限于震中距100km之内台站，5级以上地震限于震中距50km之内台站，在进行地壳泊松比滑动分析时，需要挑选相关性好、莫霍面一次反射转换波（Ps）清晰且到时一致的接收函数。结合31次震例分析，认为可在新疆东部选择雅满苏（YMS）、中部选择库米什（KMS）、北天山选择乌苏（WSU）、南天山中段选择乌什（WUS）、柯坪块体选择八盘水磨（BPM）、阿尔金断裂尾端选择于田（YUT）地震台用于动态监测附近区域地下介质泊松比变化，尽管喀什-乌恰交汇区地震频发，但由于乌恰（WUQ）台接收函数中莫霍面一次反射转换波Ps震相到时复杂，可能不适用于滑动分析M_S5地震前后泊松比变化。

Abstract:

We analyzed the variations characteristics of Poisson ratio in crustal media before and after the 31 moderate-strong earthquakes in Xinjiang by using P receiver function,stacking method of receiver function and time window sliding method. The results show that there are 4 events in 5 earthquakes with M_S6.0 and 5 earthquakes in 5.0 ≤ M_S ≤ 5.8 earthquakes have observed a significant low value anomaly in the Poisson's ratio before the earthquake. The morphological characteristics are of "V" type,and the earthquake occurred at the end of the formation of the"V". After the earthquake,the Poisson ratio continued to rise. According to the crustal Poisson's ratio of the descending process,variations process,seismic time,and the magnitude and epicentral distance of the earthquakes,it is considered that under the existing network density in Xinjiang,the P-wave receiver function can be used to monitor the dynamic change of Poisson's ratio of underground medium in the defense zone. Earthquakes with M_S ≥ 6.0 are limited to stations within 100km and with M_S ≥ 5.0 are limited to stations within 50km of the epicenter. In the performance of the analysis of crustal Poisson's ratio slip,it is necessary to select the good correlation and Moho surface reflection converted wave (Ps) with clear and consistent receive function. Due to the complex crustal structure in Xinjiang and the different receiving functions of different seismic stations,it is important to select the appropriate tracked stations. Combined with the analysis of 31 earthquake cases in this paper,it is considered that the selection of station are Yamansu(YMS) in the eastern part of Xinjiang,Kumishi(KMS) in the middle of Xinjiang,Wusu(WSU) in the northern Tianshan Mountains,Wushi(WUS) in the middle of the southern Tianshan Mountains,Bapanshuimo(BPM) in the Kalpin block,and Yutian(YUT) in the end of Altun break. It is feasible to choose 5 seismic stations for dynamic monitoring of the Poisson's ratio change of the underground medium in the nearby area. Although earthquake in the Kashgar-Wuqia intersection is frequent,due to the complex phase of the Moho surface reflection wave Ps in the receiving function of the Wuqia station,maybe it is not suitable to conduct slid analysis for the Poisson's ratio variations before and after the earthquake with M_S5.0.