利用S波高频衰减对天山中东段地区地壳Q值成像

Tomograpgy for Q of eastern section of the Tianshan area from high-frequency attenuation of S waves

摘要:

利用天山中东段地区25个数字地震台站记录到的2009~2014年底5076个近震波形资料以及新疆地震台网提供的观测报告，采用遗传算法对S波位移谱的高频衰减进行拟合，得到19140条衰减算子t^*数据。根据这些t^*数据，反演得到该区地壳Q_s值分布。结果表明，天山中东段地区平均Q₀值为520，其 Q_s值分布及其所揭示的衰减变化特征与研究区的地表构造明显相关。天山南北两侧的山区盆地交汇部位Q_s值较低，而高Q_s值较为集中地分布于天山造山带内部。1900年以来天山中东段地区6级以上强震大多位于低Q_s值区域，该区24个高热流点也大多位于上述天山南北两侧的低Q_s值区域，热流值与衰减值呈负相关；此外，研究区的速度结构与衰减结构也呈一定的正相关，反映了二维衰减结构特征与速度结构、二维密度结构的一致性。

Abstract:

Based on the waveform data of 5076 local earthquakes recorded at 25 stations of Xinjiang during the period of 2009~2014 and the observation reports provided by the Xinjiang Digital Seismic Network,a data set of 19140 attenuation factor t^* is obtained by fitting the high-frequency attenuation of S wave spectra with genetic algorithm. The spatial distribution of Q_S is determined by inverting the data of t^* with seismic tomography. The results show that the average Q₀ in the eastern Tianshan is 520,there is a significant correlation between Q_S value distribution or attenuation characteristics it disclosed and the surface structure of the study area. Q_S value is lower in the intersection area of mountain basin which locates north and south sides of the Tianshan Mountains,and the high Q_S distribution concentrates more inside the Tianshan orogenic belt. The M ≥ 6.0 earthquakes are basically located in low-Q_S region since 1900. 24 high heat flow points in eastern Tianshan locate in north and south sides of Tianshan Mountains where low-Q_S,indicates a negative correlation. In addition,there is a positive correlation between the velocity structure and the attenuation structure in the study area,reflecting the consistency of a 2-D structure of the attenuation,velocity and the structure of the two-dimensional density.