【作者】 赵博；

【导师】 高原；

【作者基本信息】 中国地震局地震预测研究所 ， 固体地球物理学， 2010， 硕士

【摘要】 地壳介质的各向异性主要是由大量充满流体的微裂隙的定向排列引起的,剪切波穿过这种含有微裂隙的介质时会产生分裂现象。剪切波分裂参数与地壳介质的物理性质有关,与区域应力场有关。快剪切波偏振方向与裂隙走向一致,反映了原地主压应力场方向。慢剪切波时间延迟与区域介质各向异性程度有关。在地壳剪切波分裂研究中,地震的定位误差对剪切波分裂参数有影响。本文对定位误差特别是深度方向的误差所引起的时间延迟变化进行了讨论,比较了不同大小的深度误差对归一化后的时间延迟的影响。定量分析的结果显示,深度定位误差对选择窗口内波形数据和慢剪切波时间延迟的分析影响很大。张家口-渤海地震带西端位于华北盆地、燕山隆起和太行山隆起三个构造单元的交界处。山西地震带和张家口-渤海地震带在此交汇,地质构造十分复杂。区域内分布着多条NE,ENE向和NW,WNW向的断层,GPS资料和震源机制给出的区域内的主压应力轴方向为ENE(近E-W)向。本研究对华北地区2006年1月~2009年11月的地震进行了双差定位。定位结果显示,华北地区的地震主要集中在张家口-渤海地震带上。震源的空间分布总体上呈WNW向,但在地震带内部,震源有明显的沿断层走向分布趋势。文章对震源分布沿断层走向明显的唐山地区和邢台地区做深度剖面,分析了区域内断层深部形态与震源空间分布的关系。本研究利用张家口-渤海地震带西端布设的流动台网和河北地区北部的区域台网记录到的波形数据,采用SAM分析方法分析了张家口-渤海地震带西端的地壳介质各向异性。通过对研究区域内各台站记录到的剪切波窗口在36°以内的数据进行分析,得到该区域两个快剪切波优势取向:第一优势取向96.98°±17.19°和第二优势取向32.00°±15.63°。其中第一优势取向反映了原地主压应力方向,与另一个研究获得的区域“背景”主压应力方向非常一致;第二优势取向与山西地震带北端的断层走向基本一致。研究表明,在区域南部靠近NE~NEN向的山西地震带的几个台站,其快波偏振方向与山西地震带走向基本一致。此外,还有几个台站,位于靠近局部凹陷与隆起交汇(怀安盆地边缘)地区的台站上,其快波偏振方向表现出两个优势取向,可能与台站附近复杂的地质构造环境有关,这个结果可能是源于区域主压应力方向和局部走滑断裂走向的双重作用。文章结合GPS形变资料和区域内地震震源机制解得出的结论与本研究剪切波分裂分析的结果进行对比分析,初步讨论了张渤带西端区域地壳的各向异性特征和应力场分布特点。结果表明,在本研究区内背景应力和局部地质构造都会对快剪切波偏振方向产生影响。更多还原

【Abstract】 Crustal seismic anisotropy is mainly caused by the stress-aligned fluid-saturated grain-boundary cracks. When share-wave travels through anisotropic media, it will split. The parameters of share-wave splitting are relative to the physical property of curst media and regional stress field. The polarization of fast shear-wave is consistent with the crack’s direction, which reflects the direction of the principal compressive stress. Time delay of slow shear wave is correlated to the level of anisotropy.In the study of share-wave splitting, the errors of earthquake location have an impact on share-wave splitting reference. This paper discusses the factors that can influence on the accurate location and analyses the variety of the time delay which is caused by the depth location error. We compared the influences on normalized time delays which are made by different depth errors. The result of the quantitative analysis shows that the depth error can influence selecting waveform datas in the window of shear-wave and cause a great influence on the slow share-wave time delay.The west of Zhangjiako-Bohai See seismic zone is in the boundary of three tectonic units which are North China basin, Yanshan and Taihang uplift regions. Shanxi seismic zone and Zhangjiako-Bohai sea seismic zone interchange hear, and this region has complex geologic structure. There are some NE, ENE, NW, WNW stretching faults. GPS data and focal-mechanism show that the regional principal compressive stress is ENE (near E-W) directing.In this study, earthquakes which happened in Norht China regions from January 2006 to November 2009, were relocated using the double difference algorithm. The relocation results show that the earthquakes in North China are mainly concentrated in Zhangjiakou–Bohai sea seismic zone. The spatial distributions of hypocenters show WNW directing. But in the region of internal, hypocenters distribute along faults. In this thesis, the depth profiles were made and analyzed the relationships between faults depth structures and the distributions of hypocenters in Tangshan and Xingtai region.This paper shows the research of shear-wave splitting by applying waveform data from ZBnet-W seismic network and Heibei regional seismic network, and selecting SAM method as the tool to analyze crustal anisotropy in the west of Zhangjiako-Bohai sea seismic zone. The result of analyzing the data which are in shear-waves window show that there are two predominate polarization directions of fast shear-waves. One predominate polarization direction is 96.98°±17.19°which is consistent with the direction of regional compressive stress. This direction is also consistent with the regional blackground compressive stress which is the result of another study. The other predominate polarization direction is 32.00°±15.63°, which is consistent with the direction of fault in the north of Shanxi seismic zone.This research indicates that the polarizations directions of fast shear-waves, which close to the NE-NEN Shanxi earthquake belt, are consistent with trend of this belt. In addition, the polarization directions of fast shear-waves, which are located the junction of the local depression and uplift (the edge of Huai’an basin), put out two dominant directions. It is possibly attributed to the local complex geological tectonics around these stations. This result probably stems from the effect between the local compressive stress field and trend of partial strike-slip fault.In this paper, the result of shear-wave splitting analysis is in contrast with the conclusion between the GPS deformation data and local focal mechanisms. The characteristics of crustal anisotropy and distribution of stress field was preliminary discussed in the western of the Zhangjiakou-Bohai Fault Zone. In this area, the result demonstrates that the background stress field and the local geological structure will effect the polarization direction of the fast shear-wave splitting.更多还原