摘要
本文根据山西数字地震台网31个台站和周边河北、河南、陕西、内蒙数字地震台网6个台站2009年2月-2011年11月记录的面波资料,利用双台法测定了350条路径上周期8～75s的基阶瑞利波相速度频散曲线.通过Ditmar&Yanovskaya方法反演得到33个周期分辨率为40～50km的相速度分布图像.分析研究了4个具有代表性周期的相速度分布图像和3条不同方向的相速度剖面,这些图像揭示了山西地区地壳上地幔速度结构的横向非均匀性质和相速度纵向变化特征.10s周期的相速度分布图像显示出断陷带与两侧隆起区相速度存在明显的差异,几个断陷盆地的最大沉降中心附近呈现低相速度异常;山西6级以上强震大都分布在15s周期高相速度与低相速度急剧变化的过渡带上;20～26s周期的相速度以38°N为界呈现出南高北低格局,与山西断陷盆地带莫霍界面埋深南浅北深的结果相吻合;36s～54s周期相速度图像的低速区域逐渐收缩到大同一带,进一步说明南部区域在该周期反映的深度范围已进入上地幔,而大同盆地的低速可能与该区域的新生代火山群有关.沿113°E的南北相速度纵剖面显示周期25～75s以38°N为界,南部相速度高、北部相速度低,证实了38°N线附近是晋北地块、晋南地块的"软"、"硬"块体的结合部位,可能是由于软流圈上涌幅度不同造成了深部速度的南北差异;其他两个横切裂谷的剖面显示出与人工地震测深剖面相似的特征.
In this work, seismic datas are taken from seismograms of over 100 earthquakes which are recorded from Feburary in 2009 to November in 2011 at 31 stations in Shanxi Province and other 6 broadband stations in adjacent areas, including Hebei, Henan, Shanxi and Neimeng Province. We obtained 350 high-quality Rayleigh wave phase velocity dispersion curves of fundamental mode by removing the duplicate paths and low quality data. The periods ofthe dispersion curves range from 8 to 75 seconds. Based on the method of Ditmar ＆ Yanovskaya, we obtained phase velocity dispersion maps in 33 periods with resolution ranges from 40 to 50 km. We analyzed the phase velocity distribution maps at four representative periods and the phase velocity section maps along three profiles. The phase velocity maps reveal the lateral heterogeneity of the velocity structure and the phase speed variation with depth in the crust and the upper mantle of the Shanxi fault depression zone, The phase velocity map at 10 s clearly shows the spatial differences between the rift zone and the uplift zones in the two sides, presenting low phase velocity anomalies in the maximum depression regions near the centers of several basins inside the rift zone. Moderate to strong earthquakes（M≥6）in Shanxi are mostly concentrated in the transitional zones where dramatic phase velocity changes occur at 15 s. At 20~26 s period, significant phase velocity difference can be observed across the latitude of 38°N, where phase velocity is higher in the south side than that in the north, which is in consistent with the variation pattern of Moho depth in the depression zone. This kind of velocity pattern keeps constant with the increase of period, which is consistent with the feature that the blocks in the north Shanxi is relatively weaker than those in the south. Along 113°E, the phase velocities at periods of 25~75 s are higher in the north side of latitude 38°N than in the south. This is consistent with the result of the lithospheric section in the same region, and the undulations of Moho depth shown in the other two profiles are also agree with the results from active source studies.
出处
《地球物理学进展》
CSCD
北大核心
2013年第4期1836-1848,共13页
Progress in Geophysics
基金
中国地震局星火计划(xh1005
xh12007)
山西省科技攻关项目(20100311129-2
20090311084)
山西省科技厅基础研究项目(20112012011029
2010011030-3)联合资助
关键词
山西地区
双台法
面波相速度
层析成像
Shanxi region, Two-station, Phase velocity of surface waves, Tomography
