蒙古中部地区SKS分裂研究的初步结果

为了进行蒙古中部地区的深部构造观测与模型研究， 中国地震局地球物理研究所和蒙古科学院天文与地球物理研究中心合作， 在该地区架设了60台宽频带流动地震台. 这些台站分布在被额尔齐斯—中蒙古—额尔古纳断裂隔断的加里东、 海西两个构造域. 本文选取了2011年8月—2012年7月部分台站记录的震中距在85°—135°且M_W≥5.0的远震事件， 通过SplitLab软件来进行SKS分析. 使用最小能量法、 旋转相关法和最小特征值法进行处理， 取得了蒙古中部地区各向异性的初步结果. 结果显示: 快慢波延时在0.8—2.0 s之间. 西北部区域靠近杭爱山脉与肯特山脉的区域构造走向均为ENE--WSW方向， 而快波方向大多为N40°W， 与区域构造走向近似垂直.根据HS3-NUVEL-1A板块模型计算的该地区板块绝对运动方向与快波偏振方向呈顺时针约15°夹角. 然而， 有个别台站表现出了两种模式的快波分裂， 其中一种与当地ENE--WSW向的断裂方向近似一致. 

The preliminary SKS splitting results in the central Mongolia

A passive seismic array with 60 broadband seismometers was deployed in the central Mongolia by the cooperation between Institute of Geophysics, China Earthquake Administration and Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, to carry out the deep structure observation and modeling study. The passive seismic array was distributed within the Caledonian orogen and the Hercynian orogen separated by the Ergis-central Mongolia-Eerguna fault zone. The teleseismic waveform data from part of the array with the epicentral distance of 85°—135° and M_W5.0, from August 2011 to July 2012, was selected to do SKS splitting analysis through the SplitLab package. Three methods, i.e., the minimum energy of tangential component (SC), the rotation and correlation (RC), and eigenvalue (EV), are simultaneously applied for each SKS waveform data. The preliminary anisotropy result was obtained for the central Mongolia. It shows that the time delay between fast and slow waves is within 0.8—2.0 s, and the polarization direction of fast wave is about N40°W, almost perpendicular to the geological structure strike direction of ENE--WSW. The fast direction is about 15° systematically clockwise to the absolute plate motion inferred from the HS3-NUVEL-1A model. It is also noted that not only the two different splitting modes are simultaneously observed beneath certain station, but also the fast wave direction parallel to the ENE--WSW striking direction exists beneath certain station.