长白山-镜泊湖火山区上地幔间断面接收函数研究

利用布设在长白山地区的19个PASSCAL宽频带流动地震台站近一年的远震记录和布设在镜泊湖火山区14个宽频带轻便数字地震仪三个月的远震记录，共得到高质量的423个接收函数，通过对这些接收函数的共转换点叠加得到研究区的间断面的分布及形态.研究结果表明，研究区存在410、520km和660km间断面.410km和660km间断面较为连续且具有正相关性质，410km间断面在长白山天池火山下局部上隆，660km间断面具有复杂的多界面性质.410km和660km之间的过渡带厚约250km，接近全球平均水平.珲春深震区下660km界面下陷，其上还有多组震相，这些震相在珲春深震区东西两侧不连续，推测西太平洋板块至少已经俯冲到欧亚大陆下的上地幔过渡带中.410km间断面在长白山火山区下局部上隆，660km间断面具有的复杂结构和珲春深源地震的发生均与俯冲板块在过渡带中的活动有关. 俯冲板块在受到660km间断面的强大阻力后，在660km间断面之上变为近水平扩张.推测在欧亚大陆下西太平洋板块的最前端可能已经不是一个完整的整体，或许是由几个有一定联系的板块残片组成.

Study on upper mantal discontinuities using the receiver function in the Changbaishan-Jingpohu volcanic area

Using teleseismic waveform data recorded by 19 PASSCAL broadband mobile seismic stations which worked nearly one year in the Changbaishan volcanic area and other 14 stations with portable broadband digital seismographs deployed about three months in the Jingpohu volcanic region, totally 423 high quality receiver functions were extracted. Through stacking these receiver functions in terms of midpoint stacks of P converted to S waves, the discontinuity distributions along with their patterns were obtained. The results show that beneath the studied area, 410km, 520km and 660km discontinuities exist. Both the 410km and the 660km discontinuities are relatively continuous and present positively correlative the characters. The 410km discontinuity is a local uplift beneath the Changbaishan volcano, and 660km discontinuity is of the complex multi-interface. The thickness of the transition zone between 410km and 660km is about 250km and approaches the whole world average level. The 660km discontinuity descends beneath the Huichun deep earthquake area and above the 660km discontinuity in the stack profiles, where there are some phases, which are not continuous on the two sides of the Huichun deep earthquake area. We infer that the West Pacific plate has already subducted into upper mantle transition zone beneath the Eurasia plate. We consider that the local uplift of the 410km discontinuity and the complex multi-interface nature of the 600km discontinuity as well as the occurrence of the Huichun deep earthquakes are all due to the slab activities in the transition zone. Because of the strong resistance from the 660km discontinuity, the subduction slab may become nearly horizontal and continue to subduct toward west, and beneath the Eurasia plate the front part of the West Pacific plate possibly has been split into several segments rather than remaining a whole.