利用前临界PcP-PKiKP资料研究中国东部内核边界性质

A study on inner core boundary properties of East China using pre-critical PcP-PKiKP data

前临界内核边界反射震相PKiKP与核幔边界反射震相PcP构成组合,能有效压制浅部结构及震源因素的干扰,提供了对内核边界精细结构的直接约束.本研究从华北克拉通西北部密集流动地震台阵一年观测资料中筛选出8个地震事件,得到共计73对PcP-PKiKP组合,覆盖了从朝鲜半岛到我国东北及华中地区下方的内核边界.本文系统分析了走时残差和振幅比数据,结果显示:(1)密集台阵资料有助于前临界PKiKP震相拾取,而浅源地震亦可提供高质量的PcP-PKiKP观测资料.(2)走时残差呈现了自西北向东南从正常到负异常的迅速变化(沿内核边界70km范围内>0.5s),限制了研究区域内核界面不超过3km的起伏.(3)相对振幅比变化表明了研究区内核边界密度差北西—南东向的系统增加,揭示了内核结晶环境的小尺度扰动.

Reflected from inner core boundary, pre-eritical PKiKP, associated with core-mantle boundary reflection phase PeP to suppress signal of non-inner-core origin, can provide the most direct and concise high-resolution constraint on properties of inner core boundary. Out of one- year data collected by dense portable array located on the northwestern brink of North China Craton, we get 73 pairs of PcP-PKiKP waveforms from 8 earthquake events, covering a sweep from Korean Peninsula to Northeast and Central China. Travel time residue and amplitude ratio observations have been systematically analyzed, with the following conclusions obtained： （1） Dense array could be used as a powerful tool for detecting pre-critical PKiKP and shallow-origin events can also provide good observation data. （2） Geographical distribution of travel time residues show an abrupt change into negative anomaly 〉0.5 s within 70 km distance on ICB）from northwest to southeast, indicating the undulation of inner core boundary of the studying area no larger than 3 km. （3） Relative amplitude ratios show a systematically southeastern increasing of inner core boundary density contrast, implicating small-scale perturbation of inner core crystallization environment.