牡丹江和海拉尔台下方地幔间断面结构及推论

利用牡丹江(MDJ)和海拉尔(HIA)台1988-2000年的宽频带三分量数字地震记录,通过地幔间断面产生的P-SV转换波,研究台站下方地幔间断面的分布以及日本海俯冲带对660km间断面的影响.为了提高所得结果的可靠性,采用了线性-偏振滤波方法和修正的N次根倾斜叠加方法来提取P-SV转换波.前一方法通过实验选取适当的光滑平均和提出立体角的约束;对后一方法进行了震源深度校正和间断面倾斜的修正.结果表明,在MDJ和HIA台下方,除在660,410,220和520km深度附近均存有间断面外,在140,350,570,740和1080km深度附近也存在间断面,显示了地幔中径向分层的复杂性;另外,MDJ台下方660-840km之间的间断面结果比HIA台下方的复杂,似有分层结构,可能反映了俯冲带的影响.

MANTLE DISCONTINUITIES BENEATH THE STATIONS MDJ AND HIA AND ITS IMPLICATIONS

Digital broadband seismograms recorded at the stations of MDJ and HIA for the period from 1988 to 2000 were used to study the mantle discontinuities and the influence of subducting slab under the Japan Sea on the 660km discontinuity beneath the two stations by using P SV converted phases. In order to increase the reliability of results,the rectilinearity polarization filter analysis and modified N th root slant stack methods were used to pick out P SV converted phases. Appropriate smoothing and constraint of cubical angle were applied to the former method;the modification of focal depths and correction of the deflection of discontinuities were used in the later one. It was found that there are mantle discontinuities at the depths of 660,410,220 and 520km under the stations of MDJ and HIA. Besides,the radial structures of the mantle are complicated and there are still some relatively strong discontinuities near the depths of 140,350,570,740 and 1080km. It is shown that the radial structure of the mantle is more complicated than spherical symmetry;it is also shown that the structure between 660km and 840km under MDJ station is more complicated than that under HIA station. It may show the influence of subducting slab on the 660km discontinuity beneath MDJ station.