伊豆—小笠原下方660km间断面的区域性差异

THE REGIONALIZED DIFFERENCE OF 660 km DISCONTINUITY BENEATH IZU-BONIN

利用南、北加州地震台网、华盛顿州西北太平洋地震台网单分量短周期地震仪和德国、瑞士地震台网 /台阵的三分量宽频带地震仪记录的 1 981～ 2 0 0 0年伊豆—小笠原地区下方地震的波形资料 ,使用 N次根倾斜叠加方法提取近源一侧来自间断面 Sd P转换震相 ,以研究6 6 0 km间断面区域性差异 .研究发现 ,自 3 5°N到 2 6°N的各剖面依次体现了和达 -本尼奥夫带 (Wadati- Benioff zone)倾角逐渐加大 ,且地震分布的最大深度也逐步增大 ,俯冲板块对6 6 0 km间断面存在的影响也因此产生了差异性 :没有俯冲板块影响的情况下 ,该间断面出现在 CM) 6 6 0 km深度处 ,而受到俯冲板块明显作用的地区 ,则该间断面普遍出现下陷 .转换点分布的一定程度分散性可能是间断面本身复杂结构、震相误判或一维球对称地球模型假定等因素造成的 .

Digital waveform data recorded by the vertical component short period stations at the American networks of SCSN, NCSN and PNSN and three components broadband stations at the Germany and Swiss networks and arrays of GRFN, GRSN and SDSNet for the events between 1981 and 2000 under Izu-Bonin are collected. The N-th root slant stack method was used to study the regionalized difference of the 660 km discontinuity beneath Izu-Bonin with the SdP phases converted at the velocity interface beneath sources. It is found that while the dip angles of the subducting slab (Wadati-Benioff zone) and the maximal depths of sources deepen gradually rise from 35°N to 26°N, the 660 km discontinuity shows regionalized differences: the discontinuity exists at 660 km while there is no effects from subducting slab, but it is depressed to the depth of 720 km while there are obvious effects. The dispersion of converted points is still an unsolved problem which maybe result from the complex structure of the discontinuity, converted phases which were misjudged, or the assumption of one dimensional spherical earth model.