伊豆—小笠原下方660km间断面的区域性差异
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摘要
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 .这一转换点分布的分散性是一个亟需解决的问题
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.
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.
引文
臧绍先,宁杰远.1996.西太平洋俯冲带的研究及其动力学意义[J].地球物理学报,39(2):188～202
臧绍先,周元泽.2002.N次根倾斜叠加方法在间断面研究中的应用[J].地球物理学报(待刊)
周元泽,臧绍先.2001.牡丹江和海拉尔台下方地幔间断面结构及推论[J].地球物理学报,44(6):761～773
BinaC R.1991.Mantle discontinuities[J].RevGeophys,29(Supp):783～793
CastleJC,CreagerK C.1998.Topography of the660 km discontinuity beneathIzu-Bonin:Implicationsfor tectonic historyand slab deformation[J].J GeophysRes,103:12511～12528
CastleJC,CreagerK C.2000.Local sharpness and shear wave speed jump across the660 km discontinuity[J].J GeophysRes,105:6191～6200
CastleJC,CreagerK C.1997.Seismic evidenceagainstamantlechemicaldiscontinuitiy near660 km depth beneathIzu-Bonin[J].GeophysResLett,24:241～244
CollierJD,HelffrichG R.1997.Topography of the″410″and″660″km seismic discontinuities in theIzu-Bonin subduction zone[J].GeophysResLett,24:1535～1538
EngdahlE R,Van derHilstR D,BulandR P.1998.Global teleseismicearthquake relocation with improved traveltimesandproceduresfor depth determination[J].BullSeismSocAmer,88:722～743
FukaoY,ObayashiM,InoueH,etal.1992.Subducting slab stagnantin the mantle transition zone[J].J GeophysRes,97:4809～4822
FukaoY,WidiyantaroS,ObayashiM.2001.Stagnant slabs in the upper and lower mantle transition region[J].RevGeo-phys,39:291～323
Van derHilstR D,EngdahlE R,SpakmanW,etal.1991.Tomographicimaging of subducted lithospahere below northwestPacific island arcs[J].N ature,353:37～42
VidaleJE,BenzH M.1992.Upper-mantle seismic discontinuitiesand the thermal structure of subduction zonses[J].N a-ture,356:678～683
VinnikL,NiuF,KawakatsuH.1998.Broadband converted phases from midmantle discontinuities[J].EarthPlanetsSpace,50:987～997
WicksC W,RichardsM A.1993.A detailed map of660 kilometerdiscontinuity beneathIzu-Bonin subduction zone[J].Sci-ence,261:1424～142
臧绍先,周元泽.2002.N次根倾斜叠加方法在间断面研究中的应用[J].地球物理学报(待刊)
周元泽,臧绍先.2001.牡丹江和海拉尔台下方地幔间断面结构及推论[J].地球物理学报,44(6):761～773
BinaC R.1991.Mantle discontinuities[J].RevGeophys,29(Supp):783～793
CastleJC,CreagerK C.1998.Topography of the660 km discontinuity beneathIzu-Bonin:Implicationsfor tectonic historyand slab deformation[J].J GeophysRes,103:12511～12528
CastleJC,CreagerK C.2000.Local sharpness and shear wave speed jump across the660 km discontinuity[J].J GeophysRes,105:6191～6200
CastleJC,CreagerK C.1997.Seismic evidenceagainstamantlechemicaldiscontinuitiy near660 km depth beneathIzu-Bonin[J].GeophysResLett,24:241～244
CollierJD,HelffrichG R.1997.Topography of the″410″and″660″km seismic discontinuities in theIzu-Bonin subduction zone[J].GeophysResLett,24:1535～1538
EngdahlE R,Van derHilstR D,BulandR P.1998.Global teleseismicearthquake relocation with improved traveltimesandproceduresfor depth determination[J].BullSeismSocAmer,88:722～743
FukaoY,ObayashiM,InoueH,etal.1992.Subducting slab stagnantin the mantle transition zone[J].J GeophysRes,97:4809～4822
FukaoY,WidiyantaroS,ObayashiM.2001.Stagnant slabs in the upper and lower mantle transition region[J].RevGeo-phys,39:291～323
Van derHilstR D,EngdahlE R,SpakmanW,etal.1991.Tomographicimaging of subducted lithospahere below northwestPacific island arcs[J].N ature,353:37～42
VidaleJE,BenzH M.1992.Upper-mantle seismic discontinuitiesand the thermal structure of subduction zonses[J].N a-ture,356:678～683
VinnikL,NiuF,KawakatsuH.1998.Broadband converted phases from midmantle discontinuities[J].EarthPlanetsSpace,50:987～997
WicksC W,RichardsM A.1993.A detailed map of660 kilometerdiscontinuity beneathIzu-Bonin subduction zone[J].Sci-ence,261:1424～142
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