利用地幔内反射波探测日本列岛下660km不连续面的深度变化(英文)
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摘要
通过分析发生在日本周边深源地震的宽频带波形资料,估计了日本列岛下的660km不连续面(d660)的深度变化。许多宽频带波形记录到了在d660顶部发生反射的sScS的后续波。sScS后续波与sScS间的到时差包含了震中与台站下方的d660深度变化的信息。我们成功地检测到这两种震相并将其分离,到目前为止还没有这方面研究的报道。我们由sScS与其后续波的到时差来求每个震中与记录台站下的d660的深度变化。研究结果显示,西部日本下的d660较深(大于660km),这可能是滞留在地幔转换带中的冷的太平洋板块造成的。在日本中部,d660变深,显然这不是太平洋板块本身造成的,因为日本中部已经位于该滞留板片的东部。日本东北部下的d660变得较浅,这可能是太平洋板片形状变化或下地幔热物质上涌形成局部热异常造成的。
The broadband waveform records from deep earthquakes occurred around Japan are analyzed to estimate the depth variations of the 660 km discontinuity (d660) beneath the Japan Islands. A postcursor to sScS, which is identified as a top-side reflection from the d660, is detected in many records. The differential travel time between the postcursor and sScS contains information on the d660 depths beneath the hypocenter and the receiver. We have successfully detected the postcursor and separated residuals of the differential travel times to those from the d660 reflections beneath the hypocenter and receiver, which was not done in the previous studies. The residuals are interpreted as the depth change in d660 beneath each hypocenter and receiver. A deeper d660 is found beneath western Japan, which may be caused by cold materials of the stagnant Pacific slab. Beneath central Japan, d660 also exhibits depressions, which is not attributable to the Pacific slab itself because this region is located east of the stagnant slab. The d660 becomes shallower beneath northern and central Japan, which may be caused by a local hot anomaly related to either the cusps of the Pacific slab or a hot upwelling from the lower mantle.
The broadband waveform records from deep earthquakes occurred around Japan are analyzed to estimate the depth variations of the 660 km discontinuity (d660) beneath the Japan Islands. A postcursor to sScS, which is identified as a top-side reflection from the d660, is detected in many records. The differential travel time between the postcursor and sScS contains information on the d660 depths beneath the hypocenter and the receiver. We have successfully detected the postcursor and separated residuals of the differential travel times to those from the d660 reflections beneath the hypocenter and receiver, which was not done in the previous studies. The residuals are interpreted as the depth change in d660 beneath each hypocenter and receiver. A deeper d660 is found beneath western Japan, which may be caused by cold materials of the stagnant Pacific slab. Beneath central Japan, d660 also exhibits depressions, which is not attributable to the Pacific slab itself because this region is located east of the stagnant slab. The d660 becomes shallower beneath northern and central Japan, which may be caused by a local hot anomaly related to either the cusps of the Pacific slab or a hot upwelling from the lower mantle.
引文
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[31]Ito E,Takahashi E.Postspinel transformationsinthe system Mg2Si O4-Fe2Si O4and some geophysical i mplications.Journal of Geophysical Research,1989,94:10637-10646.
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[34]Suetsugu D,Inoue T,Yamada A,et al.Temperature anom-alies and water content in the mantle transition zone from P-wave tomography and660-kmdiscontinuity structure beneath subduction zones.Jacobsen S D,Van Der Lee S.Earth s deep water cycle.Geophysical Monograph Series.Washing-ton DC:American Geophysical Union,2006:168.
[35]Collier J D,Helffrich G R.The thermal influence of the sub-ducting slab beneath South America from410and660kmdis-continuity observations.Geophysical Journal International,2001,147:319-329.
[36]Johnston S T,Thorkelson DJ.Cocos-Nazca slab windowbe-neath Central America.Earth and Planetary Science Letters,1997,146:465-474.
[37]Levin V,Shapiro N,Park J,et al.Seismic evidence for cata-strophic slab loss beneath Kamchatka.Nature,2002,418:763-767.
[38]Wessel P,Smith W H F.New version of generic mapping tools version3.0released.Eos Transactions AGU,1995,76:329.
[2]Helffrich G.Topography of the transition zone seismic dis-continuities.Reviews of Geophysics,2000,38:141-158.
[3]Fukao Y,Widiyantoro S,Obayashi M.Stagnant slabs in the upper andlower mantle transition zone.Reviews of Geophys-ics,2001,39:291-323.
[4]Zhao D.Seismic structure and origin of hotspots and mantle plumes.Earth and Planetary Science Letters,2001,192:251-265.
[5]Zhao D.Global tomographic i mages of mantle plumes and subducting slabs:insight into deep earth dynamics.Physics of the Earth and Planetary Interiors,2004,146:3-34.
[6]Huang J,Zhao D.High-resolution mantle tomography of China and surrounding regions.Journal of Geophysical Re-search,2006,111:doi:10.1029/2005JB004066.
[7]Flanagan MP,Shearer P M.Global mapping of topography on transition zone velocity discontinuities by stacking SS pre-cursors.Journal of Geophysical Research,1998,103:2673-2692.
[8]Niu F,Kawakatsu H.Determination of the absolute depths of the mantle transition zone discontinuities beneath China:effect of stagnant slabs on transition zone discontinuities.Earth Planets Space,1998,50:965-975.
[9]Lebedev S,Chevrot S,Van Der Hilst R D.The660-kmdis-continuity withinthe subducting NW-Pacificlithosphere slab.Earth and Planetary Science Letters,2002,205:25-35.
[10]Ai Y,Zheng T,Xu W,et al.Acomplex660kmdiscontinui-ty beneath northeast China.Earth and Planetary Science Let-ters,2003,212:63-71.
[11]Gudmundsson O,Sambridge M.Aregionalized upper mantle(RUM)seismic model.Journal of Geophysical Research,1998,103:7121-7136.
[12]Wicks C,Richards M.A detailed map of the660-kilometer discontinuity beneaththe Izu-Bonin subduction zone.Science,1993,261:1424-1427.
[13]Castle J C,Creager K C.Topography of the660-kmseismic discontinuity beneathIzu-Bonin:i mplications for tectonic his-tory and slab deformation.Journal of Geophysical Research,1998,103:12511-12527.
[14]Collier J D,Helffrich G R,Wood BJ.Seismic discontinuities and subduction zones.Physics of the Earth and Planetary In-teriors,2001,127:35-49.
[15]Tonegawa T,Hirahara K,Shibutani T.Detailed structure of the upper mantle discontinuities around the Japan subduction zone i maged by receiver function analyses.Earth Planets Space,2005,57:5-14.
[16]Niu F,Levander A,Ham S,et al.Mapping the subducting Pacific slab beneath southwestern Japan with Hi-net receiver functions.Earth and Planetary Science Letters,2005,239:9-17.
[17]Revenaugh J,Jordan TJ.MantlelayeringfromScSreverber-ations,2,The transition zone.Journal of Geophysical Re-search,1991,96:19763-19780.
[18]Kato M,Misawa M,Kawakatsu H.Small subsidence of the660-kmdiscontinuity beneath Japan probed by ScS reverbera-tions.Geophysical Research Letters,2001,28:447-450.
[19]Tono Y,Kunugi K,Fukao Y,et al.Mapping of the410-and660-kmdiscontinuities beneath the Japanese Islands.Journal of Geophysical Research,2005,110:doi:10.1029/2004JB003266.
[20]Helffrich G,Bina C R.Frequency dependence of the visibility and depths of mantle seismic discontinuities.Geophysical Re-search Letters,1994,21:2613-2616.
[21]Gaherty J B,Wang Y,Jordan T H,et al.Testing plausible upper-mantle compositions usingfine-scale models of the410-km discontinuity.Geophysical Research Letters,1999,26:1641-1644.
[22]Kennett B L N,Engdahl E R.Travel ti mes for global earth-quake location and phase identification.Geophysical Journal International,1991,105:429-465.
[23]Mller G.The reflectivity method:a tutorial.Journal of Ge-ophysics,1985,58:153-174.
[24]Dzi wonski A M,Anderson D L.Preli minary reference Earth model.Physics of the Earth and Planetary Interiors,1981,25:297-356.
[25]Bass J D.Elasticity of minerals,glasses,and melts.Ahrens T J.Mineral physics and crystallography:a handbook of physical constants.AGU reference shelf,volume2.Wash-ington DC:American Geophysical Union,1995:45-63.
[26]Sinelnikov Y D,Chen G,Neuville D R,et al.Ultrasonic shear wave velocities of MgSi O3perovskite at8GPa and800Kand lower mantle composition.Science,1998,281:677-679.
[27]Sinogeikin S V,Bass J D.Single-crystal elasticity ofγ-(Mg0.91Fe0.09)2Si O4to high pressures and to high tempera-tures.Geophysical Research Letters,2001,28:4335-4338.
[28]Weber M,Davis J P.Evidence of a laterally variable lower mantle structure from P-and S-waves.Geophysical Journal International,1990,102:231-255.
[29]Temme Y F,Weber M,Wicks C WJr.Absorption of P-and S-waves above subduction zone.Geophysical Research Let-ters,2000,27:1327-1330.
[30]Bina C R,Helffrich G.Phase transition Clapeyron slopes and transition zone seismic discontinuity topography.Journal of Geophysical Research,1994,99:15853-15860.
[31]Ito E,Takahashi E.Postspinel transformationsinthe system Mg2Si O4-Fe2Si O4and some geophysical i mplications.Journal of Geophysical Research,1989,94:10637-10646.
[32]Higo Y,Inoue T,Irifune T.Effect of water on the spinel-postspinel transformationin Mg2Si O4.Geophysical Research Letters,2001,28:3505-3508.
[33]Blum J,Shen Y.Thermal,hydrous,and mechanical states of the mantle transition zone beneath southern Africa.Earth and Planetary Science Letters,2004,217:367-378.
[34]Suetsugu D,Inoue T,Yamada A,et al.Temperature anom-alies and water content in the mantle transition zone from P-wave tomography and660-kmdiscontinuity structure beneath subduction zones.Jacobsen S D,Van Der Lee S.Earth s deep water cycle.Geophysical Monograph Series.Washing-ton DC:American Geophysical Union,2006:168.
[35]Collier J D,Helffrich G R.The thermal influence of the sub-ducting slab beneath South America from410and660kmdis-continuity observations.Geophysical Journal International,2001,147:319-329.
[36]Johnston S T,Thorkelson DJ.Cocos-Nazca slab windowbe-neath Central America.Earth and Planetary Science Letters,1997,146:465-474.
[37]Levin V,Shapiro N,Park J,et al.Seismic evidence for cata-strophic slab loss beneath Kamchatka.Nature,2002,418:763-767.
[38]Wessel P,Smith W H F.New version of generic mapping tools version3.0released.Eos Transactions AGU,1995,76:329.
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