利用三重震相探测中国东部海域410km深度低速层
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摘要
基于中国数字地震台网记录的日本本州地区2009年发生的一次震源深度为167.2km、震级为mb6.0地震的宽频带波形资料,利用二维射线追踪方法给出P波三重震相的理论时-距曲线,并采用试错法构建出与观测时-距曲线拟合效果最优的低速异常模型,发现在中国东部海域下方410 km间断面上、下均存在局部的P波低速异常:300—410 km深度范围内低速异常为4%—5%,而410—460/470 km深度范围内的低速异常则达到4%一7%.结合前人地震层析成像结果,发现该区域不存在明确外源热流,因而,本文认为该低速异常与俯冲板片脱水引起的部分熔融有关.
Broadband waveform data for one m_b6.0 earthquake beneath Honshu,Japan,with focal depth of 167.2 km,recorded by China Digital Seismic Network(CDSN) were retrieved.Through trial-and-error method,the anomalous models beneath the Yellow and East China Seas for the six sub-regions were obtained by matching the theoretical travel-time curves of the P triplications from the modified models for the six sub-regions by using 2-D ray tracing with the observed ones.The local lower velocity anomaly appears around the 410 km discontinuity.Above the discontinuity,the P wave velocity decreases by 4%—5%from 300 km to 410 km and below the discontinuty,the velocity decreases by4%—7%from 410 km to 460/470 km.Because thermal flow was not observed by former seismic tomographic restdts.the local low velocity anomaly should be due to the partial-melting caused by the dehydrated water from subducting slab.
Broadband waveform data for one m_b6.0 earthquake beneath Honshu,Japan,with focal depth of 167.2 km,recorded by China Digital Seismic Network(CDSN) were retrieved.Through trial-and-error method,the anomalous models beneath the Yellow and East China Seas for the six sub-regions were obtained by matching the theoretical travel-time curves of the P triplications from the modified models for the six sub-regions by using 2-D ray tracing with the observed ones.The local lower velocity anomaly appears around the 410 km discontinuity.Above the discontinuity,the P wave velocity decreases by 4%—5%from 300 km to 410 km and below the discontinuty,the velocity decreases by4%—7%from 410 km to 460/470 km.Because thermal flow was not observed by former seismic tomographic restdts.the local low velocity anomaly should be due to the partial-melting caused by the dehydrated water from subducting slab.
引文
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Li C,van der Hilst R D.2010.Structure of the upper mantle and transition zone beneath Southeast Asia from traveltime tomography[J].J Geophys Res,115:B07308.doi:10.1029/2009JB006882.
Obayashi M,Sugioka H,Yoshimitsu J,Fukao Y.2006.High temperature anomalies oceanward of subducting slabs at the 410-km discontinuity[J].Earth Planet Sci Lett,243(1/2):149-158.
Oreshin S,Vinnik L,Treussov A,Kind R.1998.Subducted lithosphere or 530 km discontinuity?[J].Geophys Res Lett,2S(7):1091-1094.
Revenaugh J,Sipkin S A.1994.Seismic evidence for silicate melt atop the 410-km mantle discontinuity[J].Nature,369(6480):474-476.
Song T R A,Helmberger D V,Grand S P.2004.Low-velocity zone atop the 410-km seismic discontinuity in the northwestern United States[J].Nature,427(6974):530-533.
Tajima F,Grand S P.1998.Variation of transition zone high-velocity anomalies and depression of 660 km discontinuity associated with subduction zones from the southern Kuriles to Izu-Bonin and Ryukyu[J].J Geophys Res,103(137):15015-15036.
Tajima F,Nakagawa T.2006.Implications of seismic waveforms:Complex physical properties associated with stagnant slab[J].Geophys Res Lett.33:L03311.doi:10.1029/2005GL024314.
Takeuchi N,Kawakatsu H,Tanaka S,Obayashi M,Chen Y J,NingJ,Grand S P,Niu F L,Ni J F,Iritani R,Idehara K,Tonegawa T.2014.Upper mantle tomography in the northwestern Pacific region using triplicated P waves[J].J Geophys Res,119(10):7667-7685.doi:10.1002/2014JB011161.
Tauzin B,Debayle E,WittlingerG.2010.Seismic evidence for a global low-velocity layer within the Earth's upper mantle[J].Nat Geosci,3(10):718-721.
Vinnik L,Farra V.2002.Subcratonic low-velocity layer and flood basalts[J].Geophys Res Lett,29(4):1049.doi:10.1029/2001GL014064
Vinnik L,Farra V.2007.Low S velocity atop the 410-km discontinuity and mantle plumes[J].Earth Planet Sci Lett,262(3/4):398-412.
Wang T,Chen L.2009.Distinct velocity variations around the base of the upper mantle beneath northeast Asia[J].Phys Earth Planet Int,172(3):241-256.
Xu P F,Zhao D P.2009.Upper-mantle velocity structure beneath the North China Craton:Implications for lithospheric thinning[J].Geophy J Int,177(3):1279-1283.
Zhao D P,Ohtani E.2009.Deep slab subduction and dehydration and their geodynamic consequences:Evidence from seismology and mineral physics[J].Gondwana Res,16(3/4):401-413.
Zhao D P,Liu L.2010.Deep structure and origin of active volcanoes in China[J].Geosci Front,1(1):31-44.
郭慧丽,徐佩芬,张福勤.2014.华北克拉通及东邻西太平洋活动大陆边缘地区的P波速度结构:对岩石圈减薄动力学过程的探讨[J].地球物理学报,57(7):2362-2371.Guo H L,Xu P F.Zhang F Q.2014.P wave velocity structure of the North China Craton and West Pacific active continental margin:Exploration for dynamic processes of lithospheric thinning[J].Chinese Journal of Geophysics,57(7):2362-2371.doi:10.6038/cjg20140729(in Chinese).
李国辉,眭怡,周元泽.2014.基于P波三重震相的下扬子克拉通地幔转换带顶部低速层初探[J].地球物理学报,57(7):2362-2371.doi:10.6038/cjg20140730.Li G H,Sui Y,Zhou Y Z.2014.Low-velocity layer atop the mantle transition zone in the lower Yangtze Craton from P waveform triplication[J].Chinese Journal of Geophysics,57(4):532-542.doi:10.6038/cjg20140730.
周晓亚.马麦宁,徐志双.2014.地幔过渡带顶面低速层的研究进展EJ].地球物理学进展,29(4):1615-1625.Zhou X Y.Ma M N,Xu Z S.2014.Progress of the low velocity zone atop the mantle transition zone[J].Progress in Geophysics,29(4):1615-1625.doi:10.6038/pg20140417(in Chinese).
Artemieva I.2011.The Lithosphere:An Interdisciplinary Approach[M].Cambridge:Cambridge University Press:47-214.
Bercovici D,Karato S I.2003.Whole-mantle convection and the transition-zone water filter[J].Nature,425(6953):39-44.
Chen W P.Tseng T L.2007.Small 660-km seismic discontinuity beneath Tibet implies resting ground for detached lithosphere[J].J Geophys Res,112;B05309.doi:10.1029/2006JB004607.
Chu R,Schmandt B,Helmberger D V.2012.Upper mantle P velocity structure beneath the Midwestern United States derived from triplicated waveforms[J].Geochem Geophys Geosyst,13:Q0AK04.doi:10.1029/2011GC003818.
Deuss A.2009.Global observations of mantle discontinuities using SS and PP precursors[J].Surv Geophys,30(4/5):301-326.
Fischer K M,Ford H A.Abt D L,Rychert C A.2010.The lithosphere-asthenosphere boundary[J].Annu Rev Earth Planet Sci,38:551-575.
Fukao Y,Obayashi M.2013.Subducted slabs stagnant above,penetrating through,and trapped below the 660 km discontinuity[J].J Geophys Res.118(B11):5920-5938.
Hirth G,Kohlstedt D L.1996.Water in the oceanic upper mantle:Implications for rheology,melt extraction and the evolution of the lithosphere[J].Earth Planet Sci Lett,144(1/2):93-108.
Huang J L,Zhao D P.2006.High-resolution mantle tomography of China and surrounding regions[J].J Geophys Res,111:B09305.doi:10.1029/2005JB004066.
ISC.2013.ISC bulletin[EB/OL].[2014-10-12].http://www.isc.ac.uk/iscbulletin/.
Karato S I.2011.Water distribution across the mantle transition zone and its implications for global material circulation[J].Earth Planet Sci Lett,301(3/4):413-423.
Kennett B L N,Engdahl E R.1991.Traveltimes for global earthquake location and phase identification[J].Geophys J Int,105(2):429-465.
Kennett B L N,Engdahl E R,Buland R.1995.Constraints on seismic velocities in the Earth from traveltimes[J].Geophys J Int,122(1):108-124.
de Kool M,Rawlinson N,Sambridge M.2006.A practical grid-based method for tracking multiple refraction and reflection phases in three-dimensional heterogeneous media[J].Geophys J Int,167(1):253-270.
Leahy G M,Bercovici D.2007.On the dynamics of a hydrous melt layer above the transition zone[J].J Geophys Res,112:B07401.doi:10.1029/2006JB004631.
Li C,van der Hilst R D.2010.Structure of the upper mantle and transition zone beneath Southeast Asia from traveltime tomography[J].J Geophys Res,115:B07308.doi:10.1029/2009JB006882.
Obayashi M,Sugioka H,Yoshimitsu J,Fukao Y.2006.High temperature anomalies oceanward of subducting slabs at the 410-km discontinuity[J].Earth Planet Sci Lett,243(1/2):149-158.
Oreshin S,Vinnik L,Treussov A,Kind R.1998.Subducted lithosphere or 530 km discontinuity?[J].Geophys Res Lett,2S(7):1091-1094.
Revenaugh J,Sipkin S A.1994.Seismic evidence for silicate melt atop the 410-km mantle discontinuity[J].Nature,369(6480):474-476.
Song T R A,Helmberger D V,Grand S P.2004.Low-velocity zone atop the 410-km seismic discontinuity in the northwestern United States[J].Nature,427(6974):530-533.
Tajima F,Grand S P.1998.Variation of transition zone high-velocity anomalies and depression of 660 km discontinuity associated with subduction zones from the southern Kuriles to Izu-Bonin and Ryukyu[J].J Geophys Res,103(137):15015-15036.
Tajima F,Nakagawa T.2006.Implications of seismic waveforms:Complex physical properties associated with stagnant slab[J].Geophys Res Lett.33:L03311.doi:10.1029/2005GL024314.
Takeuchi N,Kawakatsu H,Tanaka S,Obayashi M,Chen Y J,NingJ,Grand S P,Niu F L,Ni J F,Iritani R,Idehara K,Tonegawa T.2014.Upper mantle tomography in the northwestern Pacific region using triplicated P waves[J].J Geophys Res,119(10):7667-7685.doi:10.1002/2014JB011161.
Tauzin B,Debayle E,WittlingerG.2010.Seismic evidence for a global low-velocity layer within the Earth's upper mantle[J].Nat Geosci,3(10):718-721.
Vinnik L,Farra V.2002.Subcratonic low-velocity layer and flood basalts[J].Geophys Res Lett,29(4):1049.doi:10.1029/2001GL014064
Vinnik L,Farra V.2007.Low S velocity atop the 410-km discontinuity and mantle plumes[J].Earth Planet Sci Lett,262(3/4):398-412.
Wang T,Chen L.2009.Distinct velocity variations around the base of the upper mantle beneath northeast Asia[J].Phys Earth Planet Int,172(3):241-256.
Xu P F,Zhao D P.2009.Upper-mantle velocity structure beneath the North China Craton:Implications for lithospheric thinning[J].Geophy J Int,177(3):1279-1283.
Zhao D P,Ohtani E.2009.Deep slab subduction and dehydration and their geodynamic consequences:Evidence from seismology and mineral physics[J].Gondwana Res,16(3/4):401-413.
Zhao D P,Liu L.2010.Deep structure and origin of active volcanoes in China[J].Geosci Front,1(1):31-44.
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