南美地区下地幔速度界面结构研究
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摘要
下地幔间断面是地球内部结构研究的重要课题,对于理解地球深部的动力过程具有重要意义.美国西部密集地震台网记录到的南美洲太平洋地区深震的短周期波形资料有利于震源下方下地幔间断面的研究.本文收集了美国西北太平洋地震台网和犹他大学地震台网所记录的南美洲西部俯冲地区15个深震的19组短周期垂向台网资料,并利用4次根倾斜叠加方法提取震源下方下地幔中速度界面上发生转换的次生震相SdP,据此发现南美洲西部下方下地幔中800～1200 km深度范围内存在明显的转换点集中,主要分布在900,1000和1100 km三个深度附近,三个速度界面具有不同的起伏形态,应为在研究区域双层地幔对流中间边界层.
The lower mantle discontinuities are an important part of the structure of Earth's interior and very important for understanding the dynamic process of the deep part of the Earth. The waveform data of the deep events of South America recorded by the dense stations at western part of USA are suitable for studying lower mantle discontinuities beneath the events.In the paper, 19 sets waveform data of vertical short period component from 15 events beneath South America recorded by the PNSN and UUSS of USA were retrieved and processed with 4-th root slant stack method for picking the SdP phases from the lower mantle interfaces.With the SdPs, the conversion points related to SdPs are found to be concentrated between 800 and 1200 km and mainly distribute at the depths of 900, 1000 and 1100 km.In addition, the topography of the three layers is different.The interfaces may relate to the mid-boundary of the two-layer mantle convection.
The lower mantle discontinuities are an important part of the structure of Earth's interior and very important for understanding the dynamic process of the deep part of the Earth. The waveform data of the deep events of South America recorded by the dense stations at western part of USA are suitable for studying lower mantle discontinuities beneath the events.In the paper, 19 sets waveform data of vertical short period component from 15 events beneath South America recorded by the PNSN and UUSS of USA were retrieved and processed with 4-th root slant stack method for picking the SdP phases from the lower mantle interfaces.With the SdPs, the conversion points related to SdPs are found to be concentrated between 800 and 1200 km and mainly distribute at the depths of 900, 1000 and 1100 km.In addition, the topography of the three layers is different.The interfaces may relate to the mid-boundary of the two-layer mantle convection.
引文
[1] Kennett B L N, Bunge H-P. Geophysical Continua, Cambridge: Cambridge University Press, 2008
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[5] Geiger L, Gutenberg B. Ueber Erdbebenwellen. VI. Konstitution des Erdinnern, erschlossen aus der Intensit(a|¨)t longitudinaler und transversaler Erdbebenwellen, und einige Beobachtungen an den Vorl(a|¨)ufern. Nachrichten yon der K(o|¨)niglichen Gesellschaft der Wissenschaften zu G(o|¨)ttingen. Mathematisch-Physikalische Klasse, 1912． 623～675
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[13] Shen Y, Wolfe C J, Solomon S C. Seismic evidence for a lower mantle discontinuity beneath Hawaii and Iceland. Earth Planet. Sci. Lett. , 2003, 214:143～151
[14] van der Meijde M, van der Lee S, Giardini D. Seismic discontinuities in the mediterranean mantle. Phys. Earth Planet. Inter. , 2005,148:233～250
[15] Tanimoto T. Predominance of large scale heterogeneity and the shift of velocity anomalies between the upper and the lower mantle. J. Phys. Earth, 1990, 38:493～509
[16] Wen L, Anderson D L. The fate of the slabs inferred from seismic tomography and 130 Ma subduction. Earth Planet. Sci. Lett. , 1995, 133:185～198
[17] Kellogg L H, Hager B H, van der Hilst R D. Compositional stratification in the deep mantle. Science, 1999, 283 : 1881 ～ 1884
[18] KurashinaT, HiroseK, OnoS, et al. Phase transition in Albearing CaSiO3 perovskite : implications for seismic discontinuities in the lower mantle. Phys. Earth Planet. Int. , 2004,145:67～74
[19] Anderson D. The case for irreversible chemical stratification of the mantle. International Geology Review, 2002, 44: 97～116
[20] Engdahl R E, van der Hilst R, Buland R. Global teleseismic earthquake relocation with improved travel times and procedures for depth determination. Bull. Seism. Soc. Am., 1998, 88:722～743
[21] Gudmundsson O, Sambridge M. A regionalized upper mantle (RUM) seismic model. J. Geophys. Res, 1998,103(B4) : 7121～7136
[22] Kanasewich E R, Hemmings C D, Alpaslan T. Nth-root stack nonlinear multichannel filter. Geophysics, 1973,38 ( 2 ) : 327～338
[23] McFadden P L, Drummond B J, Karvis S. The Nth root stack: theory, application and examples. Geophysics, 1986, 51(10) :1879～1892
[24] Collier J, Helffrich G. Topography of the “410” and “660” km seismic discontinuities in the Izu-Bonin subduction zone. Geophys. Res. Lett., 1997,24:1535～1538
[25] Li C, van der Hilst R D, Engdahl E R, Burdick S. A new global model for P-wave speed variations in Earth's mantle. Geochem. Geophys. Geosys, 2001,9, Q05018, doi:10． 1029/2007GC001806
[26] Bina C R. Lower mantle mineralogy and the geophysical perspective. Reviews in Mineralogy, 1998, 37:205～239
[27] Nolet G,Moser T J. Teleseismic delay times in a 3-D Earth and a new look at the S discrepancy. GeophysJ. Int. , 1993,114:185～195
[28] Hedlin M A H, Shearer P M,Earle P S. Seismic evidence for small scale heterogeneity throughout the Earth' s mantle. Nature, 1997, 387:145～150
[29] Wen L,Anderson D L. Layered mantle convection: A model for geoid and topography. Earth and Planetary Science Letters, 1997,146:367～377
[30] Montagner J P, Guillot L. Seismic anisotropy in the Earth's mantle. In: Boschi E, Ekstrom G, Morelli A, eds. Problems in Geophysics for the New Millennium. Bologna, Editrice Compostri , 2000, 217～253
[31] Vinnik L, Kato M, Kawakatsu H. Search for seismic discontinuities in the lower mantle. Geophys. J. Int. , 2001, 147(1) :41～56
[32] Liu K H, Gao S S, Zhang Y K. Mantle layering across central South America. J. Geophys. Res., 2003, 108(Bll); 2510, doi: 10． 1029/2002JB002208
[33] Castle J C, van der Hilst R D. Searching for seismic scattering off mantle interfaces between 800 km and 2000 km depth. J. Geophys. Res., 2003, 108(B2) : 2095, doi:10． 1029/2001JB000286
[2] Dziewonski A M, Anderson D L. Preliminary Reference Earth Model (PREM). Phys. Earth Planet. Inter. , 1981,25:297～356
[3] Kennett B L N, Engdahl E R. Travel times for global earthquake location and phase association. Geophys. J. Int. , 1991,105:429～465
[4] Kennett B L N , Engdahl E R, Buland R. Constraints on seismic velocities in the Earth from travel times. Geophys. J. Int. ,1995,122:108～124
[5] Geiger L, Gutenberg B. Ueber Erdbebenwellen. VI. Konstitution des Erdinnern, erschlossen aus der Intensit(a|¨)t longitudinaler und transversaler Erdbebenwellen, und einige Beobachtungen an den Vorl(a|¨)ufern. Nachrichten yon der K(o|¨)niglichen Gesellschaft der Wissenschaften zu G(o|¨)ttingen. Mathematisch-Physikalische Klasse, 1912． 623～675
[6] Mohorovicic S. Die reduzierte laufzetkurve und abhangigkeit der herdtiefe usw. Gerlands Beitr. zur Geophysik, 1916, Bd. XIV
[7] Repetti W C. New values for some of the discontinuities in the earth [Ph. D. thesis]. St Louis: St. Louis University, 1930
[8] Kawakatsu H, Niu F. Seismic evidence for a 920 km discontinuity. Nature, 1994, 371: 301～305
[9] Wicks C W, Richards M A. Seismic evidence for 1200 km discontinuity. EOS, Trans. Am. Geophys. Un., 1993, 43 (Suppl.) :550
[10] Niu F, Kawakatsu H. Depth variation of the mid mantle seismic discontinuity. Geophys. Res. Lett. , 1997, 24:429～ 432
[11] Vanacore E, Niu F, Kawakatsu H. Observations of the mid mantle discontinuity beneath Indonesia from S to P converted waveforms. Geophys. Res. Lett., 2006, 33: 10． 1029/ 2005GL025106
[12] Kaneshima S, Helffrich G. Detection of lower mantle scatterers northeast of the Mariana subduction zone using short period array data. J. Geophys. Res., 1998, 103:4825～ 4838
[13] Shen Y, Wolfe C J, Solomon S C. Seismic evidence for a lower mantle discontinuity beneath Hawaii and Iceland. Earth Planet. Sci. Lett. , 2003, 214:143～151
[14] van der Meijde M, van der Lee S, Giardini D. Seismic discontinuities in the mediterranean mantle. Phys. Earth Planet. Inter. , 2005,148:233～250
[15] Tanimoto T. Predominance of large scale heterogeneity and the shift of velocity anomalies between the upper and the lower mantle. J. Phys. Earth, 1990, 38:493～509
[16] Wen L, Anderson D L. The fate of the slabs inferred from seismic tomography and 130 Ma subduction. Earth Planet. Sci. Lett. , 1995, 133:185～198
[17] Kellogg L H, Hager B H, van der Hilst R D. Compositional stratification in the deep mantle. Science, 1999, 283 : 1881 ～ 1884
[18] KurashinaT, HiroseK, OnoS, et al. Phase transition in Albearing CaSiO3 perovskite : implications for seismic discontinuities in the lower mantle. Phys. Earth Planet. Int. , 2004,145:67～74
[19] Anderson D. The case for irreversible chemical stratification of the mantle. International Geology Review, 2002, 44: 97～116
[20] Engdahl R E, van der Hilst R, Buland R. Global teleseismic earthquake relocation with improved travel times and procedures for depth determination. Bull. Seism. Soc. Am., 1998, 88:722～743
[21] Gudmundsson O, Sambridge M. A regionalized upper mantle (RUM) seismic model. J. Geophys. Res, 1998,103(B4) : 7121～7136
[22] Kanasewich E R, Hemmings C D, Alpaslan T. Nth-root stack nonlinear multichannel filter. Geophysics, 1973,38 ( 2 ) : 327～338
[23] McFadden P L, Drummond B J, Karvis S. The Nth root stack: theory, application and examples. Geophysics, 1986, 51(10) :1879～1892
[24] Collier J, Helffrich G. Topography of the “410” and “660” km seismic discontinuities in the Izu-Bonin subduction zone. Geophys. Res. Lett., 1997,24:1535～1538
[25] Li C, van der Hilst R D, Engdahl E R, Burdick S. A new global model for P-wave speed variations in Earth's mantle. Geochem. Geophys. Geosys, 2001,9, Q05018, doi:10． 1029/2007GC001806
[26] Bina C R. Lower mantle mineralogy and the geophysical perspective. Reviews in Mineralogy, 1998, 37:205～239
[27] Nolet G,Moser T J. Teleseismic delay times in a 3-D Earth and a new look at the S discrepancy. GeophysJ. Int. , 1993,114:185～195
[28] Hedlin M A H, Shearer P M,Earle P S. Seismic evidence for small scale heterogeneity throughout the Earth' s mantle. Nature, 1997, 387:145～150
[29] Wen L,Anderson D L. Layered mantle convection: A model for geoid and topography. Earth and Planetary Science Letters, 1997,146:367～377
[30] Montagner J P, Guillot L. Seismic anisotropy in the Earth's mantle. In: Boschi E, Ekstrom G, Morelli A, eds. Problems in Geophysics for the New Millennium. Bologna, Editrice Compostri , 2000, 217～253
[31] Vinnik L, Kato M, Kawakatsu H. Search for seismic discontinuities in the lower mantle. Geophys. J. Int. , 2001, 147(1) :41～56
[32] Liu K H, Gao S S, Zhang Y K. Mantle layering across central South America. J. Geophys. Res., 2003, 108(Bll); 2510, doi: 10． 1029/2002JB002208
[33] Castle J C, van der Hilst R D. Searching for seismic scattering off mantle interfaces between 800 km and 2000 km depth. J. Geophys. Res., 2003, 108(B2) : 2095, doi:10． 1029/2001JB000286
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