Lg波Q值随震源深度的变化作为地壳本征衰减深度的判据
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摘要
Lg波的Q_(Lg)值是描述区域地壳结构及介质衰减特性的重要参数之一,Q_(Lg)层析成像被广泛应用于地壳衰减结构横向不均匀性的研究中.但是,对Q_(Lg)在垂直方向上的不均匀性的研究较少.当发现一个地区发生Q_(Lg)值低时,我们希望进一步了解这种介质衰减深度.本文通过数值模拟合成地震图的方法,通过分析不同震源深度和介质模型计算Q_(Lg),判断Lg波发生主要衰减的深度.研究结果显示:(1)当震源深度浅时,上地壳介质衰减对于Lg波Q值的影响明显比下地壳的影响更大.而震源深度深时,两者贡献基本相当;(2)如果上地壳介质衰减强,则随着震源深度的增加,η值逐渐减小;如果下地壳介质衰减强,η值先增大后减小;但如果下地壳存在低速层,则η值持续增大;(3)如果上地壳介质衰减强,则随着震源深度的增加,Q_0逐渐增大;反之如果下地壳介质衰减强,则Q_0逐渐减小.因此,我们可以通过调查某一区域不同深度地震的Lg波衰减规律,来判断这一地区的地壳介质衰减情况.
Q_(Lg) attenuation is an important parameter used in studies of region crustal structure and media physical nature.Lg Qtomography is widely used in study of crustal horizontal heterogeneity.However,studies of vertical heterogeneity are very few in the literature.When there is a low Q_(Lg),it is essential to know the depth that generate it.In this paper,we use synthetic seismograms for models with different focal depth to estimate the depth of the intrinsic Q.Our results show that:(1)when source depth is shallow,upper crust attenuation has obvious impact on Lg wave Qthan that in lower crust.When source depth is deep,upper crust and lower crust has similar impact.(2)If upper crust has a strong media attenuation,ηdecreases as source depth increases.If lower crust has a strong media attenuation,ηincreases first and then decreases.However,when there is a low-velocity layer in lower crust,ηincreases as source depth increases.(3)If upper crust has a strong media attenuation,Q_0 increases as source depth increases.Conversely,if lower crust has a strong media decline,Q_0 decreases as source depth increases.Using this conclusion,according to the research of the Lg decline rule of different depths in a region,we can estimate the depth of high attenuation of the studied region.
Q_(Lg) attenuation is an important parameter used in studies of region crustal structure and media physical nature.Lg Qtomography is widely used in study of crustal horizontal heterogeneity.However,studies of vertical heterogeneity are very few in the literature.When there is a low Q_(Lg),it is essential to know the depth that generate it.In this paper,we use synthetic seismograms for models with different focal depth to estimate the depth of the intrinsic Q.Our results show that:(1)when source depth is shallow,upper crust attenuation has obvious impact on Lg wave Qthan that in lower crust.When source depth is deep,upper crust and lower crust has similar impact.(2)If upper crust has a strong media attenuation,ηdecreases as source depth increases.If lower crust has a strong media attenuation,ηincreases first and then decreases.However,when there is a low-velocity layer in lower crust,ηincreases as source depth increases.(3)If upper crust has a strong media attenuation,Q_0 increases as source depth increases.Conversely,if lower crust has a strong media decline,Q_0 decreases as source depth increases.Using this conclusion,according to the research of the Lg decline rule of different depths in a region,we can estimate the depth of high attenuation of the studied region.
引文
Aki K.1980.Scattering and attenuation of shear waves in the lithosphere.Journal of Geophysical Research:Solid Earth,85(B11):6496-6504.
Aki K,Richards P G.2002.Quantitative Seismology.2nd ed.Sausalito,California:University Science Books,112-113.
Bao X Y,Sandvol E,Ni J,et al.2011.High resolution regional seismic attenuation tomography in eastern Tibetan Plateau and adjacent regions.Geophysical Research Letters,38(16):L16304,doi:10.1029/2011GL048012.
Bouchon M.1982.The complete synthesis of seismic crustal phases at regional distances.Journal of Geophysical Research:Solid Earth,87(B3):1735-1741.
Campillo M,Plantet J L,Bouchon M.1985.Frequency-dependent attenuation in the crust beneath central France from Lg waves:Data analysis and numerical modeling.Bulletin of the Seismological Society of America,75(5):1395-1411.
Der Z A,Marshall M E,O′Donnell A,et al.1984.Spatial coherence structure and attenuation of the Lg phase,site effects,and the interpretation of the Lg coda.Bulletin of the Seismological Society of America,74(4):1125-1147.
He J,Wu Q J,Li Y H,et al.2017.Developments of earthquake Lg-wave attenuation study and its application in the continental China.Progress in Geophysics(in Chinese),32(2):466-475,doi:10.6038/pg20170204.
He Y F,Li K,Liu B C,et al.2015.The characteristics of Lg waves induced by the underground nuclear explosions in the waveguides using frequency-wavenumber algorithm.Acta Seismologica Sinica(in Chinese),37(2):257-265.
Herrin E,Richmond J.1960.On the propagation of the Lg phase.Bulletin of the Seismological Society of America,50(2):197-210.
Herrmann R B.1980.Q estimates using the coda of local earthquake.Bulletin of the Seismological Society of America,70(2):447-468.
Hu J F,Cong L L,Su Y J,et al.2003.Distribution characteristics of Q value of the Lg coda in Yunnan and its adjacent regions.Chinese Journal of Geophysics(in Chinese),46(6):809-813.
Kennett B L N,Mykkeltveit S.1984.Guided wave propagation in laterally varying media-II.Lg-waves in north-western Europe.Geophysical Journal International,79(1):257-267.
Knopoff L,Schwab F,Kauselt E.1973.Interpretation of Lg.Geophysical Journal International,33(4):389-404.
Liu H G,Zhou H H,Chen S Q,et al.2008.Lg coda attenuation and its distribution image beneath Ordos massif.Progress in Geophysics(in Chinese),23(2):351-358.
Mao Y,Xu Y,Hu J F,et al.2005.Regional variation of Lg coda Qin Sichuan region using stack spectral ratio method.Journal of Yunnan University,27(2):123-128.
Mitchell B J.1980.Frequency dependence of shear wave internal friction in the continental crust of eastern North America.Journal of Geophysical Research:Solid Earth,85(B10):5212-5218.
Pedersen H,Campillo M.1991.Depth dependance of Q beneath the Baltic Shield inferred from modeling of short period seismograms.Geophysical Research Letters,18(9):1755-1758.
Press F,Ewing M.1952.Two slow surface waves across North America.Bulletin of the Seismological Society of America,42(3):219-228.
Sato R.1967.Attenuation of seismic waves.Journal of Physics of the Earth,15(2):32-61.
Shi J H,Richards P G,Kim W Y.2000.Determination of seismic energy from Lg waves.Bulletin of the Seismological Society of America,90(2):483-493.
Street R L,Herrmann R B,Nuttli O W.1975.Spectral characteristics of the Lg wave generated by central United States earthquakes.Geophysical Journal of the Royal Astronomical Society,41(1):51-63.
Su W,Wu J P,Ming Y H,et al.2006.Lg coda Q0value and its relation with the tectonics in Chinese mainland and adjacent regions.Acta Seismologica Sinica(in Chinese),28(2):24-113.
Tsai Y B,Aki K.1969.Simultaneous determination of the seismic moment and attenuation of seismic surface waves.Bulletin of the Seismological Society of America,59(1):275-287.
Wang R J.1999.A simple orthonormalization method for stable and efficient computation of Green′s functions.Bulletin of the Seismological Society of America,89(3):733-741.
Xie J,Nuttli O W.1988.Interpretation of high-frequency coda at large distances:Stochastic modelling and method of inversion.Geophysical Journal International,95(3):579-595.
Xie J,Mitchell B J.1990.Attenuation of multiphase surface waves in the Basin and Range province,part I:Lg and Lg coda.Geophysical Journal of the Royal Astronomical Society,102(1):121-137.
Xie J K.1993.Simultaneous inversion for source spectrum and path Q using Lg with application to three Semipalatinsk explosions.Bulletin of the Seismological Society of America,83(5):1547-1562.
Xu Y,Mao Y,Hu J F,et al.2005.Study of Regional variations of Lg coda Q in Xinjiang using stack spectral ration method.Yunnan Geographic Environment Research(in Chinese),17(2):6-10,27.
Zhao L F,Xie X B,Wang W M,et al.2010.Seismic Lg-wave Qtomography in and around Northeast China.Journal of Geophysical Research:Solid Earth,115(B8):B08307,doi:10.1029/2009JB007157.
Zhao L F,Xie X B,Wang W M,et al.2018.A broadband crustal Lg wave attenuation model in Northeast China and the Korean Peninsula.Chinese Journal of Geophysics(in Chinese),61(3):856-871,doi:10.6038/cjg2018L0394.
Zhou L Q,Zhao C P,Xiu J G,et al.2008a.Methods and developments of research on crustal Q value by using earthquakes.Recent Developments in World Seismology(in Chinese),(2):1-11.
Zhou L Q,Zhao C P,Xiu J G,et al.2008b.Tomography of QLgin
Sichuan-Yunnan Zone.Chinese Journal of Geophysics(in Chinese),51(6):1745-1752.
何静,吴庆举,李永华等.2017.天然地震Lg波衰减研究进展及其在中国大陆地区的应用.地球物理学进展,32(2):466-475,doi:10.6038/pg20170204.
何永锋,李锴,刘炳灿等.2015.基于理论地震图方法的波导结构对地下核爆炸Lg波传播特性研究.地震学报,37(2):257-265.
胡家富,丛连理,苏有锦等.2003.云南及周边地区Lg尾波Q值的分布特征.地球物理学报,46(6):809-813.
刘红桂,周红晖,陈书清等.2008.鄂尔多斯块体Lg尾波衰减及其分布图像.地球物理学进展,23(2):351-358.
毛燕,徐彦,胡家富等.2005.用叠加谱比法研究四川地区Lg尾波Q值的区域性变化.云南大学学报(自然科学版),27(2):123-128.
苏伟,吴建平,明跃红等.2006.Lg尾波Q0值与中国大陆及邻区的地质构造关系.地震学报,28(2):24-113.
徐彦,毛燕,胡家富等.2005.用叠加谱比法研究新疆地区Lg尾波Q值的区域性变化.云南地理环境研究,17(2):6-10,27.
赵连锋,谢小碧,王卫民等.2018.中国东北和朝鲜半岛地区地壳Lg波宽频带衰减模型.地球物理学报,61(3):856-871,doi:10.6038/cjg2018L0394.
周连庆,赵翠萍,修济刚等.2008a.利用天然地震研究地壳Q值的方法和进展.国际地震动态,(2):1-11.
周连庆,赵翠萍,修济刚等.2008b.川滇地区Lg波Q值层析成像.地球物理学报,51(6):1745-1752.
Aki K,Richards P G.2002.Quantitative Seismology.2nd ed.Sausalito,California:University Science Books,112-113.
Bao X Y,Sandvol E,Ni J,et al.2011.High resolution regional seismic attenuation tomography in eastern Tibetan Plateau and adjacent regions.Geophysical Research Letters,38(16):L16304,doi:10.1029/2011GL048012.
Bouchon M.1982.The complete synthesis of seismic crustal phases at regional distances.Journal of Geophysical Research:Solid Earth,87(B3):1735-1741.
Campillo M,Plantet J L,Bouchon M.1985.Frequency-dependent attenuation in the crust beneath central France from Lg waves:Data analysis and numerical modeling.Bulletin of the Seismological Society of America,75(5):1395-1411.
Der Z A,Marshall M E,O′Donnell A,et al.1984.Spatial coherence structure and attenuation of the Lg phase,site effects,and the interpretation of the Lg coda.Bulletin of the Seismological Society of America,74(4):1125-1147.
He J,Wu Q J,Li Y H,et al.2017.Developments of earthquake Lg-wave attenuation study and its application in the continental China.Progress in Geophysics(in Chinese),32(2):466-475,doi:10.6038/pg20170204.
He Y F,Li K,Liu B C,et al.2015.The characteristics of Lg waves induced by the underground nuclear explosions in the waveguides using frequency-wavenumber algorithm.Acta Seismologica Sinica(in Chinese),37(2):257-265.
Herrin E,Richmond J.1960.On the propagation of the Lg phase.Bulletin of the Seismological Society of America,50(2):197-210.
Herrmann R B.1980.Q estimates using the coda of local earthquake.Bulletin of the Seismological Society of America,70(2):447-468.
Hu J F,Cong L L,Su Y J,et al.2003.Distribution characteristics of Q value of the Lg coda in Yunnan and its adjacent regions.Chinese Journal of Geophysics(in Chinese),46(6):809-813.
Kennett B L N,Mykkeltveit S.1984.Guided wave propagation in laterally varying media-II.Lg-waves in north-western Europe.Geophysical Journal International,79(1):257-267.
Knopoff L,Schwab F,Kauselt E.1973.Interpretation of Lg.Geophysical Journal International,33(4):389-404.
Liu H G,Zhou H H,Chen S Q,et al.2008.Lg coda attenuation and its distribution image beneath Ordos massif.Progress in Geophysics(in Chinese),23(2):351-358.
Mao Y,Xu Y,Hu J F,et al.2005.Regional variation of Lg coda Qin Sichuan region using stack spectral ratio method.Journal of Yunnan University,27(2):123-128.
Mitchell B J.1980.Frequency dependence of shear wave internal friction in the continental crust of eastern North America.Journal of Geophysical Research:Solid Earth,85(B10):5212-5218.
Pedersen H,Campillo M.1991.Depth dependance of Q beneath the Baltic Shield inferred from modeling of short period seismograms.Geophysical Research Letters,18(9):1755-1758.
Press F,Ewing M.1952.Two slow surface waves across North America.Bulletin of the Seismological Society of America,42(3):219-228.
Sato R.1967.Attenuation of seismic waves.Journal of Physics of the Earth,15(2):32-61.
Shi J H,Richards P G,Kim W Y.2000.Determination of seismic energy from Lg waves.Bulletin of the Seismological Society of America,90(2):483-493.
Street R L,Herrmann R B,Nuttli O W.1975.Spectral characteristics of the Lg wave generated by central United States earthquakes.Geophysical Journal of the Royal Astronomical Society,41(1):51-63.
Su W,Wu J P,Ming Y H,et al.2006.Lg coda Q0value and its relation with the tectonics in Chinese mainland and adjacent regions.Acta Seismologica Sinica(in Chinese),28(2):24-113.
Tsai Y B,Aki K.1969.Simultaneous determination of the seismic moment and attenuation of seismic surface waves.Bulletin of the Seismological Society of America,59(1):275-287.
Wang R J.1999.A simple orthonormalization method for stable and efficient computation of Green′s functions.Bulletin of the Seismological Society of America,89(3):733-741.
Xie J,Nuttli O W.1988.Interpretation of high-frequency coda at large distances:Stochastic modelling and method of inversion.Geophysical Journal International,95(3):579-595.
Xie J,Mitchell B J.1990.Attenuation of multiphase surface waves in the Basin and Range province,part I:Lg and Lg coda.Geophysical Journal of the Royal Astronomical Society,102(1):121-137.
Xie J K.1993.Simultaneous inversion for source spectrum and path Q using Lg with application to three Semipalatinsk explosions.Bulletin of the Seismological Society of America,83(5):1547-1562.
Xu Y,Mao Y,Hu J F,et al.2005.Study of Regional variations of Lg coda Q in Xinjiang using stack spectral ration method.Yunnan Geographic Environment Research(in Chinese),17(2):6-10,27.
Zhao L F,Xie X B,Wang W M,et al.2010.Seismic Lg-wave Qtomography in and around Northeast China.Journal of Geophysical Research:Solid Earth,115(B8):B08307,doi:10.1029/2009JB007157.
Zhao L F,Xie X B,Wang W M,et al.2018.A broadband crustal Lg wave attenuation model in Northeast China and the Korean Peninsula.Chinese Journal of Geophysics(in Chinese),61(3):856-871,doi:10.6038/cjg2018L0394.
Zhou L Q,Zhao C P,Xiu J G,et al.2008a.Methods and developments of research on crustal Q value by using earthquakes.Recent Developments in World Seismology(in Chinese),(2):1-11.
Zhou L Q,Zhao C P,Xiu J G,et al.2008b.Tomography of QLgin
Sichuan-Yunnan Zone.Chinese Journal of Geophysics(in Chinese),51(6):1745-1752.
何静,吴庆举,李永华等.2017.天然地震Lg波衰减研究进展及其在中国大陆地区的应用.地球物理学进展,32(2):466-475,doi:10.6038/pg20170204.
何永锋,李锴,刘炳灿等.2015.基于理论地震图方法的波导结构对地下核爆炸Lg波传播特性研究.地震学报,37(2):257-265.
胡家富,丛连理,苏有锦等.2003.云南及周边地区Lg尾波Q值的分布特征.地球物理学报,46(6):809-813.
刘红桂,周红晖,陈书清等.2008.鄂尔多斯块体Lg尾波衰减及其分布图像.地球物理学进展,23(2):351-358.
毛燕,徐彦,胡家富等.2005.用叠加谱比法研究四川地区Lg尾波Q值的区域性变化.云南大学学报(自然科学版),27(2):123-128.
苏伟,吴建平,明跃红等.2006.Lg尾波Q0值与中国大陆及邻区的地质构造关系.地震学报,28(2):24-113.
徐彦,毛燕,胡家富等.2005.用叠加谱比法研究新疆地区Lg尾波Q值的区域性变化.云南地理环境研究,17(2):6-10,27.
赵连锋,谢小碧,王卫民等.2018.中国东北和朝鲜半岛地区地壳Lg波宽频带衰减模型.地球物理学报,61(3):856-871,doi:10.6038/cjg2018L0394.
周连庆,赵翠萍,修济刚等.2008a.利用天然地震研究地壳Q值的方法和进展.国际地震动态,(2):1-11.
周连庆,赵翠萍,修济刚等.2008b.川滇地区Lg波Q值层析成像.地球物理学报,51(6):1745-1752.
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