地球自由振荡课件

,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,地球自由振荡,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,单击此处编辑母版标题样式,地球自由振荡,*,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,单击此处编辑母版标题样式,地球自由振荡,地球自由振荡,(1),申文斌,武汉大学,E-mail: wbshen,2013,年,4,月,22,日,1,Contents,Introduction,Principle,Data and Results,Conclusions,Introduction,地球自由振荡？,想象刚性地球，敲它一下,.,想象分层地球，敲它一下,.,想象,.,3,rd,Harmonic,etc.,2,nd,Harmonic,1,st,Harmonic,Fundamental,L,x,自由振荡,是一组驻波的叠加,驻波是两个转播方向相反的波干涉后的结果,本征频率,本征函数,一维情形（引自胡小刚博士论文答辩,2007,）,4,地球,自由振荡的周期, 54 min,振幅, 0 : overtones),l,:,the angular degree,m:,azimuthal order (m=-l, , 0, l),径向,本征函数,球面,本征函数,Solutions (e.g. Aki 1981),：,1-D,Aki1981,中译本,p376:,在,x=0,和,x=L,处，,y(x)=0,则有如下通解（,Sturm-Liuville,理论,):,本征解及本征频率,Solutions (e.g. Aki 1981),：,3-D,Aki1981,中译本,p376-396:,求解如下方程,满足如下条件：,球体振荡：,环形振荡和球形振荡,环形振荡,:,球形振荡：,径向,本征函数,球面,本征函数,环形振荡,T,：,没有径向分量，只有,球面剪切波分量,球形振荡,S,：,既有径向分量，又有球面剪切波分量,环形振荡和球形振荡,注释,没有径向分量，振荡时质点在与地心同心的球面上运动。不会引起地球体积变化，不影响重力场；重力仪观测不到？,环形振荡只存在于地幔中，不可能存在于液态外核中，但有可能存在于固体内核中,环形振荡,n,T,m,l,:,球形振荡,n,S,m,l,:,既有径向分量，又有球面剪切波分量。即振荡时质点在径向和球面上都有运动，球形振荡可影响整个地球，并可存在于液态外核中。重力仪可观测到球型振荡信号，,0,S,0,: radial only,(20.5 minutes),0,S,2,: football mode,(Fundamental, 53.9 minutes),0,S,3,:,(25.7 minutes),0,S,29,:,(4.5 minutes),.,.,Rem:,0,S,1,= translation,.,球形振荡,:,12,固态内核在液态外核中的平动,(,1,S,1,周期约为,48,小时,),由固态内核与液态外核边界上密度的变化以及液核的浮力对,1,S,1,的频率有较大影响,1,S,1,有可能存在于地核中,(Slichter mode),13,1,T,2,(12.6 minutes),0,T,2,: (44.2 minutes),0,T,3,(28.4 minutes),Rem:,0,T,1,= rotation,0,T,0,= not existing,环形振荡,14,S :,T :,0,T,0,3,0,S,0,2,n, l, m ,15,实际地球,：,自转,椭率,3D,一组多重态中的不同独态具有不同的频率,(,频率与方位角序号,m,有关）,由,(,n, l, m,),确定的单个振型称为独态,(singlet),其中,m,=,0,，,1,，,.,l,由,(,n,l,),确定的,2,l,+1,个振型称为一组多重态,(multiplet),采用,SNREI (spherically symmetric, non-rotating, perfectly elastic, isotropic),地球模型,，,m,简并,(Degeneracy):,频率与方位角序号,m,无关,自由振荡信号谱线分裂,16,自转,(Coriolis),椭率,3D,沿地球自转方向波传播地较快,地球的横向不均匀影响波的转播速度,沿地球赤道传播的波比从地球一极,传播,到另一极的波多运动,67km,用微扰方法研究,自由振荡信号谱线分裂,自由振荡信号谱线分裂,17,自转,(Coriolis),长周期自由振荡信号谱线分裂主要受地球自转影响,18,质点在旋转球面上沿东西方向运动时，会受到竖直方向的科里奥利力。,科里奥利力,可改变环形振荡时质点的运动方向，从而导致本来只有水平位移的环形振荡具有,垂直,方向的分量。因此垂直向地震仪、重力仪也能记录到环形振荡信号。,地球横向不均匀,也会导致环形振荡产生,垂直,方向的分量,重力仪记录到的环形振荡信号,19,耦合,实际地球的自转、椭率、横向不均匀会导致自由振荡信号间的相互影响，使得自由振荡信号的频率和能量发生改变,使环形振荡垂直方向的分量增强,20,用超导重力数据检测长周期地球自由振荡信号,超导重力仪的布朗噪音大于弹簧重力仪以及宽带地震仪,超导重力仪不适合观测高频自由振荡信号。,在频率范围,1,1.5 mHz,，新型超导重力仪与最好的地震仪,STS-1,相差无几，而在频率低于,1 mHz,时，超导重力仪的噪音水平甚至低于宽带地震仪,STS-1/Z,。,观测微弱长周期自由振荡信号必须进行气压改正,Data and Results,21,在频率范围为,0.26,0.39mHz,的长周期自由频段中，法国超导重力仪,C026,的重力信号变化曲线与局部气压噪音变化曲线几乎完全重合。,在长周期自由振荡频段局部气压变化对重力观测信号的影响 （胡小刚,2007,）,22,在长周期自由振荡频段，局部气压导纳的值与气压变化的强弱有关，因此局部气压导纳又表现出很强的时间依赖性。,在长周期自由振荡频段局部气压变化对重力观测信号的影响（胡小刚,2007,）,23,7,个超导台站在,7,个长周期自由振荡子频段的气压导纳值以及气压与重力变化间的相关系数,（胡小刚,2007,）,子频段,0.260.39,0.390.52,0.520.65,0.650.78,0.911.04,1.041.56,1.562.08, corr., corr., corr., corr., corr., corr., corr.,C023,4.145,0.81,3. 934,0.77,3.268,0.63,2.817,0.55,2.407,0.32,1.415,0.21,0.071,0.05,C026,3.966,0.97,3.800,0.94,3.196,0.93,2.995,0.88,2.651,0.86,1.582,0.56,0.032,0.01,CD029-L,3.866,0.92,3.489,0.84,3.343,0.79,2.793,0.73,2.481,0.66,1.846,0.42,0.866,0.18,CD029-U,3.864,0.91,3.406,0.82,3.405,0.74,2.891,0.73,2.721,0.70,1.921,0.44,0.718,0.17,CD030-L,3.523,0.93,3.101,0.91,3.208,0.88,2.942,0.82,3.169,0.83,2.412,0.66,1.994,0.49,CD030-U,3.602,0.89,3.142,0.90,3.230,0.85,2.537,0.80,3.206,0.82,2.202,0.60,1.917,0.49,C031,3.151,0.85,2.406,0.73,2.563,0.68,1.964,0.61,2.425,0.58,1.359,0.38,0.627,0.16,CD037-L,3.450,0.72,3.394,0.67,2.468,0.50,3.218,0.60,1.907,0.32,1.415,0.21,0.471,0.05,RT038,4.074,0.82,3.416,0.70,3.240,0.51,1.981,0.32,2.587,0.30,1.675,0.04,2.243,0.13,表示气压导纳的绝对值，单位为,nms,-2,hPa,-1,。,corr.,为相关系数的绝对值。,24,2004,年,12,月,26,日苏门答腊大地震,5,小时后，,6,台超导重力仪观测数据的振幅谱，数据的长度为,1440,分钟,(60,小时,),，振幅谱的频率范围为,0.260.9 mHz,（胡小刚,2007,）,25,用小波方法消除潮汐信号；进行有效的气压改正，我们在国际上首次利用,单台,设备的观测数据，并在较高信噪比的情况下直接检测到了,2,S,l,的,3,个分裂峰,(,胡小刚,2007,),26,Rosat et al.(2004,）的观测结果,27,在国际上首次从重力记录中观测到,1,T,2,，,1,T,3,（胡小刚,2007,）,(1),时间长度为,45,小时,(2),时间长度为,60,小时。,28,0,S,2,的分裂,(,胡小刚,2007),29,Shen and Wu (2011): 0S2,的分裂,30,自由振荡的分裂参数,球形自由振荡的分裂参数对一维地球密度模型有线性约束作用,0S2,的五个分裂频率与其简并频率的关系：,31,Shen and Wu (2011): 0S2,的分裂,m=,-2,m=,-1,m=,0,m=,1,m=,2,Rosat et al.,(2003b) cf. PREM-re,-1.43E-04,9.00E-06,-1.35E-05,1.48E-04,-3.42E-04,Roult et al.,(2010) cf. PREM-re,-2.12E-05,2.77E-04,1.56E-04,2.44E-05,-1.02E-04,Abd El-Gelil et al.,(2010) cf. PREM-re,-1.70E-07,4.00E-05,2.32E-04,1.66E-04,-5.04E-05,This paper,cf. PREM-re,-1.20E-06,7.60E-05,1.73E-04,9.94E-05,-2.04E-05,Table 1.,Differences Between the Observations (by different authors) and the Model Predictions,for,0,S,2,Multiplet (Unit: mHz).,32,Shen and Wu (2011): 3S1,的分裂,33,3S1,观测结果（,Shen and Wu 2011,）,Model or author(s),m= -1,m=0,m=1,PREM-re,0.942267,0.944215,0.945472,PREM-re + SAW12,0.942925,0.944914,0.946144,Chao & Gilbert (1980),0.942705.5,e-5,0.945359.0,e-5,0.945634.0,e-5,Resovsky and Ritzwoller (1998),-,0.9443641.0,-,Roult et al. (2010),0.942561.241 e-4,0.944193.444 e-4,0.945791.493 e-4,This paper,0.942598,4.25,e-5,0.944113,2.65,e-4,0.945864,2.13,e-4,a,As a reference, this table also lists the observation of the frequency (m=0) of,3,S,1,given by Resovsky,and Ritzwoller (1998), who did not provide the triplet,3,S,1,.,Table 2.,Comparison of the Observed Triplet Frequencies of,3,S,1,Given in This Study with the Model Predictions,as well as the Corresponding Results Given by Previous Studies (Unit: mHz),a,34,3S1,观测结果（,Shen and Wu 2011,）,Author(s),m= -1,m=0,m=1,Obs.,PREM-re,Chao & Gilbert (1980),4.33,e-4,1.14,e-3,1.58,e-4,Resovsky and Ritzwoller (1998),-,1.49,e-4,-,Roult et al. (2010),2.93,e-4,-2.50,e-5,3.18,e-4,This paper,3.31,e-4,-1.02,e-4,3.92,e-4,Obs.,PREM-re + SAW12,Chao & Gilbert (1980),-2.25,e-4,4.36,e-4,-5.14,e-4,Differences,-,-5.50,e-4,-,Roult et al. (2010),-3.65,e-4,-7.24,e-4,-3.54,e-4,This paper,-3.27,e-4,-8.01,e-4,-2.80,e-4,Table 3,. Differences Between the Observations and the Model Predictions for the,3,S,1,Triplet (Unit,：,mHz),35,Conclusions,地球自由振荡是各种形式的驻波,驻波特性取决于地球结构,研究驻波有助于限制（了解、精化）地球模型,科学家已探测出多种模态,数据源：地震波书记（,IRIS,）；超导重力 数据（,GGP,）,Slichter,模的探测,各种模态的分裂的探测,36,Thanks for your attention,Copyright reserved by WenBin Shen,ma,il: wbshen,37,