Detection and interpretation of the Earth's free oscillations excited by the great Sumatra-Andaman earthquake with GGP station data

The mode serials of the Earth’s free oscillation provide some important information on the Earth’s deep structure and superconducting gravimeters （SG） can investigate the phenomena of the Earth’s free oscillations with high accuracy. The great Sumatra-Andaman earthquake fully excited the Earth’s free oscillations and these signals were perfectly recorded by five superconducting gravimeters in the globe. After the pre-treatment and spectral analysis on the SG observation data, we obtained the experimented mode serials of the Earth’s free oscillations consisting of 147 modes with GGP station data. These observed modes were themselves some new important data for the study of the Earth’s deep structure. On the basis of the discussions on some checked inner-core-sensitive modes, we distinguished three layers from the inner core, and the boundary of the upper layer was compatible with the formerly known transition zone in the inner core based on seismic body waves and supported that there were the hemispherical variation and very lower shear velocity zone in the lower inner core.

Detection of Earth's free oscillation excited by the Japan Mw9.0 Earthquake using different tiltmeter and strainmeter

The observatory network of the Crustal Deformation China Seismological Bureau was equipped with vertical pendulum tiltmeter,borehole tiltmeter,tunnel extension meters,multi-component borehole strainmeter,body strainmeter and other tilt and strain observation instruments.All of these instruments have recorded the Earth’s free oscillation excited by the Japan Mw9.0 Earthquake.By analyzing those observations,all of the spheroidal oscillation modes(0S3-0S30)and toroidal oscillation modes(0T3-0T20)excited by the Japan Mw9.0 Earthquake were detected in this paper.In addition,comparing the different observation results which obtained by those instruments,we revealed their capacity to observe different kinds of oscillation and different frequency band modes,and analyzed report the reason.We found that the body strainmeter and the vertical pendulum tiltmeter have better observing results for spheroidal oscillation.Because of high noise in low frequency band,the borehole tiltmeter cannot observe the low-order spheroidal oscillation.In terms of observing the toroidal oscillation,the multi-component borehole strainmeter got a best result.The vertical pendulum tiltmeter observes a few toroidal oscillation modes,and the tunnel extension meters can only observe some low-order modes.

Detecting the Earthquake Excited Spheroidal Free Oscillation of the Earth by Use of Observational Data at Huzhou Seismic Station

By using the digital observations of the pendulum tiltmeter, water tube tiltmeter,extensometer and volumetric strainmeter at Huzhou station and with the power spectrum density estimation method,we acquired the_0S_5-_0S_50 fundamental sphere free oscillations caused by the Japan earthquake on March 11,2011,then compared it with the PREM model. The relative errors are mostly bigger than 1.2‰. The extensometer and volume strainmeter can clearly detect _0S_2,_0S_3and_0S_4,which are closely related to the deep structure and earth's interior.

Earth's Free Toroidal Oscillations Observed by the JCZ-1 Seismometer

We firstly detected the Earth's free toroidal oscillations excited by three large earthquakes in Japan,2011,Chile,2010 and Indonesia,2005 from the observed data of the JCZ-1 seismometer at Wuhan Seismic Station. The eigenperiods of basic modes (0T2 - 0T67 ) and first modes (1T2 ～ 1T50 ) were detected,and their error ratios were less than 0. 5% by comparing the observed eigenvalues with the theoretical eigenvalues in PREM. We supplemented some modes- 0T11,0T15 , 0T19 , 1T4 , 1T5 and 1T14 ,which were not mentioned in PREM,and also observed the spectral line multi-peak phenomenon from 0T2, 0T6 , 0T7 and 0T8 . These results show that the JCZ-1 seismometer is able to precisely observe the Earth's long period toroidal free oscillations.

Spheroidal oscillations of the Earth stimulated by the Sumatra-Andaman earthquake with CDSN data

The 0S2-0S54 spheroidal modes of Earth＇s free oscillations, triggered by the great Sumatra-Andaman earthquake of 26 December 2004 are retrieved from VHZ data recorded by seven upgraded stations of China Digital Seismograph Network （CDSN）. We compare these spheroidal modes with theoretical free oscillation spectra calculated from the Preliminary Reference Earth Model （PREM） and find a coincidence between their periods. Spectral splitting phenomenon is observed obviously in 0S2, 0S3, 0S4, 2S1 and 1S2 free oscillation modes. What is most noticeable is that the oscillation mode 2S1 is reported for the second time （the first time by Rosat et al） without any data stacking. We simulated the split singlet of 0S2 mode on seven CDSN stations based on general focal mechanism and seismic moment of the earthquake. The result shows that seismic moment of the earthquake can reach 10^23 N.m. We also find that the recording of Earth＇s free oscillations carries abundant information of source mechanism and earthquake location, which is applicable to the detailed study of source rupture parameters.

Spheroidal Oscillations in the Earth Excited by the Wenchuan Earthquake

Based on the digital observational data from pendulum tilt-meters and water tube tilt-meters, the spheroidal free oscillations of the Earth, excited by the M_S8.0 Wenchuan earthquake of May 12, 2008, were obtained using the method of power spectral density estimation without any calculation to erase solid tides. The result matches well with the PREM results. Compared to the theoretical free oscillation from the PREM model, all relative errors are concentrated on 0.1% except for _0S_7, whose relative error is greater than 0.3%. This research provides a new method to determine the spheroidal modes of Earth's free oscillations from observations of the pendulum tilt-meter and water tube tilt-meter, which may be useful in the future study of the Earth's free oscillations.

Process Analysis of In-situ Strain during the M_s8.0 Wenchuan Earthquake—Data from the Stress Monitoring Station at Shandan

There were huge life and property losses during the Ms8.0 Wenchuan earthquake on May 12, 2008. Strain fluctuation curves were completely recorded at stress observatory stations in the Qinghai-Tibet plateau and its surroundings in the process of the earthquake. This paper introduces the geological background of the Wenchuan earthquake and the profile of in-situ stress monitoring stations. In particular, data of 174 earthquakes （Ms4.0-Ms8.5） were processed and analyzed with various methods, which were recorded at the Shandan station from August 2007 to December 2008. The results were compared with other seismic data, and further analyses were done for the recoded strain seismic waves, co-seismic strain stepovers, pre-earthquake strain valleys, Earth＇s free oscillations before and after the earthquake and their physical implications. During the Wenchuan earthquake, the strainmeter recorded a huge extensional strain of 70 seconds, which shows that the Wenchuan earthquake is a rupture process predominated by thrusting. Significant precursory strain anomalies were detected 48 hours, 30 hours, 8 hours and 37 minutes before the earthquake. The anomalies are very high and their forms are very similar to that of the main shock. Similar anomalies can also be found in strain curves of other shocks greater than Ms7.0, indicating that such anomalies are prevalent before a great earthquake. In this paper, it is shown that medium aftershocks （Ms5.5- 6.0） can also cause Earth＇s free oscillations. Study of free oscillations is of great significance to understand the internal structure of the Earth and focal mechanisms of earthquakes and to recognize slow shocks, thus providing a scientific basis for the prevention and treatment of geological disasters and the prediction of future earthquakes.

Relationships between Earth’s Rotation or Revolution and Geographical Extent of the Global Surface Monsoons

Monsoon seasons, occasionally also known as wet seasons or trade-wind littoral seasons, are found in the regions where there is a complete seasonal reversal of the prevailing surface winds. Accompanying these shifts in the prevailing surface winds are modulations in rainfall activity. Given the fact that our knowledge of the monsoons is mainly based on the interpretation of the mean values of precipitation, cloudiness and winds;relationships between earth’s rotation or revolution and geographical extent of the global surface monsoons deserve to be highlighted. In the abundant literary and audiovisual production devoted to monsoons worldwide and despite the fact that everyone agrees with physical law which shows that Coriolis force acts to the right in the northern hemisphere (to the left in the southern hemisphere), there is no reference to the relationship between Coriolis force (due to earth’s rotation) effects on troposphere general circulation and geographical extent of the global surface monsoons. Furthermore knowing that the ITCZ oscillations on either side of the equators (due to earth’s revolution) determine the seasons (mainly winter and summer), it is clear that earth’s revolution also plays a crucial role in the seasonal reversal of the prevailing surface winds observed in the regions where monsoons are found. Our main objective is to provide a rational answer to the question: what is a monsoon?

Check of Earth's free oscillations excited by Sumatra-Andaman Large Earthquake and discussions on the anisotropy of inner core

Sumatra-Andaman Large Earthquake on Dec. 26,2004 generated not only the Indian Ocean Tsunami but also the Earth's free oscillations (EFO). The signals of Earth's free oscillations were perfectly re-corded by the superconducting gravimeter C0-32 at Wuhan station in China. After the pre-treatment and spectral analysis on the observational data from Wuhan station,we obtained more than ninety EFO modes including 42 fundamental modes,2 radial modes and 49 harmonic modes. On the basis of the discussions on some observed harmonic modes and abnormal splitting phenomena,we considered that the real rigidity might be lower than the theoretical prediction of PREM model in the inner core and however the anisotropy of compressive wave was brightly higher than the present estimations in the inner core. This suggested that the anisotropy of the inner core could be much more complicated than our present understanding,and there might be some new geophysical phenomena in the formation process of the inner core.

Detection of spheriodal free oscillation excited by Peru 8.2 M_(s) earthquake with five international superconducting gravimeter data

In this paper, authors obtain the spectral peaks of the earth free oscillation and check all normal modes from 0S0 to 0S48 accurately, with the Fourier analysis and the maximum entropy spectrum method dealing jointly with six groups of the observational residual data from five international superconducting gravimeter stations. By comparing the observational results in this paper with three former groups of observations or models, authors notice an extra discrepancy between two observational 0S2 modes excited separately by Peru earthquake and Alaska earthquake, which probably mirrors the anisotropy of the Earth's inner core. The analysis on the splitting 1S2 mode shows that the asymmetric factor of rotationwise spectral splitting is possible to be different from that of anti-rotationwise spectral splitting.

THE PARAMETER KERNELS FOR THE LINEAR INVERSION OF THE FREE OSCILLATION OF THE EARTH (Ⅰ)

In the linear inversion of the radial variation of the parameters of the Earth by usingthe observed frequencies of various normal modes of free oscillation of the earth, it is neces-sary to know the values of the kernels of the parameters ρ, μ and λ. This paper describesthe methods of the derivation of the formulas of these kernels. This is the first part of thepaper in which only the toroidal oscillations are considered. They are much simpler thanthose of the spheroidal ones, that we will consider in the second part of the paper. The data of the two types of oscillations are equally important in the solution of theinversion problem, and should be employed simultaneously, and we know that the toroidaloscillations are much simpler than the spheroidal ones, it seems wise to divide the whole programof the inversion problem into steps: first, by employing the toroidal data to correct the twoparameters ρ and μ in the mantle, then by using the spheroidal data to correct the remain-ing parameters, i.e.

Constraining the focal mechanism of the Lushan earthquake with observations of the Earth's free oscillations

The amplitudes of the Earth's free oscillations have a close relationship to earthquake focal mechanisms. Focal mechanisms of large earthquakes can be well analyzed and constrained with observations of long period free oscillations. Although the 2013 Lushan earthquake was only moderately sized, observable spherical normal modes were excited and clearly observed by a superconductive gravimeter and a broadband seismometer. We compare observed free oscillations with synthetic normal modes corresponding to four different focal mechanisms for the Lushan earthquake. The results show that source parameters can be analyzed and constrained by spherical normal modes in a 2.3–5 mHz frequency band. The scalar seismic moment M0 has a major influence on the amplitudes of free oscillations; additionally, the strike, dip, rake and depth of the hypocenter have minor influences. We found that the synthetic modes corresponding to the focal mechanism determined by the Global Centroid Moment Tensor show agreement to the observed modes, suggesting that earthquake magnitudes predicted in this way can readily reflect the total energy released by the earthquake. The scalar seismic moment obtained by far-field body wave inversion is significantly underestimated. Focal mechanism solutions can be improved by joint inversion of far- and near-field data.

由中国CDSN台网检测到的汶川地震所激发的地球球型自由振荡

2008年5月12日汶川发生M8．0特大地震，这次特大地震使得地球自身产生了整体的连续振动。本文采用地震发生之后中国数字地震台网（CDSN）所记录到的5天地震波形，对VHZ频段进行了功率谱密度分析。由于CDSN台网的地震仪对低频信号具有压制特点，所以没有对资料进行固体潮处理，从而获得了大地震激发的73个（0S4～0S76）基频球型自由振荡和6个谐频球型自由振荡（1S2，3S2，1S4，1S0，1S7，4S2），并与PREM模型的理论自由振荡周期进行了对比，结果表明观测振荡周期与PREM预测的振荡周期吻合很好。所得结果可以进一步用来研究地震震源机制和地球内部结构。并对大地震的震源破裂分布给出一定的约束。

利用SG-C053超导重力仪检测智利8.8级地震激发的地球自由震荡

利用SG-C053超导重力仪的观测资料,研究了2010年2月27日智利Ms8.8地震引发的球形自由振荡0S0～0S48的所有基频振型,检测结果与PREM模型的理论值相比,二者基本相符。

Li_2CO_3/K_3PO_4复合助熔剂对新型Y_2O_2S:0.09Ti长余辉磷光体发光性能的影响

采用高温还原法合成了一种新型无稀土掺杂Y2O2S：0．09Ti长余辉发光材料。基于助熔剂种类对长余辉发光材料特性的重要作用，选择了对余辉衰减初期和后期余辉强度有明显作用的Li2CO3和K3PO4两种助熔剂，研究了不同配比（以下用x表示，x=Li2CO3／（Li2CO3＋K3PO4））的复合助熔剂对Y2OS：0．09Ti磷光体晶体结构和发光性能的作用，以获得具有较好综合发光性能的Y2O2S：0．09Ti磷光体。采用PL光谱和余辉测试仪对材料的发光特性进行了表征，用XRD研究了其晶体结构的变化。XRD结果表明，在复合助熔剂范围内（x=0-1．0）均可获得单相性的Y2O2S：0．09Ti磷光体。同时发现复合助熔剂比例不同制备的样品中，Y2O2S：0．09Ti磷光体晶体择优取向也发生明显的变化，且高比例Li2CO3有助于Y2O2S：0．09Ti磷光体的晶体形成。复合助熔剂比例x对样品的激发峰与发射谱主峰位置（565nm）基本没有影响；但助熔剂比例x对发射峰强度则有明显影响，随着x增加，该磷光体的发光强度先增后减，在x=0．8时发光强度最大。

Check of free oscillation signal with SG data

The observation of the Earth’s free oscillation is an important way to study the Earth’s inner structure and geophysical parameters. Many geophysicists have investigated the Earth’s normal modes with strainmeters and spring gravimeters. Since the superconducting gravimeters appeared, people have gained a new kind of more stable instruments to detect the normal modes. The measurement for the Earth’s free oscillation with the superconducting gravimeters is one of the main goals of the Global Geodynamics Project. In this note, we have investigated the Earth’s normal modes excited by Peru Ms 7.9 Earthquake on June 23, 2001 with the superconducting gravimeter C032 at the Wuhan station. After having completed the subtraction of gravity tides with the 20th order polynomial fitting, and the correction for pressure and the analysis of the noise spectrum of the superconducting gravimeter, we accurately observed all base normal modes from 0S0 to 0S32 and the splittings of 0S2 and 0S3. Those results show a good

Multichannel singular spectrum analysis of the axial atmospheric angular momentum

Earth＇s variable rotation is mainly produced by the variability of the AAM（atmospheric angular momentum）. In particular, the axial AAM component X_3, which undergoes especially strong variations,induces changes in the Earth＇s rotation rate. In this study we analysed maps of regional input into the effective axial AAM from 1948 through 2011 from NCEP/NCAR reanalysis. Global zonal circulation patterns related to the LOD（length of day） were described. We applied MSSA（Multichannel Singular Spectrum Analysis） jointly to the mass and motion components of AAM, which allowed us to extract annual, semiannual, 4-mo nth, quasi-biennial, 5-year, and low-frequency oscillations. PCs（Principal components） strongly related to ENSO（El Nino southern oscillation） were released. They can be used to study ENSO-induced changes in pressure and wind fields and their coupling to LOD. The PCs describing the trends have captured slow atmospheric circulation changes possibly related to climate variability.

THE COMPONENT OF 29.8 YEARS IN POLAR MOTION AND △ l. o.d. AND OSCILLATION OF EARTH'S INNER CORE

This paper deals with the components of pcriod of 29.8 yr in polar motion and △ I. o. d. The oscillation of inner core (OIC), as a most possible cause of them, is proposed. Parameters of oscillation are found and its effects on Earth’s mass center (EMC), distance of observatories to EMC, gravity and latitude are estimated.

THE OSCILLATION OF CERTAIN ZONAL MEAN CHARACTERISTICS OF MOTION ON A SPHERIC EARTH'S ATMOSPHERE——PART 2:ANISOTROPIC QUASI-EDDY MOTION

This paper is an extension of the author's paper (Xie,1982) to the spherical earth.It is found that the simi- lar results are obtained under the assumption of isotropic distribution of horizontal kinetic energy along the zonal and meridional directions.It points out the limitation of the results already obtained and paves the path for the approach of anisotropie semi-eddy or quasi-eddy motion of the atmosphere.

新疆钻孔体应变资料提取地球自由振荡研究

基于功率谱方法,利用新疆铁门关台、温泉台、乌什台3套钻孔体应变资料提取2011年3月11日日本9.0级地震激发的地球自由振荡信息,将观测值频率与PREM模型理论值进行对比分析。结果表明,实测值与理论值基本一致,验证了PREM模型的准确性,显示出利用体应变资料提取地球自由振荡信息的可行性。3个台提取结果显示出一些共性和差异,与震源条件及钻孔所处地质构造有关。