贝叶斯算法在拟合自由核章动参数中的应用

用高精度重力技术检测地球自由核章动(FCN)参数(包括周期和Q值等)的难点是资料观测信噪比低,传统的方法是使用最小二乘拟合,但是获得的FCN共振参数精度不理想.本文利用武汉国际潮汐基准站高精度超导重力仪和全球超导重力仪观测的时变重力资料,根据贝叶斯算法拟合地球自由核章动(FCN)参数.我们将贝叶斯拟合方法与传统最小二乘法实施了对比分析,研究了不同台站资料差异.讨论了潮波选择和不同海潮模型等因素对FCN参数的影响.结果表明用贝叶斯算法获得的FCN品质因子与空间大地测量VLBI结果吻合的更好,这说明贝叶斯算法可靠性高,为研究地球深内部构造参数(核幔边界粘滞系数等)提供了有效依据.     

超导重力仪检测2011年日本东北Mw9.0级地震前的重力扰动信号

对大地震前的扰动现象的研究有助于认识地震孕育的动力学过程,震前重力扰动已成为关注的热点之一. 对大地震前的扰动现象的研究有助于认识地震孕育的动力学过程,震前重力扰动已成为关注的热点之一. 为检验日本M_w9.0级地震是否存在震前扰动现象,本研究利用全球超导重力仪记录到的地震前后7天内20组秒采样数据进行分析. 经潮汐、大气改正等处理去除仪器的漂移及残余潮汐效应,得到非潮汐重力变化曲线.结果表明大部分振幅大于30×10^-8 m·s^-2的曲线反映了全球M_w≥6级地震引起的高频波动信号,其中11组数据在3月9日M_w7.3级前震之前出现了扰动现象.震前扰动可分解为三个频段,其中,低于0.1 Hz和高于0.18 Hz的分量分别反映了地震波动信号及非构造信息,中间频段(0.118~0.18 Hz)信号能够较大程度地压制地震波动信号、并同时保留异常扰动信息.它的振幅在3月7日10时之前基本保持约1×10^-8 m·s^-2,之后开始逐渐增大,到3月9日7.3级前震前后达到最大,此后振荡衰减,振幅保持约(5~10)×10^-8 m·s^-2,直至主震发生.中间频段信号的变化特征与主震前的应力迁移过程以及实验记录到的地震成核过程有许多相似之处;不过,震前重力异常是否与主震前的应力加速积累有关,仍待进一步研究.     

Anomalous Signals Prior to Wenchuan Earthquake Detected by Superconducting Gravimeter and Broadband Seismometers Records

Using 1 Hz sampling records at one superconducting gravimeter(SG) station and 11 broadband seismometer stations,we found anomalous signals prior to the 2008 Wenchuan(汶川) earthquake event.The tides are removed from the original SG records to obtain the gravity residuals.Applying the Hilbert-Huang transform(HHT) and the wavelet analysis to the SG gravity residuals leads to time-frequency spectra,which suggests that there is an anomalous signal series around 39 h prior to the event.The period and the magnitude...     

Loading effect of a self-consistent equilibrium ocean pole tide on the gravimetric parameters of the gravity pole tides at superconducting gravimeter stations

The gravimetric parameters of the gravity pole tide are the amplitude factor δ, which is the ratio of gravity variations induced by polar motion for a real Earth to variations computed for a rigid one, and the phase difference κ between the observed and the rigid gravity pole tide. They can be estimated from the records of superconducting gravimeters (SGs). However, they are affected by the loading effect of the ocean pole tide. Recent results from TOPEX/Poseidon (TP) altimeter confirm that the ocean pole tide has a self-consistent equilibrium response. Accordingly, we calculate the gravity loading effects as well as their influence on the gravimetric parameters of gravity pole tide at all the 26 SG stations in the world on the assumption of a self-consistent equilibrium ocean pole tide model. The gravity loading effect is evaluated between 1 January 1997 and 31 December 2006. Numerical results show that the amplitude of the gravity loading effect reaches 10⁻⁹ m s⁻², which is larger than the accuracy (10⁻¹⁰ m s⁻²) of a SG. The gravimetric factor δ is 1% larger at all SG stations. Then, the contribution of a self-consistent ocean pole tide to the pole tide gravimetric parameters cannot be ignored as it exceeds the current accuracy of the estimation of the pole tide gravity factors. For the nine stations studied in Ducarme et al. [Ducarme, B., Venedikov, A.P., Arnoso, J., et al., 2006. Global analysis of the GGP superconducting gravimeters network for the estimation of the pole tide gravimetric amplitude factor. J. Geodyn. 41, 334–344.], the mean of the modeled tidal factors δ_m = 1.1813 agrees very well with the result of a global analysis δ_CH = 1.1816 ± 0.0047 in that paper. On the other hand, the modeled phase difference κ_m varies from −0.273° to 0.351°. Comparing to the two main periods of the gravity pole tide, annual period and Chandler period, κ_m is too small to be considered. Therefore, The computed time difference κ_L induced by a self-consistent ocean pole tide produces a negligible effect on κ_m. It confirms the results of Ducarme et al., 2006, where no convincing time difference was found in the SG records.     

武汉和京都台站超导重力仪高精度潮汐重力观测结果

利用高精度潮汐重力场观测研究地球物理学和地球动力学问题已成为当今地学工作者的共识.由于某些信号十分微弱且具有区域和全球分布特征,相当一部分信号被混合在常规仪器的观测噪声水平上,因此获得全球分布的第一手高精度观测资料显得尤为重要.超导重力仪具有精度高,连续性和稳定性好等特征,期望能在测定区域和全球重力场的精细结构方面发挥重要作用.有18个台站参加的全球地球动力学合作项目于1997年7月份开始实施,其主要目的是解决诸如固体潮、地核近周日晃动、核模、地球自转和极移,地球和大气海洋的耦合机理以及由构造运动引起的重力场变化等热点问题.我们曾研究过中比法三国的超导重力仪潮汐观测资料,获得了欧洲和亚洲不同地区潮汐常数及分布特征.本文将利用武汉和日本京都三台超导重力仪观测资料研究亚洲地区大陆和海岛上的潮汐波振幅因子和相位滞后的时间变化特征以及各参数的误差估计等,同时将检测由大气和海潮变化产生的重力信号.文章分数据处理方法、潮汐参数测定、大气重力信号、海潮重力信号、潮汐参数的时间变化、非潮汐重力场变化特征等几方面叙述.     

Precise tidal gravity recorded with superconducting gravimeters at stations Wuhan (China) and Kyoto (Japan)

 Three long series of tidal gravity observations, totalizing approximately 24 years and recorded with three superconducting gravimeters, T004, T008, and T009, at stations Wuhan (China) and Kyoto (Japan), are studied. The tidal amplitude factors and phase differences are determined precisely using Eterna and Nsv techniques. The precision of the main tidal amplitudes is at the same level of 0.01 μGal. The atmospheric gravity signals are corrected using the coefficients determined with a regression method between tidal gravity residual and station air pressure. The oceanic gravity signals are modeled based on five global oceanic models. It is found that the oceanic models developed by the analysis of measurements from Topex/Poseidon altimeters have the best fit to the superconducting gravimeter measurements, since the observed residuals and the discrepancies between the amplitude factors and the theoretical tidal models are reduced more significantly. The long-period gravity variations are dominated by the non-linear drift phenomena of the instruments, and the short-term variations in gravity are due to the background noise at the stations. Received: 20 January 2000 / Accepted: 15 September 2000     

重力场的潮汐变化观测及其研究

基于我国武汉超导重力仪长周期序列潮汐观测数据,研究了重力场潮汐变化特征,精密确定了地球潮汐常数,讨论了重力观测中的海潮负荷和大气效应问题;根据地球自由核章动在周日重力潮汐观测中的共振效应确定了自由核章动的复本征周期和品质因子Q值,研究了极移重力效应;并对进一步利用重力潮汐观测研究地球物理问题进行了讨论。     

运输工具对相对重力仪测量精度的影响分析

简要介绍了当前常用重力仪类型和标称精度,并就运输工具性能好坏、重力测段大小、路线距离长短和观测时间长短对相对重力仪的观测精度的影响进行测定分析,结果表明:影响重力仪观测精度的主要因素与汽车运输工具有关,选择越野性能好,减震效果好的汽车作为完成高等级流动重力测量任务的前提条件。     

超导重力仪观测数据分析

超导重力仪作为目前研究时变重力场的主要仪器具有很高的灵敏度和稳定性、很低的噪音水平和漂移以及很宽的动态频率响应范围。探测时间序列中隐含的周期信号是超导重力仪观测数据分析的主要目标之一,通过快速傅里叶变换(FFT)和最小二乘谱分析方法分析超导重力数据中隐含信号的检测,并对两种方法结果进行了分析比较。并最终用小波分析的方法进行了检校。     

Shallow-water loading tides in Japan from superconducting gravimetry

Gravity observations from superconducting gravimeters are used to observe loading effects from shallow-water tides on the Japanese east and west coasts. Non-linear third-diurnal and higher-frequency shallow-water tides are identified in the tide-gauge observations from these coastal areas. The most energetic constituents in the tide gauge observations are also seen in the gravity observations due to their loading effects on the deformation of the Earth. Even though the shallow-water tides at the Japanese east coast have an amplitude of only a few millimetres, they are still able to generate a loading signal at gravity sites located several hundred kilometres inland. In particular, the S₃, S₄ and S₅ solar tides occur in both gravity and tide gauge observations. It is indicated that in other shelf regions with large shallow water tides, the shallow water loading signals account for a significant signal, which should be taken into account.Acknowledgement The authors would like to thank the Hydrographic and Oceanographic Department (Japan Coast Guard), Japan Meteorological Agency and Hokkaido Development Agency for access to the tide-gauge data. Also, the Global Geodynamic Project Information System and Data Center (GGP-ISDC) is acknowledged for providing the gravity data.