Detection of the oscillations of Earth's core by a collaboration observation with superconducting gravimeters and laser strain meters-Comparison between the Kamioka site and Matsushiro site-

这项研究计划探测来自地核的微弱简正模式信号，基于在神冈和松城使用两台超导重力仪(SGS)的观测，并通过比较设置在神冈的超导重力仪和激光应变仪。筑波大学的池田和JSPS的Severine Rosat在项目期限内作为合作研究人员加入了这个项目。1.发展了一种新的非线性简正波分析方法，可将简正波的频率和Q值作为未知参数处理；2.分析了神冈、松下和南极雪花台等全球SG网获得的主要是苏门答腊-安达曼地震(Mw=9.0-9.3)的SG记录；3.改进了激光应变仪的质量和对苏门答腊-安达曼地震记录的分析；4.提高了区域大气…重力效应的估计精度5.考察用于海潮改正的现代全球海洋潮汐模型的精度，并通过模型计算结果与三陆海域海底压力测量的实际数据进行对比，研究非潮汐海面高度变化；6.利用绝对重力仪提高SG标度因子的定标精度。2004年12月26日，神冈新安装SG时，两个月后，苏门答腊-安达曼地震发生。径向基模OS_o是由地球周长变化引起的全球形变组成的，它的时间衰变一直被观测到，直到2005年3月28日第二次苏门答腊岛地震在许多SG站点发生。这项研究的一个显著结果是：我们成功地揭示了_OS_o模不仅与纬度有关还与经度有关的地理幅度分布，这可能反映了地球结构的大尺度横向不均匀。基于法国斯特拉斯堡和澳大利亚堪培拉获得的苏门答腊-安达曼地震的两个SG数据集，利用本项目开发的新的分析方法，试图找出Slichter三元组和核心底音等微弱的核心信号。虽然我们发现了一些与这些模式密切相关的峰值，但分析结果还没有揭示出这样的内核信号，因为这两个站点通常不会观测到一些频谱峰值。苏门答腊岛事件激发的海啸波的影响也被安装在Syowa站的几台仪器观测到，其中包括SG。我们将预测的海啸效应与SG和SST-1观测到的结果进行了比较。提高Syowa站周围水深测量的精度是提高观测值与预报值对比精度的关键。较少

This research project was planed to detect weak normal mode signals from the Earth's core based on the observations with two superconducting gravimeters (SGs) at Kamioka and Matsushiro and by a comparison between the SG and laser strain meters set at Kamioka. H. Ikeda of the Tsukuba University and Severine Rosat of JSPS fellow did join to this project as the cooperative researchers though the term of the project.We have done the followings ;1.Developing a new non-linear analysis method for the normal mode analysis, which can treat both the frequency and Q-value of normal modes as unknown parameters,2.Analysis of the SG records mainly of the Sumatra-Andaman earthquake (Mw=9.0-9.3), which were obtained from the world wide SG network including Kamioka, Matsushiro and the Syowa Station in Antarctica,3.Improving the quality of the laser strain meter and the analysis of the records of the Sumatra-Andaman earthquake,4.Improving the estimation accuracy of gravity effect of the regional atmosph … More eric air mass changes,5.Investigating the accuracy of modern global ocean tide models, which are used in the correction for the ocean tides, and also studying the non-tidal sea surface height variations by comparing some model computation results with the actual data obtained from the ocean bottom pressure measurements in Off-Sanriku,6.Improving the calibration accuracy of the scale factor of SG by using an absolute gravimeter.In December 26th 2004, two months later when the SG was newly installed at Kamioka, the Sumatra-Andaman earthquake occurred. The fundamental radial mode _oS_o, which consists of a global deformation of the Earth with changes in its circumference, has been strongly excited by this event and its time decay has been observed till the occurrence of the second Sumatra event in March 28th 2005 at many of SG sites. A notable result obtained by this research project is; we have succeeded to reveal that the _oS_o mode shows a geographical amplitude distribution depending on not only the latitude but also on the longitude, which may reflect a large scale lateral inhomogeneity in the Earth's structure. The observed geographical pattern is consistent with the model prediction based on a 3-D seismic tomography model.Based on the two SG data sets for the Sumatra-Andaman event, which were obtained at Strasbourg (France) and Canberra (Australia) and using the new analysis method developed by this project, we have tried to find out such weak core signals as the Slichter triplets and the core undertones. Although we found some peaks to be closely related to these modes, the analysis results have not revealed such inner core signals yet, because some spectrum peaks fond are not observed commonly at these two sites.The effect of tsunami waves excited by the Sumatra event was also observed by several instruments set at the Syowa Station including the SG. We have compared the predicted tsunami effects with those observed from the SG and SST-1. Improvement of the accuracy of the bathymetry around the Syowa station is essential to improving the comparison accuracy between the observations and predictions. Less