https://scholars.lib.ntu.edu.tw/handle/123456789/45144
標題: | 全球P波波速三維構造之多重尺度層析成像(2/2) | 作者: | 喬凌雲 | 關鍵字: | 全球P 波波速三維構造;全球遠距震央重新定位;經驗走時變化;多重尺度層析成像;Mantle P-heterogeneity;Global teleseismic earthquake relocation;Empirical traveltimes;Multiscale seismic tomography | 公開日期: | 2004 | 出版社: | 臺北市:國立臺灣大學海洋研究所 | 摘要: | 利用短週期走時資料進行層析成像以建構全球P波波速三維構造模型開始迄今十九年以來,對於提供地球深層重要的構造線索,以至於系統化的改變地球物理學者對於地表觀測與深部動力機制聯繫的瞭解已有深遠之影響。 It has already been 19 years since the first global seismic traveltime tomography using the short period teleseismic P-arrivals. Significant contributions made upon improving our knowledge of the deep interior of the Earth have been made. In recent years, due to the fast accumulation of traveltime data of improved quality, the continuously growing computing-power and the development of inversion techniques, more and more global models of P velocity heterogeneity, each with their own nominal resolution, have been reported from different research groups. However, there are still significant controversies among these published models in terms of highlighting the structure of the deep interior of the Earth. These ambiguities might be attributed to either different adopted data sets or different schemes of parameterization, regularization and inversion algorithms. We have established communication with Dr. Engdahl of the United States Geological Survey (USGS), and obtain and compiled the updated travel time data since Engdahl et al. (1998). They have relocated hundred-thousands of events that are well-constrained teleseismically by arrival-time data reported to the International Seismological Centre (ISC) and to the U.S. Geological Survey’s National Earthquake Information Center (NEIC). We believe that by adopting the same data set, it is a good opportunity to clearly appraise the implications of the inverted P-velocity model obtained from different inversion techniques. Up to now, we have succeeded, within this research, developing the first fully 3-D, linear spherical wavelet bases that significantly improves upon the discontinuity problem embedded within the original spherical Haar basis developed by our previous work (along with the derivation of the 3D Gaussian sampling and weighting functions needed for the high order approximation of the numerical integration that builds the Gram matrix); as well as building the Empirical TravelTimes (ETT) directly from the observed traveltime data and constitute a better set of summary rays that both reduces the total amount of observations and improves the sampling geometry without sacrificing useful information embedded within the raw data. 1 Preliminary inversion performed upon the subset built from the 1998-2001 data has revealed results similar to tomographic models built by other leading groups. That is, we have very good correlation between the P-velocity structure and the dynamics implied from the surface tectonics such as the distribution of ridges and subducted slabs within the top of upper mantle (above about 400 km depth); and the pronounced large-scale 2 L , lowermost mantle structure. It is unfortunate that our current setup cannot handle such humongous size of the Engdahl data set (over millions of rays for just the 1998-2001 subset) even after we have cleverly go through the summary ray processing by the previously mention, new EET scheme. To overcome this difficulty is certainly the most important focus of our future work such that the multiscale tomography that has been developed by our group that is the only inversion scheme naturally equipped with a non-stationary regularization scheme and may potentially pushes the resolution to the upper limit of what the data constraints might impose. We will continue our research in this respect. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/14851 | 其他識別: | 922611M002021 | Rights: | 國立臺灣大學海洋研究所 |
顯示於: | 海洋研究所 |
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