关键词: 地磁测深, C-响应, 整体光滑, 异构数据, 海洋效应

Abstract: Geomagnetic depth sounding is an effective method for exploring deep structure of the earth. There are dense geomagnetic observatories in China, which lays a foundation to obtain the electrical structure of the transition zone and the upper part of the lower mantle beneath China. However, the corresponding C-responses estimation methods which are applied now cannot get the stable C-responses for many observatories. Thus, a large amount of geomagnetic data is wasted. Therefore, in order to make full use of the geomagnetic data, the estimation of C-responses needs to be systematically studied. Because of the heterogeneous characteristics of the data quality of China's geomagnetic observation data, such as the quality of the data, the length of the record, the types of data(absolute and relative observation)and data discontinuity condition, many geomagnetic data are abandoned, this limits the resolution of mantle electrical structure studies. In this paper, the following techniques are used to improve the stability of the data and increase the number of the available geomagnetic observatories, in the meantime, the stability of the C-responses curves can be effectively improved:1)obtaining the stable spectrums of the different components for each frequency by the BIRRP(Bounded Influence, Remote Reference Processing)software, and using the global smoothing technique to suppress data noise on geomagnetic data; 2)As for the geomagnetic data which only records the relative variation of the D, H and Z components and doesn't have the baseline value, the horizontal component is decomposed by the approximate estimation method to obtain the C-responses of the relative variation data, and then the relative variation data is used directly for the C-responses estimation; 3)the effects of discontinuous data and short-record data on C-responses estimation are discussed. Under normal conditions, the discontinuity of the data has little influence on C-responses, and when the data length is shorter than 5 years, we can hardly get the available C-responses whose periods are longer than 40 days. All these experiments can provide a basis for the data processing of these kinds of observation data; 4)for coastal observatories, the ratio method is used to eliminate the influence of ocean effect on the C-responses functions. After carefully processing the data of more than 100 geomagnetic observatories in China by the above techniques, the stable C-responses function of 42 observatories is finally obtained, among them, the number of the observatories with C-responses ranging from 1.3 to 113.7 days is 24, and the observatories with C-responses ranging from 1.3 to 42.6 days are 18. The techniques of this paper can process heterogeneous data well and obtain more stable C-responses, which provides more basic data for high-resolution geomagnetic depth sounding inversion researches in China.

Key words: geomagnetic depth sounding, C-responses, global smoothing, heterogeneous data, ocean effect