In order to investigate the characteristics of short period geomagnetic variations in Shaanxi region, a temporary measurement profile from Shiquan in the southern part of Shaanxi to Ningxian in Gansu was set up in September of 1996 to carry out simultaneous observation of three-component geomagnetic variations along the profile. The vertical transfer functions, the horizontal transfer functions and the spectral component's relationship of each period segment at each site in the period range from 3 min to 2 h were statistically calculated. Random data theory was applied to the data processing for reference, which led to a relatively good result. Analysis of the data point out that short period geomagnetic variations are affected by the regional influence of underground anomalous inductive current concentration between Wugong and Qianling in the nearly E-W direction and by the influence of local inductive current in nearby area of measurement site. The main distribution feature is that vertical transfer functions reverse between Wugong and Qianling and frequency responses of the transfer functions have maximum at period about 20 min.
In this paper, the magnetotelluric response to 3-D earth topography was studied using the finite difference method for rectangular cells. Three numerical modeling calculations were carried out; the results indicate that the finite difference method is applicable to the magnetotelluric problem in estimating the 3-D topographic responses.
In late December of 1991, observation of three-component geomagnetic short period variations was carried out in Chengmai county of Hainan province, along a short measurement profile with small spatial intervals of detection points. Within the period range of 20 s to 500 s, we have discovered that the vertical variations are basically correlated with the horizontal variations in north direction in all measurement points, the real parts of complex transfer functions demonstrate that an asymmetric spatial variation of short wavelength superimposed on regional monotonic tendencious spatial variation. Inversion of the observed data along the small profile was carried out by using the invention method of generalized inverse matrix of fmite element forward calculation for the electromagnetic induction of the 2-D conductivity model to investigate the conductivity structure of the profile. We conclude that the anomaly of geomagnetic short periodic variation in the small area originated from the Wangwu-Wenjiao fault in the northern part of Hainan island.Key words: geomagetic variation anomaly of short period magneto-variational sounding magnetic transfer funtion inversion of generalized inverse matrix *
A temporary profile from Shiquan in the southern part of Shaanxi Province to Ningxian in Gansu Province for observation of geomagnetic short period variations was set up. The characteristics of geomagnetic short period variations in the profile region was analyzed through geomagnetic transfer functions at measurement sites (Fan, et al, 1998). According to the theory of multi-scale analysis of wavelet transform, the components affected by regional origin in the region is extracted in this paper. The components of regional origin is used as original data in the inversion study for investigation of 2-D conductivity structure corresponding to the regional origin. The inversion method (Zhdanov, Traynin, 1997) which is based on the minimum of the total energy of the residual field between observational electro-magnetic field and the calculated theoretical field of conductivity model and the conception of migrated residual field is introduced into our inversion of the data of magneto-variation sounding. The result of the inversion gives the underground conductivity structure in depth range of 100 km beneath the profile, and shows that a high conductivity area is located under Wugong and Qianling. The main characteristics of the inversion method is briefly discussed, that is, it can reflect the depth and the distribution of anomalous conductivity area comparatively well, and large number of parameters of inversion model is allowed to be used in the inversion.
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