| Telluric current is a kind of natural current system on solid earth, It originated from potential distribution due to crustal material difference, which is caused by space current system disturbances, underground fluid flow, material movements in the deep earth etc. Generally the current field is composed of two parts, one is telluric current, the other is local current, large spatial scales current comes from external earth space current system, while local current is from various potential process of the crust, telluric current change is a comprehensive response to both change, so telluric current is closely related to geomagnetic variation field, they have the same change composition morphological, for their field sources are both from various current system of external earth induction in the earth or the current generated by material migrating in deep earth spreading to the earth surface. In the recent years, telluric current studies included earthquake prediction, the mechanism of natural electric field, high-voltage transmission loss calculation and other basic research. However, all these studies didn’t consider the important links between telluric current and tectonic activities, hydrogeology, electromagnetic perturbations and earth’s deep structures. With the accumulation of observations data and deeper research, these issues require further consideration and resolution.In this paper, telluric current is calculated by the stations observed geoelectric field vector and shallow resistivity using differentiating the Ohm’s law, it has two orthogonal to the plane components. Telluric streamline diagram and vector diagram were obtained using vector interpolation, the divergence and vorticity of telluric current gotten through its vector field could be used to characterize it’s distribution and changes over time. In addition, time variation of telluric current is related to geomagnetic field, based on the second sampling(1 Hz) data of some stations, the spectral range of geoelectric and magnetic field were taken into consideration;furthermore, geomagnetic induced currents(GIC) was calculated, and compared with measured telluric current to analyze its spatial distribution, based on plane wave theory of electromagnetic field propagation and the resistivity the of sounding data. The study can be discussed from the following five aspects.(1) Geomagnetic Induced Current(GIC) calculated by geomagnetic variation field using plane wave model has great relevance with the original observations, before and after electrical storm main phase, geoelectric field has amplitude difference with Geomagnetic Induced Electric field(GIE), but their phases have a good consistency. Considering geoelectrical storm is large area electromagnetic disturbance, and the source has a certain balance and synchronization, so the way that using the maximum amplitude of geoelectrical storm to obtain telluric current is of special significance, telluric current vortex center drift north obviously during geoelectrical storm.By 1 Hz sampling frequency spectrum of the geomagnetic field to field spectral contrast, Serson et al. electromagnetic spectrum was supplemented, the frequency of geoelectric ripple was expanded, and 4.8 h and 12 h and other frequency components was clear.(2) Temporal and spatial distribution of telluric current is related to tectonic activity and near-surface hydrologic environment. Through the study of telluric current spatial distribution,it’s found that the Tan-lu fault zone in North China has a significant differentiation for telluric current, on two sides of the fault zone, its directions are irrelevant or even in the opposite, in the faulted area, it still has a local continuity. In the Sichuan-Yunnan region, large fault zone has collection effect on streamlines, along the fault trend, they will bundle divergence or convergence.When the distribution change,it could mean fault activity, earthquake germination, so we canconsider this method to monitor seismic activity.(3) In the east coast of China, telluric current directions usually point to ocean, except few stations’ directions change significantly with seasons. In Hainan and Chongming Island, the direction telluric current related to the hydrological conditions of surrounding flow,the monsoon influences the winter and summer currents,and then forms circulation in different directions in the North Bay and Hainan Island, thereby affects the telluric current direction of the island, on the other hand, the telluric current direction of Chongming Island is mainly by controlled by local current of Yangtze river deposition in different directions.(4) Mainland China has four relatively complete telluric vortex field,respectively locate in the northeast, north, southwest and northwest. Three are at latitude near 30°N(2) and 38°N(1),the last one is in the northeast region. In order to study the telluric current vortex phenomenon better, this paper established the eddy current model. The source of the vortex is some kind of space equivalent loop current generated geomagnetic variation field perpendicular to the ground,although the eddy current is relatively small, but the presence of highly conductive geological block enables the induced magnetic field of equivalent electric current ring cause eddy currents on the ground.(5) By deriving the formula for eddy current heating conductor block, the heating effect of the eddy current distribution area was discussed, and the eddy current heating effect for the formation and its response to the local climate was simulated. The eddy current has a series of spin-off effects, the vortex caused conductive block center calorific value is larger than surround,which may heat the geological block formation in local area, near the vortex geomagnetic Z component should be greater than the surrounding non-vortex rotary region, this phenomenon can be confirmed by some other geophysical observations. In the telluric current vortex area, a special conductive structure, conductive blocks near the surface and a good current path are necessary conditions to generate vortices.In this paper, some new methods were proposed, which largely extended the application of geophysical observations, such as characterizing the flow field by telluric current. In addition, the data processing use the relative change value instead of the mean measured value, which in largely avoid the reference value difference caused by the drift electrode, observation system instability and other incidental factors, and make observations comparable over a wide range,which is also the foundation of large scale telluric current flow and vortex phenomena research.Although the research is preliminary, it still has a certain degree of innovation and significance,but because of the situation of observation stations scarce, data quality is not high and the basic theory is ambiguous, this study needs further work. Thus, at the end, some new data processing methods and new theories were prospected, hoping to provide ideas for follow-up research in this field. |
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