Controlled Source Audio Magnetotelluric Method Static Effect Correction Method

Controlled-source Audio-frequency Magnetotelluric(CSAMT) are developing from the Magnetotelluric(MT), which is used to correct the weakly MT signal. The CSAMT is a kind of geophysical methods that are detecting the different resistivities on different depths by changing the transmitting and receiving frequencies. In recent years, CSAMT is successfully used in the area of mining, terrestrial heat, groundwater, oil and gas, and so on. Static shift is one of the difficult problems that have to be solved in CSAMT. Since the static shift disturbs the data and leads to wrong interpretation, so we have to do static correction in order to achieve a better quality CSAMT data. The generation mechanism and characteristics of the static shift are discussed in this paper. The galvanic distortion due to small-scale surface and shallow electric inhomogeneities often leads to distortion of observed and inverted resistivity data. The apparent resistivity curve in the loglog coordinate system has parallel static shift effect while the phase curve has no effect.In order to do the static correction, first we need to distinguish the static shift from the anomalies in the data, and then consider the field geological conditions to choose a suitable technique method. there are many static correction methods, including: The filtering methods based on the numeric analysis; The curve-shift method which has a friendly man-machine interactive interface; and the method using the phase data analysis or using magnetic data analysis; the curve-shift method; and The wavelet analysis method and so on.Starting from the principles of the static correction, in this paper we establish the static shift model in the underground layered stratum and in the homogeneous stratum, compute the apparent resistivity and phase data by using 2D forward arithmetic, attempt to distinguish the static shift from anomalies by using the correlation coefficient or wavelet analysis. After doing the research studies of some kinds of static correction, several static correction methods are chosen in this paper: the filtering method, the curve-shift method, EMAP, and the wavelet analysis method. The advantages and disadvantages have been summarized in this paper by comparingeach method's effect.In practical CSAMT data processing, we take the two metal diggings for example, there is a serious static shift in the collected data. After static correction, a good quality data was achieved. In conclusion, these static correction methods gained a good applicable effect.