Study On Boundary Recognition Method Of Magnetotelluric Anomalies

Magnetotelluric sounding is a geophysical exploration method using natural alternating electromagnetic field to study the electrical structure of the earth's interior.It is widely used in deep structure research and mineral resources exploration.In the process of processing and interpreting the observation data of magnetotelluric method,it is a very important step to judge the location and scope of the geological body and obtain the information of the underground structure.In this paper,we study and study the two-dimensional and three-dimensional forward magnetotelluric forward theory and the first derivative boundary recognition theory system,and establish a typical two-dimensional ground electric model,and use the two-dimensional finite element forward program to calculate the TM mode and the apparent resistivity and impedance phase of the TE model,and study the numerical edge recognition method.On the basis of the boundary recognition effect of the two dimensional forward results,the recognition and the recognition of the methods are summarized,and the three dimensional finite element forward modeling of magnetotelluric(magnetotelluric)is carried out in three-dimensional space.The boundary recognition method is used to identify the three-dimensional forward results of the apparent resistivity and impedance phase of different frequencies.The results show that: for two-dimensional ground electricity model,the total horizontal derivative method has the best recognition effect,the vertical derivative method and the analytic signal amplitude method are the second.The first derivative boundary recognition method has the effect for the three-dimensional ground electric model.Because the resolution of the TE and TM modes in the magnetotelluric sounding is different,the method of identifying the boundary in the low frequency section can only be used.Identifying the boundary of the anomalous body plane in one direction,in the high frequency section,it has a good recognition effect on the whole top top boundary of the abnormal body.The simulation of the model shows that the first derivative boundary recognition method can be applied to the magnetotelluric sounding method,and can accurately reflect the boundary and position of the abnormal body,but it still deviate from the real position of the abnormal body.Finally,the boundary recognition method is applied to the actual AMT data processing of a certain place in Qinghai.The result is good for the location and boundary of the abnormal body,and further proves the applicability of the first derivative boundary recognition method in the magnetotelluric sounding.