Impedances for the mantle electromagnetic soundings
Deep electromagnetic soundings of the Earths mantle are considered in the view of approximate impedance boundary conditions (IBCs) at a contact between resistive (air) and conductive (earth) media. The IBCs are linear or differential equations relating spectra of the time-harmonic field components through impedances and through their spatial derivatives as well. The impedance equations serve the purpose of determining the impedances from the observed records of the field components. Impedances in general depend on the particular sounding methods, on the properties of the conductive medium, as well as on the adopted model of the space, the later aspect being important at considering the way in which the induced currents locking, even at infinity.Moreover, the impedances depend on the exciting field that originates from sources of several different types in the period range of hours to years commonly used for the mantle electromagnetic soundings. Thus, quoting Gulelmi and Gokhberg we can say that the Earth does not have its own impedance. The benefit of employing the impedances comes from acknowledging that they are independent from the temporal variations of the source power. In practice, impedances obtained from the different sounding methods are often inverted jointly with the aim of the estimating the mantle conductivity distribution throughout as broad a depth range of the mantle as possible. The main subject of the review consists in assessing the accuracy of such a mixed impedance approach by analyzing relations between the approximated IBCs for the known settings of the induction models and across the ranges of applicability of different types of impedances.
mantle sounding magnetotelluric magnetovariation impedance
Vladimir Semenov Vladimir Shuman
Institute of Geophysics of the Polish Academy of Sciences, Warsaw Institute of Geophysics of the National Academy of Sciences of Ukraine, Kiev
国际会议
The 19th International Workshop on Electromagnetic Induction in the Earth(第十九届国际地球电磁感应学术研讨会)
北京
英文
782-787
2008-10-23（万方平台首次上网日期，不代表论文的发表时间）