Regularized smooth and focusing inversion of MT data

This model is excited by plane EM waves with four different frequencies 1, 10, 100 and 1000 Hz. Following the traditional approach used in practical MT observations, we calculate the synthetic observed apparent resistivities and phases based on two off-diagonal elements of the magnetotelluric tensor at each observation point. The quantities Py (apparent resistivity) and j)y (impedance phase) are assigned to the nominal TE mode, whereas p y and (j y are assigned to the nominal TM mode. Note, that this 2-D nomenclature is artificial and approximate in nature for 3-D structures. However, it is widely used in practical MT observations, and often only the quantities Py, j y, p y and (t y are available for inversion. That is why we use the same approach in the model study. The apparent resistivity and phases of impedance were calculated at 195 receivers placed on the nodes of a square grid on the surface. The distance between the observation points is 100 m in the x and y directions. 

The data vector consists of 780 simulated field components (195 sites for 4 frequencies). The synthetic data set is generated by a full integral equation method and it has been contaminated by 3 percent random noise. The model parameters are the unknown anomalous conductivity values of each cell in the volume over which the inversion is carried out. 

It has been demonstrated by Wannamaker (1999) that the best results for elongated anomalies are obtained with TM mode. The anomalous body has a strike 

the modeling study demonstrates that both methods can resolve a three- 

---