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In this paper, a new geometric inversion method is proposed for obtaining the elastic parameters of an anisotropic focal regions More precisely, the eigenvalues of a vertical transversely isotropic elasticity tensor of a focal region are inverted up to a constant for a given only one moment tensor with the accuracy depending on the strength of anisotropy. The reason for using only one moment tensor is that although there might occur several earthquakes in the same focal region, the orientation of the sources is similar to each other. Hence, one cannot obtain independent equations from each earthquake in order to use them in the inversion of elastic parameters of the focal region. Moreover, this method can be applied for real‐time inversion once the moment tensor of an earthquake is evaluated. The inversion method relies on the geometric fact that a moment tensor can be written as a linear combination of the eigenvectors of the anisotropic focal region's elasticity tensor. Then, in the inversion, we use the fact that each coefficient of this unique decomposition is proportional to the eigenvalues of the focal region's elasticity tensor. Two approximations are used in this inversion method, in particular for the potency and the source orientations. The strength of anisotropy of the focal region determines how accurate these approximations are, and, hence, it also determines the resolutions of the inverted eigenvalues. Because of the anisotropy of the focal region, the errors in the inversion do depend on orientations of the dip and rake angles but not on the strike angle since the focal region is vertically transversely isotropic. The accuracy of the inversion for the five parameters of vertical transversely isotropic is shown for every 10°‐gridded orientation of the dip and rake angles on the stereographic projection. The results are very promising along some orientations as shown in the figures. The last section of the paper deals with the inversion of eigenvalues, up to a constant, for a given set of moment tensors; not by using only one moment tensor. It turns out that the best fit corresponds to the average of inversions obtained for different orientations of the sources. [ABSTRACT FROM AUTHOR]

The invariants of the moment tensor such as its norm, eigenvalues and trace are closely related to the physical properties of the seismic source and the focal region, for example, seismic moment, radiation pattern, non‐double‐couple components. In this study, we investigate the relationship between these invariants and the eigenvalues and eigenvectors of the transversely isotropic elasticity tensor of the focal region. More specifically, we study how these invariants change as the source orientations vary with respect to the symmetry axes of the transversely isotropic elasticity tensor, by plotting these invariants on the stereographic net. Fortunately, one can plot them since they are independent of the strike of the fault when the focal region is a vertical transversely isotropic medium. Eigenvalues of the elasticity tensor control the invariants of the moment tensor; for instance, the ratio of the maximum and minimum norms achieved for some orientations of source is equal to the ratio of the two specific eigenvalues of the elasticity tensor. Moreover, the separation of the eigenvectors of the moment tensor from the eigenvectors of the source tensor is related to the deviation of the eigenvalues of the transversely isotropic elasticity tensor from the eigenvalues of the closest isotropic elasticity tensor. It is also found that this deviation is responsible for the percentages of non‐double‐couple components of the resulting moment tensor. This linear algebra point of view makes it easier to understand why and how the structure of the moment tensor changes for different orientations of sources. [ABSTRACT FROM AUTHOR]

A prototype electromagnetic vibrator, referred to here as E‐Vib, was upgraded and developed for broadband hardrock and mineral exploration seismic surveys. We selected the iron oxide mine in Blötberget, central Sweden, for a test site in 2019 for the newly developed E‐Vib because of the availability of earlier seismic datasets (from 2015 to 2016) for verification of its performance for hardrock imaging purposes. The two‐dimensional data acquisition consisted of a fixed geometry with 550 receiver locations spaced at every 5 m, employing both cabled and wireless seismic recorders, along an approximately 2.7 km long profile. The E‐Vib operated at every second receiver station (i.e. 10 m spacing) with a linear sweep of 2–180 Hz and with a peak force of 7 kN. The processing workflow took advantage of the broadband signal generated by the E‐Vib in this challenging hardrock environment with varying ground conditions. The processed seismic section shows a set of reflections associated with the known iron oxide mineralization and a major crosscutting reflection interpreted to be from a fault system likely to be crosscutting the mineralization. The broadband source data acquisition and subsequent processing helped to improve signal quality and resolution in comparison with the earlier workflows and data where a drophammer seismic source was used as the seismic source. These results suggest new possibilities for the E‐Vib source for improved targeting in hardrock geological settings. [ABSTRACT FROM AUTHOR]