Theoretical modelling of the coherence and admittance functions

The flexural strength and consequently the elastic thickness (Te) of the lithosphere are often calculated utilizing the statistical relationships between gravity anomalies and topography data. The elastic thickness of the lithosphere is one of the most important parameters in determining the geological properties and characteristics of the crust as well as its rheological behavior. This prospective study was designed to investigate the use of the gravity and topography data in order to calculate the two fundamental functions, i.e. admittance and coherence, which are the basic functions for determining the elastic thickness of the lithosphere. In this research, the theory of the two objective functions is modeled. The study offers some important insights into the involved parameter and how they affected the functions. Additionally, the results show the impact of initial assumptions of different parameters on the retrieved value of the Te parameter. Taking into account the initial assumptions about parameters such as the elastic thickness () of the plate, the loading ratio () and the degree of correlation () between the surface and subsurface loading regimes applied to the plate and using spectral methods, the value of these two functions are calculated. After examining the theoretical models, the real-data analysis is conducted in order to examine the observed values and compare them with the theoretical values. Based on what was mentioned in the following, this function can be able to retrieve the elastic thickness of the lithosphere. We concluded that:One of the more significant findings to emerge from this study, by examining the theoretical models, is that the best function to determine the elastic thickness of the lithosphere is to use the Bouguer coherence function. A comparison of the results reveals that the characteristic curves of the admittance function will change drastically with the change of the involved parameters. Consequently, having complete knowledge of the structure of the region and involved parameters is essential while using free air admittance in order to determining Te. As it was illustrated in this research, the characteristic curve of the coherence function can be used to determine Te based on the roll over wavelength. For the reason that there was no significant change in the shape of characteristic curve of the functions with the initial value of the loading ratio (), this parameter had less impact on the inversion process. Having considered rare correlation between free air gravity and topography, it is reasonable to accept that the free air coherence method is less applicable in determining Te than Bouguer coherence. The findings from previous studies provide support for the key arguments.