Surface Wave Tomography (SWT) is used to build shear-wave velocity models. In some studies, it is assumed that surface waves propagation follows a straight line between the source and the receiver. This assumption might be violated in near-surface studies because of high level of complexity and lateral heterogeneity. In curved-ray SWT, the actual ray paths between every receiver couple are computed. Curved-ray SWT can increase the accuracy of the model and will increase the computational effort. It is important to investigate the gained model improvement together with the associated additional computational cost from curved-ray over straight-ray SWT for near-surface applications. We apply straight- and curved-ray SWT on a generated 3D synthetic dataset and compare the results in terms of accuracy and computational costs.

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Over the last years, new techniques are being researched in order directly estimate relevant geological properties of the rocks present in the subsurface without using an inversion process, this can be achieved by obtaining relationships between the data obtained by geophysical surveys and the data obtained in one place by well logging, core analysis or other techniques in which the actual physical properties of the rocks are measured. Using the apparent resistivity measurements from an MT survey and the resistivity measured from an exploratory well, we want to assess if it is possible to obtain a polynomial function that can be used to correct the misfit between the depth-apparent resistivity model obtained by MT surveys and the depth-resistivity model obtained by means of exploratory wells, and we want to assess if the polynomial expression obtained can be used to retrieve an accurate electrical model in nearby areas from the exploratory well in which only apparent resistivity measurements have been acquired.@en

Joint inversion of different geophysical methods is a powerful tool to overcome the limitations of individual inversions. Body wave tomography is used to obtain P-wave velocity models by inversion of P-wave travel times. Surface wave tomography is used to obtain S-wave velocity models through inversion of the dispersion curves data. Both methods have inherent limitations. We focus on the joint body and surface waves tomography inversion to reduce the limitations of each individual inversion. In our joint inversion scheme, the Poisson ratio was used as the link between P-wave and S-wave velocities, and the same geometry was imposed on the final velocity models. The joint inversion algorithm was applied to a 2D synthetic dataset and then to two 2D field datasets. We compare the obtained velocity models from individual inversions and the joint inversion. We show that the proposed joint inversion method not only produces superior velocity models but also generates physically more meaningful and accurate Poisson ratio models.

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Surface waves are widely used to model shear-wave velocity of the subsurface. Surface wave tomography (SWT) has recently gained popularity for near-surface studies. Some researchers have used straight-ray SWT in which it is assumed that surface waves propagate along the straight line between receiver pairs. Alternatively, curved-ray SWT can be employed by computing the paths between the receiver pairs using a ray-tracing algorithm. The SWT is a well-established method in seismology and has been employed in numerous seismological studies. However, it is important to make a comparison between these two SWT approaches for near-surface applications since the amount of information and the level of complexity in near-surface applications are different from seismological studies. We apply straight-ray and curved-ray SWT to four near-surface examples and compare the results in terms of the quality of the final model and the computational cost. In three examples we optimise the shot positions to obtain an acquisition layout which can produce high coverage of dispersion curves. In the other example, the data have been acquired using a typical seismic exploration 3D acquisition scheme. We show that if the source positions are optimised, the straight-ray can produce S-wave velocity models similar to the curved-ray SWT but with lower computational cost than the curved-ray approach. Otherwise, the improvement of inversion results from curved-ray SWT can be significant.

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