Forward Modelling
What is forward modelling in geophysics?
Forward modelling is one of the main methods used for interpretation in which the data will be mathematically synthesized based on a physical or mathematical model with a given set of geometries and physical properties (such as density, magnetic susceptibility, conductivity and seismic velocity). The calculated data can be compared with real data. For the two datasets to be similar (fit each other), the geometries and physical properties in the forward model are adjusted. This process can be done repeatedly to reconstruct a model similar to the real geological structure. Forward modelling can also help us find the size and contribution of geological structures in geophysical data. Our new and modern codes and software enable us to model frequency- and time-domain electromagnetic, magnetic, gravity, gravity gradiometry, magnetotelluric and first arrival travel-time seismic data. For 3D cases, we use unstructured tetrahedral meshes, the advantage of which is that it can honour the topography to as fine a resolution as the topography is known. Here are some real examples of our geophysical modelling services :
P.S. Because of the policy of real data, information on figures has been removed.
2D and 3D Gravity and Magnetic Modelling
The gravity and magnetic data involve variations in the density and magnetic susceptibility of geological structures. Therefore, forward modelling of gravity and magnetic data can give us a better understanding of the relationship between the data and variations in physical properties. The size, depth and density (or magnetic susceptibility) of heterogeneities have the strongest effects on gravity (or magnetic) data. Synthesizing the gravity and magnetic responses of different components of the geology can be done to assess the size and character of the various responses.
Gravity Gradiometry Terrain Correction using 3D Forward Modelling
Gravity gradiometry data can be strongly affected by topography. To eliminate this effect, leaving only the contributions from density variations in the subsurface, a terrain correction can be calculated and subtracted from the observed data. The terrain correction is typically computed using a Fourier-based technique. Such approaches can be efficient; however, we can use 3D forward modelling (using unstructured meshes), which incorporates accurate topography as a means of more accurately computing the terrain correction. Data corrected using the forward modelling approach have less of a remnant topography signature than data corrected using the Fourier-based approach.
(Figure: SK, Canada)
3D Electromagnetic Modelling
Electromagnetic (EM) geophysical methods can detect conductive structures in the ground. In the controlled source EM (CSEM) method, sources and receivers are loops of wires. The CSEM method can be categorized into frequency-domain (FDEM) and time-domain (TDEM) electromagnetic methods. EM methods can be used for a wide range of subsurface explorations. The investigation depth for TDEM is greater than for FDEM. Different systems have different applications. They can be sensitive to a different range of conductivities, and they can have different investigation depths. EM responses of different structures in complex geology can be confusing. Forward modelling can help us have a better understanding of EM responses coming from different structures.
Seismic Refraction (First Arrival Travel-Times) Modelling
Using the travel times between the source and the receiver, we can determine the depth of different geological boundaries and the elastic properties of rocks based on the difference in the seismic velocity and acoustic impedance of structures and materials. One of the main applications of seismic refraction is for determining the depth to bedrock. Exploration, however, faces many problems (such as hidden layers and blind layers). Forward modelling can be a suitable method for investigating the effects of different thicknesses and seismic velocities of geological layers on seismic refraction data.