High Resolution Tomography Examples

Since 2002, we have been using the highly advanced Seismic Refraction processing method of Wavepath Eikonal Tomography (WET). This new technique allows to perform a significantly better analysis of elastic sections, with a much higher resolution and precision than previous techniques. In the example shown below, taken from a project in Central America, we can appreciate this greater resolution, which allows us to readily see small fractures and even boulders!. The elastic materials interpreted in this profile are peat (blue-black), alluvial/colluvial (light blue-blue), altered rock (yellow-green) and compact rock (pink-yellow).
 

Since we have seismic resolution with such detail, it would be quite helpful to be able to analyze it in 3D space. For this purpose, and since 2003, we have been using for the first time among geophysical consulting firms, a 3D analysis software such as Fracsis, which allows us to do a global three-dimensional analysis by combining morphology, geological and geophysical information. The example shown below is from a dam axis on one of the main mining operations in Northern Perú                                                                                                                   .

Seismic Refraction Tomography in the Chavimochic Irrigation Project, La Libertad

Chavimochic was a large-scale irrigation project in northern Perú, and consisted of water intakes, tunnels, canals and dams. We worked in several stages of the construction project, including 52 km of seismic refraction profiles. The following is an example taken from one of our surveys there.


Geophysical tomography consists in reconstructing an underground section by measuring physical properties from the edges of this section. To achieve this, an energy field is generated in one edge and measured in another, after the energy travels below surface from origin to detection. Ideally, in order to obtain an appropriate amount of measurements for reconstruction of a tomographic section, raypaths should go through the subsurface in all directions. It is common practice, however, to only have a set of two wells available, one to place energy sources at different depths, and the other to place receivers, also at various depths. In seismic tomography, the energy sources commonly used are impacts or explosions, while the detectors are piezoelectric geophones.

This tomography section was reconstructed from the project's water intake, using two available wells. The objective was to monitor the effect of the grouting that had been done through well 4b (left). Purple colors show high bedrock velocities at the lower portion of well 3a (right) and high velocity lenses, probably reflecting cement lenses, throughout the rest of the section. Blue colors show areas where grouting has not penetrated, being more dramatic on the upper half of well 3a.