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BOREHOLE SEISMIC METHODS

Overview

Seismic survey is the most common geophysical method for studying the structure of rocks that provides convincing and fairly reliable results when carrying out geological exploration.

For the moment, a large number of vertical seismic profiling (VSP) method variations have been developed: operations in single boreholes, shooting between boreholes as well as between borehole and land surface. Unfortunately, in near-surface seismic surveys such approaches are used undeservingly rarely or in simplified modifications, although they allow increasing resolution and detail of investigations.

How it works

There are 4 types of shallow seismic surveys on land exist where we can deploy a borehole sparker source in the most effective way:

  • Low Frequency Acoustic Logging: sparker travels with receiver at fixed distance in the same borehole.
  • Vertical SeismoAcoustic Profiling (VSAP): sparker is fixed in the same borehole with receiver(s) that is (are) being moved along it.
  • Reverse Vertical Seismic Profiling (RVSP): sparker travels in borehole; receivers are fixed on the surface.
  • Crosshole Seismic Testing (CST): sparker travels in one borehole; receivers travel in another (other) borehole(s).

Nevertheless, crosshole seismic testing can be carried out not only on pressure waves!  At the moment, there are 4 main designs of CST exist: a) single-ray parallel sounding on pressure waves, b) multiwave parallel sounding (i.e. on pressure and shear waves), c) tomographic sounding on pressure waves, d) multiwave tomographic sounding. In more sophisticated realizations of the method, the day surface is taken into account during observations or studies are conducted in shafts and galleries in an arbitrary plane.

Application

  • high-risk and hazardous facilities: nuclear power plants, hydro-electric power plants, high-rise buildings, chemical plants, etc.;
  • improving the seismic properties of soils by creating a pile field at sites composed of dispersed and water-saturated soils;
  • non-destructive testing of construction stages (e.g., the creation of a wall in the ground), monitoring the formation of ice wall, carrying out the injection operations;
  • locating karst areas.