Methods

SEISMIC MEASUREMENT PROCEDURES – THE METHODOLOGY

Seismic measurement systems are used in many different areas, - for example in research, natural resource exploration or subsurface exploration.

The basic principle of a seismic measurement is always similar: During a seismic subsurface investigation, vibrations are generated at the surface with the help of seismic sources. These vibrations propagate in the subsurface at a material-dependent velocity and are reflected and refracted by the individual geological layer boundaries. With the help of geophones placed on the surface, the travel times and amplitudes of the individual waves are measured and displayed in a seismogram. Based on the data obtained in this way, an image of the subsurface can now be generated.

For each seismic measurement, the method used must be adapted to the individual target of the investigation. This includes the choice to apply refraction and/ or reflection seismic measurements and further choosing the dimensions of the seismic profiles, including source and receiver positions.

In reflection seismic measurements, elastic waves are observed that are reflected at the individual layer boundaries and discontinuities in the subsurface back to the surface. From thetraveltime of the seismic wave between its excitation point at the surface and its arrival at the surface, the material-dependent wave velocity, the depth and course of the geological layer boundaries in the subsurface can be determined. The setting of the measurement devices at the surface must be adapted to the respective task. 

APPLICATION EXAMPLES

• Determination of soil stratification and fault zones

• Subsoil investigation

• Mapping of landfills

• Exploration of reservoirs (natural gas, oil, geothermal energy)

   

   

In refraction seismics, the different, material-dependent wave velocities of the individual layers in the subsurface are the result. For this purpose, the first arrivals of the seismic waves at the geophones in the measurement line are analysed. Using the velocities calculated from the travel time, the thicknesses of the individual layers can be calculated. A pre-condition for a refraction seismic survey is that the seismic velocity of the lower layer is greater than that of the layer on top.

APPLICATION EXAMPLES

• Determination of bedrock depth or cover thickness

• Determination of elastic soil properties, e.g. shear strength and modulus of elasticity

• Determination of rock edges and rock classes

POSSIBLE FIELDS OF APPLICATION OF GEOPHYSICAL MEASUREMENT SYSTEMS

Construction projects / site stabilisation

• Detection of unstable areas, e.g. in mining areas

• Measurement and evaluation of soil stability in the run-up to construction projects

• Investigation of subrosion phenomena and destabilisation processes

• Risk assessment of already constructed areas and used sites

Earthquake zones

• Soil evaluation for earthquake-resistant building development

• Measurement data for damage assessments after earthquakes

Dike areas

• Evaluation of dike conditions

• Dike investigation for stable flood protection

• Efficient investigaion to determine dike stability

• Determination of the rough structure of the dike

• Identification of extensive zones of weakness

Archaeology

• Checking the ground conditions at historical excavation sites

• Optimisation of exact excavation positions

Geothermal energy

• Soil quality tests prior to drilling

• Determination of location and depth of geothermal reservoirs

Glaciology

• Measurements in permafrost or on glaciers

• Testing the composition of the rock volume under the ice

• Effects of glacier melt and changes in permafrost areas

• Verification of system reliability at high altitudes and at very low temperatures