Alternative (spectral) seismics (a little theory and practice)
The spectral seismic profiling (SSP) is based on use of the next objective, real physical effects:
- The echo - signal, as such, is absent in overwhelming majority of solid mediums, including rocks. The response to percussion action is long oscillatory acoustic process and it is not the echo - signal. Purpose(assignment) of a spectral seismics - spectral analysis of long oscillatory process, instead of search in this signal of nonexistent echo - signals.
- The dependence between spectral structure of long oscillatory process, and geological structure in a point of percussion action looks like:
f0i - i-th harmonic component of acoustic signal;
Vsh – speed of shear waves;
hi – i-th dimension, for example, the depth of some boundary.
- Natural elastic oscillations are the shear waves.
- The speed of shear waves Vsh in rocks is almost constant, it equals 2500m/s ± 10%
SSP-section is aggregate of spectral images of seismic signal. Therefore the SSP-section is the primary information and does not depend from any subjective factors. It distinguishes a SSP-method from methods of traditional seismics.
- The funnel-shaped object at SSP-section is the stable indication that this profile crosses tectonic faulting zone.
- All column of sedimentary rock above the tectonic faulting is characterized high microcracking. Therefore the recovery at drilling practically is equal to zero in tectonic faulting zone. In tectonic faulting zone there is the lowered soil bearing capacity. It is important that the soil bearing capacity will be reduced after the beginning of construction work. The discovery of these properties of sedimentary rock in tectonic failures zones allows, on the one hand, to understand the reasons of many sudden destructions of engineering structures, and with another, to forecast their destruction effectively. It is possible to extract water in tectonic failures zones owing to the higher permeability of sedimentary rock.
- The tectonic failures zones besides are and geopathogenic zones.
The realization of correct from the point of view metrology of the spectral analysis seismic signal became possible as a result of creation special geophone. The electrical signal on plugs of such geophon has spectrum that is identical to a spectrum of an acoustic signal in a contact place of geophon with rock.
The technique of realization spectral seismic profiling each time is corrected according to a problem put by.