page_title: Semblance analysis
section_title: Process
hierarchical_section_title: Semblance analysis / Process
caption_attribution_description: English: wiggle plot of seismic data
context_page_description: Semblance analysis is a process used in the refinement and study of seismic data. The use of this technique along with other methods makes it possible to greatly increase the resolution of the data despite the presence of background noise. The new data received following the semblance analysis is usually easier to interpret when trying to deduce the underground structure of an area. Weighted semblance can be used for increasing the resolution of traditional semblance or make traditional semblance capable of analyzing more complicated seismic data.
context_section_description: Semblance analysis allows for the refinement of seismic data. This is done by developing a velocity spectra display to determine the velocity through different layers at depth. The easiest way to accomplish this is by recording the normal incidence path (NIP). The NIP is where you have the shot and the geophone in the same location and the path taken by the recorded sound waves is perpendicular to the boundaries between the layers. This path represents the shortest amount of time that can be taken to reach a layer and return. With this information it becomes fairly easy to calculate the velocity of the waves as they travel through each layer by using the equation for the root mean square velocity starting with the top layer and working downward.
  Once all of the velocities for the layers are known then it is possible to calculate the time needed for the wave to travel the distance down to the midpoint between each geophone and the shot point for each of the layers. As the geophones are farther away from the shot, the more the time taken for the wave to travel there increases, this forms a hyperbola in a graph of time vs. distance. The velocity data is used to correct the curves of the hyperbolas and create a flat line where all points are at an equal depth. The final step for the semblance analysis is to sum all of the data that has been corrected for velocity. This is done with the use of a computer filter to sum together all of the events that the traces share, then remove the ones they don't. The result is a single data set that has all of the primary peaks strongly displayed with most of the noise removed.
caption: Corrected data.
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