In most cases (as shown in the figure below), a seismogram shows data from three components:

  1. North-South
  2. East-West
  3. Vertical/depth(z)

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However, if these components are not marked and all we have are three figures, then is there a way to identity which figure corresponds to which component?

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    $\begingroup$ Truth be told, I dont know enough to answer, but I do not think there is a way. There might be ways of making a good guess if you knew the location of the source and seismometer. Different wave forms will be recorded stronger/weaker depending on the direction they arrive at the seismometer. $\endgroup$ – Neo Aug 31 '14 at 14:46
  • $\begingroup$ You might be able to infer it accurately from the calibration pulse, assuming you have it and know what its characteristics are. $\endgroup$ – RBarryYoung Aug 31 '14 at 20:41

Yes, the vertical component of the seismogram looks different than the horizontal components. There are surface seismic waves (Love waves or Q-waves) that are horizontally-polarized. The ground motion due to these waves is horizontal and parallel to the plane of the ground surface. Therefore these waves will be most visible in the horizontal components of the seismogram. In some cases it may be possible to use the horizontal components to estimate the bearing to the epicenter. Surface waves travel more slowly than body waves, and their amplitude decays at a lower rate, therefore they may be easier to recognize in seismograms measured farther from the epicenter.

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  • $\begingroup$ But is there a definitive way to distinguish between the N-S and E-W components? $\endgroup$ – Neo Aug 31 '14 at 15:36
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    $\begingroup$ No. The signals on the two horizontal records vary continuously with the bearing to the epicenter. You need to know the orientation of your seismometer and which channel is which. $\endgroup$ – Mark Rovetta Aug 31 '14 at 17:08

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