The honest-to-god answer is that P-waves can travel through ALL types of matter, but S-waves can only travel through solids (Hence S).
So the further away you get from the epicenter, the more likely you are to encounter mediums through which the S-wave is inhibited.
As for the last question (I don't know which you wanted to have answered) seismic stations use the disturbance in an electrical field or current to measure and analyze the seismic event. Therefore, it doesn't require proximity so much as it requires precise and accurate local recording and transmittance to the facility (even if across the world) with precise instrumentation for analysis.
Jun 3rd, 2015
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