A single seismic station can still tell how far it sits from the epicentre, purely from the delay between the P arrival and the S arrival, roughly the distance divided by eight. The farther out the station, from 20 to 400 km, the wider those two marks pull apart on the trace. Magnitude Mw is logarithmic: one step up means ten times the amplitude and about thirty-two times the energy. Early-warning systems exploit that same delay — the P wave runs ahead, so the alert outruns the destructive S wave.
A single seismic station can still tell how far it sits from the epicentre, purely from the delay between the P arrival and the S arrival, roughly the distance divided by eight. The farther out the station, from 20 to 400 km, the wider those two marks pull apart on the trace. Magnitude Mw is logarithmic: one step up means ten times the amplitude and about thirty-two times the energy. Early-warning systems exploit that same delay — the P wave runs ahead, so the alert outruns the destructive S wave.
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