The travel time of a seismic wave at a station is the time it takes to go from the focus to the station. The travel-time curve of a wave is the graph of its travel time against the epicentral distance of the station.
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Example 11.4 (An earthquake away)
Observed travel times are for P and for S at , and at . A station that records an S wave (8 minutes 13 seconds) after the P wave therefore lies from the epicentre: about . At the delay would only be .