During one earthquake, seismic waves space sent anywhere the globe. Though they might weaken with distance, seismographs room sensitive sufficient to tho detect these waves. In order to identify the ar of an earthquake epicenter, seismographsfrom at least three various places are essential for a particular event. In figure 13.9, over there is an example seismogram native a terminal that has a young earthquake.
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Once three seismographs have been located, uncover the time interval in between the come of the P-wave and the come of the S-wave. First, recognize the P-wave arrival, and read under to the bottom of the seismogram to keep in mind at what time (usually marked in seconds) the the P-wave arrived. Then perform the same for the S-wave. The come of seismic waves will certainly be known by boost in amplitude – look for a pattern adjust as lines gain taller and an ext closely spaced (ex. Number 13.10).
By looking in ~ the time between the arrivals of the P- and S-waves, one can determine the street to the earthquake from that station, with much longer time intervals indicating longer distance. These distances are determined using a travel-time curve, i beg your pardon is a graph the Pand S-wave arrival time (see number 13.11).
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Though the distance to the epicenter can be determined using a travel-time graph, the direction cannot be told. A circle through a radius that the street to the quake deserve to be drawn. The earthquake occurred somewhere along that circle. Triangulation is forced to determine precisely where it happened. Three seismographs room needed. A circle is attracted from each of the three different seismograph locations, where the radius of each circle is equal to the street from that station to the epicenter. The spot whereby those 3 circles intersect is the epicenter (Figure 13.12).