## Overview

During an earthquake, seismic waves are sent out everywhere the globe. Though they might threaten with distance, seismographs are sensitive sufficient to still detect these waves. In order to determine the location of an earthquake epicenter, seismographsfrom at leastern three different places are necessary for a certain occasion. In Figure 13.9, tright here is an instance seismogram from a terminal that has a minor earthquake.

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Once 3 seismographs have been situated, uncover the time interval in between the arrival of the P-wave and the arrival of the S-wave. First, recognize the P-wave arrival, and check out down to the bottom of the seismogram to note at what time (normally noted in seconds) that the P-wave arrived. Then execute the very same for the S-wave. The arrival of seismic waves will certainly be recognized by a boost in amplitude – look for a pattern adjust as lines get taller and also more carefully spaced (ex. Figure 13.10).

By looking at the moment between the arrivals of the P- and S-waves, one can determine the distance to the earthquake from that terminal, through longer time intervals indicating much longer distance. These distances are identified making use of a travel-time curve, which is a graph of Pand also S-wave arrival times (view Figure 13.11).

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Though the distance to the epicenter have the right to be identified making use of a travel-time graph, the direction cannot be told. A circle with a radius of the distance to the quake deserve to be drawn. The earthquake developed somewright here alengthy that circle. Triangulation is forced to identify exactly wright here it occurred. Three seismographs are necessary. A circle is drawn from each of the 3 different seismograph places, wbelow the radius of each circle is equal to the distance from that station to the epifacility. The spot wbelow those three circles intersect is the epicenter (Figure 13.12).

how many seismographs are needed to find the epicenter of an earthquake