## Overview

During one earthquake, seismic waves room sent all over the globe. Despite they may weaken through distance, seismographs space sensitive enough to quiet detect this waves. In order to identify the location of an earthquake epicenter, seismographsfrom at the very least three different places are required for a certain event. In figure 13.9, there is an instance seismogram native a terminal that contains a minor earthquake.

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Once three seismographs have been located, find 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 also read down to the bottom the the seismogram to keep in mind at what time (usually significant in seconds) that the P-wave arrived. Then carry out the same for the S-wave. The come of seismic waves will certainly be recognized by an increase in amplitude – look because that a pattern change as lines obtain taller and more closely spaced (ex. Figure 13.10).

By looking at the time between the come of the P- and S-waves, one have the right to determine the street to the earthquake from the station, with much longer time intervals indicating longer distance. These distances are figured out using a travel-time curve, i beg your pardon is a graph the Pand S-wave arrival times (see figure 13.11).

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Though the street to the epicenter deserve to be figured out using a travel-time graph, the direction can not be told. A circle through a radius the the distance to the quake deserve to be drawn. The earthquake arisen somewhere follow me that circle. Triangulation is compelled to determine exactly where the happened. 3 seismographs are needed. A circle is drawn from every of the three various seismograph locations, where the radius of every circle is same to the street from that station to the epicenter. The spot whereby those 3 circles intersect is the epicenter (Figure 13.12).

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