## Overview

During an earthquake, seismic waves space sent anywhere the globe. Though they may weaken v distance, seismographs room sensitive sufficient to still detect these waves. In order to recognize the location of an earthquake epicenter, seismographsfrom at least three different places are required for a details event. In number 13.9, over there is an instance seismogram from a terminal that includes a young earthquake.

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Once three seismographs have actually been located, find the time interval in between the arrival of the P-wave and also the come of the S-wave. First, identify the P-wave arrival, and also read under to the bottom of the seismogram to note at what time (usually marked in seconds) that the P-wave arrived. Then do the exact same for the S-wave. The arrival of seismic waves will be known by an increase in amplitude – look for a pattern change as lines acquire taller and an ext closely spaced (ex. Figure 13.10).

By looking at the time in between the arrivals of the P- and also S-waves, one can determine the street to the earthquake from that station, with longer time intervals indicating longer distance. These distances are established 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 can be figured out using a travel-time graph, the direction cannot be told. A circle with a radius of the distance to the quake can be drawn. The earthquake arisen somewhere follow me that circle. Triangulation is forced to determine exactly where the happened. 3 seismographs space needed. A circle is drawn from every of the three different seismograph locations, wherein the radius of each circle is equal to the distance from that terminal to the epicenter. The spot whereby those three circles intersect is the epicenter (Figure 13.12).

how many seismic stations are needed to locate the epicenter of an earthquake