## Overview

During an earthquake, seismic waves room sent almost everywhere the globe. Despite they may weaken with distance, seismographs space sensitive enough to quiet detect these waves. In bespeak to recognize the location of an earthquake epicenter, seismographsfrom at least three different places are needed for a specific event. In figure 13.9, over there is an example seismogram from a terminal that consists of a minor earthquake.

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Once three seismographs have been located, uncover the time interval between the arrival of the P-wave and also the arrival of the S-wave. First, determine the P-wave arrival, and read under to the bottom that the seismogram to note at what time (usually marked in seconds) the the P-wave arrived. Then perform the same for the S-wave. The arrival of seismic waves will be well-known by an increase in amplitude – look because that a pattern readjust as lines gain taller and more closely spaced (ex. Figure 13.10).

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

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Though the street to the epicenter have the right to be figured out using a travel-time graph, the direction cannot be told. A circle through a radius that the street to the quake have the right to be drawn. The earthquake developed somewhere along that circle. Triangulation is compelled to determine precisely where it happened. Three seismographs are needed. A one is attracted from each of the three different seismograph locations, wherein the radius of every circle is equal to the street from that terminal to the epicenter. The spot wherein those three circles crossing is the epicenter (Figure 13.12).