## Overview

During an earthquake, seismic waves room sent almost everywhere the globe. Though they may weaken with distance, seismographs space sensitive sufficient to quiet detect these waves. In bespeak to recognize the ar of one earthquake epicenter, seismographsfrom at least three various places are essential for a specific event. In figure 13.9, there is an instance seismogram from a station that includes a boy earthquake.

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Once three seismographs have been located, discover the time interval in between the arrival of the P-wave and also the come of the S-wave. First, recognize the P-wave arrival, and also read under to the bottom of the seismogram to note at what time (usually significant in seconds) the the P-wave arrived. Then carry out the very same for the S-wave. The come of seismic waves will be recognized by an increase in amplitude – look for a pattern change as lines acquire taller and more closely spaced (ex. Number 13.10).

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

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Though the street to the epicenter deserve to be determined using a travel-time graph, the direction cannot be told. A circle with a radius that the distance to the quake have the right to be drawn. The earthquake developed somewhere follow me that circle. Triangulation is required to determine precisely where that happened. 3 seismographs room needed. A circle is attracted from each of the three various seismograph locations, whereby the radius of each circle is same to the distance from that terminal to the epicenter. The spot whereby those 3 circles crossing is the epicenter (Figure 13.12).