## Overview

During an earthquake, seismic waves space sent anywhere the globe. Despite they might weaken through distance, seismographs space sensitive sufficient to tho detect these waves. In bespeak to determine the place of one earthquake epicenter, seismographsfrom at least three different places are required for a details event. In figure 13.9, there is an example seismogram native a terminal that includes a young earthquake.

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Once 3 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, recognize the P-wave arrival, and also read down to the bottom of the seismogram to note at what time (usually significant in seconds) that the P-wave arrived. Then do the exact same for the S-wave. The come of seismic waves will be recognized by an increase in amplitude – look for a pattern readjust as lines obtain taller and much more closely spaced (ex. Number 13.10).

By looking at the time between the arrivals of the P- and S-waves, one can determine the street to the earthquake from that station, with much longer time intervals indicating much longer distance. These distances are figured out using a travel-time curve, which is a graph that Pand S-wave arrival times (see number 13.11).

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Though the distance to the epicenter can be determined using a travel-time graph, the direction can not be told. A circle with a radius that the distance to the quake have the right to be drawn. The earthquake occurred somewhere along that circle. Triangulation is required to determine exactly where the happened. Three seismographs space needed. A one is attracted from every of the three different seismograph locations, wherein the radius of every circle is same to the street from that station to the epicenter. The spot whereby those 3 circles crossing is the epicenter (Figure 13.12).

why is a minimum of three seismic stations needed to find the epicenter of an earthquake?