## Overview

During one earthquake, seismic waves are sent everywhere the globe. Though they may weaken with distance, seismographs room sensitive sufficient to tho detect these waves. In order to recognize the ar of an earthquake epicenter, seismographsfrom at the very least three different places are required for a specific event. In figure 13.9, over there is an instance seismogram from a terminal that consists of a minor 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 arrival of the S-wave. First, recognize the P-wave arrival, and read down to the bottom of the seismogram to keep in mind at what time (usually marked in seconds) the the P-wave arrived. Then execute the exact same for the S-wave. The come of seismic waves will be known by rise in amplitude – look because that a pattern change as lines acquire taller and an ext closely spaced (ex. Figure 13.10).

By looking at the time between the come of the P- and also 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 identified using a travel-time curve, i m sorry is a graph of Pand S-wave arrival times (see figure 13.11).

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Though the street to the epicenter can be determined using a travel-time graph, the direction cannot be told. A circle v a radius of the street to the quake have the right to be drawn. The earthquake emerged somewhere follow me that circle. Triangulation is required to determine precisely where that happened. Three seismographs room needed. A circle is attracted from every of the three various seismograph locations, wherein the radius of every circle is equal to the distance from that station to the epicenter. The spot where those three circles intersect is the epicenter (Figure 13.12).

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