## Overview

During an earthquake, seismic waves room sent all over the globe. Though they may weaken with distance, seismographs room sensitive sufficient to tho detect these waves. In stimulate to determine the place of one earthquake epicenter, seismographsfrom at the very least three different places are necessary for a particular event. In number 13.9, there is an example seismogram from a station that has a boy earthquake.

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Once 3 seismographs have been located, uncover the time interval in between the come of the P-wave and the come 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) that the P-wave arrived. Then perform the same for the S-wave. The come of seismic waves will be known by boost in amplitude – look because that a pattern readjust as lines acquire taller and an ext closely spaced (ex. Number 13.10).

By looking in ~ the time between the arrivals of the P- and also S-waves, one have the right to determine the distance to the earthquake from the station, with much longer time intervals indicating longer distance. These ranges are determined using a travel-time curve, which is a graph that Pand S-wave arrival time (see number 13.11).

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Though the distance to the epicenter deserve to be figured out using a travel-time graph, the direction cannot be told. A circle v a radius of the street to the quake deserve to be drawn. The earthquake occurred somewhere along that circle. Triangulation is forced to determine specifically where that happened. Three seismographs are needed. A one is drawn from each of the three various seismograph locations, where the radius of each circle is same to the distance from that station to the epicenter. The spot whereby those 3 circles intersect is the epicenter (Figure 13.12).