Earthquake Epicenter Triangulation

okay so let's take a look at how to

locate the epicenter of an earthquake

using the triangulation method alright

so here is a map of the world and we're

going to zoom in a particular region

we'll look at North America and let's

imagine that there was an earthquake

somewhere in North America

well the question arises where was the

epicenter of that earthquake now we may

be able to get a general idea of where

the epicenter was based on looking at

the severity of damage

eyewitness reports etc but if you want

to pinpoint the actual location of the

epicenter you have to do some

calculating and so let's look at how

we're going to do that first off in

order to pinpoint the epicenter you need

a minimum of three seismic stations so

let's pop a few of these seismic

stations on the map let's say we have

one here in California one up here in

Canada and one down south here labeled

one two and three now these are

locations where we have seismometers

actively monitoring the shaking in the

Earth's crust of course we have seismic

stations all over the world in order to

use this triangulation method we need at

least three of these or data from three

of them so step one is going to be to

take the data the the seismogram from

each of these stations and determine

each of their epicenter distances that

is to say I want to know how far point

one is from the earthquake how far point

two is from the earthquake and how far

point three is from the earthquake and

this is fairly easily accomplished you

would simply find out the difference in

arrival times for the p-waves and

s-waves and then use a travel time graph

to calculate the distances so let's say

you have done that and you have

established that seismic station 1 is

approximately 700 kilometers from the

earthquake so something like this but

the problem is we don't know if it's 700

condors in this direction in this

direction in this direction we don't

know it could be 700 kilometers in any

direction so what we can do is draw a

circle around Oh point one with the

radius of 700 kilometers

and now we know that the epicenter is

somewhere on that circle somewhere on

that line but again that's not good

enough because we want to pinpoint the

location so let's turn our attention to

location two and say we did our math and

we found that location two is 3,000

kilometers from the epicenter now again

it could be 3,000 kilometers in any

direction so we will draw a circle

around point two with the radius of 3000

kilometers now notice something if you

did this properly your circles should

intersect most likely in two places what

that means is that the earthquake had to

happen either here at this intersection

or here at this intersection but again

that's not good enough because we want

to know exactly where the epicenter was

which leads us to Station three we take

our seismogram we do our math and we

determine that Station 3 is

approximately 3,500 kilometers from the

epicenter so again it could be in any

direction so we take a drawing compass

and we draw our circle with radius 3,500

kilometers now if this works out


all three circles should intersect in

one single point and that point is your

epicenter shown by the pink star this is

what we call the triangulation method

for locating the earthquake epicenter