How do we Locate the Epicenter of an Earthquake? 

In the last lesson we learned how we can use a seismogram to determine the distance to the epicenter.  Aside from knowing the distance we may want to also know where in the world the earthquake occurred.  

TO FIND THE LOCATION OF THE EPICENTER WE NEED 3 SEISMOGRAMS

Step 1:  Find Distances to the Epicenter

The first thing we need to do is figure out the distance from each seismogram to the epicenter, using the same method we learned in the last lesson. 

Seismogram 1:   

       Difference in arrival times = 4 min 0 sec

       Distance to epicenter = 2,800 km

Seismogram 2: 

        Difference in arrival times = 5 min 40 sec

       Distance to epicenter  = 4,000 km

Seismogram 3: 

       Difference in arrival times = 3 min 0 sec 

       Distance to epicenter = 1,800 km 

Step 2:  Draw Circles

Now that we know the distance from each location to the epicenter, we need to mark those distances on a map.  However, since we don't know the direction to the epicenter, we need to DRAW CIRCLES AROUND EACH STATION WITH A RADIUS EQUAL TO THE DISTANCE WE JUST FOUND. 

Step 3:  Mark the Epicenter

The three circles that we drew should intersect, or nearly intersect, at one point.  That point is the epicenter of the earthquake.  Mark the epicenter with a big X.