# locating earthquake epicenters

## finding the epicenter

Here are the steps to finding an earthquake epicenter using three seismograms: 1. Determine the epicenter distance from three different seismographs. The longer the time between the arrival of the P-wave and S-wave, the farther away is the epicenter. So the difference in the P- and S-wave arrival times determines the distance between the epicenter and a seismometer. 2. Draw a circle with a radius equal to the distance from the epicenter for that seismograph. The epicenter is somewhere along that circle. Do this for three locations. Using data from two seismographs, the two circles will intercept at two points. A third circle will intercept the other two circles at a single point. This point is the earthquake epicenter (Figure 1.1). Of course, its been a long time since scientists drew circles to locate an earthquake epicenter. This is all done digitally now. but its a great way to learn the basics of how locating an epicenter works. Three circles drawn from three seismic stations each equal to the radius from the station to the epicenter of the quake will intercept at the actual epicenter. Click image to the left or use the URL below. URL:

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

in order to locate the epicenter of an earthquake, you need the distance to the epicenter from at least ____ stations.

``````a) one

b) two

-->  c) three

d) four or more
``````

the longer the time between the arrival of the p-wave and s-wave, the closer the epicenter is.

``````a) true

-->  b) false
``````

p-waves arrive before s-waves.

``````-->  a) true

b) false
``````

seismographs display

``````a) p-waves

b) s-waves

c) surface waves

-->  d) all of the above
``````

the epicenter of the 2011 japan quake was

``````a) deep

b) intermediate

-->  c) shallow

d) unknown
``````

where was the epicenter located in the 2011 japan earthquake?

``````a) off of china

-->  b) off of japan

c) hiroshima

d) off of australia
``````

how do you determine the distance to an earthquake epicenter from a seismic station?

``````-->  a) calculate the difference in arrival time between the p- and s-waves.

b) take the number of seconds for the p-wave to arrive and multiply by 100 miles.

c) it is the difference in arrival time between the s-waves and the surface waves.

d) take the number of seconds for the surface waves to arrive and multiple by 100 miles.
``````

once you know the distance to an epicenter, how do you determine the location of the epicenter?

``````-->  a) draw a circle of the correct radius from three seismic stations. where the three circles

b) draw a circle of the correct radius from the seismic station.

c) find the correct radius from the seismic station and calculate the direction of the epicenter from the seismograph.

d) its not possible to do this.
``````

what is the number of seismic stations you need to find an epicenter and why?

``````a) you need two because two will intersect at two points but one is offshore so it is not the epicenter.

b) you need one because the epicenter will be somewhere along that circle.

-->  c) you need three because three is the minimum number of circles that will intersect at

d) its not possible to do this.
``````

if you could only get epicenter distances from two seismic stations, how could you find the epicenter?

``````a) you would need to look at rock types to see where a quake would be more likely to happen geologically.

-->  b) you would need to look for earthquake damage near both points of intersection to see

c) you would need to look at where the earthquake faults are.

d) its not possible to do this.
``````

## diagram questions

No diagram questions associated with this lesson