<img src="https://d5nxst8fruw4z.cloudfront.net/atrk.gif?account=iA1Pi1a8Dy00ym" style="display:none" height="1" width="1" alt="" />
Dismiss
Skip Navigation

5.15: Locating Earthquake Epicenters

Difficulty Level: Basic Created by: CK-12
Atoms Practice
Estimated2 minsto complete
%
Progress
Practice Locating Earthquake Epicenters
 
 
 
MEMORY METER
This indicates how strong in your memory this concept is
Practice
Progress
Estimated2 minsto complete
%
Estimated2 minsto complete
%
Practice Now
MEMORY METER
This indicates how strong in your memory this concept is
Turn In

Can you find an earthquake epicenter?

The epicenter of the 2011 Japan earthquake was just offshore of Sendai. This is where the Pacific Plate plunges into a subduction zone. The earthquake had a relatively shallow depth of 20 miles (32 km). Remember that shallow quakes typically cause the most damage. How do scientists find an earthquake epicenter?

Finding the Epicenter

One seismogram indicates the distance to the epicenter. This is determined by the P-and S-wave arrival times. If a quake is near the seismograph, the S-waves arrive shortly after the P-waves. If a quake is far from the seismograph, the P-waves arrive long before the S-waves. The longer the time is between the P-and S-wave arrivals, the further away the earthquake was from the seismograph. First, seismologists calculate the arrival time difference. Then they know the distance to the epicenter from that seismograph. They can connect all the points that are that distance from the seismic station. This makes a circle around the station!

Next, the seismologists try to determine the location of the earthquake epicenter. To do this they need the distances to the epicenter from at least three seismographs. Let’s say that they know that an earthquake’s epicenter is 50 kilometers from Kansas City. They draw a circle with a 50 km radius around that seismic station. They do this twice more around two different seismic stations. The three circles intersect at a single point. This is the earthquake’s epicenter (Figure below).

Seismographs in Portland, San Francisco, and Salt Lake City are used to find an earthquake epicenter.

Of course, it's been a long time since scientists drew circles to locate an earthquake epicenter. This is all done digitally now. but it's a great way to learn the basics of locating an epicenter.

Summary

  • To find an earthquake epicenter you need at least three seismographs.
  • Find the distance from each seismograph to the earthquake epicenter.
  • The interception of the three circles is the epicenter.

Practice

Use the resource below to answer the questions that follow.

  1. What is a seismogram?
  2. What waves does a seismogram show?
  3. What is the S-P interval?
  4. How many data stations are required to determine the epicenter?
  5. What is triangulation?

Review

  1. How do you determine the distance from the seismograph to the earthquake epicenter?
  2. How do you find the epicenter from three seismographs?
  3. What role does the S-P interval play in locating an earthquake epicenter?

    Notes/Highlights Having trouble? Report an issue.

    Color Highlighted Text Notes
    Please to create your own Highlights / Notes
    Show More

    Vocabulary

    seismogram

    A record of ground motion at a seismic station.

    Image Attributions

    Show Hide Details
    Description
    Difficulty Level:
    Basic
    Grades:
    6 , 7
    Date Created:
    Jan 04, 2013
    Last Modified:
    Aug 29, 2016
    Files can only be attached to the latest version of Modality
    Please wait...
    Please wait...
    Image Detail
    Sizes: Medium | Original
     
    SCI.ESC.366.L.2
    Here
    Add Note
    Please to create your own Highlights / Notes