Locating an Earthquake's Epicenter
Overview
Locating the epicenter of an earthquake- basic intro
Locating an Earthquake's Epicenter
Be sure students watch the video- may choose to do this as a class before students complete the short reading and questions.
Triangulation: using more than one data point to plot information. Think of a triangle.
References: Earth and Space Science- Glencoe
Glencoe/McGraw-Hill., & American Museum of Natural History. (2012). Earth & space iScience. Columbus, OH: Glencoe/McGraw-Hill.
Learning Objectives:
- What is the difference between a seismometer and a seismogram?
- Explain the steps involved in triangulation to find the epicenter of an earthquake.
- Suppose P-waves from an earthquake arrive at a seismometer location at 12:51 and 31 seconds. S-waves from the earthquake arrive at the same seismometer at 12:52 and 13 seconds. How would you use this information to begin to find the epicenter of the quake?
Mapping Earth's Interior:
Scientists that study earthquakes are called seismologists. They use the properties of seismic waves to map Earth's interior. P-waves and S-waves change speed and direction depending on the material they travel through. Through extensive earthquake studies, seismologists have discovered that S-waves cannot travel through the outer core. By studying the speed of P-waves, seismologists have discovered that the inner and outer cores are composed mostly of iron and nickel. They have found that seismic waves are slower in hot material like in areas of the mantle beneath mid-ocean ridges and hotspots and are faster in cool areas of the mantle like near subduction zones.
Locating an Earthquakes Epicenter
An instrument called a seismometer measures and records ground motion and can be used to determine the distance seismic waves travel. Ground motion is recorded as a seismogram which is a graphical illustration of seismic waves. Seismologists use a method called triangulation to locate an earthquake's epicenter. This method uses the speeds and travel times of seismic waves to determine the distance to the earthquake epicenter.
- Find the arrival time difference - first, determine the number of seconds between the arrival of the first P-wave and the first S-wave. This time difference is called the lag time.
- Find the distance to the epicenter - next, use the earthquake distance graph to use the lag time that was calculated and the solid line on the graph (where they intersect), and read the corresponding distance from the epicenter on the x-axis.
**AFTER watching the video and reading the information above answer the guiding questions in your notebook. Be sure to use complete sentences and show your work.