Locating and Measuring Earthquakes

Objectives:

1.    Define magnitude and the Richter scale.

2.    List ways to make your classroom and home more earthquake safe.

3.    Explain how a seismograph is used to record earthquake waves and locate an earthquake's epicenter.

Vocabulary words:

seismologist    seismograph      seismogram     magnitude    tsunamis

Resources:

Notes: (10-2)

As we discussed earlier, earthquakes occur all throughout the day (~1 every 10seconds) because the Earth is undergoing continual change as its plates drift atop the asthenosphere.  Seismology is the study of seismic waves (earthquakes).   Although the study of earthquakes have increased our understanding of the plates and their movements, the measuring equipment remains relatively simple.

• Studied by a seismologist

• Measuring Earthquakes

•         Measured using a seismograph (seismometer) - 3 stations N-S, E-W, up-down

•               A siesmograph is simply a drum with paper, turned slowly by a clock, and pendulum with a pen attached.  As the ground shakes the drum moves back and forth making the tracing on the piece of paper.

•             As the ground shakes, the pendulum remains stationary (Newton's 3rd) recording the amount of movement by the base.

•             The tracing is now called a seismogram (recorded seismic activity) and is an indication of the energy associated with the seismic activity.

(mgnews.msfc.nasa.gov/.../imagesummer2000/ seismograph.jpg)

(www.geo.lsa.umich.edu/~crlb/COURSES/ 107/Lec5/seismogram.jpe)

Richter scale:

• Based on the strength of the seismic wave

• Measures the intensity of ground movement that is released by the earthquake

• Is not concerned with the length of the fault

• Each step up the scale equals a 32 times as much energy increase

• How much more energy does a 7.0 earthquake have compared to a 6.0?

322 = 1024

(www.sdgs.usd.edu/images/maps/ quake/RichterScale.gif)

Movement magnitude:

• Another measurement used by seismologist

• Indicates the energy released by the earthquake

• Uses the length of fault, movement of rock, & the stiffness of the rock

Locating the earthquake:

• Uses a process called triangulation

• 3 seismic stations are required

• based on the speed of the waves

(earthquake.usgs.gov/4kids/learning/ images/triangulation.gif)