8.2 Measuring Earthquakes

Prentice Hall 2006Earth Science

Objectives

• Identify the three types of seismic waves• Explain how to locate the

epicenter of an earthquake• Describe the different ways

earthquakes are measured.

Vocabulary

• Seismograph• Seismogram• Surface wave• P wave• S wave• Moment magnitude

8.2 Objective 1

• Identify the three types of seismic waves

Identify the three types of seismic waves

• The study of earthquake waves is called _________.

• The recording instrument is called a _______________.

• The record from a seismograph is called a _______________.– A seismogram records

the ______________ of the Earth.

Tarbuck 6.6

Tarbuck 6.7

Identify the three types of seismic waves

• Types– _____________ waves • have a __________

motion and have the _________ velocity of all waves.

Tarbuck 6.8

Identify the three types of seismic waves

• Types– Surface waves

• have a complex motion and have the slowest velocity of all waves.

– Body waves • Primary waves.

– also called _____ waves

– P waves exhibit a _______________ (compression-rarefaction) motion.

– Primary waves travel through ________________________________.

– P waves have the ______________of all seismic waves.

Identify the three types of seismic waves

• Types– Surface waves

• have a complex motion and have the slowest velocity of all waves.

– Body waves • Primary waves.

– also called P waves– P waves exhibit a push-pull

(compressional) motion.– Primary waves travel

through solids, liquids, and gases.

– P waves have the greatest velocity of all seismic waves.

• Secondary (S) waves– create a

___________ motion.

– only travel through ___________.

– velocity is ____________________________________.

8.2 Objective 2

• Explain how to locate the epicenter of an earthquake

Locating an Earthquake• The focus is the place within Earth where

Earthquake waves originate.

• Epicenter – is the point on the surface directly

above the focus.

– The epicenter is located using the ______________________________________________________, which can be related to distance.

Locating an Earthquake• The focus is the place within Earth where

Earthquake waves originate.

• Epicenter – is the point on the surface directly above

the focus.– The epicenter is located using the

difference in arrival times between P & S wave recordings, which can be related to distance.

• ______________are needed to locate an epicenter.– A circle equal to the

epicenter distance is drawn around each station.

– The ___________ of the three circles is the epicenter.

Earthquake distribution• Earthquake zones are closely associated with plate

boundaries particularly ______________________________________________________________________________________________

Shows distribution of earthquakes w/ > 5.0 magnitude between 1980 & 1990.

8.2 Objective 3

• Describe the different ways earthquakes are measured.

Earthquake intensity & magnitude

• Three scales–Modified Mercalli–Richter–Moment Magnitude

Tarbuck Table 1Earthquake intensity & magnitude

• _____________________ is a measure of the degree of earthquake shaking at a given locale based on the amount of damage.

• Intensity is most often measured by the ________________________________________

Earthquake intensity & magnitude

• Magnitude – is a concept introduced by

Charles Richter in 1935.– measured by the Richter

scale ML based on the ____________________________________________________________

– Each unit of the Richter magnitude equates to roughly a ____ fold energy increase.

– ____________________estimate adequately the size of very large earthquakes.

Earthquake intensity & magnitude

• Moment Magnitude scale – a ___________________magnitude measurement– measures very large earthquakes.– derived from the _______________________that

occurs along a fault zone, the ___________ of the rupture surface, and _______________strength of the faulted rock

• Largest earthquakes