This document provides an overview of earthquakes, including key vocabulary terms. It describes how earthquakes are caused by movement along faults in the earth's lithosphere. When seismic waves from an earthquake are detected by seismometers, seismologists can use the timing of the waves to triangulate the earthquake's epicenter via its focus point below the surface. The magnitude scales described quantify an earthquake's intensity or total energy released.

1. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 1
Lots of Vocabulary
 Earthquake (531) – the vibrations in the ground that result from movement along breaks in
Earth’s lithosphere
 Fault (533) – a break in Earth’s lithosphere where one block of rock moves toward, away from,
or past another
 Seismic wave (534) – energy that travels as vibrations on and in Earth
 Focus (534) – These waves originate where rocks first move along the fault, at a location inside
Earth
 Epicenter (534) – the location on Earth’s surface directly above the earthquake’s focus
 Primary wave (535) – Also called p-waves, it causes particles in the ground to move in a push-
pull motion similar to a coiled spring
 Secondary wave (535) – Also called S-waves, it causes particles to move up and down at right
angles relative to the direction the wave travels
 Surface wave (535) – causes particles in the ground to move up and down in a rolling motion
 Seismologist (536) – scientists that study earthquakes
 Seismometer (537) – an instrument that measures and records ground motion and can be
used to determine the distance seismic waves travel
 Seismogram (537) – a graphical illustration of seismic waves
What are Earthquakes?
 Earthquakes are the _________________________________ in the ground that result from
movement along breaks in Earth’s lithosphere
 These breaks are called _______________________
 The __________________ that move tectonic plates also push and pull on rocks along the
fault and if these become big enough the blocks of rock on either side of the fault can move
horizontally or vertically
 The _____________________ the force the larger and more disastrous the earthquake
Where do Earthquakes Occur?
Earthquakes and Plate Boundaries
 Earthquakes result from the build up and release of ___________________along active plate
boundaries
 Some earthquakes occur more than ______________km below Earth’s surface

2. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 2
 The deepest earthquakes occur at ________________________ plate boundaries
o Here the denser oceanic plate ____________________ into the mantle
o These earthquakes release tremendous amounts of ____________________
 Shallow earthquakes occur along ____________________ plate boundaries, like mid-ocean
ridges
 Shallow earthquakes also occur along ______________________ boundaries
 Along continental convergent boundaries, earthquakes of varying depths occur
Rock Deformation
 When a force such as pressure is applied to rock along plate boundaries, the rock can
change_______________ . This is called rock deformation.
 Eventually rocks can be deformed so much that they ____________________ and move.
 This is a lot like bending a stick until it breaks
Faults
 When stress builds in places like a plate boundary, rock can form faults.
 A fault is a break in Earth’s ____________________________ where one block of rock moves
toward, away from, or past another
 When rocks move in _______________ direction along a fault, an earthquake occurs
 The direction depends on the force applied
Types of Faults
 Reverse Fault
o Forces push two blocks of rock__________________________ .
o The rock above the fault moves up relative to the block of rock below the fault
o Occurs at ________________________ boundaries
 Normal Fault
o Forces pull two blocks of rock_____________________.
o The rock above the fault moves down relative to the rock below the fault
o Occurs at ______________________ plate boundaries
 Strike-Slip
o Two blocks of rock slide _______________________ past each other in opposite

3. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 3
directions
o Occurs at _________________________ plate boundaries
Earthquake Focus and Epicenter
 When rock moves along a fault, they release energy that travels as
_________________________ on and in Earth called seismic waves
 These waves _________________________ where rocks first move along the fault, at a
location inside Earth called the focus
 An earthquakes focus can occur anywhere between Earth’s surface and depths of greater than
___________km
 Earthquakes are often referred to by their ____________________________
 The epicenter is the location on Earth’s ___________________ directly above the earthquake’s
focus
Seismic Waves
 During an earthquake, a rapid release of ________________along a fault
produces seismic waves
 Seismic waves travel outward in ___________ directions through rock
 Similar to a stone being dropped in water, seismic waves move outward in
___________________
 Seismic waves _________________ energy through the ground and
produce the motion that you feel during an earthquake
 The energy released is stronger near the epicenter and
______________________ in energy and intensity as you move outward
Types of Seismic Waves

4. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 4
 Primary Waves (P-Waves)
o Causes rock particles to vibrate in the ____________________ direction that waves
travel
o ___________________ seismic wave
o _______________ to be detected and recorded
o Travels through solids and _________________________
 Secondary Waves (S-Waves)
o Causes rock particles to vibrate _____________________________________ to the
direction that waves travel
o ________________________ than P-waves, but faster than surface waves
o Detected and recorded after P-waves
o Only travels through __________________________
 Surface Waves
o Cause rock particles to move in a ___________________________ or elliptical motion
in the _________________ direction that waves travel
o _______________________ seismic wave
o Generally causes the _______________________ damage
Mapping Earth’s Interior

5. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 5
 Scientists that study _____________________________________ are called seismologists
 They use the properties of seismic waves to map Earth’s interior
 P-waves and S-waves change _______________________ and direction depending on the
__________________________ they travel through
Inner and Outer Core
 Through extensive earthquake studies, seismologists have discovered that
________________________ cannot travel through the outer core
 This discovery proved that Earth’s outer core is _________________________unlike the solid
inner core
 By analyzing speed of P-waves traveling through the core, seismologists also discovered that
the inner and outer cores are composed of mostly ______________________ and
_________________________
The Mantle
 Seismologists also have used seismic waves to model ___________________________
currents in the mantle
 The _________________________ of seismic waves depend on the temperature, pressure,
and chemistry of the rocks that the seismic waves travel through.
 Seismic waves tend to ____________________________ as they travel through hot material
o For example, seismic waves are slower in areas of the mantle beneath mid-ocean ridges
or near hotspots
 Seismic waves are _________________________ in cool areas of the mantle near
_________________________ zones

6. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 6
Locating an Earthquakes Epicenter
 An instrument called a seismometer measures and records ground _____________________
and can be used to determine the distance seismic waves travel
 Ground motion is recorded as a seismogram, a graphical ___________________________of
seismic waves
 Seismologists use a methods involving the speed and travel times of the waves to determine
the distance to the earthquake ___________________________ from at least three different
seismometers, this is called triangulation.
How to Find an Epicenter?
 Step 1:
 Determine the number of seconds between the arrival of the first P-wave and the first
S-wave on the seismogram.
 This is called lag time.
 Lag time = (arrival time of 1st
S-wave) – (arrival time of 1st
P-wave)
 Step 2:
o Use a graph showing lag time versus distance.
o Use the lag time to find the distance.

7. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 7
 Step 3:
o Using a ruler and a map scale, measure the distance between the seismometer and the
earthquakes epicenter.
o Draw a circle with a radius equal to the distance.
o When three circles are plotted, the epicenter will be where the three circles intersect.

8. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 8
Determining Earthquake Magnitude
 Scientists use 3 different scales to measure and describe earthquakes:
o The _______________________________________________________
o The _______________________________________________________ Scale
o _________________________________________ magnitude scale
The Richter Scale
 The Richter magnitude scale uses the amount of ground ___________________________ at a
given ___________________________________ from an earthquake to determine magnitude
 It begins at _______________________________, but there is no upper limit to the scale
 Each 1 unit increase represents ________________________ times the amount of ground
motion recorded on a seismogram.
o For example, a magnitude 8 earthquake produces ______________________ times
greater shaking than a magnitude 7
 The largest earthquake ever recorded was a magnitude 9.5 in _______________________ in
1960. The earthquake and following tsunamis left nearly 2000 people dead and 2 million
people homeless.

9. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 9
Moment Magnitude Scale
 Seismologists use the moment magnitude scale to measure the total amount of
_____________________ released by the earthquake.
 The energy released depends on the ______________________________ of the fault that
breaks, the motion that occurs along the fault, and the ___________________________ of the
rocks that break during an earthquake.
 The units in this scale are ___________________________________________
 For each increase of one unit on the scale, the earthquake releases
_________________________ times more energy
o That means a magnitude 8 earthquake releases more than 992 times the amount of
energy than that of a magnitude 6 earthquake.
The Modified Mercalli scale
 Another way to measure and describe an earthquake is to evaluate the
_____________________ that results from shaking
o Shaking is directly related to earthquake _____________________________
 The Modified Mercalli scale measures earthquake intensity based on descriptions of the
earth’s effects on people and structures
o The Mercalli scale ranges from ________, when shaking is not notice able, to
___________, when everything is destroyed.
 __________________ geology also contributes to earthquake damage.
o In an area covered by loose sediment, ground motion is exaggerated.
o http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf

10. Chapter 15 Lesson 1: Earthquakes – p530-540 – page 10
*Side Notes: Roman Numerals
 V=Values: X = 10 ; V = 5 ; I = 1
 Add similar values that are next to one another such as III (1+1+1 = 3)
 Add a smaller value that comes after a larger value, such as XV (10 + 5 = 15)
 Subtract a smaller value that precedes a larger value, such as IX (10 – 1 = 9)
 Use the fewest possible numerals to express the value (X rather than VV)
 Counting goes like
 I, II, III, IV, V, VI, VII, VIII, IX, X, XI, XII, XIII
 *Practice: What is the value of Roman numeral XVI? XIV?
Earthquake Risk
 Not all earthquakes occur near _____________________ boundaries
 Seismologist study the _______________________________ of an earthquake at a given
location to assess the risk
 Areas that experienced earthquakes in the _______________________ will likely experience
earthquakes again
o The New Madrid Fault in the central United States has a history of severe earthquakes
in ____________________________ registering magnitudes of 7.8 and 8.1
 However, on average only about _________________ earthquakes with magnitudes greater
than 7.0 occur worldwide each ____________________.