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

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

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

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

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

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.

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.

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.

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

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 ____________________.