Chapter 8: EarthquakesGuided NotesEarth Science

8.1 What is an Earthquake?

Earthquakes

An _____________________is the vibration of Earth

produced by the rapid release of energy.

Focus and Epicenter

___________________ is the point within Earth

where the earthquake __________________.

_____________________ is the location on the

surface directly __________________ the focus.

Faults

_________________ are fractures in Earth where

movement has occurred.

Causes of Earthquakes

Elastic Rebound Hypothesis

Most earthquakes are produced by the rapid

release of __________________ energy stored in

__________ that has been subjected to great forces.

When the ________________ of the rock is

exceeded, it suddenly _____________, causing the

vibrations of an earthquake.

Aftershocks and Foreshocks

An _________________ is a small earthquake that

follows the main earthquake.

A __________________ is a small earthquake that

often precedes a major earthquake.

8.2 Measuring Earthquakes

Earthquake Waves

________________________ are instruments that record

earthquake waves.

____________________ are traces of ______________,

electronically recorded ground motion made by

seismographs.

________________________ are seismic waves that travel

along Earth’s outer layer.

Body Waves

Identified as P waves or S waves

P waves

Are _________________ waves that push

(__________________) and pull (_____________)

in the direction that the waves travel

Travel through solids, liquids, and gases

Have the ________________ velocity of all

earthquake waves

S waves

Seismic waves that travel along Earth’s

_____________________

Shake particles at ____________________

to the direction that they travel

Travel only through ________________

Slower velocity than P waves

A _____________________ shows all three types of

seismic waves—surface waves, P waves, and S waves.

Locating an Earthquake

Earthquake _____________________

The ____________________ is located using the

difference in the arrival times between P and S wave

recordings, which are related to __________________.

Earthquake _____________________

Travel-time graphs from three or more

_______________________ can be used to find

the exact location of an earthquake

_____________________.

Earthquake _____________________

About _______________ of the major earthquakes

occur in a few narrow zones.

Historically, scientists have used two different types of

measurements to describe the size of an earthquake--

_____________________ and ____________________

Richter Scale

Based on the amplitude of the _________________

seismic wave.

Each unit of __________________ magnitude

equates to roughly a __________________ energy

increase

Does not estimate adequately the size of very large

______________________

Momentum Magnitude

Derived from the amount of __________________

that occurs along the ________________________.

_________________________________________

is the most widely used measurement for

earthquakes because it is the only

______________ scale that estimates the energy

________________ by earthquakes.

Measures very ___________________ earthquakes

8.3 Destruction From Earthquakes

Seismic Vibrations

The damage to buildings and other structures from

earthquake ________________depends on several factors.

These factors include the _________________ and

__________________ of the ________________, the

nature of the material on which the structure is built, and

the _________________ of the structure.

Building Design

Factors that determine structural damage:

___________________ of the earthquake

________________________ stone or brick

buildings are the most serious safety

threats

Nature of the material upon which the

_______________________ rests

The _________________ of the structure

Liquefaction

___________________ material turns fluid

Underground objects may ____________ to surface

Tsunamis

Cause of Tsunamis

A ____________________ triggered by an earthquake

occurs where a slab of the ocean floor is displaced

_____________________ along a ______________.

A tsunami also can occur when the ________________ of

a quake sets an underwater _________________________

into motion.

______________________ is the Japanese word for

“seismic sea wave.”

Movement of a Tsunami

Tsunami Warning System

Large _________________ are reported to ____________

from Pacific seismic stations.

Although ____________________ travel quickly, there is

sufficient time to evacuate all but the area closest to the

________________.

Other Dangers

Landslides

With many earthquakes, the

greatest damage

to structures is from

__________________ and ground

___________________, or the sinking of the ground

triggered by ____________________.

Fire

In the San Francisco

earthquake of _______, most

of the destruction was caused

by ___________ that started when __________

and _________________ lines were cut.

Predicting Earthquakes

Short-Range Predictions

So far, methods for short-range

predictions of _____________________ have not

been successful.

Long-Range Forecasts

Scientists don’t yet understand enough

about how and where ______________________ will

occur to make accurate long-term

_____________________.

A

_____________________________ is an area along a

___________________ where there has not been any

_________________________ activity for a long period

of time.

8.4 Earth’s Layered Structure

Layers Defined by Composition

Earth’s interior consists of three major zones defined by

their chemical composition—the ________________,

____________________, and _________________.

Crust

Thin, rocky __________________

layer

Varies in

________________________

Roughly 7 km in oceanic regions

Continental crust averages

_____________

Exceeds _________ in mountainous

regions

Seismic Wave Paths Through the Earth

Continental Crust

Upper crust composed of

________________ rocks

Lower crust is more akin to

_____________

Average _____________ is about

2.7 g/cm3

Up to _______________________

years old

Oceanic crust

_____________________

composition

Density about

___________________

Younger (________________________

years or less) than the

continental crust

Mantle

Below crust to a depth of

____________ kilometers (km)

Composition of the

uppermost mantle is the _______________________

rock ___________________ (changes at greater depths).

Core

Below _______________

Sphere with a

_________________ of _____________ kilometers

(km)

Composed of an

_________________________ alloy

Average

__________________ of nearly 11 g/cm3

Layers Defined by Physical Properties

Lithosphere

____________________and uppermost

_________________ (about ______________ thick)

Cool, rigid, solid

Asthenosphere

Beneath the ________________________

Upper __________________

To a _______________ of about 660 kilometers

Soft, weak layer that is easily deformed

Lower Mantle

660–2900 km

More _________________ layer

Rocks are very hot and capable of

_______________ flow.

Inner Core

Sphere with a radius of ___________________

Behaves like a ________________

Outer Core

__________________ layer

2270 km thick

_______________________________________ of

metallic iron within generates Earth’s

___________________________________.

Discovering the Earth’s Layers

Moho

______________________ of seismic

waves increases abruptly ___________________ 50 km of

_____________

________________________ crust from

underlying mantle

Shadow Zone

Absence of _____________________ from

about _______ degrees to ____________ degrees around

the globe from an earthquake

Can be explained if Earth contains a

______________ composed of materials _______________ the

overlying mantle.

Crust

Early ____________________ data and

drilling technology indicate that the continental crust is

mostly made of lighter, __________________________

rocks.

Mantle

Composition is more

__________________________.

Some of the lava that reaches Earth’s

surface comes from

_________________________________

within.

Core

Earth’s core is thought to be mainly dense

_____________ and __________________, similar to metallic

meteorites. The surrounding _________________ is

believed to be composed of rocks similar to stony

____________________.