EARTHQUAKES

FORCES IN EARTH’S CRUST

How does stress change Earth’s crust?Stress is a force that acts on rock to change its shape

or volume.Stress= force / unit of area

Pressure = Force / Area

The movement of Earth’s plates can create strong forces that slowly bend

or fold many rocks like a caramel candy bar.

An earthquake is the shaking of the ground cause by seismic waves.

Tension, compression and shearing work over millions of years to change the shape and volume of

a rock.

TENSION occurs where two plates pull apart.

The stress force that pulls on the crust and thins rock in the middle is called

tension.

COMPRESSION occurs where two plates come together.

The stress force that squeezes rock until it folds or breaks.

SHEARING occurs where two plates slip past each other. Shearing can cause rock to break and slip apart or to change its

shape.

HOW DO FAULTS FORM?When enough stress builts up in rock, the

rock breaks, creating a fault.

Normal Fault.- Rock is pull apart by tension.

The fault cuts through rock at an angle, so one block sits over the

fault ( hanging wall) and the other block lies under the fault ( footwall).RIO GRANDE RIVER flows through a

wide valley in Mexico.

NORMAL FAULT

REVERSE FAULTS.- The blocks move in the reverse direction. The hanging wall

moves up and the footwall moves down.

R. F. form where compression pushes the rock of the crust together.

The northern Rocky Mountains rise high above the Western United States

and Canada.

STRIKE-SLIP FAULT. – The rocks slip past each other sideways, with little

up or down motion.They form when compression pushes

the rock of the crust together. The hilly plains in Southern California.San Andreas fault is an example of a

transform boundary.

Type of faults

SAN ANDREAS FAULT

SAN ANDREAS FAULT

1. Normal Fault.- hanging wall slips down relative to the footwall.

2. Reverse Fault.-The hanging wall moves up relative to the footwall.

3. Strike-slip fault Rocks on either side4. Of the fault move past to each other.

1 2 3

Plate movements create new landformsOver millions of years, the forces of plate

movement can change a flat plain into features such as :

anticlines and synclines, folded mountains, fault-block mountains, and

plateaus.

ANTICLINE

ANTICLINE

FOLDS are bends in rock that form when compression

shortens and thickens Earth’s crust. A fold can be a few

centimeters across or hundreds of kilometers wide.

ANTICILINES AND SYNCLINES( By Compression forces)

Upward and downward fold in rock.A fold in rock that bends downward in to

form a V shape is a syncline.The central Appalachian Mountains in

Pennsylvania.

EARTHQUAKES PLATE MOVEMENT

SYNCLINES

SYNCLINES

FOLDED MOUNTAINSCollision of plates , compression and

folding of crust over a wide area.Largest Mountain Ranges:

Himalayas ( Asia ), Alps ( Europe )

FOLDED MOUNTAINS

Folded mountains/ anticiclines

Salt Lake City to Los AngelesCross the Great Basin , region with many

mountains, valleys or basins.Region formed by tension and faulting.

Fault-block mountains formed where two plates move away from each other.

SALT LAKE CITY/ UTAH

GREAT BASIN . NEVADA

GREAT BASIN NATIONAL PARK NEVADA

GREAT BASIN /NEVADA

PLATEAUSLarge area of flat land elevated high

above sea level.Forces that raise mountains , uplift a

large flat block of rock ( crust).Plateaus have many different flat layers.Colorado Plateau in the “Four Corners” , regions of Colorado, Utah , Colorado and

New Mexico.

COLORADO PLATEAU

LESSON 2

EARTHQUAKE is the shaking and trembling that results from movement

of rock beneath Earth’s surface.

LOMA PRIETA .- SAN FRANCISCO

SEISMIC WAVES are vibrations, that are similar to sound waves.

They travel through Earth carrying energy released by an earthquake.

TYPES OF SEISMIC WAVES• Focus point• Epicenter

• P waves.- waves that compress and expand

• S Waves .- waves that vibrate side to side. Vibrations at an angle 90 to the

direction that they travel.

P Waves travel through liquids and solids.

S waves can not move through liquids.S waves reached the surface and shake

structures violently. Surface waves are P or S waves that

reach the surface.S.W. move more slowly than P or S waves, but they can produce sere

ground movements.

KABUL INDU KUSH REGION ( AFGHANISTAN )

Most earthquakes start in the lithosphere within about 100 Km.

beneath Earth’s surface.Seismic Waves carry energy.

CAN VIBRATE THE GROUND SIDE TO SIDEP WAVES

CAN MAKE THE GROUND ROLL LIKE THE OCEAN WAVE

CCOMPRESS AND EXPAND THE GROUND

S WAVES

SURFACE WAVES

SEISMOGRAPH is an instrument that records and measures an earthquake’s

seismic waves.

The magnitude or size of an earthquake is measured on a seismograph using the

RICHTER scale.

The amount of earthquake damage or shaking is rated using the Modified

Mercalli scale.

The Moment Magnitude Scale rates the total energy an earthquake releases.