Mrs. Bartley’s Earthquakes Chapter 4 Mrs. Bartley’s Earthquakes

Forces Inside Earth Objectives Explain how earthquakes result from the buildup of stress in Earth’s crust Contrast normal, reverse, and strike-slip faults

Causes of Earthquakes Passing the Elastic Limit Causes Faulting Applied stresses can cause rocks to bend and stretch Eventually rocks will break away from one another Area in which the rocks break and move is called a fault Vibrations produced is called an earthquake Earth’s crust movement causes the stresses applied

Tension The rocks on the crust are being stretched as two plates are moving apart The middle becomes thinner until a normal fault occurs

Types of Faults p.120 Normal Fault Earth’s plates move apart Movement of the plates causes tension Rocks above the fault surface move downward in relation to the rocks below the fault surface

Rio Grande Rift Valley

Compression This stress force squeezes rock until it folds or breaks This can create a reverse fault

Types of Faults p.121 Reverse Faults Compression forces are applied because Earth’s plates are coming together Causes rocks to bend and break Rocks above the fault surface are forced up and over the rocks below the fault surface

Northern Rocky Mountains

Shearing This stress force pushes rock in two opposite directions This can cause a strike-slip fault

Types of Faults p.121 Strike-slip Fault Earth’s plates move sideways to one another Creates a shear force Rocks on either side of the fault surface are moving past each other without much upward or downward movement

San andreas fault

Earthquake Information Objectives Compare and contrast primary, secondary, and surface waves Explain how an earthquake epicenter is located using seismic wave information Describe how seismic wave studies indicate the structure of Earth’s interior

Types of Seismic Waves p.125 Earthquake focus Focus – the point in Earth’s interior where the energy waves are produced Seismic waves Seismic wave - the energy waves that move outward from the earthquake focus and make the ground quake Epicenter The point on Earth’s surface directly above the earthquake focus

Types of Seismic Waves p.127 Primary waves Energy waves that cause rocks to move back and forth in the same direction Compression and stretching forces are created Secondary waves Energy waves that cause rocks to move at right angles to the wave

Types of Seismic Waves Energy waves that reach the Earth’s surface Surface waves Energy waves that reach the Earth’s surface Energy waves that move rocks in an elliptical motion

Locating an Epicenter p.130 Seismic waves do not travel through earth’s surface at the same speed Primary waves are the fastest Surface waves are the slowest Seismograph stations Record the information from the earthquake by recording the different types of waves as they reach the station

Locating and Epicenter p.131 Epicenter Location If information is received from the earthquake at three stations, then the epicenter can be located A circle is drawn around each station on a map The radius is equal to the distance from the station to the epicenter The point in which all three circles intersect is the earthquake epicenter

Using Seismic Waves to Map Earth’s Interior The speed of the waves changes as the depth changes The speed changes in accordance to the density of the layers of Earth

Using Seismic Waves to Map Earth’s Interior Structure of Earth Inner core Solid and very dense Composed of mostly nickel and iron Outer core Liquid layer that surrounds the inner core Composed of nickel and iron

Using Seismic Waves to Map Earth’s Interior Mantle Largest layer located above the inner core Composed of silicon, oxygen, magnesium, and iron Crust Outermost layer Solid and similar in composition to the mantle

Using Seismic Waves to Map Earth’s Interior Moho Discontinuity Boundary between the crust and the mantle Seismic waves speed up as they reach this area Seismic waves speed up as they reach more dense areas and slow down when the reach less dense areas The more solid the layer the more dense

Using Seismic Waves to Map Earth’s Interior Shadow zone The area between 105-140 degrees from the epicenter Area in which seismic waves can’t be detected What is the cause? Secondary waves can’t be transmitted through liquid layers Primary waves are slowed and deflected by the outer core and speed up again when the reach the solid inner core

Destruction by Earthquakes Objectives Define magnitude and Richter scale List ways to make your classroom and home more earthquake safe

Measuring Earthquakes p. 135 Seismology Seismologists - People who study earthquakes and seismic waves Use instruments called seismographs Record seismic waves A drum with a sheet of paper vibrates and a stationary pen marks the vibrations on the paper The height of the lines are used to measure the energy released from the earthquake called the magnitude

Measuring Earthquakes p.128 Earthquake Magnitude Usually determines the strength of the break Doesn’t determine the duration or the size For each increase of 1is 10 times stronger An earthquake of 4 is 10 times stronger than an earthquake of 3

Tsunamis p.137 Caused by the movement of the ocean floor Causes a disruption in the water Some are so wide that a large ship can travel over the wave without knowing Recent earthquake in the Indian Ocean created a tsunamis that was 100 feet high and moving at 500 mph

Earthquake Safety Quake proofing your home Place heavy objects near the floor Fix gas appliances in place

9.4 Living on a Fault Objectives Recognize that most loss of life in an earthquake is caused by the destruction of human-made structures Consider who should pay for making structures seismic safe

Who should pay for earthquake preparation? Seismic safe structures Structures that are resistant to the vibrations of Earth’s crust Structures are made with moorings Made of steel and are filled with alternating layers of rubber and steel These structures absorb the energy produced from the earthquake