Chapter 9

Chapter 9 Earthquakes

9.1 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

Types of Faults • 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

Types of Faults • 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

Types of Faults • 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

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

Locating an Epicenter • 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 • 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

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

Measuring Earthquakes • 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 • 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 • 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

Chapter 9

Chapter 9

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