Earthquakes Forces in Earth’s Crust Earthquakes and Seismic Waves Monitoring Earthquakes Earthquake Safety Table of Contents

Earthquakes Plate Tectonic Boundaries

Earthquakes Forces in Earth’s Crust How does stress in the crust change Earth’s surface? Where are faults usually found, & why do they form? What land features result from the forces of plate movement?

Earthquakes Stress The movement of Earth’s plates create enormous forces that squeeze or pull the rock in the crust A force that acts on rock to change its shape or volume is stress. Stress adds energy to the rock The energy is stored in the rock until it changes shape or breaks

Earthquakes 3 Kinds of Stress in Earth’s Crust 1.Tension- pulls on the crust, stretching rock so that becomes thinner in the middle. 2. Compression-squeezes rock until it folds or breaks. 3. Shearing-pushes a mass of rock in two opposite directions

Earthquakes - Forces in Earth’s Crust Types of Stress The stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle.

Earthquakes Types of Stress The stress force called compression squeezes rock until it folds or breaks. - Forces in Earth’s Crust

Earthquakes Types of Stress Stress that pushes a mass of rock in two opposite directions is called shearing. - Forces in Earth’s Crust

Earthquakes Faults When enough stress builds up in rock, the rock breaks, creating a fault. A fault is a break in the rock of the crust where rock surfaces slip past each other Most faults occur along plate boundaries, where the forces of plate motion push or pull the crust so much that the crust breaks There are three main types of faults: Normal faults, reverse faults, & strike-slip faults

Earthquakes

Kinds of Faults Tension in Earth’s crust pulls rock apart, causing normal faults. - Forces in Earth’s Crust

Earthquakes Normal Fault Tension causes a normal fault. In a normal fault, the fault is at an angle, & one block of rock lies above the fault while the other block lies below the fault. The block of rock that lies above is called the hanging wall. The rock that lies below is called the footwall.

Earthquakes Kinds of Faults A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction. - Forces in Earth’s Crust

Earthquakes Reverse Faults Compression causes reverse faults. A reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction.

Earthquakes Kinds of Faults In a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up and down motion. - Forces in Earth’s Crust

Earthquakes Strike-Slip Fault Shearing creates strike-slip faults. In a strike-slip fault, the rocks on either side of the fault slip past each sideways, with little up or down motion.

Earthquakes Anticlines & Synclines Found on many parts of the Earth’s surface where compression forces have folded the crust The collision of two plates can cause compression & folding of the crust over a wide area Where two normal faults cut through a block of rock, fault movements may push up a fault-block mountain.

Earthquakes Changing Earth’s Surface Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus. - Forces in Earth’s Crust

Earthquakes Landforms Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines & synclines, folded mountains, fault-block mountains, and plateaus.

Earthquakes Anticline A fold in rock that bends upward into an arch is an anticline.

Earthquakes Synclines A fold in rock that bends downward to form a valley is a syncline.

Earthquakes Plateaus The forces that raise mountains can also uplift, or raise plateaus. A plateau is a large area of flat land elevated high above sea level.

Earthquakes Colorado Plateau

Earthquakes Changing Earth’s Surface Over millions of years, the forces of plate movement can change a flat plain into landforms such as anticlines and synclines, folded mountains, fault-block mountains, and plateaus. - Forces in Earth’s Crust

Earthquakes Building Vocabulary A definition states the meaning of a word or phrase. As you read, write a definition of each Key Term in your own words. Key Terms:Examples: - Forces in Earth’s Crust stressStress is a force that acts on rock to change its shape or volume. tensionThe stress force called tension pulls on the crust, stretching rock so that it becomes thinner in the middle. compressionThe stress force called compression squeezes rock until it folds or breaks. shearingStress that pushes a mass of rock in two opposite directions is called shearing. normal faultTension in Earth’s crust pulls rock apart, causing normal faults. reverse faultA reverse fault has the same structure as a normal fault, but the blocks move in the opposite direction. Key Terms:Examples: hanging wall footwall strike-slip fault anticline syncline plateau The block of rock that lies above a normal fault is called the hanging wall. The rock that lies below is called the footwall. In a strike-slip fault, the rocks on either side of the fault slip past each other sideways, with little up or down motion. A fold in rock that bends upward into an arch is an anticline. A fold in rock that bends downward to form a valley is a syncline. A plateau is a large area of flat land elevated high above sea level.

Earthquakes End of Section: Forces in Earth’s Crust

Earthquakes Types of Seismic Waves Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface. - Earthquakes and Seismic Waves

Earthquakes Types of Seismic Waves P waves are seismic waves that compress and expand the ground like an accordion. S waves are seismic waves that vibrate from side to side as well as up and down. - Earthquakes and Seismic Waves

Earthquakes Types of Seismic Waves Surface waves move more slowly than P waves and S waves, but they produce the most severe ground movements. - Earthquakes and Seismic Waves

Earthquakes Measuring Earthquakes The Mercalli scale was developed to rate earthquakes according to the amount of damage at a given place. - Earthquakes and Seismic Waves

Earthquakes Seismic Wave Speeds Seismographs at five observation stations recorded the arrival times of the P and S waves produced by an earthquake. These data are shown in the graph. - Earthquakes and Seismic Waves

Earthquakes Seismic Wave Speeds X-axis––distance from the epicenter; y-axis––arrival time. Reading Graphs: What variable is shown on the x-axis of the graph? The y- axis? - Earthquakes and Seismic Waves

Earthquakes Seismic Wave Speeds 7 minutes Reading Graphs: How long did it take the S waves to travel 2,000 km? - Earthquakes and Seismic Waves

Earthquakes Seismic Wave Speeds 4 minutes Estimating: How long did it take the P waves to travel 2,000 km? - Earthquakes and Seismic Waves

Earthquakes Seismic Wave Speeds 2,000 = 3.5 minutes 4,000 = 4.5 minutes Calculating: What is the difference in the arrival times of the P waves and the S waves at 2,000 km? At 4,000 km? - Earthquakes and Seismic Waves

Earthquakes Locating the Epicenter Geologists use seismic waves to locate an earthquake’s epicenter. - Earthquakes and Seismic Waves

Earthquakes Main Idea Detail Identifying Main Ideas As you read the section “Types of Seismic Waves,” write the main idea in a graphic organizer like the one below. Then write three supporting details. The supporting details further explain the main idea. Seismic waves carry the energy of an earthquake. P waves compress and expand the ground. S waves vibrate from side to side as well as up and down. Surface waves produce the most severe ground movements. - Earthquakes and Seismic Waves

Earthquakes Seismic Waves in the Earth Click the Video button to watch a movie about seismic waves in the earth. - Earthquakes and Seismic Waves

Earthquakes End of Section: Earthquakes and Seismic Waves

Earthquakes The Modern Seismograph Seismic waves cause the seismograph’s drum to vibrate. But the suspended weight with the pen attached moves very little. Therefore, the pen stays in place and records the drum’s vibrations. - Monitoring Earthquakes

Earthquakes Instruments That Monitor Faults In trying to predict earthquakes, geologists have developed instruments to measure changes in elevation, tilting of the land surface, and ground movements along faults. - Monitoring Earthquakes

Earthquakes Using Seismographic Data The map shows the probability of a strong earthquake along the San Andreas fault. A high percent probability means that a quake is more likely to occur. - Monitoring Earthquakes

Earthquakes Sequencing As you read, make a flowchart like the one below that shows how a seismograph produces a seismogram. Write each step of the process in a separate box in the order in which it occurs. How a Seismograph Works Incoming seismic waves Vibrate the rotating drum The suspended pen remains motionless and records the drum’s vibration. - Monitoring Earthquakes

Earthquakes Links on Earthquake Measurement Click the SciLinks button for links on earthquake measurement. - Monitoring Earthquakes

Earthquakes End of Section: Monitoring Earthquakes

Earthquakes Earthquake Risk Geologists can determine earthquake risk by locating where faults are active and where past earthquakes have occurred. - Earthquake Safety

Earthquakes How Earthquakes Cause Damage 1.Shaking: the shaking caused by seismic waves can trigger movement of the soil at high elevations and destroy man made structures. 2.Liquefaction: is the result of shaking the soil particles often caused by increased water content and reduces the strength or stiffness of the soil. 3.Aftershocks: are caused by additional releases of energy in rocks after the larger earthquake occurred in the same area. 4.Tsunamis: “harbor waves” result from a large body of water displacement caused by a disturbance in the water.

Earthquakes How Earthquakes Cause Damage A tsunami spreads out from an earthquake's epicenter and speeds across the ocean. - Earthquake Safety

Earthquakes Designing Safer Buildings To reduce earthquake damage, new buildings must be made stronger and more flexible. - Earthquake Safety

Earthquakes Asking Questions Before you read, preview the red headings and ask a what, how, or where question for each heading. As you read, write answers to your questions. Where is the quake risk highest?Earthquake risk is the highest along faults and where past earthquakes have occurred. How do earthquakes cause damage?Earthquake damage occurs as a result of shaking, liquefaction, aftershocks, and tsunamis. How can you stay safe during an earthquake? The best way to stay safe during an earthquake is to drop, cover, and hold. What makes buildings safe from earthquakes? Buildings can be made safer by being built stronger and with greater flexibility. - Earthquake Safety QuestionAnswer

Earthquakes Earthquake Damage Click the Video button to watch a movie about earthquake damage. - Earthquake Safety

Earthquakes More on Earthquake Risk Click the PHSchool.com button for an activity about earthquake risk. - Earthquake Safety

Earthquakes End of Section: Earthquake Safety

Earthquakes Graphic Organizer Reverse Tension Shearing Strike-slip

Earthquakes End of Section: Graphic Organizer