Chapter 5: Earthquakes Section 1: What are Earthquakes? (pg 130) Every day, somewhere on the planet, an _________________________ is happening. A part of Earth science is _______________________, or the study of earthquakes. Seismologists are the scientists who study earthquakes. Where Do Earthquakes Occur? Most earthquakes take place near the edges of ______________________________________________. Tectonic plates are giant pieces of Earth’s thin, outer layer. Tectonic plates move in different directions and at different ___________________. Since earthquakes can push, pull, and slide past each other, there are many _______________________, or breaks in the Earth’s crust. Earthquakes occur along faults. What Causes Earthquakes? As tectonic plates push, pull, or slide past each other, _______________________ increases along faults near the plate’s edges. Rocks in the plates _______________________. _______________________ is the change in the shape of rock. Rock along a fault deforms in 2 ways: o ___________________ matter- like a piece of molded clay o ___________________ matter- like a rubber band Elastic Rebound The return of elastically deformed rock to its undeformed shape (back to the shape it was) is called ______________________________________________. During elastic rebound, _______________________ is released and travels as _______________________ waves. The seismic waves cause an _______________________. Faults at Tectonic Plate Boundaries Specific plate motions take place at different plate boundaries. Each motion creates a particular type of fault that can produce _______________________. and Fault Types Plate Motion Plate Motion Fault Type strike-slip fault reverse fault Divergent _______________________ occurs when two plates slip past each other. Transform motion creates strike-slip faults, which _______________________ horizontally past each other. Convergent motion occurs when two plates __________________ together. Convergent motion creates _______________________ faults, which are pushed together along reverse faults. _______________________ motion occurs when two plates pull away from each other. Earthquake Zones Earthquakes can happen in __________________________________ along tectonic plate boundaries. Earthquakes zones are places where a large number of _______________________ are located. How Do Earthquake Waves Travel? Waves of energy that travel through the Earth are called ______________________________________________. Seismic waves that travel through the Earth’s _______________________ are called body waves. There are two types of body waves: P waves and ____________________. Seismic waves that travel through the Earth’s surface are called _______________________. Each type of seismic wave travels differently. P Waves Waves that travel through solids, liquids, and gases are called _______________________ (pressure waves). They are the _______________________ seismic waves. P waves are also called primary waves, because they are always the ____________________ waves of the earthquake to be detected. S Waves Rock can be deformed from side to side. After being deformed from side to side, the rock springs back to its original position and S waves are created. _______________________ or shear waves, are the second-fastest seismic waves. S waves ____________________ travel through parts of the Earth that are completely ____________________. S waves arrive later than P waves and are therefore called secondary waves. Surface Waves Surface waves move along the Earth’s ____________________ in the upper part of the ____________________. There are two types of surface waves: 1. Up, down, and around 2. Back and forth Surface waves travel more _______________________and are more destructive. Section 2: Earthquake Measurement (pg 136) Locating Earthquakes Seismologists know when and where earthquakes begin by using _______________________, which are instruments located at or near the surface of the Earth that record _______________________. When the waves reach a seismograph, the seismograph creates a _______________________. A seismogram is a tracing of earthquake motion and is created by a seismograph. Determining Time and Location of Earthquake Seismologists use seismograms to find an earthquakes _______________________. An epicenter is the point on the Earth’s surface directly above an earthquake’s starting point. A _______________________ is the point inside the Earth where an earthquake begins. The S-P Time Method The simplest method by which seismologists find an earthquake’s epicenter is the ___________________________. First seismologists collect several seismograms of the same earthquake from different _______________________. Then, the seismograms are placed on a timedistance graph. The seismogram tracing of the first P wave is lined up with the P-wave timedistance curve and the first S wave is lined up with the S-wave curve. The distance of each can be found by reading the _______________________ axis. A seismologist can then locate an earthquake’s _______________________. Measuring Earthquake Strength and Intensity Seismograms can also be used to determine the earthquake’s _______________________. The Richter Magnitude Scale Seismologists use the Richter magnitude scale, also called the ______________________________________, to measure the strength of _______________________. ______________________________________________created the scale because he wanted to compare earthquakes by measuring ground motion recorded by seismograms. Earthquake Ground Motion A measure of the strength of an earthquake is called _______________________. The Richter scale measures the ground motion from an earthquake and adjusts for distance to find its strength. Each time the magnitude increases by one unit, the measured ground motion becomes 10 times larger. Effects of Different-Sized Earthquakes Magnitude 2.0 Estimated Effects Can be detected only by seismograph 3.0 4.0 5.0 6.0 7.0 Modified Mercalli Intensity Scale Can be felt at epicenter Can be felt by most people in the area Causes damage at the epicenter Can cause widespread damage Can cause great, widespread damage A measure of the degree to which people feel an earthquake and the amount of damage caused by an earthquake is called _______________________. Seismologists use the ________________________________________________________________ to measure earthquake intensity. An intensity level I describe an earthquake that is not felt by most people. An intensity level XII indicates total _______________________ of an area. The effects of one earthquake vary from place to place, any earthquake will have more than one intensity value. _____________________ values are usually higher near an earthquake’s epicenter. Section 3: Earthquakes and Society (pg 140) Earthquake Hazard ______________________________________________ is a measurement of how likely an area is to have damaging earthquakes in the future. An area’s earthquake-hazard level is determined by past and present _________________ activity. The greater the seismic activity, the ________________ the earthquake-hazard level. Worldwide Earthquake Frequency (Based Observations since Descriptor Major Strong Moderate Light Very Minor Earthquake Forecasting on 1990) Magnitude 8.0 and higher 7.0-7.9 6.0-6.9 3.0-3.9 2.0-2.9 Average Number Annually 1 800 About 6,200 About 49,000 _______________________ when and where earthquakes will happen and their strength is difficult. Seismologists have discovered some _______________________ in earthquakes that allow them to make _______________________. Strength and Frequency Earthquakes vary in _______________________. The strength of earthquakes is related to how often they occur. The Gap Hypothesis Another method of forecasting an earthquake’s strength, location, and frequency is based on the ___________________. The gap hypothesis is a hypothesis that states that sections of active faults that have had few earthquakes are more likely to be the sites of _______________________ earthquakes in the future. The areas along a fault where few earthquakes have occurred are called ____________________________________. Using the Gap Hypothesis Not all seismologists believe the gap hypothesis is the _______________________ way of forecasting earthquakes. But sometimes seismologist’s _______________________ of when an earthquake occurs is very close to where it actually happens. Earthquake and Buildings If buildings are not built to withstand earthquakes, then they can be destroyed. Today, older buildings in seismically active places, such as California, are being made more earthquake _______________________. The process of making older structures more earthquake resistant is called _______________________. Earthquake Resistant Buildings Architects and engineers use the newest ____________________ to design and construct buildings and bridges to better withstand earthquakes. Are You Prepared For An Earthquake? Plan ahead so you will know what to do before, during, and after an _______________________. Before the Shaking Starts First you should _______________________ your home against earthquakes by putting heavier objects on lower shelves and talking to your parents about having your home _______________________. Next, find _______________ places in each room of your home. Then, make a _______________ with others (family, neighbors, or friends) to meet in a safe place after an earthquake. When the Shaking Starts If you are inside when an earthquake occurs, crouch or lie down under a ________________ or desk in the center of the room. If you are outside when an earthquake occurs, lie face down away from ________________, power lines, and trees and cover your head with your hands. After the Shaking Stops Try and calm down as quickly as possible. Then, remove yourself from immediate _______________________, such as down power lines and broken glass.