Earth Science – Lesson 12 – Flashcards
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What is an earthquake?
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movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move
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What is Elastic rebound?
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the sudden return of elastically deformed rock to its undeformed shape
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What is focus?
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location along the fault at which the first motion of an earthquake occurs; depths vary.
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What is shallow foci?
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0-70 km; 90% of continental earthquakes; most damaging earthquakes
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What is Intermediate foci?
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70-300 km
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What is deep foci?
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300-650 km; usually by subduction zones
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What is the Epicenter?
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the point on the Earth's surface directly above the focus
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What are Seismic waves?
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vibrations produced as energy is released by rocks as they slip into a new position
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Name 2 main types of waves:
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1. Body waves 2. Surface waves
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What are Body waves?
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waves that travel through the body of a medium
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What are Surface waves?
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waves that travel along the surface of a body rather that through the middle; Form from the conversion of energy when P and S waves reach Earth's surface. Slowest-moving, cause the most damage
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Name 2 types of Body waves-
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1. P waves-primary/compression waves 2. S waves-secondary/shear waves
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What are P waves?
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primary/compression waves; -Fastest;always the first waves detected -Particles of rock move in a back and forth direction that is parallel to the direction in which the wave is traveling -Can travel through solids, liquids or gasses (more rigid the material is, the faster the wave travels)
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What are S waves?
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secondary/shear waves; -Second fastest waves; second waves detected -Particles of rock move in a side-to-side direction that is perpendicular to the direction in which the wave is moving -Can only travel through solid material
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Name 2 types of Surface waves-
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1. Love waves- 2. Rayleigh waves-
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What are Love Waves?
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Cause rocks to move side to side and perpendicular to the direction in which the waves are traveling
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What are Rayleigh waves?
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Cause rocks to move in an elliptical, rolling motion
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How can waves tell us about the earth's interior?
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The different speed and direction S and P waves travel through the Earth's interior can help scientists learn about the Earth's interior
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Who was Andrija Mohorovicic?
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1909 Croatian scientist Discovered the boundary between the crust and the mantle (10-30 km)
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Name the 3 compositional layers
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-crust, mantle, core
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Name the 5 mechanical layers
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-lithosphere, asthenosphere, mesosphere, outer core, inner core
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What are Shadow zones?
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locations on Earth's surface where no body waves from a particular earthquake can be detected
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Where do most earthquakes occur?
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Most earthquakes occur at the 3 main tectonic environments because stress on rocks is greatest here
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Describe earthquakes at Convergent Oceanic Environments-
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Earthquakes occur as the overriding plate scrapes against the top of the submerging plate
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Describe earthquakes at Divergent Oceanic Environments-
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Spreading motion at the mid-ocean ridge causes earthquakes
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Describe earthquakes at Continental Environments-
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As continental plates converge, diverge, or slide past each other horizontally rocks undergo stress. Stress causes mountains to form and earthquakes to occur
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What are fault zones?
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-Regions of numerous, closely spaced faults -Occur at plate boundaries where plates subduct, collide, or move past each other horizontally -When enough stress builds up, movement occurs along one or more fault. This may cause major earthquakes
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True/False: All earthquakes occur near plate boundaries
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False: Not all earthquakes occur near plate boundaries -Old, large fault zones may be located away from plate boundaries. These may cause earthquakes -1811 and 1812 earthquakes in New Madrid, Missouri
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What is Seismology?
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the study of earthquakes
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What is a Seismograph?
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An instrument that detects and records vibrations in the ground Modern ones measure vertical motion, and horizontal motion (east-west and north-south)
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What does a Seismogram do?
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Tracing of earthquake motion that is recorded by a seismograph -P waves recorded first, S waves recorded second, Surface waves recorded last
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How do scientists determine distance to an epicenter?
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To determine distance to an epicenter, scientists analyze the arrival times of the P and S waves. Longer lag time= further away the epicenter Earthquake's start time can also be determined this way
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How do scientists determine the location of the epicenter?
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To determine the location of the epicenter, scientists use computers to triangulate the epicenter based on information from several seismograph stations. Must have information from at least three seismograph
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What are the two measurements of an earthquake
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1) Magnitude (strength), and 2) intensity (damage)
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What is Magnitude?
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Magnitude- Measure of the strength of an earthquake Due to amount of ground motion caused by an earthquake Measurement expressed by using scales: Richter and moment magnitude scale
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What is the Richter Scale?
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measures magnitude based on ground motion
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What is the Moment magnitude scale?
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preferred by scientists, based on strength, size of the area of the fault that moves, average distance fault block moves, and rigidity of the rocks in the fault zone
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What is Intensity?
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In Earth science, the measure of the amount of damage caused by an earthquake.
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How is intensity measured?
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Measured in the Modified Mercalli scale (Roman numerals I-XII)
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How do most injuries result from earthquakes (5 things)
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Most injuries result from -the collapse of buildings and other structures -falling objects and flying glass -Landslides -Fires/explosions caused by broken electric/gas lines -Floodwaters from collapsing dams
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What are Tsunamis?
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giant ocean wave formed after a volcanic eruption, submarine earthquake, or submarine landslide Movement of the ocean crust causes a series of long, low waves that increase in height as they near the shore (tsunamis)
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T/F: Most buildings are designed to withstand the swaying motion caused by earthquakes
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False. Most buildings are not designed to withstand the swaying motion caused by earthquakes
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How does the type of ground determine how a building responds in an earthquake?
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The type of ground can affect the way in which the building responds to seismic waves -Sand and clay vibrates violently
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What are things you can do to prepare BEFORE an earthquake?
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Keep canned food, bottled water, flashlights, batteries, portable radio, and first aid kit. Plan how to react at home, in a car, or at school
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What are things you can do to DURING an earthquake?
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Stay calm! At home, move to a safe position (under a doorway, under a desk/table) away from glass, heavy furniture. At school, follow teacher/principal's directions In a car, stop away from tall buildings, trees, tunnels, power lines, or bridges. Remain in the car until the tremors stop
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What are things you can do to AFTER an earthquake?
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Be cautious. Wear shoes around broken glass. Avoid downed power lines and objects touched by downed wires
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What can scientists do to predict earthquakes?
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-Scientists study past earthquakes to predict where/when future earthquakes will occur -Currently there is no reliable way of predicting exactly when or where an earthquake will occur -Scientists are trying to detect changes in Earth's crust that can signal an earthquake with instruments placed along faults
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Name 3 methods scientists are using to predict earthquakes:
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1) Seismic gap 2) Foreshocks 3) Changes in rocks
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How are earthquakes predicted using Seismic gap?
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An area along a fault where relatively few earthquakes have occurred recently but where strong earthquakes occurred in the past
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How are earthquakes predicted using Foreshocks?
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Sometimes earthquakes are preceded by little earthquakes called foreshocks. Can precede earthquakes by a few seconds or weeks
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How are earthquakes predicted using changes in rocks?
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Tilting of rock, magnetic and electrical changes in rock detected by water put in cracks, and natural gas seepage may indicate earthquakes
