Inside Earth: Chapter 2: Earthquakes
Study Guide
Vocabulary:
Earthquake: Violent shaking caused by movement of rock under the Earth’s surface
Stress: a force that acts on rock to change its force or volume
Shearing: stress that pushes a mass of rock in two separate directions
Tension: stress pulls on the crust, stretching rock so that it becomes thinner in the middle
Compression: stress that squeezes rock until it folds or breaks
Strike-Slip Fault: created by shearing; when rocks on either side of the fault slip past each other sideways
with little up or down motion
Normal Fault: caused by tension; the fault is at an angle; one block of rock lies above the fault while the
other block lies below the fault
Reverse Fault: caused by compression; same as a normal fault but block moves in opposite direction
Syncline: fold in rock that bends downward in the middle to form a bowl
Anticline: fold in rock that bends upward into an arch
Plateau: faults cause a large area of flat land to be pushed upward, high above sea level
Focus: the point beneath Earth’s surface where rock that is under stress breaks, triggering an earthquake.
Epicenter: the point on the surface, directly above the focus (located by use of seismic waves)
Seismic Waves: vibrations that travel through Earth carrying the energy releases during an earthquake
Seismograph: records the ground movements caused by seismic waves as they move through the Earth
Magnitude: measurement of an earthquake’s strength
Intensity: measures an earthquake’s damage
Liquefaction: occurs when an earthquake’s violent shaking suddenly turns loose, soft soil into liquid mud
Aftershock: an earthquake that occurs after a larger earthquake in the same area
Tsunamis: large waves formed when earthquakes displace water
Base-isolated building: a building designed to reduce the amount of energy that reaches a building during
an earthquake
Scales Used to Measure Earthquakes1. Mercalli Scale: developed in the early twentieth century to rate earthquakes according to their
intensity (strength of ground motion in a given place)
2. Richter Scale: a rating of the size of a seismic wave that was once measured by a type of
mechanical seismograph but is now measured with electronic seismographs; does not work well for
large or distant earthquakes
3. Moment Magnitude Scale: rating system that estimates the total energy released by an earthquake;
can be used for all size earthquakes, near and far
4 Devices Geologists Use To Monitor Faults1. Creep Meters: uses a wire stretched across a fault to measure horizontal movement of the ground;
one side is anchored to a post and the other has a weight attached to it so that it can move if the fault
moves
2. Laser Ranging Device: uses a laser beam to detect even small fault movements; measures change in
time needed for the laser beam to travel to a reflector and bounce back
3. Tilt Meter: measures tilting of the ground along a fault line (similar to a carpenter’s level)
4. Satellite Monitors: uses radar to make images of faults (uses radio waves to measure the distance
from the fault to the satellite)
3 Categories of Seismic Waves:
1. P-waves
 Primary waves
 First waves to arrive
 Compress and expand the ground like an accordion
 Cause buildings to contract and expand
 Move through solids and liquids
2. S-waves
 Secondary Waves
 Arrive after P-waves
 Waves that vibrate from side to side and up and down
 Shake the ground back and forth
 Shake structures violently
 Can ONLY move through solids
3. Surface waves
 When P and S waves reach the surface, some of them are turned into surface waves
 Move slower than P waves and S waves
 Produce the MOST SEVERE GROUND MOVEMENTS
 Can make ground roll like ocean waves or shake building from side to side
How are Tsunamis created? How do they cause damage?
 Ground moves and displaces water
 Water spreads out from the earthquakes epicenter
 Causes a ripple to form that gets bigger as it moves to shore
 When wave crashes on land it destroys buildings, water supply, and can cause people
to get hurt or die
Earthquake Safety:

INDOORSo Drop, Cover, Hold
o Go beneath a table, in a doorway, or under something sturdy
o Avoid windows and mirrors

OUTDOORSo Move to an open area
o Avoid vehicles, power lines, trees, and buildings
o Sit close to the ground
ESSAY:
Explain what occurs along a fault BEFORE, DURING, and AFTER an earthquake. You must
include the following terms: stress, energy, fault, focus, epicenter, and seismic waves.