Study Guide
Chapter 4 Test
Know all of your vocabulary! Take your Vocab Folder home to study.
What is stress?
Answer: Stress is a force that acts on rock to change its shape or volume.
What works over millions of years to change the shape and volume of rock?
· Tension-the stress force that pulls on the crust and thins rock in the middle.
· Compression-the stress force that squeezes rock until it folds or breaks.
· Shearing-the stress that pushes a mass of rock in two opposite directions.
What is a fault?
Answer: A fault is a break in the rock of the crust where rock surfaces slip past each other.
How do faults form?
Answer: When enough stress builds up in rock, the rock breaks, creating a fault.
Name and describe the 3 main types of faults.
o Normal Fault-the fault cuts through rock at an angle, so one block of rock sits over the fault, while the other block lies under the fault.
*The hanging wall moves down!
o Reverse Fault-this fault has the same structure as a normal fault, but the blocks move in the reverse direction.
*The hanging wall moves up!
o Strike-Slip Fault-the rocks on either side of the fault slip past each other sideways, with little up or down motion. (transform boundary)
How does plate movement create new landforms?
o Anticlines-a fold in a rock that bends upward into an arch.
o Syncline-a fold in rock that bends downward to form a V-shape.
o Folded mountains-the collision of two plates can cause compression and folding of the crust over a wide area. Folding produced some of the world’s largest mountain ranges—The Himalayas in Asia AND The Alps in Europe.
o Fault-block mountains-two plates move away from each other and tension forces create many normal faults. As the hanging wall of each normal fault slips downward, the block in between now stands above the surrounding valleys, forming a fault-block mountain.
o Plateau-the forces that raise mountains can also uplift, or raise, plateaus (large areas of the land elevated high above sea level).
What causes earthquakes?
Answer: The forces of plate movement produce stress in Earth’s crust, adding energy to rock and forming faults. Eventually the stress increases along a fault until the rock slips or breaks, causing an earthquake.
What are seismic waves?
Answer: Seismic waves are vibrations that are similar to sound waves. They travel through Earth carrying energy released by an earthquake.
What is the focus?
Answer: The focus is the area beneath Earth’s surface where rock that was under stress begins to break or move. This action triggers the earthquake.
What is the epicenter?
Answer: The point on the surface directly above the focus is the epicenter.
Types of seismic waves:
1) P Waves—The first waves to arrive are primary waves, or P Waves. These waves compress and expand the ground like an accordion.
2) S Waves—The secondary waves that come after the P Waves are S Waves. These waves vibrate from side-to-side or up and down.
3) Surface Waves—When P Waves and S Waves reach the surface, some of them become Surface Waves. These move more slowly that P and S Waves, but they can produce severe ground movements.
How are earthquakes measured?
Answer: Geologists measure earthquakes in two ways.
1) The amount of earthquake damage or shaking that is felt is rated using the Modified Mercalli Scale.
*The Modified Mercalli Scale rates the amount of shaking from an earthquake. It is rated by people’s observations, without the use of instruments. This scale is used in regions where there aren’t many instruments to measure an earthquake. It uses Roman numerals to rate the damage and shaking at any given location.
2) The magnitude (SIZE) of an earthquake is measured on a seismograph using the Richter Scale or the Moment Magnitude Scale.
*An earthquakes magnitude (size) is a single number that geologists assign to an earthquake based on the earthquake’s size.
*THE EARLIEST MAGNITUDE SCALE IS CALLED THE RICHTER SCALE.
*The Moment Magnitude Scale rates the total energy an earthquake releases.
A magnitude of below 5 is a small earthquake and causes little damage.
A magnitude above 6 is a large earthquake and can cause great damage.
The most powerful earthquakes, with a magnitude of 8 or above, are rare and cause tremendous damage.
How is an epicenter located?
Answer: Geologists use seismic waves to locate an earthquake’s epicenter using data from thousands of seismograph stations set up all over the world.
How do seismographs work?
Answer: Seismic waves cause a simple seismograph’s drum to vibrate, which in turn causes the pen to record the drum’s vibrations. The suspended weight with the pen attached moves very little. This allows the pen to stay in place and record the drum’s vibrations. The rest of the seismograph is anchored to the ground and vibrates when seismic waves arrive.
What is a seismogram?
Answer: The pattern of lines, called a seismogram, is the record of an earthquake’s seismic waves produced by a seismograph.
What patterns do seismographic data reveal?
Answer: Geologists have created maps, by using seismographic data, of where earthquakes occur around the world to show that earthquakes often occur along plate boundaries.
Where in the United States are the possibilities of major earthquakes more likely?
Answer: Plates meet along the Pacific coast in California, Washington state, and Alaska, causing many faults.
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