Science: Chapter 5 Section 1 Earthquakes
Terms in this set (92)
What is stress in Earths plates?
A force that acts on an area of rock to change its shape or volume.
What does the Earths Stress add to rocks?
Where is the energy stored from Earth's stress?
In the rock until the rock changes shape or breaks.
What are the three types of crust stress?
Tension, compression and shearing.
What does tension do to the crust?
Pull the crust, stretches rocks so that they become thinner in the middle. (like bubble gum)
Where does tension occur?
Where 2 plates are moving apart.
What does compression do to the crust?
It squeezes rock until it folds or breaks.
Where does compression occur?
One plate pushing against another to compress the rock (trash compactor).
What does shearing do to the crust?
Pushes a mass of rock in two opposite directions.
How is a fault created?
Too much stress builds up.
What is a fault?
A break in the rock of the curst where surfaces slip past each other.
Where do most faults occur?
Along plate boundaries where the forces of the plate motion push or pull the crust that it breaks.
What are the three main types of faults?
Normal faults, reverse faults and strike-slip faults.
What are normal faults?
Fault is at an angle. Hanging wall slips down relative to the footwall.
What is a reverse fault?
The hanging wall moves up relative to the footwall.
What are two examples of reverse faults?
Klamath Mountains and Rocky Mountains
What is a strike-slip fault?
Rocks slip past each other.
What is an example of a strike-slip fault?
San Andreas Fault
What landforms occur from plate movement over time?
Anticlines, synclines, folded mountains, fault-block mountains and plateaus
How are folds in the crust created?
Compression shortens and thickens part of the Earths crust.
What is an anticline?
A fold in rock that bends upward into an arch.
What is an syncline?
A fold in rock that bends downward to form a valley.
What mountain ranges did folding create?
Himalayas, alps Northern Coast Range.
How is a fault block mountain formed?
2 normal faults cut through block of rock. Two parallel normal faults leave land in the middle and when they slip down it appears the land in the middle gets higher.
What is an example of a fault block mountain in California?
Panamint Range (death Valley)
What is a plateau?
A large area of flat land elevated high above sea level.
What are the characteristics of a plateau?
flat, different layers, wider than tall
What type of fault is formed when plates diverge or pull apart?
What type of fault is formed when plates are pushed together?
Name five kinds of landforms caused by plate movement?
Anticlines, synclines, folded mountains, plateaus and fault block mountains.
Why do faults often occur along plate boundaries.
Forces of plate motion push or pull the crust so much taht the crust breaks.
What is the force that causes part of the crust to become shorter and thicker?
When the hanging wall of a fault slips down with respect to the footwall the result is what kind of fault?
What is an earthquake?
The shaking that results from the sudden movement of rock along a fault
Are most earthquakes large or small?
Small (cant feel them)
When plate movement produces stress in the Earth's crust what else is produced that causes the earthquake?
In what layer do most earthquakes begin?
What is the focus?
Area beneath Earths surface where rock that is under stress triggers earthquake
What is the point on the surface directly above the focus called?
What are seismic waves?
Vibrations that travel through Earth carrying the energy released during an earthquake.
What are the three main categories of seismic waves?
P waves, S Waves and Surface waves
What are P Waves?
Primary waves the first waves to appear that compress and expand the ground like an accordion.
What are S Waves?
Secondary waves that vibrate from side to side as well as up and down. Can not move through liquid.
What are surface waves?
Move more slower than P and S waves. They make the ground roll like the ocean.
What type of seismic wave causes the ground to roll like the ocean?
What are three most common methods to measure earthquakes?
Mercalli scale, Richter scale and moment magnitude scale.
What is a Mercalli scale?
Rates earthquakes according to their intensity or strength.
Why does an earthquakes intensity decrease with distance from the epicenter?
Most of the earth absorbs the energy.
What is magnitude?
A number that geologists assign to an earthquake based on the earthquakes size.
What is a Richter scale?
Assigns a magnitude number to an earthquake based on size of seismic wwaves.
What instrument measures seismic waves?
What is the moment magnitude scale?
A rating system that estimates the total energy released by an earthquake.
What earthquake measurement works best for earthquakes of all sizes, near or far?
Moment Magnitude Scale
What is the highest level of magnitude for an Earthquake?
Are earthquakes with a magnitude of 8 or higher common?
No very rare.
How do geologists locate the epicenter of an earthquake?
The seismic waves - where they are strongest when recorded on seismograph. Use three different seismographs to locate center.
What waves reach the seismograph first?
P waves then S waves.
How does a seismograph work?
Seismic waves cause the seismograph drum to vibrate moving the pen.
What is a seismogram?
The record of an earthquakes seismic waves produced by a seismograph.
What is the function of the weight in a seismograph?
To keep the seismograph anchored to the ground.
What is the pattern of lines that the seismograph makes called?
What do geologists use to monitor faults?
Creep Meters, Tiltmeters, laser ranging devices, and GPS satellites.
What do fault instruments measure?
Change in elevation, tilting of the land surface and ground movement along the fault.
What is a tilt meter?
Measures tilting or raising of the ground (2 bulbs that are filed with liquid connected by hollow stem. Liquid flows from one bulb to the other).
What is a creep meter?
A wire stretched across a fault to measure horizontal movement of the ground. (wire anchored to post on one side and other side the wire is attached to a weight that can slide if fault moves)
What is laser ranging devices?
Use a laser beam to detect horizonal fault movements. (device times a laser beam as it travels to a reflector and back).
How do scientists use GPS satellites to monitor faults?
See changes in elevation and horizontal movement along faults.
What do scientists use to try to predict future earthquakes?
Seismographs and fault monitoring devices.
How do scientists map faults?
Seismic waves hita fault and the waves reflect off the fault.
What is it good for scientists to know where faults are?
Determine the earthquake risk for an area.
What is friction?
The force that opposes the motion of one surface as it moves across another.
What does friction exist?
Because surfaces are not smooth.
Can scientists predict when an earthquake will happen?
How can geologists determine earthquake risk?
By locating where faults are active, where most damage was caused and where post earthquakes have occurred.
Where in the United States is the rick for earthquakes the highest?
Pacific coast - California, Washington and Alaska
Why does the Eastern part of the United States have the lowest rick of earthquakes?
It is far from other plate boundaries.
Why are intensity maps important?
These maps show areas near faults where most damage occurs and can occur again.
What do geologists study earthquakes that happened many years ago?
Estimate risk of future earthquakes.
What are the causes of earthquake damage?
Shaking, liquéfaction, aftershocks and tsunamis.
What damage does earthquake shaking cause?
Can cause landslides or avalanches where soil is loose.
What damage does liquefaction cause?
Loose and soft soil turns into liquid mud sinking and pulling apart buildings.
What is liquefaction?
Soil turns into liquid mud.
What is an aftershock?
Earthquake that occurs after a larger earthquake in same area.
How long after an Earthquake can aftershocks occur?
Hours, days or months later.
What are tsunamis?
A huge wave caused by plate movement pushing water out of its way.
What is the best way to protect yourself during an earthquake?
Drop, cover and hold.
If you are indoors when an earthquake happens where should you go?
Under big sturdy table or desk or inner wall.
During earthquake what things inside your house should you avoid?
mirrors, glass, wall hangings and windows.
If an earthquake happens when you are outside where should you go?
open area away from power lines, trees and buildings and sit down.
How do people reduce the damage of future earthquakes?
Buildings are made stronger and more flexible
What is a base isolated building?
Building that rests on shock absorbing rubber pads to keep building from violent shaking.
How can utilities by protected from earthquakes?
Flexible gas and water lines and automatic shut off valves.