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Chapter 6 Earthquakes
Transcript of Chapter 6 Earthquakes
Evan, Steven, Morgan, and Rachel
Earthquake Hazard and safety
Earthquakes and Seismic Waves
Elastic Strain Energy
Energy stored as a change in shape.
This energy is eventually released as earthquakes.
Faults and Earthquakes
As rocks slowly move past each other, elastic potential energy builds up along a strike slip fault.
Is the location on a fault where rupture and movement begin.
Most fault zones are about 40 to 200 kilometers wide.
The San Andreas Fault is a good example of a Fault Zone.
What is an earthquake?
An earthquake is the rupture and sudden movement of rocks along a fault.
Plate Boundaries and Earthquakes
Lithospheric plates interact at different boundaries and produce earthquakes.
Earthquakes and Plate Boundaries
How are earthquakes measured?
Scientists determine the earthquake's size by measuring how much the rock slipped along the fault, and analyzing the heights of the seismic waves.
Recording Seismic waves
Seismograph: Instrument used to record and measure movements of the ground caused by seismic waves.
Reading a seismogram
A pen is attached to a penduldum.
The drum moves as the ground shakes.
The pen records the motion on the paper wrapped around the drum.
Record of the seismic waves: seismogram
Seismograms are used to calculate the size of earthquakes and to determine their locations.
The heights of the waves on the seismogram indicate the sizes of ground motion for each type of wave.
Scientists can make a graph using average S-waves and P-waves speeds.
Seismic waves are the waves of energy that are released at the epicenter of an earthquake, or the point on Earth's surface directly above the earthquakes focus.
There are three types of seismic waves, Primary waves, Secondary waves, and Surface waves.
Primary waves, also called P-waves, are compressional waves. P-waves cause rock to vibrate as they move through the particles. They are also the fastest seismic wave.
Secondary waves, or S-waves, are also known as shear waves. These waves cause particles to vibrate perpendicular to it's travel. S-waves travel about 60% of the speed of Primary Waves.
When S-waves and P-waves reach the last few kilometers of Earth's crust the energy gets trapped. This energy forms surface waves. These waves travel very slowly and travel along the surface. Thee waves make rock particles to move with a side to side motion and a rolling motion.
Locating an Epicenter
1. Find the arrival time difference of the waves.
2. Find the distance from the epicenter.
3. Plot the distance on a map.
Measuring Earthquake Size
Divergent Plate Boundary:
Rocks that break apart under
tension stress, forming normal
The magnitude scale is based on a seismogram's record of the amplitude of ground motion.
Most common hazard:
the earthquake ruptures gas pipes causing fires.
The magnitude of an earthquake is determined by the buildup of elastic strain energy in the crust.
Some water pipes break and make it hard for firefighters to fight the fire.
Most measured magnitude values range between 0 and 9.
Convergent Plate Boundary:
Rocks that break under
compression stress, forming
Richter Magnitude Scale
Steep hills during earthquakes can cause landslides.
This first magnitude scale was published in 1935 by Charles Ritcher.
Using Seismic Wave Data:
Comparing seismic waves is like watching people running in a race. When they start, the fast and slow waves are close together, but at the end they are very far apart.
Landslide: sudden movement of loose soil and rock.
These magnitudes are only accurate for earthquakes between 3.0 and 7.0 in magnitude.
Transform Plate Boundary:
Rocks slide horizontally past
one another, forming strike-
Landslides can destroy homes, block roads and destroy all electrical wires.
Moment Magnitude Scale
This scale is based on the amount of energy released during an earthquake.
It gives a consistent measure of earthquake size.
The seismic moment is related to this scale.
All seismic waves start at the same place but get to where they want to go at different times. This is because they travel at different speeds and have different paths that they travel on. P-waves and S-waves travel under the surface in the mantle and the Surface waves travel in the Earth's crust.
Liquefaction: solids that act like liquids
The Big Idea: Earthquakes cause seismic waves that can be devastating to humans and other organisms.
Scientist use P- and S- waves to investigate the layering of Earth's interior. They do this by seismic waves hitting other layers of the Earth which changes the waves speed and direction.
A Shadow Zone is a large area of Earth that doesn't receive any seismic waves.
The reason that there are shadow zones is because secondary waves can only travel through solids so they stop when they reach the outer core. Primary waves can travel through the outer core but it still bends it's path.
The intensity depends on the distance from the epicenter and geology.
The maximum is usually found near the epicenter.
Sediments and rocks also affect the intensity.
Plotting Intensity vales
Effects of Shaking
Earthquakes away from Plate Boundaries
Features of Earthquakes
The sediment is mostly strong but when the earthquake shakes the sediment it can act like a liquid and be very dangerous.
Scientists measure seismic waves to determine the facts about Earthquakes. Waves that travel differently helps to locate the epicenter.
Scientists plot the values on the map.
The data is then contoured.
This is similar as topography.
Most earthquakes form along plate boundaries, however, some earthquakes form away from plate boundaries.
Main Idea Lesson 1: Most earthquakes occur at plate boundaries when rocks break and move along faults.
Main Idea Lesson 2: Earthquakes cause seismic waves that provide valuable data.
Main Idea Lesson 3: Data from seismic waves are recorded and interpreted to determine the location and size of an earthquake.
Main Idea Lesson 4: Effects of an earthquake depends on its size and the types of structures and geology in a region.
One large ocean wave caused by earthquakes.
They cause many homes and buildings to flood.
The highest wave can reach 30 meters.
Signs of tsunamis: the shoreline rapidly moves back toward the sea and exposes a large area of land.
Earthquake safety: Before an earthquake
Create an earthquake plan with family
1. Have a meeting spot that is safe
2. Have an backpack full of supplies including:
water for everyone
battery powered radio
first aid kit
Earthquake safety: During an Earthquake
Move away from windows
Seek sturdy shelter
Stay in the open
a. away from power lines
b. anything that could hurt you
Earthquake safety: After an earthquake
Stay calm, Stay away from danger
To stay safe
adult shut off any valves for water and gas pipes
if smell gas leave building
be careful around shards of glass
stay away from beaches in case of Tsunamis