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Transcript of Earthquakes
Rocks break under compression stress
Forms reverse faults
The most devastating earthquakes occur at convergent plate boundaries
Plate Boundaries & Earthquakes
Convergent Plate Boundaries
Transform Plate Boundaries
Divergent Plate Boundaries
Rocks break under tension stress
Forms normal faults
Relatively small earthquakes occur at divergent plate boundaries
Earthquakes Away From Plate Boundaries
Sometimes earthquakes do not occur at plate boundaries, though this is uncommon
These are arguably the worst earthquakes because no one is prepared for them
One theory for why these earthquakes happen is that there are ancient faults that are slowly being compressed, so occasionally an earthquake occurs
Forms strike-slip boundaries
Earthquakes occur at relatively shallow depth
When these boundaries run through continents the earthquakes can be disastrous
Often times earthquakes occur at plate boundaries, and at each plate boundary different types of earthquakes occur
Measuring Earthquakes are important because we would like to know how much an earthquake damaged or when will an earthquake occur. We measure earhtquakes with tools like seismograqhs, seismograms, and other tools.
Earth Hazards & Safety
The movement of earth during an earthquake doesn't directly cause damage. It is the hazards that follow that is the real problem.
Earthquakes & Plate Boundaries
Earthquakes & Seismic Waves
Measuring Earthquake Size
Locating an Epicenter
On a seismograph chart you can read them by First,observe the 'x' axis Each line represents something the 'x' axis is time. Then, The fastest wave on a seismograph is the P-wave, you can tell that is fast because wavy lines will show up on the record. The height on the s-wave and p-wave indicate the sizes of the ground motion.
Most common hazard
Usually caused by ruptured gas pipes and severed electrical lines after an earthquake
Very dangerous when earthquakes break water pipes and firefighters cannot find water to fight the fires
What is an Earthquake?
What are Seismic Waves?
How do Seismic Waves Travel?
Types of Seismic Waves
Using Seismic Wave Data
Earthquakes cause landslides in areas with steep slopes
Soil and rock moves down the slop during a landslide
Landslides destroy homes, block roads, and mess up pipes and electrical lines
When an Earthquake shakes wet sediment, it can move like liquid
Liquefaction under buildings can result in the building sinking and collapsing
An earthquake is the rupture or sudden movement of rocks near a fault.
Heat energy from Earth's interior is turned to kinetic energy during an earthquake
Stress causes strain that breaks and moves rocks
The kinetic energy is transferred to rocks near faults
The energy moves the rocks and makes them change shape
Energy stored as a change in shape is called elastic strain
When the rocks cannot stretch to change shape anymore, the fault breaks and slips as an earthquake
People living near the shoreline have the threat of tsunamis or ocean waves caused by earthquakes
Sometimes known as seismic sea waves
Caused when the seafloor moves as the result of an earthquake
Sometimes the waterline recedes rapidly before a tsunami strikes
In the ocean tsunamis are long and flat so much so that a ship might ride over one without notice, they only reach their true height at the shore
Tsunamis can reach up to 30m in height
Avoiding Earthquakes Hazards
By: Audrey Hempel, Faith Meltvedt, Kaili Chen, and Thomas Matheos
Travel through both solids and liquids
Moves by compressing and expanding the material it is moving through
Fastest seismic wave
Move at 5 kilometers a second to 7 kilometers a second
Slower than the P-wave
Only travels through solids
Travel at 90° angles with primary waves
Changes the shape of rocks
Travel at 60% the speed of primary waves
Seismic waves are waves of energy produced at the focus of the earthquake
The reason that things shake in an earthquake is because seismic waves are traveling through those things
Recording Seismic waves
Faults and Earthquakes
As rocks in a fault move past each other slowly, elastic strain builds up.
Eventually, rocks rupture and break along the fault, sending out complex waves into the surrounding rocks
Elastic strain that was stored in the rocks is released by seismic waves and breaking rocks
The mechanical seismographs record the ground motion in two orientations. First The ground motion is horizontal going back and fourth. Second is the ground is shaking vertical, up and down. A seismogram records the seismic wave. These can be used to measure the size of the earthquakes and their locations.
Determining Earthquake Hazards
Scientists locate active faults where earthquakes are likely to occur. They then locate places where factors for hazards such as loose sediment of steep slopes are prominent. With this information they compose maps where hazards are likely to take place after an earthquake.
Long Term Planning
Cities can prepare for earthquakes to reduce destruction. Based on the area's earthquake frequency and past intensities. For example land with loose sediment, likely to experience liquefaction during an earthquake, could be used for parks instead of having buildings built on top.
Reading a Seismograph
Seismographers use the difference in the P-Waves and S-Waves. First they find the arrival time difference. Next, the find the distance form the epicenter. Finally, they plot the distance on a map. An example would be this picture.
Determining The Differences Of An Epicenter
To find the distance of a epicenter you need to use a graph showing the p- and s-wave like the one shown below. Then look at the y-axis that will give a line going across middle to determine the time differences. The x-axis will be left with the corresponding distance on the graph.
To measure an earthquakes size you would need to measure the heights of the seismic waves, since the magnitude scale is based on the record of the seismograph's amplitude you can see the ground motion of the earthquake. The magnitude of an earthquake determines how the elastic strain energy builds up. There is no specific number limit but it does range around to 0 - 9.
Richer Magnitude Scale
The Richter magnitude scale was fist invented by Charles Richer in 1935, he created this because he wanted to use it in the southern part of California with specific type of seismograph that people used there. These particular scales are not accurate for earthquakes their magnitude is smaller by 3.0 and larger by 7.0 .
Many Earthquakes occur near faults. Earthquakes can occur at any type of fault, and even away from plate boundaries.
Moment Magnitude Scale
The Moment Magnitude scale is based on the amount of energy released by an earthquake. A seismic moment can be calculated by multiplying the area of the fault times the amount the rocks slide down. This relates to the moment magnitude because it still gives the consistent measurement of the earthquake size.
There are three different types of seismic waves. They are all uniquely destructive.
Speed Differences Of Seismic Waves
Effects Of Shaking
Plotting Intensity Values
The effects of shaking of an earthquake depends on the distance from the epicenter and the local geology. So the farther the epicenter the less the ground shakes, but this is not the only thing that cause shaking of the ground soil and loose rocks in the ground also cause the ground to shake.
After all the research for mapping earthquakes and the effects under earth had on causing earthquakes it comes down to this. When intensity values are assigned, scientist plot the values on a map and all the data are contoured.
Seismic waves travel using elastic train
Elastic strain is an energy stored as a change in a shape
By subtracting the speeds of seismic waves, you can determine the epicenter
Seismic waves travel away from the focus in all directions
As the waves get farther from the focus, the energy in the waves decreases
Cause rock particles to move side to side
Travels in a rolling motion
Slowest seismic wave
Vibrate the crust more strongly than other waves
Generally cause the most damage at Earth's surface
Scientists can investigate seismic waves and use data from them.
Earthquakes And Structures
Types Of Structures
Many deaths during earthquakes are caused by buildings collapsing
Non-reinforced buildings tend to collapse more than reinforced buildings
Taller buildings collapse more than single-story buildings
Building made of flexible materials (wood, for instance) collapse less frequently than buildings made of less flexible materials (like concrete, brick, or adobe)
Scientists compare the speed of seismic waves to the speed of a human running
At the focus, the primary waves aren't that far ahead of the secondary waves, but as they move away from the focus it becomes more obvious
To help prevent destruction to buildings, improvements can help buildings tolerate the shaking of an earthquake.
Circular moorings are one such improvement. They are made of steel plates with alternating layers of rubber and steel inside the plates. The rubber absorbs seismic waves, protecting the building from major damage from earthquakes as high as 8.3 magnitude.
Steel Rods - steel rods are added to older buildings to reinforce the structures. This is retrofitting or fixing existing structures.
Before An Earthquake
During An Earthquake
Before an earthquake strikes you should create and practice an earthquake disaster plan. It should include a safe meeting place after the earthquake. You should have a suppy kit, just in case. It need scanned food, water, a battery powered radio, a flashlight, and first aid supplies if an earthquake strikes.
In order to protect yourself in an earthquake, location is key
If you are indoors, you should stay there
Move away from windows an objects that could fall on you
Make sure to take cover under a sturdy desk
If you're outside, stay in the open away from power lines or anything else that might hit you
When an earthquake happens, seismic waves start traveling through Earth's interior. These seismic waves are what cause the shaking and destruction in an earthquake.
Speeds Of Seismic Waves
Paths Of Seismic Waves
The speed and direction of seismic waves change as they enter new materials
Their paths also change when they travel through rock and magma with different densities
There are "shadow areas" where seismic waves don't ever travel through
Earthquake Facts For Kids
Earthquakes involve the movement of rocks in the Earth’s crust. This movement causes seismic waves.Scientists use the differences in speed of these seismic waves to locate the epicenter. The epicenter is the point on the surface directly above where the earthquake originated.
We use seismometers to measure the strength of earthquakes. It is hard to feel a magnitude 3 earthquake but easy to feel a magnitude 5 earthquake.The damage caused by earthquakes varies on their depth and fault type. There was an earthquake on March 11, 2011 in Tohoku, Japan, that had a magnitude of 9.0 and killed over 15000 people.
Most of the destruction in the Toyoko earthquake was caused by tsunamis.The 2004 earthquake that occurred in the Indian Ocean near Sumatra, Indonesia triggered a series of tsunamis that killed over 200000 people in 14 countries. The February 2011 earthquake in Christchurch, New Zealand followed nearly 6 months after a magnitude 7.1 earthquake shook the region. The earthquake killed 181 people and significantly damaged the central city. The economic damage caused by the earthquake and aftershocks is estimated to be around $15 billion. The most powerful earthquake ever recorded on Earth was in Valdivia, Chile. Occurring in 1960, it had a magnitude of 9.5.
Mapping Earth's Interior
Scientist can map Earth's interior and structure by analyzing the paths of seismic waves
The speed and direction of seismic waves change as they travel through different substances, which means their paths' change
Scientists have discovered that some areas (that people call shadow zones) don't ever have seismic waves travel through
The waves don't travel in these areas because their paths change around them
After an Earthquake
It is important in earthquake prone countries such as Japan to build houses and buildings that react well to earthquakes. Good engineering practises can help stop buildings collapsing under the stress of large earthquakes.
In Case Of An Earthquake
Remember to stay calm after an earthquake
Remember your family's disster plan
If water and/or gas pipes are broken, the vales shoud be shut off by an adult
If you smell gas, use a phone away from the area that you can smell the gas, and call an adult
Wear strong shoes like boots incase of glass or debris
*pictures from http://www.sciencekids.co.nz/sciencefacts/earth/earthquakes.html