Earthquakes!
Through television, the internet, and how connected the world is, we've all been witnesses in some way to some of the devastating impacts earthquakes can have. We will be looking at earthquakes in 2 different sections: first (this section) we'll take a look at what causes earthquakes, their processes (how they travel, terminology, etc.), general effects of earthquakes, where they happen most often, and how they are measured. The second section will focus on the earthquakes different effects have in MEDCs and LEDCs and why they are different, though the examination of a few case studies.
What Causes Earthquakes?
The simple answer??? PLATE TECTONICS! There are some anthropogenic (man-caused) activities, like drilling and fracking for natural gas, that can cause minor earthquakes, but the vast majority are the result of plate movement. It's quite simple if you think about it...if the plates move vertically or horizontally against each other, any slip will cause movement through waves. When the waves reach the surface, the energy leaves by massive amounts of shaking that causes destruction. The place you are most familiar with is probably the San Andreas Fault in California...which are two plates sliding past each other. The other types of plate movement, divergence and subduction, cause earthquakes as well.
Do a little demo at home
Get an old pencil and bend it. Put pressure on it by trying to bend it...and more...and more...until SNAP!!! Did you feel a kind of shock or vibration when it snapped? That's what happens with earthquakes...the plates try to move, just like the pencil, and finally, when the pressure is enough, vibrational waves travel to the surface, just like the vibrations that reach your fingers.
Processes of Earthquakes
We will look at the processes by examining two diagrams...take a look at the first:
We'll be using these terms/processes in a virtual lab...so learn them!
General Effects of Earthquakes
You can hypothesize some of the effects that earthquakes can have...basically this first thing that comes to your mind is damage from shaking. That type of damage/effect is known as a primary effect of an earthquake...that is, it is a direct result of the earthquake. Examples of primary effects are building damage, broken bridges, falling debris (could damage humans, animals, or property), landslides, floods (from collapsed dams or river banks), release of hazardous materials, and as we have seen more often lately, tsunamis. All of these can cause major or minor damage, depending on the severity of the earthquake.
As if that isn't bad enough, there are various secondary effects of earthquakes...effects that happen minutes, hours, or days after an earthquake as the result of a primary effect. For example, one of the major types of secondary effect is a fire. An earthquake can lead to a busted natural gas pipe or gas tank at a gas station and explosions from broken electrical cables...not that good of a mixture. This can cause massive fires and damages. To make maters even worse, water pipes underneath the ground can be broken, so these fires cannot be put out. Not having available clean water can also lead to an increase in disease spread.
One of the major damage earthquake events in the US happened in San Francisco in 1906. You may have learned about this in history class...the most damage in San Francisco happened as a secondary effect result of fires. It also taught us a lot about the effects of earthquakes. Read more about it at the links below.
History Channel
USGS
Foreshocks are smaller tremors that happen prior to an earthquake and aftershocks are smaller tramors following earthquakes. Both can cause damage...and surprise people. Sometimes people think a foreshock is the main earthquake and a larger one comes after and following an earthquake, it is not always time to relax as an aftershock may follow. Also, don't forget that the worst damage comes at the epicenter of an earthquake...but that does not mean it is limited to that area!
Where Do Earthquakes Happen?
Most of the "big" earthquakes (9/10) happen along destructive (convergent) plate boundaries, although we do know that there are frequent earthquakes at other places like the San Andreas Fault. This is clearly shown by looking at the two figure below, the first shows the direction of plate movement, and the second shows where earthquakes happen.
How Do We Measure Earthquakes?
As you will see in the virtual lab, we measure earthquake intensity using a seismograph. The seismograph measures seismic (shaking) activity of the earth. It is a fairly simple machine, consisting of a roll of paper that is fed continuously under a pencil or pen. When the ground shakes, the pencil moves back and forth and shows how "intense" the earthquake is. You can see one below.
What Causes Earthquakes?
The simple answer??? PLATE TECTONICS! There are some anthropogenic (man-caused) activities, like drilling and fracking for natural gas, that can cause minor earthquakes, but the vast majority are the result of plate movement. It's quite simple if you think about it...if the plates move vertically or horizontally against each other, any slip will cause movement through waves. When the waves reach the surface, the energy leaves by massive amounts of shaking that causes destruction. The place you are most familiar with is probably the San Andreas Fault in California...which are two plates sliding past each other. The other types of plate movement, divergence and subduction, cause earthquakes as well.
Do a little demo at home
Get an old pencil and bend it. Put pressure on it by trying to bend it...and more...and more...until SNAP!!! Did you feel a kind of shock or vibration when it snapped? That's what happens with earthquakes...the plates try to move, just like the pencil, and finally, when the pressure is enough, vibrational waves travel to the surface, just like the vibrations that reach your fingers.
Processes of Earthquakes
We will look at the processes by examining two diagrams...take a look at the first:
A perfect time to learn the vital terms within it:
- Focus: The point of slippage in the crust. Where the waves start.
- Epicenter: The point directly above the focus on the surface of the earth. In most cases, it is the location of the most damage.
- Fault: A fracture in the crust that has been caused by plate movement. The plate movement then will cause slipping along the fault.
- P-waves: Compression waves...the first to move. Travel very fast and not much damage. Can travel through any earth material. Go out from focus.
- S-waves: The second waves to move in...move up and down slowly and cause major damage. Cannot move through core. Go out from focus.
- Surface Waves: rolling waves that stay near the surface. Can also cause major damage. Go out from epicenter.
We'll be using these terms/processes in a virtual lab...so learn them!
Stop Here for Day 1
General Effects of Earthquakes
You can hypothesize some of the effects that earthquakes can have...basically this first thing that comes to your mind is damage from shaking. That type of damage/effect is known as a primary effect of an earthquake...that is, it is a direct result of the earthquake. Examples of primary effects are building damage, broken bridges, falling debris (could damage humans, animals, or property), landslides, floods (from collapsed dams or river banks), release of hazardous materials, and as we have seen more often lately, tsunamis. All of these can cause major or minor damage, depending on the severity of the earthquake.
As if that isn't bad enough, there are various secondary effects of earthquakes...effects that happen minutes, hours, or days after an earthquake as the result of a primary effect. For example, one of the major types of secondary effect is a fire. An earthquake can lead to a busted natural gas pipe or gas tank at a gas station and explosions from broken electrical cables...not that good of a mixture. This can cause massive fires and damages. To make maters even worse, water pipes underneath the ground can be broken, so these fires cannot be put out. Not having available clean water can also lead to an increase in disease spread.
One of the major damage earthquake events in the US happened in San Francisco in 1906. You may have learned about this in history class...the most damage in San Francisco happened as a secondary effect result of fires. It also taught us a lot about the effects of earthquakes. Read more about it at the links below.
History Channel
USGS
Foreshocks are smaller tremors that happen prior to an earthquake and aftershocks are smaller tramors following earthquakes. Both can cause damage...and surprise people. Sometimes people think a foreshock is the main earthquake and a larger one comes after and following an earthquake, it is not always time to relax as an aftershock may follow. Also, don't forget that the worst damage comes at the epicenter of an earthquake...but that does not mean it is limited to that area!
Where Do Earthquakes Happen?
Most of the "big" earthquakes (9/10) happen along destructive (convergent) plate boundaries, although we do know that there are frequent earthquakes at other places like the San Andreas Fault. This is clearly shown by looking at the two figure below, the first shows the direction of plate movement, and the second shows where earthquakes happen.
How Do We Measure Earthquakes?
As you will see in the virtual lab, we measure earthquake intensity using a seismograph. The seismograph measures seismic (shaking) activity of the earth. It is a fairly simple machine, consisting of a roll of paper that is fed continuously under a pencil or pen. When the ground shakes, the pencil moves back and forth and shows how "intense" the earthquake is. You can see one below.
A very cool thing about seismographs is that they are set up all over the world, and using data from just 3 of them can let scientists know where the epicenter of an earthquake is (you will see how in the virtual lab). Why is that important??? Well, if we can determine how strong an earthquake and where it started, we may be able to warn people before tsunamis happen. As technology gets better, we can get information to people better and have the potential to save lives. There is no current way to predict earthquakes, so this technology is the best way to save people from earthquake damage that we have.
Earthquakes are given an intensity measurement on something called the Richter Scale. The Richter Scale goes from 0-10+, and each integer (1,2,etc.) is 10x as strong as the previous. Therefore a 5 is 100x as strong as a 3. The following table shows you how strong the different numbers on the scale are and how often they occur.
Just a FYI...the 2004 Indian Ocean Earthquake that caused the major Tsunami was a 9.1-9.3 on the scale, the third largest ever recorded (Largest was a 9.5 in Chile in 1960).
Earthquakes are devistating...but they do have different effects in different parts of the world. You will learn about this in the next section.
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