Unit E Lesson E4 The Earth's Violent Crust: Then and Now
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Lesson E4: Earth's Violent Crust: Then and Now
Video Lesson
Humans have known Earth was important even when they lived in caves, used rocks to kill attacking saber-toothed cats, or grew their first crops in fertile floodplain soils. What we could never do until recently, however, was understand what Earth is or
what it is doing. Now, by making careful observations of Earth’s structure and behaviour, we can understand better the past, present, and future of our world. Of course, we are still learning!
Lesson E4: Earth's Violent Crust: Then and Now
Our Studies of Earth
We study Earth for many reasons, but one important reason is to learn more about Earth’s structure. The destructiveness of earthquakes, volcanoes, and landslides makes the study of Earth a task that can save lives. The results of mining and drilling provide materials for manufacturing and income for thousands of families. For these reasons, people have developed many methods to watch, record, measure, and predict Earth and its behaviours.
We study Earth for many reasons, but one important reason is to learn more about Earth’s structure. The destructiveness of earthquakes, volcanoes, and landslides makes the study of Earth a task that can save lives. The results of mining and drilling provide materials for manufacturing and income for thousands of families. For these reasons, people have developed many methods to watch, record, measure, and predict Earth and its behaviours.
Reading for This Lesson
Science in Action 7
Materials:
Science in Action 7
Reading: Page 361
Materials:
No other materials are required for this lesson.
Figure E.1.4.1 – We use many methods to study Earth from the surface, below and above.
Figure E.1.4.2 – Surveyors use various simple and complex tools to map the Earth.
Surveying the Landscape
Have you ever see a person wearing a hard hat and safety vest looking into what seems to be a small camera on a tripod? You will see such workers beside a busy road, on a construction site, or along a forest cutline. These are surveyors, and they are mapping the land around them.
The job of building a town, re-building a street, or building a house, requires knowledge of land and what is below the surface. Roads and buildings must be planned before being built on soil and rock. Water and sewage pipes must be buried carefully below streets, and home foundations must be dug where the ground is stable and where water will not seep into the basements. Surveying techniques are very important in locating gas, oil, minerals, and water deep below the ground. Surveying is also used to observe and analyze earthquakes, volcanoes, and landslides.
Have you ever see a person wearing a hard hat and safety vest looking into what seems to be a small camera on a tripod? You will see such workers beside a busy road, on a construction site, or along a forest cutline. These are surveyors, and they are mapping the land around them.
The job of building a town, re-building a street, or building a house, requires knowledge of land and what is below the surface. Roads and buildings must be planned before being built on soil and rock. Water and sewage pipes must be buried carefully below streets, and home foundations must be dug where the ground is stable and where water will not seep into the basements. Surveying techniques are very important in locating gas, oil, minerals, and water deep below the ground. Surveying is also used to observe and analyze earthquakes, volcanoes, and landslides.
Measuring Earthquakes
Geologists calculate the strength of an earthquake by measuring the energy in the various seismic waves and by observing the damage and destruction they cause. The old way of measuring earthquake strength was the Richter scale, which indicated how much energy was released by an earthquake using whole numbers. A weak earthquake was reported as “a 4.0 on the Richter scale”, for example. An earthquake measured as a 5.0 on the Richter scale shook 10 times more powerfully than a 4.0 earthquake. Every whole number increase was a tremor ten times more powerful. The Richter scale has not been used officially since the 1970s, but people still use the term.
Today, the correct way to report earthquake strength is by using the moment magnitude scale (MMS). On the news, earthquake strength is now reported as “magnitude 6.8” instead of “6.8 on the Richter scale”. The MMS system is similar to the Richter scale, and for most earthquakes the differences between the two scales is small. However, the Richter scale does not report large earthquakes accurately. This is important because our records of earthquakes help us build safer structures and make laws to protect future generations living in earthquake zones. MMS reports all earthquakes accurately, and it is now the official system used to report earthquake strength.
Geologists calculate the strength of an earthquake by measuring the energy in the various seismic waves and by observing the damage and destruction they cause. The old way of measuring earthquake strength was the Richter scale, which indicated how much energy was released by an earthquake using whole numbers. A weak earthquake was reported as “a 4.0 on the Richter scale”, for example. An earthquake measured as a 5.0 on the Richter scale shook 10 times more powerfully than a 4.0 earthquake. Every whole number increase was a tremor ten times more powerful. The Richter scale has not been used officially since the 1970s, but people still use the term.
Today, the correct way to report earthquake strength is by using the moment magnitude scale (MMS). On the news, earthquake strength is now reported as “magnitude 6.8” instead of “6.8 on the Richter scale”. The MMS system is similar to the Richter scale, and for most earthquakes the differences between the two scales is small. However, the Richter scale does not report large earthquakes accurately. This is important because our records of earthquakes help us build safer structures and make laws to protect future generations living in earthquake zones. MMS reports all earthquakes accurately, and it is now the official system used to report earthquake strength.
Figure E.1.4.3 – A seismograph records seismic wave patterns.
Watch More
The moment magnitude scale replaced the Richter scale. This video becomes quite complicated, but it includes several useful explanations.
The earliest seismographs are from ancient China.
A piece of equipment designed to measure earthquakes is called a seismograph; it is known also as a seismometer. In its simplest form, a seismograph shows that an earthquake has occurred. The earliest seismographs were invented by the Chinese almost 2000
years ago. These devices held delicately balanced brass balls that would fall when an earthquake occurred. A more useful device was developed in 1880. This seismograph used a heavy pendulum to scratch lines when Earth started to sway. We call the
record of scratches or lines produced by a seismograph a seismogram. This was the type of seismograph that helped determine the focus of the great earthquake that devastated San Francisco in 1906. Later designs used pendulums mounted horizontally,
springs, and even beams of light. Today, modern seismometers use combinations of complex electronic technology to measure all types of seismic waves. Multiple seismometers can be joined to allow computers to generate three-dimensional images of what
is happening on and below Earth’s crust.
You can access the USGS network to find information about earthquakes that have occurred worldwide in the past 24 hours.
You can access the USGS network to find information about earthquakes that have occurred worldwide in the past 24 hours.
Figure E.1.4.4 – A pendulum seismograph measures Earth’s movement.
Watch More
A seismograph is a device that stands perfectly still while recording the shaking of the ground to which it is attached.
The location of the focus and epicentre can be found when all seismograph readings have been taken. A mathematical method called triangulation is used to locate the earthquake focus by using the readings from at least three seismographs. First, the distance
from each seismograph is determined based on how long it took each type of seismic wave to reach the seismograph station. Then, each distance from the various seismographs is drawn on a map, which is like using a compass to draw a circle of that distance
from the seismograph station. The point at which the circles cross is the location of the earthquake.
Figure E.1.4.5 – Triangulation uses three or more seismograph readings.
Watch More
Triangulation of seismograph readings allows geologists to find the epicentre and focus of an earthquake.
Surveying can be used to measure earthquakes. The ground can reveal signs of pressure building before an earthquake occurs. Surveyors and surveying equipment are often set up along faults to measure the minute-by-minute movement of the plates on either
side of the fault. Because the movement of the plates is usually slow and consistent, any changes in movement can be a sign of an impending earthquake.
Predicting Earthquakes
Surveying helps to predict earthquakes, but our predictions are still quite inaccurate and often leave little time for people to evacuate to safety. Geologists use technologies such as laser measuring systems and GPS data to provide constant, precise readings from the moving plates. Other devices help to predict earthquakes by measuring changes in Earth’s magnetism or gravity.
Predicting Earthquakes
Surveying helps to predict earthquakes, but our predictions are still quite inaccurate and often leave little time for people to evacuate to safety. Geologists use technologies such as laser measuring systems and GPS data to provide constant, precise readings from the moving plates. Other devices help to predict earthquakes by measuring changes in Earth’s magnetism or gravity.
Figure E.1.4.6 – Triangulation uses three or more seismograph readings.
Watch More
Using GPS data and powerful computers, geologists are more able to predict where and when earthquakes will occur.
Geologists have noticed that many faults follow a general pattern. If an earthquake has been recorded every 150 years in a particular location, geologists can assume that another earthquake will occur in about 150 years. But such assumptions are often incorrect. At least, these predictions can help people to become better prepared in case an earthquake does occur.
Sometimes, smaller tremors are sensed by a seismograph before an earthquake. These ‘pre-quakes’ or ‘forequakes’ might signal something larger is about to occur. Seismographs allow for very accurate predictions of an earthquake but only while it is occurring. These earthquake early warnings are sent in the seconds after the earthquake has started. Because the seismic waves that travel through Earth are much faster than the slower, dangerous surface waves are, sensors on the seismographs can send out warnings as soon as the faster waves are detected. This may only give a few seconds of warning, but that might be enough to save lives.
Figure E.1.4.7 – Seconds count when earthquake safety is required.
Often, radon gas is detected in the days and months before an earthquake. You might have heard that radon detectors sometimes are used in basements. Radon is a radioactive gas given off by uranium in rocks that are breaking down. Some scientists have
discovered that more radon is given off just before an earthquake, but the earthquake might be hundreds of kilometres away, or it might occur many months after the levels first start to increase.
For hundreds of years, stories have been told of animals acting strangely just before earthquakes. Many scientists believe that the animals are sensing the early, faster earthquakes waves that the early warning systems are designed to detect, but this has been impossible to prove.
For hundreds of years, stories have been told of animals acting strangely just before earthquakes. Many scientists believe that the animals are sensing the early, faster earthquakes waves that the early warning systems are designed to detect, but this has been impossible to prove.
Figure E.1.4.8 – Animals may be able to sense earthquakes.
Think • Interpret • Decide
As long as humans have experienced earthquakes, we have been trying to predict when the next one will occur. Some people believe our animal friends can help.
Can animals predict an earthquake?
The earthquake early warning system in California is called ShakeAlert.
Think • Interpret • Decide
Consider the following questions. Watch the two videos on earthquake prediction again if you need help forming adequate responses; then, click to reveal the answers to check your work.
Consider the following questions. Watch the two videos on earthquake prediction again if you need help forming adequate responses; then, click to reveal the answers to check your work.
Think: Certain animals seem to act differently just before an earthquake. This might be because the animals have more accurate hearing or feeling that allows them to react just before the earthquake damage occurs.
Interpret: Earthquake early warning systems detect the earliest seismic waves that occur immediately after the earthquake occurs. A location farther from the focus of the earthquake has more time to react to the arriving earthquake waves.
Decide: This is a difficult question. On one hand, to give as much warning as possible for incoming earthquake waves is desirable, but the program is very expensive. It must be paid for in some way.
Figure E.1.4.9 – The Russian volcano Sarychev erupted in 2009, as captured by satellite imaging.
Figure E.1.4.10 – Not all eruptions are violent, but some cause damage and injuries.
Figure E.1.4.11 – In 1963 the Surtsey volcano suddenly erupted off the coast of Iceland.
Observing Volcanoes and Predicting Volcanic Eruptions
Volcanic eruptions have proven to be much easier to predict than earthquakes are. This is partly because eruptions occur at the surface and earthquakes usually occur deep in the crust. The precise time of the eruption cannot be predicted, but the level of danger can be determined and appropriate evacuation procedures can occur.
Surveying equipment is an effective way to predict when an eruption is about to happen. The pressure that builds in the magma chamber is usually near the surface. This pressure causes the rocks at the surface to bulge outward, and surveying equipment such as laser measuring devices detect easily these changes in shape, size, and altitude. Geologists can even set up time-lapse cameras to record images every few minutes to show the surface as it bulges outward or falls inward.
Seismographs are also effective for geologists predicting eruptions. The pressure causes the shifting of slabs of rock, and tremors become frequent and stronger as an eruption nears.
Volcanic eruptions have proven to be much easier to predict than earthquakes are. This is partly because eruptions occur at the surface and earthquakes usually occur deep in the crust. The precise time of the eruption cannot be predicted, but the level of danger can be determined and appropriate evacuation procedures can occur.
Surveying equipment is an effective way to predict when an eruption is about to happen. The pressure that builds in the magma chamber is usually near the surface. This pressure causes the rocks at the surface to bulge outward, and surveying equipment such as laser measuring devices detect easily these changes in shape, size, and altitude. Geologists can even set up time-lapse cameras to record images every few minutes to show the surface as it bulges outward or falls inward.
Seismographs are also effective for geologists predicting eruptions. The pressure causes the shifting of slabs of rock, and tremors become frequent and stronger as an eruption nears.
Figure E.1.4.12 – Mount St. Helens developed a large bulge in the weeks before its 1980 eruption.
Thermal imaging is used to help predict eruptions. Geologists always are looking for changes in the surface temperature of the volcano. The magma chamber is the “ticking time bomb” inside the volcano. A hot spot is seen on a thermal image of the volcano
usually means the magma chamber is growing and is nearing the surface in that location.
Figure E.1.4.13 – Special equipment and careful planning are necessary to collect lava.
Figure E.1.4.14 – Surveying equipment is a part of the study of volcano behaviour.
Perhaps the most amazing way scientists monitor volcanoes is in person, wearing special heat suits as they collect molten lava! The magma cools into solid rock; then, it is analyzed for its mineral content. This helps scientists track the day-to-day changes
that may lead to an eruption.
The most destructive supervolcanoes are watched carefully. The Yellowstone National Park supervolcano is monitored constantly over a very large area for changes. Part of the reason for this is the incredible impact a super-eruption has on the world. The magma chamber of this supervolcano is 80 km long and 20 km wide!
The most destructive supervolcanoes are watched carefully. The Yellowstone National Park supervolcano is monitored constantly over a very large area for changes. Part of the reason for this is the incredible impact a super-eruption has on the world. The magma chamber of this supervolcano is 80 km long and 20 km wide!
Oil, Gas, and Mineral Exploration
Alberta does not have volcanoes, and earthquakes are rare and unpredictable in this province. What we do have is plenty of mining and drilling opportunities. A common question people ask about mining and drilling is, “How do you know where to dig?” The answer is based on methods similar to those scientists use to watch volcanoes and earthquakes.
Early explorers and surveyors found the easiest oil, gas, groundwater, and mineral finds on or near Earth’s surface. If the actual substances are not at the surface, often clues on the surface help seekers to find their locations. For example, one of the most important methods for finding diamonds is to find certain rare minerals. Most oil, gas, groundwater, and minerals are now found with more complicated methods. Satellite images show the ground from far overhead.
Alberta does not have volcanoes, and earthquakes are rare and unpredictable in this province. What we do have is plenty of mining and drilling opportunities. A common question people ask about mining and drilling is, “How do you know where to dig?” The answer is based on methods similar to those scientists use to watch volcanoes and earthquakes.
Early explorers and surveyors found the easiest oil, gas, groundwater, and mineral finds on or near Earth’s surface. If the actual substances are not at the surface, often clues on the surface help seekers to find their locations. For example, one of the most important methods for finding diamonds is to find certain rare minerals. Most oil, gas, groundwater, and minerals are now found with more complicated methods. Satellite images show the ground from far overhead.
Figure E.1.4.15 – Satellite images and mapping help geologists identify clues about materials below ground.
Sensitive instruments measure Earth’s gravity and magnetic field to find small differences that might indicate something valuable could be located below. Earthquake waves can be used to “see” underground similar to the way a submarine uses sonar, and
equipment can be used to send waves of energy or sound into the crust to read Earth’s structure.
When geologists believe they have found what they are looking for, a small test-drill might be used to obtain a core sample. A core sample is taken by attaching a small, hollow bit to the end of a drill and drilling to where the desired material might be. The hollow bit collects a sample, and it is brought to the surface to be examined.
When geologists believe they have found what they are looking for, a small test-drill might be used to obtain a core sample. A core sample is taken by attaching a small, hollow bit to the end of a drill and drilling to where the desired material might be. The hollow bit collects a sample, and it is brought to the surface to be examined.
Watch More
Drilling for core samples is a very common way to search for and identify desirable materials
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to
guide your learning.
Unit E Lesson 4 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
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REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Self-Check Time!
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Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
MMS and Richter scale measure earthquakes in the same way, but the Richter scale does not measure large earthquakes as well as the MMS does.
a. A seismograph is an instrument that shows how much the Earth shakes as time passes. As each type of seismic wave reaches the seismograph, another squiggly line is drawn on the seismogram.
b. The smaller squiggles show the faster, less damaging body waves. The larger squiggles are the slower, more damaging surface waves.
c. The seismogram shows about a 13.5 second delay between the actual earthquake and the arrival of the damaging surface waves.
b. The smaller squiggles show the faster, less damaging body waves. The larger squiggles are the slower, more damaging surface waves.
c. The seismogram shows about a 13.5 second delay between the actual earthquake and the arrival of the damaging surface waves.
a. Three or more seismographs in the locations with the red dots are used to calculate the distances (labelled d1, d2, and d3) the earthquake occurred away from them by using the time it took the seismic waves to arrive at the seismograph station.
b. Three circles are drawn from each seismograph representing the possible locations of the earthquake. Where the circles intersect is where the earthquake’s epicentre will be found.
b. Three circles are drawn from each seismograph representing the possible locations of the earthquake. Where the circles intersect is where the earthquake’s epicentre will be found.
Volcanoes are measured with GPS images, laser surveying measurements, stop-motion photography, thermal imaging, gas emission testing, and seismographs.
Searching for valuable materials below ground usually starts with aerial photography, satellite images, or some very general surveying of the areas you are looking in. Very general clues, such as certain shapes in the land, will narrow the search
for where desired materials might be found. More specific mineral testing, or drilling core samples, is done later when more specific locations have been identified.