Ever Changing Earth
Earthquakes
What Causes Earthquakes?
In this section you will learn about the causes of earthquakes, how the energy from an earthquake travels, and several different ways that we measure them.
Learning Targets
- Students will learn the causes of earthquakes.
- Students will learn how earthquakes travel, are measured, and described
Success Criteria
- I can identify the causes of earthquakes.
- I can describe how earthquakes travel.
- I can describe how scientists measure the strength of earthquakes.
- I can describe how scientists measure the damage caused by earthquakes.
Roles
- Organizer, Materials Manager, Checker, Reader
Earthquake Causes
An earthquake is the sometimes violent vibration of the Earth's surface that follows a release of energy in the Earth's crust. Most earthquakes are generated by a sudden movement of segments of the crust. They can also be caused by a volcanic eruption, or by man-made explosions. The crust may first bend and then, when the stress is more than the strength of the rocks, break and "snap" to a new position. In the process of breaking, vibrations called "seismic waves" are generated. These waves travel outward from the source of the earthquake along the surface and through the Earth at different speeds depending on the material through which they move.
The San Andreas fault in California
How Does Energy From an Earthquake Travel?
Waves
Seismic (size-mick) waves are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.
Types of Seismic Waves
There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves and surface waves. Body waves can travel through the earth's inner layers, but surface waves can only move along the surface of the planet like ripples on water. Earthquakes radiate seismic energy as both body and surface waves.
P WAVES
The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave, and, consequently, the first to 'arrive' at a seismic station. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air. Click here to see a P wave in action.
S WAVES
The second type of body wave is the S wave or secondary wave, which is the second wave you feel in an earthquake. An S wave is slower than a P wave and can only move through solid rock, not through any liquid medium. It is this property of S waves that led seismologists to conclude that the Earth's outer core is a liquid. S waves move rock particles up and down, or side-to-side--perpendicular to the direction that the wave is traveling in (the direction of wave propagation). Click here to see a S wave in action.
text from http://www.geo.mtu.edu/UPSeis/waves.html
http://christchurchearthquakes-hcraven.weebly.com/seismic-waves.html
How Do We Measure Earthquakes?
Collecting Data
Scientists called seismologists use a device called a seismometer to measure seismic waves traveling through the earth. The data is collected using a seismograph.
Measuring the Strength
The Richter Scale
The Richter (rick-ter) magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.
https://earthquake.usgs.gov/learn/glossary/?term=Richter%20scale
Measuring the Damage
The Mercalli Intensity Scale
The Modified Mercalli Intensity Scale or just Mercalli Scale is a scale that was developed to describe the damage caused by an earthquake. It is not mathematical like the Richter Scale. Instead it focuses on describing the damage such as "plates rattling" and "fall of chimneys."
Apply
- Read below about the Virginia Earthquake of 2011; the most significant earthquake to affect Maryland in recent history. Apply the success criteria to the earthquake:
- I can identify the causes of the Virginia earthquake of 2011.
- I can describe how the Virginia earthquake of 2011 traveled.
- I can describe how scientists measured the strength of the Virginia earthquake of 2011.
- I can describe how scientists measured the damage caused by the Virginia earthquake of 2011.
Use the Student Sharing chart below to help you respond to each point.
The Virginia Earthquake of 2011
On August 23, 2011 tens of millions of people all over the East Coast and southeastern Canada suddenly felt the earth shaking from the largest earthquake in that area since the M5.8 earthquake in 1944 near Cornwall and Massena, New York. When the earth stopped shaking, more than 148,000 people reported their experience of the earthquake on the Did You Feel It? website representing an area occupied by one-third of the U.S. population. The total economic losses from the earthquake totaled to about $200-$300 million. This M5.8 earthquake that occurred near Mineral, Virginia provided scientists with a rare opportunity to record, observe, and analyze data that had previously not been available for this part of the United States.
MS-ESS2-2. Construct an explanation based on evidence for how geoscience processes have changed Earth's surface at varying time and spatial scales.
MS-ESS3-2 Analyze and interpret data on natural hazards to forecast future catastrophic events and inform the development of technologies to mitigate their effects.