Earthquakes
Essential Questions
Vocabulary
What are earthquakes?
Where do earthquakes occur?
Seismic Waves
Mapping Earth's Interior
Determining Earthquake Magnitude
What is an earthquake? Earthquakes are the vibrations in the ground that result from movement along breaks in Earth's lithosphere.
How do scientists monitor earthquake activity?
Scientists can use three different scales to measure and describe earthquakes including The Richter magnitude scale, the moment magnitude scale, and The Modified Mercalli scale.
Where do earthquakes occur? Earthquakes mainly occur in oceans and along the edge of continents.
Earthquake: The vibrations in the ground that result from movement along breaks in Earth's lithosphere.
Fault: A break in Earth's lithosphere where one block of rock moves toward, away from, or past each other.
Seismic Wave: The waves of energy caused by the sudden breaking of rock within the earth or an explosion.
Focus: A location inside Earth were rocks first move along the fault, and where seismic waves originate from.
Epicenter: The location on Earth's surface directly above the earthquake's focus.
Primary waves (P-waves): Cause particles in the ground to move in a push-pull motion similar to a coiled spring.
Secondary wave (S-wave): Slower waves that cause particles to move up and down at right angles relative to the direction the wave travels.
Surface wave: Cause particles in the ground to move up and down in a rolling motion, similar to ocean waves.
Seismologist: Scientists that study earthquakes.
Seismometer: An instrument that measures and records ground motion, and can be used to determine the distance seismic waves travel.
Seismogram: A graphical illustration of seismic waves.
Earthquakes are the vibrations in the ground that result from movement along breaks in Earth's lithosphere, which are called faults.
The force that move tectonic plates also push and pull on rocks along the fault.
If these forces become large enough, the blocks of rock on either side of the fault can move horizontally or vertically past each other.
The greater the force applied to a fault, the greater the chance of a large and destructive earth-quake.
During an earthquake, a rapid release of energy along a fault produces seismic waves.
Seismic waves travel outward in all directions through rock.
Seismic waves transfer energy through the ground and produce the motion that you feel during an earthquake.
The energy released is strongest near the epicenter.
Types of Seismic Waves
Surface waves: Cause particles to move in a rolling or elliptical motion in the same direction that waves travel, is the slowest seismic wave, and generally the wave that causes at Earth's siurface.
Secondary waves: Cause rock particles to vibrate perpendicular to the direction that waves travel, they only travel through solids, and are slower than P-waves, but faster than surface waves.
Primary waves: Cause rock particles to vibrate in the same direction they travel, are the fastest and first seismic wave to be detectes/recorded, and they travel through solids and liquids.
As seismic waves move away from the epicenter, they decrease in energy and intensity.
The further you are from an earthquake's epicenter, the less the ground moves.
Most earthquakes occur along pate boundaries.
Earthquakes that occur along convergent plate boundaries typically release tremendous amounts of energy, and can be disastrous.
Earthquakes result from the build up and release of stress along active plate boundaries.
Shallow earthquakes are common along divergent boundaries and transform plate boundaries.
The deepest earthquakes occur where plates collide along a convergent boundary where the oceanic plate subducts.
Earthquakes of varying depth occur where continents collide.
When a force is applied to a body of rock, depending on the properties of the rock and the force applied, the rock might bend or break.
When a force such as pressure is applied to rock along plate boundaries, the rock can change shape (rock deformation).
When stress builds in places like a plate boundary, rocks can form faults
When rocks move in any direction along a fault, an earthquake occurs.
There are three types of faults; Strike-slip, Normal and Reverse.
Strike-slip: Two blocks of rock slide horizontally past each other in opposite directions (in Transform plate boundaries).
Normal: Forces pull two blocks of rock apart. The block of rock above the fault moves down relative to the block of rock below the fault (in Divergent plate boundaries).
Reverse: Forces push two blocks of rock together. The block of rock above the fault moves up relative to the block of rock below the fault (in Convergent plate boundaries).
Earthquakes can occur anywhere between Earth's surface and depths of greater than 600km.
Seismologists us the properties of seismic waves to map Earth's interior.
P-waves and S-waves change speed and direction depending on the material they travel through.
Through extensive earthquake studies seismologists have discovered that the outer core is liquid, that both the inner and outer core are made out of mostly iron and nickel.
They also have used seismic waves to model convection currents.
Seismologists use a method called triangulation to locate an earthquake's epicenter.
This method uses the speeds and travel times of seismic waves to determine the distance to the earthquake epicenter from at least three different seismometers
First, determine the number of seconds between the arrival of the first P-wave and the first S-wave on the seismogram.
Next, use a graph showing the P-wave and S-wave lag time plotted against distance.
Finally, plot the distance on a map.
Scientists can use three different scales to measure and describe earthquakes.
The Richter magnitude scale uses the amount of ground motion at a given distance from an earthquake to determine magnitude. It is used when reporting earthquake activity to the general public.
Seismologists use the moment magnitude scale to measure the total amount of energy released by the earthquake.
The Modified Mercalli scale measures earthquake intensity based on descriptions of the earthquakes effects on people and structures.
Because earthquakes threaten people's lives and property seismologists study the probability that an earthquake will occur in a given area.