Plate Tectonics - Part B
- Earthquakes and Seismic Waves
Part B Assessment
•
Writing in Science: News Report p. 473
– Is to be completed independently
– Should be at least 1 paragraph
– Will be graded for spelling, grammar and content
– And turned in as 25% of your Test Grade
– Due on the day before the test
Earthquakes and Seismic waves
•
•
Every day, worldwide there are _____________________________________ earthquakes.
An ____________________________is the shaking and trembling that results from the movement of
rock beneath Earth’s surface.
Earthquakes and Seismic waves
•
•
•
Plate movements cause stress in Earth’s crust, adding energy to the rocks and forming faults.
Stress increases along the fault until the rock breaks, causing an earthquake.
In seconds, the earthquake releases an enormous amount of stored energy.
Earthquakes and Seismic waves
•
Most earthquakes begin in the ________________________________ within about 100 km of Earth’s
surface
•
The ____________________________ is the area beneath Earth’s surface where the rock that is
under stress breaks, triggering an Earthquake.
Earthquakes and Seismic waves
•
•
The point on the surface directly above the focus is called the _________________________.
(See page 468 in text)
Types of Seismic waves
•
•
During an earthquake, Seismic waves race out from the focus in all directions.
Seismic waves _____________________________________________________________
__________________________________________________________________________
__________________________________________________________________________.
Types of Seismic Waves
•
There are three main categories of earthquake waves: _______________________ (P waves),
____________________________ (S waves), and ___________________________ waves.
•
•
•
P waves and S waves originate from the Earthquake's _____________________________.
When these waves reach the epicenter, _________________________________waves develop.
(See diagram p. 469)
Types of Seismic Waves -P waves
•
•
The __________________________ waves to arrive are primary waves or P waves
____________________________ are seismic longitudinal waves (like a slinky) that compress and expand
the ground like an accordion
Types of Seismic Waves -S waves
•
•
After the P waves come secondary waves, or S waves.
___________________________ are seismic transverse waves that vibrate from side to side as well as up
and down, shaking the ground back and forth.
•
Unlike P waves that can move through ___________________________________________- S waves
cannot move through liquids.
Types of Seismic Waves -Surface waves
•
•
When P waves and S waves reach the surface, some of them become surface waves.
Surface waves move more slowly than P and S waves, but can produce __________________________
ground movements.
•
Some surface waves make the ground roll like ____________________ waves. Others shake buildings
from ____________________________________.
Measuring Earthquakes
•
Three commonly used methods for measuring earthquakes are the ______________________________
_______________________________________________________________________________
Measuring Earthquakes -The Mercalli Scale
•
The Mercalli scale was developed to rate earthquakes according to the __________________________
at a given place.
•
The Mercalli scale uses ________________________________ to rank earthquakes by how much
damage they cause. (See picture p. 471)
Measuring Earthquakes -The Richter Scale
•
An Earthquake’s ________________________________ is a number that geologists assign to an
earthquake based on the earthquake’s size
•
Magnitude is measured by measuring _____________________________________________ that
occur during an earthquake.
Measuring Earthquakes -The Richter Scale (con’t)
•
The __________________________________ is a rating of an earthquake’s magnitude based on the
size of the earthquake’s seismic waves.
•
The seismic waves are measured by a seismograph, which is a machine that records and measures earthquake
waves.
•
The Richter scale provides accurate measurements for nearby earthquakes but does not work well for
_________________________________________ quakes.
Measuring Earthquakes -The Moment Magnitude Scale
•
Geologists today use the ____________________________________________, a rating system that
estimates the total energy released by an earthquake.
•
•
This scale can be used to rate earthquakes of all sizes near or far.
You may hear news reports that mention the Richter scale, but the number quoted is almost always the
_____________________________________________ of the quake.
Measuring Earthquakes -The Moment Magnitude Scale (cont)
•
•
To rate an earthquake using the moment magnitude scale, the geologists first study data from seismographs.
The data show what kind of ______________________________ were produced and _____________
_______________________ they were.
•
The data also help geologists infer how much movement occurred along the fault and the strength of the
rocks that broke when the fault slipped.
•
Geologists use all this information to rate the quake on the moment magnitude scale.
Measuring Earthquakes -Comparing Magnitudes
•
•
•
An earthquake’s magnitude tells geologists how much _______________ was released by the earthquake.
Each one-point increase in magnitude represents the release of roughly 32 times more energy.
For example, a magnitude 6 earthquake releases 32 times as much energy as a magnitude 5 and about 1,000
times as much as a magnitude 4 quake.
Use the 2nd paragraph on page 472 to complete the table
Magnitude Quake
Description
Below 3
People scarcely notice
Below 5
Can cause moderate damage
Above 6
Most powerful, are rare
Chile in 1960 and Alaska in 1964
Locating the Epicenter
•
•
•
•
Geologists use ___________________________________________________________________.
Seismic waves travel at ______________________________________________.
P waves arrive at a seismograph first with S waves following close behind.
_______________________________________________________________________________
_______________________________________________________________________________
•
Complete Analyzing Data Exercise p. 472
Locating the Epicenter -Triangulation
•
Geologists draw at least ________________________________________ using data from different
seismographs all over the world.
•
•
•
•
The center of each circle is the particular seismograph’s location.
The radius of each circle is the _______________ from that seismograph to the ___________________
Where the three circles ___________________________ is the location of the epicenter.
(See diagram p. 473)
Part B Assessment
•
Copy and Complete Section Assessment p. 473 of text
____________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________