Download Chapter 12 Earthquakes

Chapter 12 Earthquakes
12.1 How and Where Earthquakes Happen
 What we know:
 Earthquakes occur from too much pressure building up as the
dynamic layers of the earth move



Asthenosphere, Lithosphere.
Most earthquakes occur near tectonic plates boundaries.
Results from elastic rebound. In the process of elastic
rebound, stress builds in rocks along a fault until they break
and spring back to their original shape. (Pg 295)
12.1 Parts of an Earthquake
 Focus: The
immediate
location of the
earthquake.
 Epicenter: The
point above
ground directly
above the focus.
12.1 What happens after an earthquake?
 Earthquakes lets out two types of seismic waves:
Body waves and Surface waves.
 Different seismic waves act differently pending on
the material of earth’s interior through which they
pass.


Each type of wave travels at a different speed and causes
different movements in Earth’s crust. (Pg 301)
Body waves have P (compression) and S (shear) waves
P waves travel through solid, liquid, and gas
 S waves only travel through solids

12.1 Shadow Zones
 Shadow Zones are areas of the Earth’s Surface where
no direct seismic waves from a particular
earthquakes can be detected. (Pg 298)
 Look at page 299 Draw the different convergent and
divergent plate boundaries on the map provided. Use
different colors to denotes the different plate
boundaries.
12.2 Studying Earthquakes
 Scientists use seismographs to record earthquake
vibrations

Measured in seismograms
 The difference in the times that P waves and S waves
take to arrive at a seismograph station helps
scientists located the epicenter of an earthquake.
 Earthquake magnitude scales describe the strength
of an earthquake. Intensity is a measure of the effects
of an earthquake.
12.2 Studying Earthquakes
 Richter scale was used when I was a student
 Now the Mercalli Intensity Scale is used.
 Scale 1-12 (Pg 304)
 Common Earthquakes in America (Pg 308)
12.3 Earthquakes and Society
 Most earthquake damage is caused by the collapse of
buildings and other structures.
 Tsunamis often are caused by ocean-floor
earthquakes.
 People who follow safety guidelines are less likely to
he harmed by an earthquake.
 Seismic gaps, tilting ground, and variations in rock
properties are some of the changes in Earth’s crust
that scientists use when trying to predict
earthquakes.