# Chapter 11- Earthquakes by glu87355

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• pg 1
```									     Chapter 11-
Earthquakes
Continuation of plate
tectonics- convection in the
asthenosphere is still the
driving force of moving
lithospheric plates.
Where do earthquakes occur?

   At plate boundaries where pressure builds
up and eventually breaks rock

– Usually not in the middle of plates

   Faults occur where boundaries meet and
rocks “pass their elastic limit”

– Earthquakes often occur near these fault lines
– Three types of faults
Types of faults

   1. Normal faults
– Caused by TENSIONAL forces
– Forces PULL OR STRETCH rocks
– Rocks above fault line move downward
2.   Reverse-
- caused by COMPRESSIONAL forces
- rocks are PUSHED toward each other
- rocks above fault line move upward
3.   Strike-slip fault
- Caused by SHEAR forces
- Rocks move PAST EACH OTHER
with little up or down motion.
Oral Pop Quiz (24points)

   Be able to NAME, SHOW and
DESCRIBE how the rocks move at
the fault line
   Be able to tell which type of forces
(compressional, tensional or shear)
cause each type of fault.
Locating earthquakes using
seismic waves
   An earthquake creates seismic waves that
travel away from the epicenter of an
earthquake.
– Epicenter is the place on the Earth’s surface
directly above where the earthquake occurred.
   Primary waves (P-waves) move away
from the earthquake’s epicenter at a
certain rate
   Secondary waves (S-waves) move away
from the epicenter at a different, slower
rate.
   Surface waves (no cool abbreviation)
move at the slowest rate.
   Point where plate movement occurs
and energy is originated is called the
focus (can be miles below the
surface).
   Point on Earth’s surface above the
focus is called the epicenter
Seismic waves

   All types of seismic waves (s,p and
surface) are detected by
seismographs and recorded on
seismograms.
To be shown during class discussion:

* Recent earthquakes

* Seismograph video clips:
   Three types of seismic waves:

   P waves travel fastest
– Move particles back and forth in the same
direction
– Cause little destruction
   S-waves travel slower, cause more damage
– Move particles back and forth at a ninety
degree angle to wave motion
   Surface waves travel slowest, cause the
most damage
– Move particles side-to-side and in a
swaying motion
Calculating distance from the
location of an earthquake
   The difference in arrival time
between p-waves and s-waves can
be timed to determine how far away
from the seismograph station the
earthquake occurred.
   With at least three stations reporting,
we can pinpoint the earthquake’s
location using TRIANGULATION
(see next slide or page 312 for
example).
Plate Boundaries
Divergent: very little earthquake activity
Volcanic activity can vary

Convergent: earthquake activity is
strong and often very deep.
Also, great amount of volcanic activity at
subduction zones.

Transform: Earthquakes are frequent
and often shallow.
Little to no volcanic activity.
Other Info:
   Seismic waves are recorded on paper
called seismograms.
   The energy from earthquakes
sometimes causes tsunamis- giant
seismic ocean waves.
   The Richter Scale is used to measure
the intensity of earthquakes
– Largest recorded 9.3 2004 Indian Ocean
– Each number jumps x32 in intensity.
   “Hot spots” are places on Earth that
possess volcanic and earthquake
activity but are NOT near plate
boundaries.
Lab Report

   How do seismologists locate the
epicenter of earthquakes?

   Similarly, how did we find the epicenter
of an earthquake in class?
Extra Credit Earthquake
Report

   By Permission Only
   Location, date and time
   Pictures
   Damage (cost), deaths, injuries
   Magnitude
   Difference in P/S waves in Punxsy
   Search USGS Top Ten for list of
earthquakes. Also a list on p. 318.
   Other research
   Plates involved
Chapter 11 Test Questions

   Explain how Primary and Secondary
waves are used to pinpoint the
location of an earthquake’s epicenter

   Calculate the difference in
earthquake magnitude using the
Richter Scale
Homework:

   Page 330 Questions 1-9.