Transcript Chapter 19

What causes an Earth quake?
Earthquakes occur when rocks fracture or break
deep within the Earth’s crust.
What are the fractures in the rock caused by?
These fractures are caused by stress (the amount of
force per unit area acting on a material).
List and describe the three types of stress?
1. Compression: decreases volume of a material.
2. Tension: pulls a material apart
3. Shear: causes a material to twist
What is the definition of strain?
The deformation of materials in response to stress.
What is it called when the rock materials return to their
original size and shape after the stress is removed?
Elastic strain
What is the term for the material being permanently
deformed due to the stress exceeding a certain value?
Ductile Deformation
What is a Fracture or system of fractures in Earth’s crust
that occurs when stress is applied too quickly or too great?
A Fault
What did California say to NY after the Earth Quake?
Don’t look at me, that wasn’t my fault!
List the three types of faults.
Normal, reverse and strike slip
Which fault has the two involved blocks being
pulling away from one another causing one of the fault
blocks to slip upward and the other downward with
respect to the fault plane (it is hard to determine whether
both or just one block has moved.)
Normal
Which fault has the general movement of the fault
blocks is toward each other, not away from each
other as in the normal fault?
Reverse Fault
Which fault has the blocks moving side by side (or
horizontal) to one another?
Strike slip Fault
Which type of fault is the San Andreas?
Strike slip Fault or transcurrent
Which fault is similar to a convergent plate
boundary?
Reverse or Thrust fault
Which fault is similar to a divergent plate boundary?
Normal fault
Which fault is similar to a transform plate boundary?
Strike Slip or transcurrent fault
Section 19.1 page 498
3 Types of seismic waves
1. Primary or P waves: Squeeze and pull rocks
together in the direction of travel. This is the fastest
wave and can travel through liquids or solids.
Section 19.1 page 498
3 Types of seismic waves
1. Primary or P waves: Squeeze and pull rocks
together in the direction of travel. This is the fastest
wave and can travel through liquids or solids.
What are the three types of seismic waves?
P waves
S waves
L waves
Which seismic wave moves the fastest and can travel
through solids and liquids?
Primary or P waves
Which seismic wave moves the second fastest and can
only travel through solids?
Secondary or S waves
Which seismic wave moves the slowest and travels
on the surface?
L waves
Which seismic wave moves the particles lengthwise?
Primary or P waves
Which seismic wave moves the particles up and
down?
Secondary or S waves
Which seismic wave moves the particles in a rolling
fashion?
L waves
Which waves move along the surface?
L waves
What is the point where earthquake originates?
Focus
Term for how far below Earth’s surface the focus is.
Focal depth
What is the point on Earth’s surface directly above the
focus?
Epicenter
What instrument detects and records vibrations in
the Earth’s crust?
Seismometer
What is the recorded data produced by the seismometer?
Seismogram
What is the relationship between the difference in time
between the P and S wave arrival and distance to the
epicenter?
The larger the difference in arrival time, the greater
the distance to the epicenter.
How many seconds is each box worth on the Y-axis?
20 seconds
How many km is each box worth on the X-axis?
200 km
How many km are represented by the number 3 on
the x-axis?
3,000 km
What is the distance to the epicenter if the P wave arrived
at 3:00 PM and the S wave arrived at 3:01. and 45
seconds?
1,000 km
What is the distance to the epicenter if the P wave arrived
at 3:00 PM and the S wave arrived at 3:03 PM and 20
seconds?
2,000 km
What is the distance to the epicenter if the P wave arrived
at 2:00 PM and the S wave arrived at 2:02 PM and 20
seconds?
1,400 km
What is the distance to the epicenter if the P wave arrived
at 1:00 PM and the S wave arrived at 1:04 PM and 40
seconds?
3,200 km
What is the distance to the epicenter if the P wave arrived
at 12:00 PM and the S wave arrived at 12:05 PM and 40
seconds?
4,000 km
What is the distance to the epicenter if the P wave arrived
at 6:00 PM and the S wave arrived at 6:08 PM and 40
seconds?
7,200 km
What is the distance to the epicenter if the P wave arrived
at 5:00 PM and the S wave arrived at 5:09 PM and 20
seconds?
8,000 km
If the S wave traveled for 4 minutes, what is the
distance to the epicenter?
1,000 km
If the P wave traveled for 11 minutes and 20 seconds,
what is the distance to the epicenter?
8,000 km
If the S wave traveled for 7 minutes and 20 seconds,
what is the distance to the epicenter?
2,000 km
If the P wave traveled for 5 minutes and 40 seconds,
what is the distance to the epicenter?
3,000 km
If the P wave traveled for 8 minutes and 20 seconds,
what is the distance to the epicenter?
5,000 km
If the S wave traveled for 17 minutes, what is the
distance to the epicenter?
6,000 km
If the S wave traveled for 17 minutes, what is the
distance to the epicenter?
6,000 km
If the epicenter distance is 5,000 km, what was the P
wave travel time?
8 minutes and 20 seconds
If the epicenter distance is 8,000 km, what was the P
wave travel time?
11 minutes and 20 seconds
If the epicenter distance is 4,000 km, what was the S
wave travel time?
12 minutes and 40 seconds
If the epicenter distance is 4,000 km, what was the S
wave travel time?
12 minutes and 40 seconds
If the epicenter distance is 3,200 km, what was the P
wave travel time?
6 minutes
If the epicenter distance is 5,200 km, what was the S
wave travel time?
15 minutes and 20 seconds
If the epicenter distance is 2,000 km, what was the P
wave travel time?
4 minutes
What is the next step to finding the epicenter after
you have found the distance to the epicenter?
Using the distance you found, draw a circle around
the city using a compass.
How many circles do you need to draw to find the
epicenter?
3
What is the name of the process when you use three
circles to find the epicenter?
Triangulation
If the epicenter distance for city A is 3,000 km, and
the epicenter distance for city B is 2,000 km, how
many additional stations do you need to find the
epicenter?
One
If the epicenter distance for city A is 3,000 km, and
the epicenter distance for city B is 2,000 km, which
city had to wait the longest for the waves to arrive?
City A
Where does most of our knowledge of the Earth’s
interior comes from?
The study of seismic waves
What happens to the waves after they go into a new
material?
These waves change speed and direction when they
encounter different materials.
What is the term for the change in direction of a
wave as it enters a new medium?
Refraction
What happens to the speed of the wave as it enters
a more dense medium?
The wave travels faster in a more dense medium.
What three things about the Earths interior do we
now know thanks to all of the information we have
from studying the seismic waves?
From this information we can determine the density,
thickness, and composition of the various layers of
the Earth’s interior.
Describe the outer core, and how do we know?
It is a liquid and we know because it blocks the S
waves.
What do we think the composition of the inner core
is?
A solid mass of iron and nickle
What is the density of the Stiffer Mantle?
Between 3.4 and 5.6 g/cm^3
What is the density of the liquid Outer Core?
Between 9.9 and 12.2 g/cm^3
What is the density of the Inner Core?
Between 12.8 and 13.1 g/cm^3
What drives the plates and creates strain resulting in
Earth quakes?
Convection cells in the Asthenosphere
How many pounds per square inch is one
atmosphere?
14.7 pounds per square inch
What is the pressure at the Stiffer Mantle Outer
Core boundary?
Approximately 1.5 million atmospheres
What is the pressure at the Outer Core and Inner
Core boundary?
Approximately 3.1 million atmospheres
What is the pressure at center of the Earth?
Approximately 3.6 million atmospheres
What is the temperature at the Outer Core and Inner
Core boundary?
Approximately 6,300 degrees Celcius
What is the term for the area on Earth that receives
no S or P waves called?
The Shadow zone
What creates the shadow zone?
The liquid outer core blocks the S waves, and the P
waves have been refracted around this area.
How can meteorites provide evidence of Earth’s
interior?
Meteorites that have orbited the Sun are thought to
have formed the same way the Earth has formed. By
this rational, the inside of a meteorite will have a
similar composition to that of the Earth.
How many earthquakes occur each year?
Over one million, you just can’t feel most of them!
What is the amount of energy released by an
earthquake?
Magnitude
What is the numerical scale used to measure the
magnitude of an earthquake, using values based on
the size of the earthquake’s largest seismic waves?
Richter scale
How many times larger is an Earth quake that is a 7 on the Richter scale
compared to a 6?
A number 7 Earth quake is 10 times larger than a 6.
How much more energy is released if the Earth
quake is a 7 on the Richter scale compared to a 6?
An earthquake at a number 7 is 32 times more
energy than a 6.
Which scale Takes into account the size of the fault
rupture, the amount of movement along the fault,
and the rocks’ stiffness?
Moment magnitude scale
Which scale Rates the type and extent of damage
and other effects of the earthquake as noted by
observers?
Modified Mercalli Scale
How does a cities proximity to an epicenter relate to
the amount of damage it will sustain?
The closer a city is to the epicenter, the more
damage it will sustain.
How does the depth of a focal point to the surface
relate to damage?
The closer the focal point is to the surface, the more
damage will occur.
In general, where do most of the World’s Earth
quakes occur?
At Plate boundaries
Specifically, where do 80 percent of the World’s
Earth quakes occur?
The Circum-Pacific belt or Ring of Fire
List and describe 2 Earthquake Hazards
1. Structural failure, buildings collapse on people
2. Land and Soil Failure, landslides or other mass
movements can occur
3. Fault Scarps, people can fall into large openings
4. Tsunami, large waves of water can drown people
What kind of risk do we have where we live?
Moderate
What are Earthquake predictions based on?
Probability, which is determined based on history of
an area and the rate at which strain builds up.
What are sections of active faults that haven’t
experienced significant earthquakes for a long
period of time?
Seismic Gaps