Download Forces Within Earth

Forces Within Earth
Objectives
• Define stress and strain as they apply to rocks.
• Distinguish among the three types of faults.
• Contrast three types of seismic waves.
Vocabulary
– stress
– secondary wave
– strain
– surface wave
– fault
– focus
– primary wave
– epicenter
Forces Within Earth
Forces Within Earth
• Earthquakes are natural vibrations of the ground
caused by movement along fractures in Earth’s
crust, or sometimes, by volcanic eruptions.
Earthquakes rip buildings, anything,
apart…
The earth shifted 30+ feet here
You can see the fault line
Improperly built buildings
disappear…
Forces Within Earth
Stress and Strain
• Most earthquakes occur when rocks fracture, or
break, deep within Earth.
• Fractures form when stress exceeds the strength
of the rocks involved.
• Stress is the forces per unit area acting on
a material.
Forces Within Earth
Stress and Strain
• There are three kinds of stress
that act on Earth’s rocks:
– Compression is stress that decreases
the volume of a material.
– Tension is stress that pulls a
material apart.
– Shear is stress that causes a
material to twist.
• Strain is the deformation of
materials in response to stress.
Forces Within Earth
Stress and Strain
• There is a distinct relationship between stress and
strain that can be plotted as a stress-strain curve.
– A stress-strain curve usually
has two segments: a straight
segment and a curved segment.
– Low stresses produce the
straight segment, which
represents the elastic strain
of a material.
– If the elastic strain is reduced to
zero, the deformation disappears.
Forces Within Earth
Faults
Types of Faults
– There are three basic types
of faults:
• Reverse faults are
fractures that form as
a result of horizontal
compression.
• Normal faults are fractures
caused by horizontal tension.
• Strike-slip faults are fractures
caused by horizontal shear.
Forces Within Earth
Earthquake Waves
• Most earthquakes are caused by movements
along faults.
• Irregular surfaces in rocks can snag and lock,
causing stress to build in the rocks.
• When the rocks reach their elastic limit they
break, and this produces an earthquake.
Forces Within Earth
Earthquake Waves
Types of Seismic Waves
– The vibrations of the ground
during an earthquake are called
seismic waves.
– Every earthquake generates
three types of seismic waves.
• Primary waves, or P-waves,
squeeze and pull rocks in the
same direction along which
the waves are traveling.
Forces Within Earth
Earthquake Waves
Types of Seismic Waves
• Secondary waves,
or S-waves, cause
rocks to move at right
angles in relation
to the direction of
the waves.
• Surface waves
travel along Earth’s
surface, moving in
two directions as they
pass through rock.
Forces Within Earth
Earthquake Waves
Types of Seismic Waves
– P-waves and S-waves, also called body waves, pass
through Earth’s interior.
– The focus of an earthquake is the point of failure of
rocks at the depth where an earthquake originates.
– The epicenter of
an earthquake is
the point on
Earth’s surface
directly above
the focus.
Seismic Waves and Earth’s Interior
Seismometers and Seismograms
Seismic Waves and Earth’s Interior
Seismometers and Seismograms
• A seismogram is the record produced by a
seismometer.
Seismic Waves and Earth’s Interior
Clues to Earth’s Interior
Measuring and Locating Earthquakes
Seismic Belts
Earthquakes and Society
Objectives
• Discuss factors that affect the amount of damage
done by an earthquake.
• Explain some of the factors considered in earthquake
probability studies.
• Define seismic gaps.
Vocabulary
– tsunami
– seismic gap
Earthquakes and Society
Seismic Risk
What is a mineral?
Mineral Characteristics
Definite Crystalline Structure
– At times and fairly rare, a mineral will form in an open
space and grow into one large crystal, possibly taking
the shape of one of the six major crystal systems.
Tetragonal
Cubic
Orthorhombic
Hexagonal
Monoclinic
Triclinic
Identifying Minerals
• Classify minerals according to their physical and
chemical properties.
Vocabulary
– luster
– fracture
– streak
– specific gravity
– hardness
– ore
– cleavage
– gem
Identifying Minerals
Mineral Identification
Color
– One of the most noticeable characteristics of a mineral
is its color.
– Color is sometimes caused by the presence of trace
elements or compounds within a mineral.
– In general, color is one of the least reliable clues to a
mineral’s identity.
Identifying Minerals
Mineral Identification
Luster
– Luster is the way that a mineral reflects light from
its surface.
– metallic or nonmetallic.
Identifying Minerals
Mineral Identification
Texture
– Texture describes how a mineral feels to the touch.
– The texture of a mineral might be described as smooth,
rough, ragged, greasy, soapy, or glassy.
Streak
– Streak is the color of a mineral when it is broken up
and powdered.
Hardness
– Hardness is one of the most useful and reliable tests
for identifying minerals.
– Hardness is a measure of how easily a mineral can
be scratched.
What is this?
Identifying Minerals
Mineral Identification
Cleavage and Fracture
– Minerals break along planes where atomic bonding
is weak.
Identifying Minerals
Mineral Identification
Density and Specific Gravity
– Density is expressed as a ratio of the mass of a
substance divided by its volume, or D = M/V.
Identifying Minerals
Special Properties
• Special properties of minerals also can be used
for identification purposes.
– light to be bent in two directions, a process known as
double refraction, when it passes through the mineral.
– Calcite (CaCO3) fizzes when it comes into contact with
hydrochloric acid (HCl).
– Magnetite, an iron ore, is naturally magnetic.
– The mineral sphalerite produces a distinctive rotten-egg
odor when it is rubbed vigorously across a streak plate.
Identifying Minerals
Mineral Uses
• Minerals are virtually everywhere.
• They are used to make computers, cars,
televisions, desks, roads, buildings, jewelry,
beds, paints, sports equipment, and
medicines, just to name a few uses.
Identifying Minerals
Mineral Uses
Ores
– An ore is a mineral that contains a useful substance
that can be mined at a profit.
– Examples of ores include Coal (shown), Hematite,
which contains the element iron and bauxite, which
contains the element aluminum.
Identifying Tectonic Plate Movement
• Plate tectonic theory, 1915 when Alfred Wegener
"continental drift"
• Coastlines look like they fit together like a puzzle
• Fossils of similar species found on continents
that are now separated by great distance
• Glaciers also separated by great distances
• Paleomagnetic studies
• Seismometers showed earthquakes, volcanoes,
and other active geologic features for the most
part aligned along edges of tectonic plates
Superposition
Superposition
• Top Picture—
A is the oldest,
then C then G
then P then B
then D then J
Lowest layers
are older then
came volcanic
intrusion through
and between
layers
Devil’s Tower
Soil used to cover it
Erosion wore away
softer dirt
You can see erosion paused for a while right here
Cooled Magma
Remains of Organisms in the Rock Record
Types of Fossils
• original preservation
– soft and hard parts, have not undergone any
kind of change since the organisms’ deaths
– Such fossils are uncommon, need special
circumstances
Altered Hard Parts
– Altered hard parts organic material removed and
changed
– Permineralization pore spaces in a fossil are filled in
with mineral substances
Remains of Organisms in the Rock Record
Types of Fossils
Altered Hard Parts
– Altered hard parts are fossils in which all the organic
material has been removed and the hard parts of a
plant or animal have been changed either by mineral
replacement or by recrystallization.
– Permineralization is the process by which pore
spaces in a fossil are filled in with mineral substances.
– During the process of recrystallization, the exterior of
the shell or a bone remains the same, but the shell
microstructures are destroyed.
• APPMC—
• Archaic [Archaeozoic,
microorganisms]
• Professional [Proterozoic,
microorganisms]
• Paleontologists
[Paleozoic, small sea
creatures to plants and
amphibians]
• Mezmorize [Mesozoic,
dinosaurs]
• Centurions [Cenozoic,
mammals]
Renewable Resources
Non-renewable
Energy