Download Earthquakes & Volcanoes

Earthquakes & Volcanoes
BIG Ideas:
1.
2.
3.
Most geologic activity occurs at
the boundaries between plates.
Earthquakes are natural
vibrations of the ground, some of
which are caused by movement
along fractures in Earth’s crust.
Volcanoes develop from magma
moving upward from deep within
Earth.
I. Forces Within Earth
Faults form when the forces
acting on rock
exceed the rock’s
strength.
 Fault: a break or
crack in Earth’s
crust along which
movement has
occurred.

Most active
faults are
located at or
near plate
boundaries.
 Earthquakes
result when
movement
occurs along a
fault.

Locations of Earthquakes
from 1980 to 1990
A. Stress and Strain
 Stress:
the total force acting
on crustal rocks per unit area.
 Strain: the deformation of
materials in response to stress.
 Rocks that are strained past a
certain point will fracture and
spring back to original shape.
Deformation:
•a change in the shape or size of an
object due to an applied force
•misshapen
•contort, twist and press out of shape
Elastic Rebound Theory
Three Types of Stress
1.
2.
3.
compression: decreases
volume of material
tension: pulls material apart
shear: causes material to
twist
B. Types of Faults
Facts:
•1000 km (621 miles)
long
•15-20 km (9-12
miles) deep
Parts of an Earthquake
Focus: spot within the Earth’s crust
(lithosphere) where the origin of the
Earthquake is located (where slippage along
a fault occurs).
Epicenter: spot on the surface of the Earth
directly above the focus.
C. Earthquake Waves


Seismic Waves: vibrations of the
ground produced during an
earthquake.
Every earthquake generates
three (3) types of seismic
waves…
Types of Seismic Waves:
1. PRIMARY Waves:
P-WAVES
 travel the fastest
 FIRST to be recorded
 travel through solid
AND liquid
 compressional waves
that push and pull

Think Slinky!
2. SECONDARY
Waves:
S-WAVES
 second to be
recorded
 only travel
through solid
material (NOT
through liquid)
 shear waves that
move side to
side (like a rope)

Which layer of Earth will
S-Waves NOT travel
through?
3. SURFACE (LAND) Waves:
travel only along Earth’s surface
 slowest wave (last to be recorded)
 cause the surface of Earth to move
sideways and up and down (like
ocean waves)

Which waves are the most
destructive?

Surface Waves (also
known as L-WAVES) cause
the greatest damage.
II. Seismic Waves and
Earth’s Interior
A. Seismograph:
instrument
that detects
and records
seismic waves
Seismogram: record produced
by seismograph
Analyzing a Seismogram:
B. Clues to Earth’s Interior
III. Measuring and Locating
Earthquakes
 Scientists
measure the
strength and chart the location
of
earthquakes
using seismic
waves
A. Earthquake Measurement
magnitude: measure of energy
released by an earthquake
Richter Scale

measures energy
of the largest
seismic waves
(magnitude)
produced during
an earthquake
Los Angeles
New York City
 Which
city would better
withstand a catastrophic
earthquake?
 WHY?
B. Locating Earthquakes
scientists graph the arrival times
of the P and S waves
 the longer the S wave takes to
arrive, the further away the
quake

 THREE
(3) seismic graph
stations are required to locate
the epicenter
Finding the epicenter…
Damage

Ground Rupture: Damage due to
ground motion will depend on
Amplitude,
 Duration of vibrations,
 Nature of material building is built on,
 Design of structure




Fire
Landslides
Tsunamis

tidal (harbor) wave - vertical displacement
at seafloor due to earthquake causes giant
"ripple" in ocean
Nimitz Freeway - Oakland,
1989
Loma Prieta - Ground
Rupture
Mexico City, 1985
After
Before
Tsunamis: Giant ocean wave or a
series of waves usually associated
with an undersea earthquake or
landslide
Formation of a tsunami
IV. Volcanoes

Opening where magma erupts onto
Earth’s surface.


MAGMA: molten
(liquid) rock
UNDERGROUND
LAVA: molten rock
that is ON THE
SURFACE


VENT: opening
through which
lava flows
VOLCANO: the
build up of
material around
the vent
A. MAJOR VOLCANIC ZONES
Most volcanic activity is
associated with:



subduction,
rifting, or
seafloor spreading
1. Pacific Ring of Fire
2. Mid-Ocean Ridges:
 rifting
and
 seafloor spreading
3. Hot Spots: Volcanism
within plates


Hot Spot volcanic activity is
exceptional because…
this activity is NOT related to
plate boundaries!
B. TYPES OF VOLCANOES
1. SHIELD: LAYERS OF LAVA
WIDE AND FLAT
Hawaiian Islands
2. CINDER CONE: STEEP LAYERS
OF PYROCLASTIC MATERIAL
small, most common type of volcano
3. COMPOSITE: STEEP WITH
LAYERS OF ALTERNATING LAVA
AND PYROCLASTIC MATERIAL
Mount Saint Helens
SKYLIGHT – WINDOW INTO THE
EARTH’S INTERIOR