Transcript Earthquakes - SharpSchool

Earthquakes
Earthquake: shaking and trembling that
results from the movement of rock
beneath Earth’s surface
-The forces of plate movement cause
earthquakes
-Most begin in the lithosphere
Forces that cause Earthquakes
Stress: force that acts on rock to change its
shape or volume
Types of Stress
1. Tension: pulls on the crust, stretches the
rock, becomes thinner in the middle
(divergent)
2. Compression: squeezes rock until it folds or
breaks (Convergent)
3. Shearing: pushes rock in two opposite
directions
Types of Faults
A fault is a fracture in the earth’s crust where
there has already been some movement.
1. Normal fault: occur where plates diverge,
hanging wall lies below the footwall
2. Reverse fault: place where the rock of the
crust is pushed together, hanging wall pushes
over top of footwall
3. Strike-slip fault: rocks of the fault slip past
each other sideways, little up or down
motion.
Folding Earth’s Crust
1. Anticline: rock that bends upward into an
arch
2. Syncline: rock that bends downward to form
a valley.
3. Plateau: a large area of flat land elevated
high above sea level
-Some of the worlds largest mountains formed
from the folding of earth’s crust
Where do they occur?
Focus: place where the rock breaks, causing the
earthquake
Epicenter: point on Earth’s surface above the
focus
Seismic waves: vibrations that travel through
the earth carrying the energy released during
an earthquake
Types of Waves
P waves: primary waves, first to arrive;
compress and expand the ground
- Travel through solids and liquids
- Look like coiled and stretched spring
S waves: secondary waves, vibrate side to side
as well as up and down
- Cannot travel through liquids
- Shakes structures violently
Surface waves: move more slowly than P & S
waves, roll the ground like ocean waves
Earthquakes Measuring Scales
Mercalli scale: rate earthquakes according to
damage at a given place
Richter scale: rate of an earthquake’s magnitude
based on the size of the seismic waves
- Magnitude: number based on earthquakes size
(no max)
Moment magnitude scale: a rating system that
estimates the total energy released by an
earthquake
- Every point increase represents 32 times more
energy
How to locate the origin(epicenter)
of an earthquake
• Scientists measure the difference between the
arrival times of P & S waves
• Farther away an earthquake is, the longer the
arrival time of the P & S waves
USGS Website: http://earthquake.usgs.gov/
Track some earthquakes
How to monitor earthquakes
Seismograph: an instrument that records and
measures seismic waves
Seismogram: the record of an earthquakes
seismic waves, produced by the seismograph
Measuring fault zones
Tiltmeters: measures the tilting or raising of the
ground
- Water level scale (like a carpenter’s level)
- Measures vertical movement
Creep Meter: uses a wire stretched across a
fault to measure horizontal (side to side)
movement of the ground
- Works on a pulley system (stretches wire to
move a weight)
Laser-ranging device: uses a laser beam to
detect horizontal fault movements
- Laser beam is shot to reflector and sent back
to origin of laser (timed test)
GPS Satellites: use satellites to measure
changes in tilt and horizontal movement
- Global Positioning System
- Satellite transmits signals to receivers(below)
on both sides of faults
What determines the intensity
of an Earthquake?
Friction: the force that opposes motion
between two surfaces
- Low friction = small earthquake
- High friction = high stress on rocks = big
earthquake
• Scientists monitor stress on fault zones to try
to predict earthquake, but NOTHING IS
CERTAIN
How can an Earthquake cause damage?
1. Shaking: triggers landslides or avalanches,
can cause damage to or destroy structures
2. Liquefaction: causes building to sink and pull
apart by changing soil to liquid mud
3. Aftershock: earthquake that occurs after a
larger earthquake in the same area (could be
hours, days, or months later)
4. Tsunami: water displaced by an earthquake
that forms from subduction of the ocean
floor
A History of Earthquakes
United States
• Prince William Sound, Alaska – March 28, 1964
Magnitude 9.2
• San Francisco, California – April 18, 1906
Magnitude 7.8
Around the World
• Sumatra, Indonesia – December 26, 2004
Magnitude 9.1
• Haiti – January 12, 2010
Magnitude 7.0