Download EARTHQUAKES 22.5

EARTHQUAKES
• science of earthquakes
EARTHQUAKE
Earthquake = a movement of Earth’s lithosphere
that occurs when rocks in the lithosphere
suddenly shift, releasing stored energy.
The energy released by earthquakes is carried by
vibrations called seismic waves.
As a result of the Loma
Prieta Earthquake, 62
people died and $6
billion in damage was
15 sec
done.
5 sec
3 sec
5:04 pm
pubs.usgs.gov
TSUNAMI
• Sometimes earthquakes can cause tsunamis.
• Tsunami = a series of ocean waves generated
by displacements in the sea-floor
(earthquake), landslides, or volcanic activity
http://www.bbc.co.uk/news/scienceenvironment-12739417
STRESS in the Earth’s Crust
• Earthquakes happen because of the ways the
plate movements affect the lithosphere.
• The forces of plate movement cause
deformation, or changes in the shape or
volume of rock.
STRESS
• Stress = force that squeezes rock together,
stretches or pulls them apart, or pushes them
in different directions
similar to when you are stressed…
• Think of trying to bend a material…
– Chalk…break
– Wire…bend
• Kit Kat
• Twizzlers
• As tectonic plates move, they cause stress in
the crust, which in turn produces faults and
folds.
FAULT
• Fault = a break in a mass of rock along which
movement occurs.
• Ex. San Andreas fault
geology.com
Aerial view of the San Andreas fault slicing through the Carrizo Plain in the Temblor Range east of the city
of San Luis Obispo. (Photograph by Robert E. Wallace, USGS.)
FOLD
• Fold = a bend in layers of rock.
• Rocks tend to fold (rather than break) when
they are under high temperature or pressure.
http://geomaps.wr.usgs.gov/parks/rxmin/rock3.html
Earthquakes & Seismic Waves
• The buildup of stress along a fault provides
the energy that powers the earthquake.
• Earthquakes occur because stress forces have
exceeded the strength of the rock.
• The location beneath the earth’s surface
where an earthquake begins is called the
focus.
• The location on the earth’s surface directly
above the focus is called the epicenter.
Seismic waves
move out in all
directions from
the focus
Physics of Earthquakes
• Within earth’s crust, forces cause two sides of
a fault to move past each other.
• Sometimes rock may snag and remain locked
because of friction.
• Stress builds up.
• When rocks are strained beyond limits, they
break and slide past each other releasing huge
amounts of energy.
• As rocks break and move, potential energy is
transformed into kinetic energy in the form of
waves.
• Three main types of seismic waves:
– P waves
– S waves
– Surface waves
P waves
• Longitudinal waves (similar to sound waves)
• Cause particles in material to vibrate in the
direction of the wave’s motion.
• Compress & expand the ground like accordion.
• FASTEST.
• Travel through solid & liquid.
http://www.classzone.com/books/earth_scien
ce/terc/content/visualizations/es1002/es1002
page01.cfm
S waves
• Transverse waves (like light and other
electromagnetic radiation)
• Cause the particles in the materials they pass
through to vibrate at right angles to the
direction the wave travels.
• Cannot travel through liquids
http://www.classzone.com/books/earth_scien
ce/terc/content/visualizations/es1002/es1002
page01.cfm
Surface Waves
• Develop when seismic waves reach the earth’s
surface.
• Move more slowly than P waves or S waves.
• Produce larger ground movements and
greater damage.
• Some are transverse, others are similar to
ocean waves.
Measuring Earthquakes
• Geologists record seismic waves using
seismographs.
• Seismograph can detect and record seismic
waves.
• Earthquake can be located using seismic
waves recorded by many different
seismographs…triangulation.
http://www.geo.mtu.edu/UPSeis/locating.html
earthquake.usgs.gov
Richter Scale
• Developed in 1935 by Charles Richter.
• Most well-known scale.
• Based on times and amplitudes of seismic
waves.
• NO LONGER USED by geologists.
Moment Magnitude Scale
• Gives a measure of the amount of energy
released by an earthquake.
• Each unit increase = 32 times increase in the
energy released
Modified Mercalli Scale
• Developed in 1931 by seismologists Harry
Wood and Frank Neumann.
• Based on observations of ground shaking and
damage in area affected by earthquake.
• Twelve levels, Roman Numerals.
Seismographic Data
• Most earthquakes are concentrated along
plate boundaries, where many faults are
found.
• Can earthquakes happen anywhere else?
• Some earthquakes occur in the interior of
plates.
Earth’s Interior
• Scientists have analyzed how seismic waves
travel through the Earth.
• Speeds of seismic waves are affected by the
temperature, composition, and density of the
rocks they pass through.
• Outer core is liquid because s waves cannot
pass through it.
http://www.classzone.com/books/earth_science/terc/content/vis
ualizations/es1009/es1009page01.cfm
• http://video.pbs.org/video/1690329036/