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earthquake: shaking and
trembling that results from
sudden movement of part of the
Earth’s crust
Caused by
release of
energy
(lithospheric
plates)
OCCURS FOR MANY REASONS:
•ground shakes from erupting
volcano
•collapse of a cavern
•impact of meteor
•major cause- stress that builds
up and causes faulting
Elastic rebound theory: rocks
that are strained past a certain
point will fracture and spring back
to their original shape
Depth inside the Earth at which
an earthquake occurs depends
upon the kind of plate boundary
focus: point beneath the Earth’s
surface where the rocks break or
move apart
•Point on fault plane where 1st
movement occurs
epicenter: point on Earth’s
surface directly above the focus
•site of most violent shaking
focus
P waves (primary):
•move fastest
•back and forth waves
•move through solid, liquid or gas
•push-pull waves
S waves (secondary):
•travel slower
•move side to side
•travel through solids
L waves (surface):
•move slowest
•move like ripples on a pond
Blue primary waves followed by
red secondary waves move
outward in concentric circles
from the epicenter of an
earthquake off British
Columbia and Washington
State.
Seismograph: instrument that
detects and measures seismic
waves
Seismogram:seismograph’s
record of waves; has wavy
lines recorded on paper
Seismogram
Seismologist: scientists who
study earthquakes
Tracing made by a seismograph
can be used to tell how far
away an earthquake’s epicenter
is from the station that
recorded it:
•Need distance from 3 different
stations in order to determine location
•Point where all 3 circles meet is
location of epicenter
Locating an Earthquake
seismograms can be used to
determine strength or
magnitude of energy produced
by an earthquake
Richter scale: measures how much
energy an earthquake releases by
assigning a number from 1 to 10each is 10x’s higher
Pacific Ring of Fire: major
earthquake zone that forms a
ring around the Pacific Ocean
Successful earthquake
prediction must correctly
forecast:
•where it will occur
•when it will occur
•what magnitude it will be
Possible methods for
prediction:
•detect slight tilting of
ground before an earthquake
•natural gas seepage
•Microquakes (foreshocks)
Foreshocks & Aftershocks
• Foreshock: small earthquakes
that occur prior to a major quake
• Aftershock: small earthquakes
generated by adjustments of
materials that follow a major
quake.
Animal Behavior
• Unusual behavior prior to an
earthquake event
• behavior of animals
• 2004 Indonesia Tsunami
– In Thailand, elephants broke their
chains and ran to a mountaintop
– People survived by following animals
(monkeys, elephants, dolphins)
fleeing from the coast.
– Very few animal corpses were found
Fault
• Fractures in
the Earth
where
movement has
occurred.
• Causes by
stress
• faulted rocks have two blocks:
– hanging wall: block of rock above
fault
– foot wall: block of rock below
fault
Types of Faults
• normal fault: formed when
hanging wall moves down relative
to the foot wall
• reverse fault: formed when
hanging wall moves up relative to
the foot wall
• strike-slip fault: rocks on either
side of fault are moving past each
other
• fold:
bend in the rock (rock deformed
but doesn’t break)
•anticline: upward fold in the rock
(forms ridges)
•syncline: downward fold in the rock
(forms valleys)