Transcript What is an earthquake?

What is an earthquake?
shaking and trembling that
results from sudden movement
of part of the Earth’s crust
Caused by
release of
energy
(lithospheric
plates)
What are the causes of
Earthquakes?
•ground shakes from erupting
volcano
•collapse of a cavern
•impact of meteor
•major cause- stress that builds
up and causes faulting
What is the theory of Elastic
rebound?
Elastic rebound theory: rocks
that are strained past a certain
point will fracture and spring back
to their original shape
What is the focus?
focus: point beneath the Earth’s
surface where the rocks break or
move apart
•Point on fault plane where 1st
movement occurs
What is the epicenter?
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 only
L waves (surface):
•move slowest
•move like ripples on a pond
•only travel along the
surface
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.
What is a Seismograph?
instrument that detects and
measures seismic waves
Seismogram:seismograph’s
record of waves; has wavy
lines recorded on paper
Seismologist: scientists who
study earthquakes
How are Earthquakes measured?
Locating an Earthquake
 Earthquake
•
Distance
The epicenter is located using the
difference in the arrival times between
P and S wave recordings, which are
related to distance.
 Earthquake
Direction
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
How is Earthquake strength
determined?
seismograms can be used to determine
strength or magnitude of energy
produced by an earthquake
Richter scale: measures how much
energy an earthquake releases
(magnitude)by assigning a number from
1 to 10
Earthquake Magnitudes
Some Notable Earthquakes
What is the Pacific Ring of
Fire? major earthquake zone that
forms a ring around the Pacific Ocean
What damage occurs from
Earthquakes?
•
•
•
•
•
Building collapse
Liquefaction
Tsunamis
Landslides
Fire
Successful earthquake
prediction must correctly
forecast:
•where it will occur
•when it will occur
•what magnitude it will be
What are possible methods
for predicting Earthquakes?
•microquakes
•behavior of animals
•detect slight tilting of
ground before an earthquake
•natural gas seepage