# EarthquakesBC

```Earthquakes
What are
Earthquakes?
The shaking or trembling caused by
the sudden release of energy
Usually associated with faulting or
breaking of rocks
Described by the Elastic Rebound
Theory
What is the Elastic Rebound Theory?
Explains how energy is stored
in rocks
– Rocks bend until the
strength of the rock is
exceeded
– Rupture occurs and the
rocks quickly rebound to
an undeformed shape
– Energy is released in
from the fault
What is the Elastic Rebound Theory?
Elastic Rebound
Type of Faults (A Review)
 Normal
 Reverse
 Strike-Slip
Seismic Waves
Through no fault of our own, seismic
waves are generated from the breaking of
the rock
These waves of energy that travel through
the Earth after an earthquake
• Some of these waves are what you feel
during an earthquake
Types of Waves
Surface – travel along the surface, cause
the most damage (Your teacher may
divide these further into Love and
Raleigh Waves) (Slower than Body)
Body – travel through the Earth
• P waves- pushes and pulls the rock
(twice as fast as S wave)
• S wave – slower, displaces rock at
right angles, don’t travel through liquids
P &amp; S Animation
P,S &amp; Surface Animation
Another P,S &amp; Surface Animation
Seismic Wave Motion
S
Waves
Prove
Liquid
Outer
Core
Proof of Moho
(Mohorovičić discontinuity)
• Moho: The dept at which the Pwave velocity exceeds 8.1 Km/S is
referred to as the moho (after the
seismologist Mohorovicic). The moho
is both a seismic and a compositional
boundary, marking the transition
between crust and mantle materials.
Proof of
Moho
Notice the
increase in
velocity around
80 meters, just
before the
transition to the
mantle!
Focus and Epicenter
Focus: the point at which energy is
released, causing the earthquake
Epicenter: the point on the surface of the
Earth that is directly above the earthquake
focus.
Earthquakes generate seismic
waves which can be detected
with a sensitive instrument
called a seismograph.
Seismographs
Perhaps the earliest
seismograph was invented in
China A.D. 136 by a m an
named Choko.
Richter Scale
Measures magnitude of an earthquake
1-10
2 is the smallest able to be felt by humans
Mercalli Scale
Measures intensity
Uses Roman
numerals
I – XII
I – no damage
XII – total damage
Associated Hazards
Landslides
Volcanic eruptions
Tsunamis
Tsunamis
Tsunami
Fault Generating Tsunami
Fault Generating Tsunami
Tsunami Damage,
Gleebruk, Indonesia
Chedi Resort,
Phuket, Thailand,
wave height ~4+ m
(?, from estimates of
water level from
beach umbrellas on
grassy area above
the beach)
Damage in Banda Aceh
Earthquake and Tsunami Damage,
Banda Aceh, Sumatra
Earthquake and
Tsunami Damage,
Sri Lanka
Train and tracks destroyed, SW coast of Sri Lanka
Geist, Titov and Synolakis, Tsunami: Wave of Change,
Scientific American, January, 2006.
Tsunami wave trough, Sri Lanka coast
Commonly, the water recedes (a
wave trough) significantly for a
few minutes before the first
wave crest arrives. People often
go out to explore the beach or
gather fish or shells at that time.
Tsunami wave, Sri Lanka; note strong
current
Banda Aceh, Sumatra, before tsunami
http://geo-world.org/tsunami/
Banda Aceh, Sumatra, after tsunami
Also: http://www.digitalglobe.com/
Another Hazard Associated with
Earthquakes
Liquefaction
San Francisco are built on sandy soil or fill.
Many homes built on this type of soil were badly
damaged during the 1989 Loma Prieta
earthquake by liquefaction.
Liquefaction occurs in saturated soils, that
is, soils in which the space between
individual particles is completely filled with
water. This water exerts a pressure on the
soil particles that influences how tightly the
particles themselves are pressed together.
Model of liquefaction
Example of liquefaction
Latest Earthquakes in the World
Past 7 days
Film Clips
Destruction
Earthquake Swallows Car
Seismic Wave Demonstrator
The End
```