Download low-pressure system - Mater Academy Lakes High School

Natural Hazards
What is an Earthquake?
 Ground movement caused by the sudden release of
seismic energy due to tectonic forces.
The focus of an earthquake is the
actual location of the energy
released inside the Earth’s crust.
The epicentre is the point on the
Earth’s surface directly above the
focus.
Why do earthquakes occur?
 Seismic energy is usually caused by the brittle
failure (fracturing) of rocks under stress.
Figure showing
the distribution of
earthquakes
around the globe
 This commonly occurs due to movement along
tectonic plate boundaries
Earthquake Magnitude
Magnitude
Earthquake Effects
Approx. number
each year
< 2.5
Usually not felt, but recorded
900,000
2.5-5.4
Often felt, only minor damage
30,000
5.5-6.0
Slight damage to buildings and
other structures
500
6.1-6.9
May cause a lot of damage in very
populated areas
100
7.0-7.9
Major earthquake. Serious
damage.
20
> 8.0
Great earthquake. Can be totally
destructive near the epicentre.
1 every 5-10 years
San Francisco - Great Earthquake
 Magnitude 7.7 - 8.3
Earthquake Hazards
 These are important hazards to understand:
 the natural hazard that on average kills the highest
number of people per year (> 1 million during the past
century)
 commonly strikes without warning
 no time for evacuation
 not a predictable trend to earthquake numbers,
magnitude or location


1000's of large earthquakes every year
~ 20 are > M7.0 and these account for 90% of the energy
released and 80% of all the fatalities
Earthquakes and Tsunami’s
 An earthquake under the ocean has the potential to
form a tsunami.
 The earthquake must vertically displace overlying
water (extensional or compressional faults - not
transform)
Extension
Compression
Transform
How does an earthquake form a
tsunami?
2004 South Asian
Boxing Day event
 Biggest earthquake
in 40 years!
 Magnitude 9.2
 150 km off the west
of Northern
Sumatra
 Generated a
disastrous tsunami
in 12 countries
Tsunami
Above: Countries most effected by the
tsunami
Animations of
the Boxing
Day tsunami
showing how
the tsunami
radiated from
the entire
length of the
1,600 km (994
miles) rupture.
How do we mitigate the hazard
from tsunamis?
 Monitoring


process is very technology-intensive
high costs for many poorer countries
 Building restrictions in hazard
prone areas
 Seawall construction
Same Storm - Different Name
Cyclone Categories
Category
Wind Speed
(mph)
Damage at
Landfall
Storm Surge
(feet)
1
74-95
Minimal
4-5
2
96-110
Moderate
6-8
3
111-130
Extensive
9-12
4
131-155
Extreme
13-18
5
> 155
Catastrophic
19+
The Saffir-Simpson Hurricane Scale
Pressure Systems
A low-pressure system
is a large body of
circulating air with low
pressure at its center and
higher pressure outside
of the system.
It has warm, moist air
and generally brings
stormy weather with
strong winds.
Hurricane Katrina
 Hurricane Katrina was
the most costly and
most deadly hurricane
in the history of the
USA.
 Category 5
 At least 1,836
fatalities
 Damage estimated at
US$ 81.2 billion
What damage is produced?
Wind





responsible for the loss
of power and utilities
wind damage affects
larger areas than surge
flying debris
tree loss
What damage is produced?
Flying debris


debris propelled
at high speeds
How do we mitigate the hazard
from a cyclone?
 Monitoring
 early warning systems
 Infrastructure
 cyclone walls
 communal shelters
 Education and planning