Download Natural Hazards Part 2 - Ms

Earthquakes
and
Tsunamis
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 epicenter 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
Why so many earthquakes in
Southern California?

located in a tectonically active area
 Pacific
& North American Plate
San Andreas Fault – Salton Sea to San
Francisco
 Elsinore
 San Jacinto

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
Just another bend in the fault . .
Bends in fault lines makes it difficult for the
plates to slide past each other easily.
 So stress may build up for many years,
before a big earthquake occurs.
 There are several places in the San
Andreas Fault Zone where bends in faults
may lock the fault and allow stress to build
up.

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
How do we mitigate the hazard
from earthquakes?
Reinforce buildings
 Education
 Disaster plan

What can we expect
after a massive
earthquake?
Power Outage

Power will go out immediately, everywhere,
and restoration times vary. In the most
heavily damaged areas, electricity will
remain out for weeks or longer. Some
residences will suffer broken gas lines when
their houses slip from unbolted foundations.
Water

Water will stop flowing in many taps for weeks
or months. In many communities, strong
ground shaking will break old, brittle water
pipes and connectors, and there will be so
many breaks that it will prove cheaper and
faster to replace the entire conveyance system,
rather than hunt and repair every break. The
process will be neither cheap nor fast, and
communities will compete for repair priority.
Wastewater

Many wastewater pipes are also old and
brittle, and run alongside water pipes
under the streets. Broken sewer pipes will
contaminate broken water pipes, and in
some places, tap water will be unsafe to
drink for as long as a year.
Telecommunications

Telecommunications will be out for at least a
day, because of some damage and much
overuse. Phone systems will be oversaturated
because millions are trying to make calls at
once. How cell phone towers are affixed to
buildings is not regulated, so towers will be
damaged by shaking. Two thirds of the region's
internet lines will be ruptured by the fault.
Transportation

Transportation by road and rail will be
disrupted by fault rupture and landslides, and
take months to repair. Retrofitting of state
highway bridges prevents their collapse, but
not those under most local jurisdictions. For
months, getting around the southland will take
longer, and travel time delays add more than
$4 billion to economic losses.
Hospitals

Hospitals in the hardest hit counties of
Riverside, San Bernardino, and Los Angeles
will be operating at reduced functionality. At a
time when thousands of disaster victims need
hospital care, some hospital buildings will be
closed by structural damage; many others will
be unusable because of non-structural damage
such as broken water pipes and unsecured
equipment.
Public Schools

Public schools--grades K-12 and community
colleges--are protected by the Field Act,
legislation that sets special construction and
inspection standards. Structurally, public
schools will hold up well, although nonstructural and contents damage will pose
problems. Private schools and universities are
not protected by the Field Act and some will
suffer both structural and non-structural
damage.
Ports

The Ports of Los Angeles and Long Beach
are important contributors to the region's
economy. They will not suffer much damage
from this far-away earthquake, but their flow
of goods will be disrupted for months, as
many principal train routes and truck routes
are damaged by fault rupture.
7 Steps to Earthquake Safety
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)

Divergent
Convergent
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
Second largest recorded earthquake



The earthquake occurred at a convergent
tectonic plate boundary (subduction zone)
An estimated 1,600 km (994 miles) of faultline
slipped about 15 m (50 ft)!
The earthquake released 20 x 1017 Joules of
energy
 Equivalent to:
 475,000,000 kg of TNT
 23,000 Hiroshima atomic bombs!
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.
A village
near the
coast of
Sumatra
lays in ruin
after the
tsunami.
How do we mitigate the hazard
from tsunamis?

Monitoring
 process
is very technologyintensive

high costs for many poorer
countries
 often
no technology available to
monitor local tsunamis


for example,
Papua New Guinea has no
monitoring stations


reliant on the Pacific Tsunami
Warning Center
tsunami in 1998 was not detected
How do we mitigate the hazard
from tsunamis?

Building restrictions in
hazard prone areas
 In
Hawaii, Hilo harbor and
downtown was destroyed
by the tsunamis of 1946
and 1960
 The town is now rebuilt on
higher ground and the
devastated area is a park
How do we mitigate the hazard
from tsunamis?

Seawall construction
 cause
early wave breaking
 prevent wave run up into urban areas
How do we mitigate the hazard
from tsunamis?

Education
 warning
systems
 evacuation plans
 general understanding
of the hazards involved
Punishment
From God
45%
Natural event
35%
Bomb 20%
Population reaction:
Papua New Guinea (1998)