GG231 Midterm Review
Lesson 1 – Introduction
Risk – the product of the probability of a hazardous event and the expected damage if the event
does occur.
Hazard – (Natural) A natural process that poses potential threat to people and property
Disaster – A brief event that causes great damage or loss of life in a limited geographic area.
Response Sequence to a Disaster (Recovery)
The first two weeks after a disaster are the period of emergency, during which normal
activities cease or are changed. In the restoration phase which typically lasts several
months, normal activities return, although perhaps not at pre-disaster levels. Finally during
reconstruction the capital stock is replaced, major new construction is completed and
normal activities return. *Fig 1.16 page 24
Types of Disasters
• Natural Hazards
atmospheric
hydrological
geological
biological
• Technological Hazards
hazardous materials
destructive processes
devices, machines
installations
sector, organization
• Violence and war hazards
Weapons
release of dangerous natural forces
release of dangerous technological forces
armed forces and weapon systems
strategies and tactics
Vulnerability to Hazards
Much of human vulnerability has little or no relationship to the particular hazard, such as
tornadoes or chemical release. It is related to activities and circumstances of everyday life.
Vulnerability is more likely to be dependent on age, gender and health status, and how
society treats its members or different groups. Vulnerability also depends upon the quality
and siting of buildings and land uses; public infrastructure and services; and ways of life
and political authority. Above all vulnerability involves the general and active capacities of people, what enables
them to avoid, resist and recover from harm. While, a hazards perspective tends to explain
risk and disaster in terms of external agents and their impacts, vulnerability looks to the
internal state of a society and what governs that. Vulnerability in the modern world
depends upon the legal, political and moral frameworks of civil society. In more traditional
societies, it depends upon customary obligations and communal support structures
Hewitt identifies six forms of vulnerability:
• exposure to dangerous agents and environments
• weaknesses predisposition of persons, buildings, communities or activities to greater harm
• lack of protection against dangerous agents and for weaker persons and items
• disadvantage lack of the resources and attributes to affect risks or respond to danger
• lack of resilience limited or no capability to avoid, withstand or offset and recover from disaster
• powerlessness inability to influence safety conditions, or acquire means of protection and relief
Intervening Conditions
Intervening conditions are those not directly related to a given hazard or human
vulnerability to particular stresses. It includes circumstances that intervene between the
two. For instance, as you will learn in Module One, the impact of an earthquake on a city can
be influenced by particular soil type, topography, vegetation cover and water tables.
However, these conditions are not dependent on the tectonic activity nor the built
structures. They have their own, distinct geographic patterns. They intervene between
seismic events and vulnerable structures and to a different extent from place to place
(Hewitt, 1999).
Similarly, institutional and cultural phenomena may buffer or focus damage without being
tied to specific vulnerabilities or agents of damage. The form and development of
settlements, occupations and who is obliged to live where, also happen to be critical for
storm or flood risks. International grain prices and local grain stocks can influence whether
famine will be allowed to develop in a particular country. Food distribution policies and
market prices can decide who and how many people, will starve, even where sufficient food
is actually available (Hewitt, 1999).
Risk Assessment
Risk considers the exposure to dangers, adverse or undesirable prospects and the
conditions that contribute to danger. Risk analysis considers potential and assessed
dangers. Typically one considers past damages to define levels of danger attached to groups,
activities and everyday life. By understanding or predicting the risk we can possibly reduce
or eliminate the possibility of a disaster. This is not a course on risk assessment, such as
smoking and life expectancy, car insurance, etc. This form of risk has a long history in
favourable and adverse future results, profits and losses, game theory, winning and losing
and has been covered extensively in texts on insurance. The main focus in this course is the
question of public safety and social security, focusing on the adverse outcomes and
possibilities for prevention and mitigation.
Most deadly disasters
Natural - http://www.disastercenter.com/disaster/TOP100K.html
Technical - http://www.disastercenter.com/disaster/TOP100P.html Lesson 2 – Earthquakes, Tsunamis
Main Causes of Earthquakes
The earthquake hazard is a function of a number of factors. The physical processes are
linked to factors such as where did the quake originate or at what depth below the earth's
surface, the structure of the bedrock, etc.
Focus
where rupture on fault plane started – seismic energy leaves this point (a.k.a. the
hypocenter)
Epicenter
point on surface above the focus
Earthquakes are frequently triggered along a fault line you are probably familiar with the
San Andreas Fault in California. The tsunami that struck Indonesia in 2004 also originated
from an earthquake that started along a fault.
Normal Fault
A fault along which the hanging wall has moved down relative to the footwall.
Reverse Fault
A fault along which the hanging wall has moved upward relative to the footwall
Thrust Fault
Low angle reverse fault along which older rocks are displaced over younger rocks.
Tectonic Plate
A very large, fault bounded block of crust and upper mantle that slowly moves on top of the
asthenosphere. Tectonic plates form at mid oceanic ridges and are destroyed at subduction
zones.
Subduction Zone
An elongate zone, typically hundreds to over a thousand km long, where two crustal plates
converge, one moving slowly under the other. (Largest earthquakes are subduction ones)
Damage
Another scale is used to measure the impact or damage from the earthquake the Modified
Mercalli Scale. This scale focuses more on the impact to society such as the number of
deaths, buildings collapsed, etc.
Primary Damage
The primary damage comes from injuries and death caused by failed buildings. It is direct
damage that is physical or mechanical. It can be minimal, with only cracked plaster, or as
extensive as failure of the structure. The shaking weakens the bearing strength of the
ground. (Secondary damage is just the other damages that are incurred. )
Shaking
Much of the primary damage that occurs from a quake is related to the shaking of the ground and
the subsequent failure of structures.
Waves
To understand the process of a quake and the potential damage you should be familiar with seismic
waves. You should be able to identify
• Body Waves
P Wave – seismic wave that travels from the hypocenter of an earthquake by
compressing and extending rock and fluids along its path. FASTEST
S Wave – A seismic wave that travels in a snake like fashion through solid material
from the hypocenter.
• Surface or Long waves
Rayleigh – seismic wave that travels at earths surface with a retrograde elliptical
motion
Love – same as Rayleigh except travels in snake like form.
Long-term Predictions
Long-term predictions can come from examining historical data, research and mapping of
previous and historical events. The development of a record of activity can provide an
estimate of the recurrence interval (how often an earthquake will occur or repeat itself).
Similarly, if there has been a large break in activity when a quake should have occurred
based on the recurrence interval then it is expected that one is overdue and could happen
soon. This is referred to as a seismic gap.
Short-Term Prediction
Another method for predicting quakes is to consider evidence (short-term precursors) that
occurs shortly before the quake. In all cases, there is evidence to support these predictions
but it is weak and in general such methods have not been embraced by the scientific
community. Examples of these methods include the following:
o Foreshocks: By tracking the rate of small shocks it is possible an increase in activity
will provide warning of a larger quake
o Animals: barking dogs, chickens laying eggs evidence to support correlation?
o Lunar tides: It is theorized that when there is a stronger pull on the earth through
moon and sun gravitational pulls then the chance of a quake occurring is greater
Reliable prediction is still years away but will be likely based on:
• Patterns and frequency of quakes, foreshocks
• Deformation of the ground surface including uplift and subsidence
• Seismic gaps along faults where there are sites of inactivity
• Geophysical and geochemical changes in groundwater levels, temperatures,
soil and water chemistry Lesson 3 – Volcanoes
Types of Volcanoes
Shield volcano
massive mound- or shield-like mountains largest in the world
e.g. Iceland, Hawaii
non-explosive eruptions lava flows down the side
Composite Volcano or StratoVolcanoes
cone shape
e.g. Mount St. Helens (Washington), Mount Pinatubo (Philippines), Mount Unzen (Japan)
combination of explosive activity (producing pyroclastic deposits) and lava flows
responsible for most volcanic related deaths
Volcanic Domes
highly explosive eruptions
e.g. Lassen Peak and Mono Craters (California)
Cinder Cones
accumulation of tephra near a vent primarily lava deposits
small volcanoes usually on the flank of a larger volcano, faults or fissures
can be fast-growing features
e.g. Paricutin (Mexico)
Typical eruptions
Non-Explosive
Icelandic and Hawaiian
Explosive
Strombolian
Vulcanian
Plinian
Measuring the Volcanic Hazard
Energy released is measured by Volcanic Explosivity Index (VEI). It is a measure of the volume of
material erupted and the height of the ash plume. The lowest measure is 0 which represents a non-
explosive event and interestingly there is no upper limit to this scale. Mount St. Helens which was a
very large event registered a 5. The largest in recorded history was Tambora, Indonesia in 1815. It
was recorded as a 7. Volcanic Hazards
The hazards associated with volcanoes can occur in a number of forms but primarily involved the
movement of material away from the centre of the volcano and contact with surrounding buildings,
crops and population. (5 types of hazards associated with volcanoes)
Lava Flows
o Slow moving usually not life threatening
o Environment and property damage momentum of moving flow, heat destroy trees,
crops, houses
o There are three types of lava flows: pillow, pahoehoe and aa
Pillow
o elongate, interconnected flow lobes that are elliptical or circular in cross-
section
o volumetrically the most abundant type because they are erupted at mid-
ocean ridges and because they make up the submarine portion of seamounts
and large intraplate volcanoes
Pahoehoe
o characterized by a smooth, billowy, or ropy surface.
o ropy surface develops when a thin skin of cooler lava at the surface of the
flow is pushed into folds by the faster moving, fluid lava just below the
surface
o flows tend to be relatively thin, from a few inches to a few feet thick
Aa
o characterized by a rough, jagged, spinose, and generally clinkery surface
o flows advance much like the tread of a bulldozer
Ash Fall
o Ash fall consists of fine-grained fragmented debris, ash and abrasive volcanic
glass. Large eruptions create hazards by covering property, causing breathing
problems and plane crashes. An example is the Tambora volcano in Indonesia
which erupted in 1815 killing 12,000 people outright. An additional 80,000
died of starvation and disease.
o Ash Fall can create a number of hazards (see page 82 of the text for more
details):
Destroys crops and trees
Surface water contaminated by sediment
Structural damage to buildings
Health hazards irritation to respiratory system and eyes
Silica-rich ash for
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