1. Risk Assessment
GEOL 4093
Dr. David M. Bush

2. Reading Material
• 1. Understanding Your Risks: Identifying Hazards and
Estimating Losses
• 2. Multi-Hazard Risk Assessment and Vulnerability Study:
Project Impact, Culebra Inc.
• 3. Multi Hazard Identification and Risk Assessment
• 4. Living With Earth's Extremes
• 5. The Ten Most Wanted: A Search for Solutions to
Reduce Recurring Losses From Natural Hazards
All will be provided as pdf files on CD or on line.

4. Risk Assessment
• Determining likely impacts of a hazardous
event
• Combines:
– Information on physical hazard
– Information on vulnerability

5. Risk Assessment Provides
Estimates of:
• Deaths and injuries
• Property damage
• Economic losses

6. Risk Assessment Leads to:
• Mitigation
• Preparedness
• Warning
• All in attempt to reduce negative impacts of
hazards

7. Course Organization
• Physical Processes (hazards)
– Geologic
– Meteorologic
• Risk Assessment
– Probability
– Maps
• Mitigation
– Reducing damages
– Preparedness

8. Most risk assessment to date is actually
better termed hazard assessment
That is, the assessment of the
physical phenomena themselves

9. We’ll Concentrate on
Natural Hazards
• Geologic
– Seismic (earthquakes, tsunamis)
– Volcanic
– Other (subsidence, mass wasting, expansive soils)
• Meteorologic
– Hurricanes
– Northeasters
– Tornados
– Floods

10. We may briefly touch on:
• Technologic hazards
• Biologic
• Fires
• Other

11. Numbers of Major Disasters
• The following two slides show some information
about natural disasters in an unusual way
• The first table shows type of disaster
• The second table is by 5-year periods
• Both tables show the number of occurrences of
disasters when damage exceeded 1% of annual GNP,
when more than 1% of a country’s population was
affected, when more than 100 deaths occurred
• Keep in mind that this is not total damage, population
affected, or deaths, but number of occurrences

12. Major Disasters 1963-1992
9
1
1
Tsunamis
12
9
2
Volcanoes
54
2
1
Landslides
102
20
24
Earthquakes
21
167
53
Drought
153
100
73
Tropical Storms
202
162
76
Floods
100+ dead
1+% pop
1+% GNP
Disaster

13. Disasters per 5-year Period
205
139
66
1988-1992
162
116
58
1983-1987
138
99
55
1978-1982
96
56
31
1973-1977
98
54
15
1968-1972
89
39
16
1963-1967
100+ dead
1+% pop
1+% GNP
Period

14. Two Components of
Risk Assessment
• Trying to determine the likely impacts of a
hazardous event.
• 1. Physical aspects of hazards
– Frequency, intensity, location
• 2. Vulnerability
– Exposed populations, structures, critical
facilities, natural resources

15. Why Assess Risk?
• Provides estimates of:
– Deaths and injuries
– Property damage (our main concern)
– Economic losses

16. What can you do with this
information?
• Reduce risk through:
– Mitigation
– Preparedness
– Warning strategies

17. What do you already know about
natural hazards in the
United States?
• Think about:
– Where hurricanes strike
– Where tornados occur
– Flood zones
– Seismic zones
– Coastal erosion
• Hazard-prone areas are generally well
known, but details often lacking

18. Natural Hazards
• Natural processes or events that existed
throughout Earth history, but have only
become “hazardous” when they have
negative impact on humans
• To put things in perspective, think of many
other natural processes or events that are not
“hazardous”

19. Anthropocentric Perspective
• Natural processes only called “hazardous”
when they threaten human life, health, or
interests, either directly or indirectly
• Actually has lead to “adversarial” style of
hazard management—natural processes are
seen as the “enemy” and efforts are made to
manipulate the environment into submission

20. Rapid Onset Hazards
• Catastrophic events
• Strike quickly but with devastating
consequences
• Large comet or meteorite impact
• Also earthquakes, flash floods, sudden
windstorms

21. Other end of time spectrum:
• Droughts can last decades
• Worldwide, droughts are the most
devastating natural hazard because of long
duration and large area affected

22. Technological Hazards
• Exposure to naturally occurring hazardous
substances
• Examples: radon, mercury, asbestos fibers,
coal dust
• Usually through use of these substances in
our built environment

23. Anthropogenic Hazards
• Human generated
• Pollution and degradation of the natural
environment
• Examples: acid rain, contamination of
surface and ground water, depletion of
ozone layer, global warming

24. Primary Effects
• Result from the event itself
• Water damage from a flood
• Wind damage caused by a cyclone
• Collapse of a building caused by ground
motion during an earthquake

25. Secondary Effects
• Result from hazardous processes associated
with, but not directly caused by, the main event
• Forest fires sparked by lava flows
• House fires caused by gas lines breaking during an
earthquake
• Disruption of water and sewage services as a
result of a flood
• Flood from dam failure during earthquake or
intense rains

26. Tertiary (and higher order) Effects
• Long term or even permanent changes
• Loss of wildlife habitat or “permanent”
changes in a river channel during a flood
• Regional or global climatic changes and
resulting crop losses after major volcanic
eruption
• Changes in topography or land elevation as
a result of an earthquake (1964 Alaska EQ)

27. How many people impacted?
• Last two decades of 20th Century:
• 3 million deaths world wide
• 800 million people suffered adverse effects
such as loss of property or health

28. Numbers of Events (Hazards)
• United Nations estimate, in the 1990’s
• Landslides—tens of thousands
• Earthquakes—tens of thousands
• Thunderstorms—1 million
• Floods—100,000
• Plus many thousands of tropical storms,
hurricanes, tsunamis, droughts, volcanic
eruptions

29. Cost of Natural Hazards
• World Bank estimate, in the USA:
• $40 Billion per year in physical damage
• Windstorms, floods, earthquakes alone cost
the USA $18 million per day
• What do you think is the costliest natural
hazard in the southeastern USA?

30. Vulnerability
• Status of people and property in an area
subject to hazards
• Depends on type(s) of hazards as well as
type of development

31. Vulnerability depends on:
• Obviously, living in a hazardous area
• Population density
• Scientific understanding of the area
• Public education and hazard awareness
• Early warning system
• Communication
• Emergency personnel
• Building codes
• Cultural factors—people’s response to warnings

32. Awful Truth
• Almost no one dies in the USA from
hurricanes, but property damage is extreme
• Tens or hundreds of thousands may die in
Bangladesh from a hurricane, but property
damage low
• However, besides the disparity in deaths,
the relative value of monetary losses is
much higher in developing nations

33. Poverty vs. Affluence
• Both can cause pressures on environment
• Extensive deforestation for fuel wood of
Haiti or lands bordering the Sahara desert
• Extensive development around San
Francisco Bay on filled land susceptible to
liquefaction during an earthquake

34. Human intervention can increase
vulnerability
• 1. Habitation of lands susceptible to hazards
(floodplains or deltas)
• 2. Increasing the severity or frequency of natural
hazards (agriculture leading to increased soil
erosion, groundwater withdrawal leading to
subsidence, levees increasing flood levels, global
climate changes leading to increased intensity and
frequency of hurricanes)

35. Hazard Assessment
• Where
• Magnitude
• Frequency
• Likely effects of occurrence
• Provide information to planners and
decision makers
• Usually means a map or maps

36. Landslide susceptibility map and recommended land use for
Congress Springs area near San Francisco

39. A Probability Map. Shows areas
with highest probability of
exceeding a certain magnitude of
ground motion during an EQ

40. Seismic risk map for USA
shows expected damage for
maximum EQ intensity. Map
does not indicate frequency.

41. Hazard Assessment Uses
• Decisions about evacuation or contingency
funding
• Decisions concerning levels of response and
readiness
• Land use and zoning
• Building codes
• Scientists use for early alerts and further
study

42. Risk Assessment
• Incorporates expected (predicted) economic
losses, injuries and deaths, and loss of
functioning of services
• Key is establishing the probability that a
hazardous event of a particular magnitude
will occur within a given time period

43. Social and Economic Aspects of Risk
• Locations of buildings, facilities, and
emergency systems in the community
• Their potential exposure to the physical
effects of the hazardous situation or event
• Vulnerability—potential loss of life, injury,
or loss in value—when subjected to those
physical effects

44. Probability and Risk
• Being exposed to earthquake hazards by
living in Southern California for seven
months carries the same risk of death as:
• Smoking 1.4 cigarettes
• Drinking 0.5 liters of wine
• Having a single chest X-ray
• All increase chance of death by 1 in a million

45. Another way to express risk
• In terms of cost
• Dollar value of damages
• Expected deaths and injuries
• Both methods help decision makers and
scientists compare and evaluate hazards, set
priorities, and decide where to focus
attention and resources

46. Goals of this course
• Increase awareness of natural hazards
• To recognize risks from natural hazards
• Identify specific locations and things at risk
• Understand management/policy/political
decisions (and be skeptical)
• Understand losses from hazards beyond $$
• Scientists must play greater role

47. Integrated system designed to reduce landslide hazards