22
Geotechnical News • December 2017
GEOHAZARDS
Courting Disaster:
The Increasing Challenge of Risk Assessments
(A version of this article first appeared in the Sep/Oct 2017 edition of Innovation Magazine)
R.H.Guthrie, M.Sc., Ph.D., P.Geo.
Introduction
On April 6, 2009, at approximately
3:32 AM, a magnitude 6.3 earth-
quake devastated the medieval Italian
town of L’Aquila, about 90 km east
of Rome, killing more than 300 and
leaving thousands homeless (Roberts,
2014; Cartlidge, 2014). Ultimately,
it wasn’t just the devastating human
toll that made this event newsworthy,
but the legal consequences to a group
of Italian scientists that formed part
of the Italian National Commission
for Forecasting and Preventing Major
Risks (the Major Risks Commission).
Those six scientists (three seismolo-
gists, a volcanologist and two seismic
engineers) were tasked with estimat-
ing the risk of a major earthquake to
the town in light of several small and
medium sized events that occurred
in previous months (Cartlidge, 2014)
and local prognosticators and scare-
mongers predicting a major event. The
Major Risks Commission estimated
that there was little risk of a large
earthquake. The earthquake occurred
despite the prediction, and in 2012, the
scientists were sentenced to 6 years
in prison and €9,000,000 (Cartlidge,
2012). The ruling was overturned 2
years later, but the impact to the global
scientific community was sobering.
As geotechnical scientists and engi-
neers, we are called upon to make
judgements about the conditions
and characteristics of the earth and
earth processes. Those judgements
are intended to guide development;
to contribute to the understanding of
environmental, economic, or societal
safety; to advise civil design, and to
prevent catastrophic outcomes of the
human footprint. All too often we are
expected to perform Herculean leaps
of knowledge based on very limited
data for a litigious society that relies
on our expertise.
And let’s be clear. The public does
rely on our expertise, and as a self-reg-
ulating profession that claims expert
knowledge about the workings of the
earth, we encourage and promote that
model.
We owe ourselves, and the public, a
duty of care to limit our own liability
by being aware of, and communicat-
ing, what we know, and conversely
what we don’t know. We also owe it
to ourselves and the public to clearly
communicate the notion of residual
risk and uncertainty, and how that
residual risk can change as a result
of changing conditions (including
development).
Definitions
Definitions of hazard and risk may be
superfluous; however, they are still
widely misused in geotechnical engi-
neering and warrant reviewing in light
of the present topic.
Hazard
Hazard is widely-used to describe
threats to humans and what they value
including life, well-being, material
goods and the environment (Perry,
1981). Ambiguity arises wherein the
term hazard is used as both a collo-
quialism and as a specialist term with
different meanings or levels of preci-
sion for different disciplines (Nadim,
2013). In geotechnics, hazard should
be limited where practical to the prob-
ability, within a specific time and area,
that an event or events (geotechnical,
geological or geomorphological pro-
cesses) will adversely affect humans
or the things humans value. Other
conditions can be described as threats,
dangers or susceptibility.
Risk
Risk is also widely-used to describe
threats to humans and what they value.
Geotechnical engineers and the public
frequently misuse the word risk to
mean hazard, or indeed, any measure
of probability (such as susceptibil-
ity). In reality, risk must embody
both the probability of a hazard (or
the sum of hazards) occurring, and
the consequence(s) of that event. The
most general risk equation is given as:
R = H x C
Where R=risk, H=hazard and
C=consequence.
In reality, the basic risk equation is
normally divided into component parts
including: spatial and temporal prob-
ability of a hazard, or a probabilistic
model of hazards, and the magnitude
(volume, area, intensity, runout etc…),
the elements at risk and the vulner-
ability, exposure and value of those
elements.
A more refined equation therefore
looks something like the following:
Where R
S
= specific risk,
P=probability, H
T,S
=temporal and spa-
tial likelihood of a hazard of a given
magnitude respectively, E
V
, V and E
X
is the value, vulnerability and expo-
sure respectively of a given element
at risk.
It shouldn’t surprise the reader to
learn that many of these terms can be
further broken down.
R P H x E xVxE
s
TS
v
x
=
( )
∑
(
)
