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Public Health Consequences of Earthquakes

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Title: Public Health Consequences of Earthquakes


1
Public Health Consequences of Earthquakes
  • Eric K. Noji, M.D., M.P.H.
  • Centers for Disease Control and Prevention
  • Washington, D.C.

2
INTRODUCTION
  • Background and Nature of Earthquakes
  • A major earthquake affecting a large city has the
    potential to be the most catastrophic natural
    disaster for the United States.

3
Scope/Relative Importance of Earthquake
Disasters
During the past 20 years, earthquakes alone have
caused more than a million deaths worldwide (5).
Nine countries account for more than 80 of all
fatalities this century, and almost half of the
total number of earthquake deaths in the world
during this period have occurred in just one
country--China (Figure 8--1).
4
The United States has been relatively fortunate
in terms of earthquake-related casualties so far
(7). Only an estimated 1,600 deaths have been
attributed to earthquakes since colonial times,
with over 60 of these having been recorded in
California.
5
As mentioned above, population growth in areas of
high seismic risk in the United States has
greatly increased the number of people at risk
since the last earthquake of great magnitude
struck (1906 in San Francisco). Researchers
estimate that a repetition of the 1906 San
Francisco earthquake, which measured 8.3 on the
Richter scale, could cause 2,000 to 6,000 deaths,
6,000 to 20,000 serious injuries, and total
economic losses exceeding 120 billion (11,12).
6
Earthquakes have even occurred on the east
coast. For example, Charleston, South Carolina,
experienced a magnitude 6.8 (Intensity X)
earthquake in 1886 that killed 83 people and was
felt over most of the United States east of the
Mississippi River (13).
7
Factors that Contribute to Earthquake Disasters
Depending on its magnitude, its proximity to an
urban center, and the degree of earthquake
disaster preparedness and mitigation measures
implemented in the urban center, an earthquake
can cause large numbers of casualties.
8
FACTORS AFFECTING EARTHQUAKE OCCURRENCE AND
SEVERITY
  • Natural Factors

9
Earthquake Strength
Magnitude and intensity are two measures of the
strength of an earthquake and are frequently
confused by laypeople (22). The magnitude of an
earthquake is a measure of actual physical energy
release at its source as estimated from
instrumental observations. A number of magnitude
scales are in use. The oldest and most widely
used is the Richter magnitude scale, developed by
Charles Richter in 1936. Although the scale is
open-ended, the strongest earthquake recorded to
date has been of Richter magnitude 8.9.
10
Topographic Factors
Topographic factors substantially affect the
impact of earthquakes. Violent ground shaking
in areas constructed on alluvial soils or
landfill, both of which tend to liquify and
exacerbate seismic oscillations, can produce
significant damage and injuries at a given
location far from the actual earthquake epicenter
(23). Both the impact of the 1985 earthquake on
Mexico City, where an estimated 10,000 people
died, and that of the 1989 Loma Prieta earthquake
are good examples of how local soil conditions
can play important roles in producing building
damage of greater severity than what may occur in
areas closer to the earthquake's epicenter.
11
Volcanic Activity
Earthquakes often occur in association with
active volcanoes, sometimes triggered by magmatic
flow and sometimes releasing pressure that allows
magmatic intrusion. The so-called harmonic
tremors associated with actual magmatic flow are
generally not damaging however, relatively
severe earthquakes can immediately precede or
accompany actual volcanic eruptions and can
contribute to devastating mudslides.
12
Public Health Impacts of Earthquakes Historical
Perspective
In most earthquakes, people are killed by
mechanical energy as a direct result of being
crushed by falling building materials. Deaths
resulting from major earthquakes can be
instantaneous, rapid, or delayed (25).
13
As with most natural disasters, the majority of
people requiring medical assistance following
earthquakes have minor lacerations and contusions
caused by falling elements like pieces of
masonry, roof tiles, and timber beams (28). The
next most frequent reason for seeking medical
attention is simple fractures not requiring
operative intervention (29). Such light injuries
usually require only outpatient-level treatment
and tend to be much more common than severe
injuries requiring hospitalization.
14
Major injuries requiring hospitalization include
skull fractures with intracranial hemorrhage
(e.g., subdural hematoma) cervical spine
injuries with neurologic impairment and damage
to intrathoracic, intra-abdominal, and
intrapelvic organs such as pneumothorax, liver
lacerations, and ruptured spleen (32). Most
seriously injured people will sustain combination
injuries, such as pneumothorax in addition to an
extremity fracture.
15
Hypothermia, secondary wound infections, gangrene
requiring amputation, sepsis, adult respiratory
distress syndrome (ARDS), multiple organ failure,
and crush syndrome have been identified as major
medical complications in past earthquakes.
16
As noted above, trauma caused by the collapse of
buildings is the cause of most deaths and
injuries in most earthquake (5). However, a
surprisingly large number of patients require
acute care for nonsurgical problems such as acute
myocardial infarction, exacerbation of chronic
diseases such as diabetes or hypertension,
anxiety and other mental health problems such as
depression (39,40), respiratory disease caused by
exposure to dust and asbestos fibers from rubble,
and near drowning caused by flooding from broken
dams.
17
Huge amounts of dust are generated when a
building is damaged or collapses, and dust
clogging the air passages and filling the lungs
is a major cause of death for many
building-collapse victims (6,33,46). Fulminant
pulmonary edema from dust inhalation may also be
a delayed cause of death (47).
18
There is a growing body of evidence that
nonstructural elements (e.g., facade cladding,
partition walls, roof parapets, external
architectural ornaments) and building contents
(e.g., glass, furniture, fixtures, appliances,
chemical substances) can cause substantial
morbidity following earthquakes (49).
19
FACTORS INFLUENCING EARTHQUAKE MORBIDITY AND
MORTALITY
  • Natural Factors
  • Landslides

20
Tsunamis ("Seismic Sea Waves")
Submarine earthquakes can generate damaging
tsunamis (also known as seismic sea waves), which
can travel thousands of miles undiminished before
bringing destruction to low-lying coastal areas
and around bays and harbors. A tsunami can be
created directly by underwater ground motion
during earthquakes or by landslides, including
underwater landslides. Tsunamis can travel
thousands of miles at 300-600 mph with very
little loss of energy.
21
Aftershocks
Most earthquakes are followed by many
aftershocks, some of which may be as strong as
the main shock itself. Many fatalities and
serious injuries occurred from a strong
aftershock that followed 2 days after the
September 19, 1985, Mexico City earthquake that
killed an estimated 10,000 people (45). In some
cases landslides may be triggered by an
aftershock, after having been primed by the main
shock. Some major debris flows start slowly with
a minor trickle and then are triggered in waves.
In these cases there may be sufficient warning
that allows a community that is aware of this
hazard to evacuate in time.
22
Time of Day
Time of day is an important determinant of a
population's risk for death or injury, primarily
because it affects people's likelihood of being
caught in a collapsing building. For example,
the 1988 Armenia earthquake occurred at 1141 AM,
and thus many people were trapped in schools,
office buildings, or factories. If the
earthquake had occurred at another time of day,
very different patterns of injury and places of
injury would have occurred.
23
Human-Generated Factors
Fires and dam bursts following an earthquake are
examples of major human-caused complications that
aggravate the destructive effects of the
earthquake itself. In industrialized countries,
an earthquake may also be the cause of a major
technological disaster by damaging or destroying
nuclear power stations, research centers,
hydrocarbon storage areas, and complexes making
chemical and toxic products. In some cases, such
"follow-on" disasters can lead to many more
deaths than those caused directly by the
earthquake (60).
24
Fire Risks
One of the most severe follow-on or secondary
disasters that can follow earthquakes is fire
(62). Severe shaking may cause overturning of
stoves, heating appliances, lights, and other
items that can ignite materials into flame.
Historically, earthquakes in Japan that trigger
urban fires cause 10 times as many deaths as
those that do not (62). The Tokyo earthquake of
1923, which killed more than 140,000 people, is a
classic example of the potential that fires have
to produce enormous numbers of casualties
following earthquakes.
25
Dams
Dams may also fail, threatening communities
downstream. A standard procedure after any
sizeable earthquake should be an immediate damage
inspection of all dams in the vicinity and a
rapid reduction of water levels in reservoirs
behind any dam suspected of having incurred
structural damage.
26
Structural Factors (cont.)
Glass (1976) was one of the first to apply
epidemiology to the study of building collapse
(67). He identified the type of housing
construction as a major risk factor for injuries.
Those living in the newer style adobe houses
were at highest risk for injury or death, while
those living in the traditional mud and stick
construction houses were at the least risk.
Figure 8-6 shows the breakdown of earthquake
fatalities by cause for each half of this
century. By far the greatest proportion of
victims have died in the collapse of unreinforced
masonry (URM) buildings (e.g., adobe, rubble
stone, or rammed earth) or unreinforced
fired-brick and concrete-block masonry buildings
that can collapse even at low intensities of
ground shaking and will collapse very rapidly at
high intensities.
27
Structural Factors (cont.)
Time and again, wood-frame buildings such as
suburban houses in California have been
pronounced among the safest structures one could
be in during an earthquake. Indeed, these
buildings are constructed of light wood
elements--wood studs for walls, wood beams and
joists for floors, and wood beams and rafters for
roofs (75). Even if they did collapse, their
potential to cause injury is much less than that
of unresistant old stone buildings, like those
often used for businesses, offices, or schools.
The relative safety of wood-frame buildings was
shown quantitatively following the 1990
Philippine earthquake. People inside buildings
constructed of concrete or mixed materials were
three times more likely to sustain injuries (odds
ratio OR 3.4 95 confidence interval
CI,1.1-13.5)than were those inside wooden
buildings (76).
28
Nonstructural factors
Nonstructural elements and building contents have
been known to fail and cause significant damage
in past earthquakes. Facade cladding, partition
walls, roof parapets, external architectural
ornaments, unreinforced masonry chimneys, ceiling
tiles, elevator shafts, roof water tanks,
suspended ceilings and light fixtures, raised
computer floors, and building contents such as
heavy fixtures in hospitals are among the
numerous nonstructural elements that can fall in
an earthquake, sometimes causing injury or death
(78).
29
FACTORS INFLUENCING EARTHQUAKE MORBIDITY AND
MORTALITY
  • Individual Risk Factors
  • Demographic Characteristics

30
Entrapment
As might be expected, entrapment appears to be
the single most significant factor associated
with death or injury (81). In the 1988 Armenia
earthquake, death rates were 67 times higher and
injury rates more than 11 times higher for people
who were trapped than for those who were not
(33). In the 1980 southern Italian earthquake,
entrapment requiring assistance to escape was the
most important risk factor the death rate was
35.0 for trapped people versus 0.3 for
untrapped people (82). In the Philippine
earthquake of 1990, people who died were 30 times
more likely to have been trapped than were
injured survivors (OR 29.74 95 CI,
12.35-74.96) (66).
31
Occupants' Behavior
The behavior of people during an earthquake is an
important predictor of their survival (85). In
several recent earthquakes (e.g., 1990
Philippines and 1992 Egypt earthquakes), there
were widespread reports of deaths and injuries
due to stampedes, as panicked building occupants
and students rushed for the nearest exits
(76,86). On the other hand, a review of the
first reaction of people following an initial
earthquake shock revealed that those who
immediately ran out of buildings had a lower
incidence of injury than did those who stayed
inside (65,66). Other reports, however, suggest
that running outside may actually increase the
risk of injury. For example, during the 1976
Tangshan earthquake, many were struck by the
collapse of outer walls after running out of
their houses.
32
Time Until Rescue
Although the probability of finding live victims
diminishes very rapidly with time, entrapped
people have survived for many days. People have
been rescued alive 5, 10, and even 14 days after
an earthquake (91) these "miracle rescues" are
often the result of exceptional
circumstances--for example, someone with very
light injuries is trapped in a void deep in the
rubble with air and possibly water available.
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