Public Health Consequences of
Earthquakes
Eric K. Noji, M.D., M.P.H.
Centers for Disease Control and
Prevention
Washington, D.C.
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.
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).
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.
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).
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).
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.
FACTORS AFFECTING
EARTHQUAKE
OCCURRENCE AND
SEVERITY
Natural Factors
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.
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.
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.
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).
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 outpatientlevel treatment and tend to be much more
common than severe injuries requiring
hospitalization.
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.
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.
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.
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 buildingcollapse victims (6,33,46). Fulminant
pulmonary edema from dust inhalation
may also be a delayed cause of death
(47).
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).
FACTORS INFLUENCING
EARTHQUAKE MORBIDITY
AND MORTALITY
Natural Factors
Landslides
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.
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.
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 11:41 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.
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).
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.
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.
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.
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).
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).
FACTORS INFLUENCING
EARTHQUAKE MORBIDITY
AND MORTALITY
Individual Risk Factors
Demographic Characteristics
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).
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.
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.