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 Stateshas 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 FactorsTopographic 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 outpatient-level 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 building-collapse 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.

AftershocksMost 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 FactorsFires 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 RisksOne 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 factorsNonstructural 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

EntrapmentAs 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' BehaviorThe 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.