Earthquakes were responsible for an estimated 1.87 million deaths in the 20^th century with an average of 2,052 fatalities per event affecting humans between 1990 and 2010 1^,2. The magnitude 8.9 Japan earthquake and resulting tsunami in March 2011 was responsible for more than 28,000 deaths; in comparison, the smaller magnitude 7.0 earthquake occurring in Haiti in January 2010 resulted in an estimated 222,500 fatalities 2. In recent history, the Pacific Rim is the most affected by seismic activity, with 81% of the world's largest earthquakes occurring in this region 3.

Earthquakes result from sudden energy releases in the earth’s crust, which create seismic waves that result in ground shaking. Earthquakes are usually caused by slippage on a fault due to built up friction between tectonic plates but can also be caused by volcanic eruptions or manmade explosions 4. Millions of earthquakes occur each year, though only a small proportion is strong enough to be felt and even fewer cause damage. Earthquakes occur at focal depths of 700 km to just under the earth's surface, and the strength of shaking diminishes with increasing distance from the earthquake's source 5. Earthquake magnitude measures the energy released by an earthquake and is described by the moment magnitude scale, which is a logarithmic scale, so that a magnitude 5 earthquake is about 10 times less powerful than a 6, and 100 times less that a magnitude 7. A magnitude 2.5 earthquake is not generally felt by humans, whereas earthquakes with magnitude >7.0 may cause widespread destruction 6. Earthquake impact is assessed by the Modified Mercalli Intensity Scale, which describes the severity of damages from the event on a scale from I to XII, with I being no damage and XII being complete destruction with no surviving structures. Building design, geography and development indicators are important factors in earthquake vulnerability. The objectives of this review were to describe the impact of earthquakes on the human population, in terms of mortality, injury, and displacement and to identify country and event characteristics factors associated with these outcomes. This is one of five reviews on the human impacts of natural disasters, the others being volcanoes, floods, tsunamis, and cyclones.

The impact of earthquakes events was summarized using two methods, a historical review of earthquake events, and a systematic literature review for publications relating to the human impacts of earthquakes with a focus on mortality, injury, and displacement.

Historical Event Review

A historical database of significant earthquakes between 1980 and 2009 was created. Four publically available data sources were used to create the most complete possible listing of events, allow for inclusion of both human and geophysical factors, and enable cross checking. The two primary sources were the Centre for Research on the Epidemiology of Disasters International Disaster Database (CRED EM-DAT)7 and the National Oceanic and Atmospheric Administration’s National Geophysical Data Center (NOAA-NGDC) Significant Earthquakes Database 8. Earthquakes included in EM-DAT met one or more of the following criteria: ≥10 deaths; ≥ 100 affected; declaration of a state of emergency; or a call for international assistance. Earthquakes included in the NOAA-NGDC database met one of the following criteria: ≥10 deaths; moderate damage (US$ 1 million or more); magnitude ≥7.5; Modified Mercalli Intensity X or greater; or the earthquake generated a tsunami. All events reported by EM-DAT were retained (n=706), and zeroes were converted to missing values for injury, homeless, and affected measures; for deaths and total affected, zeroes were converted to missing values only when no other information was reported. Earthquakes from the NOAA-NGDC database were retained if one of the following criteria were satisfied: magnitude ≥5.5; ≥10 deaths; or ≥100 injured (n=579).

Two additional sources, the United States Geological Survey (USGS) Earthquake Hazards Program Global Database 9 and the Northern California Earthquake Data Center (NCEDC)10 were used to collect information on specific earthquake characteristics (coordinates, magnitude, focal depth, additional information when available). When available data from these sources were added for events reported by EM-DAT and/or NOAA-NGDC; new events were added only when mortality was reported by USGS. Earthquakes occurring in uninhabited areas that did not cause injury or death were removed. The final list comprised 953 earthquakes occurring between 1980 and 2009; information on mortality, injury or displacement was reported by one or more sources in 738 events. See https://www.jhsph.edu/refugee/publications_tools/index.html for the database of earthquake events.

The following outcome categories were used to assess risk factors for earthquake-related mortality: no deaths (0 deaths); low (1-9 deaths); medium (10-99 deaths); and high (≥100 deaths). Bivariate tests for associations between mortality and the following characteristics were performed using χ² (categorical measures) and ANOVA (continuous measures): decade, World Health Organization (WHO) region, World Bank income level, gross domestic product (GDP), GINI (measure of income inequality), focal depth, and magnitude. All covariates were significantly associated with earthquake mortality in the univariate analysis and were subsequently included in a multinomial logistic regression model to assess the adjusted odds of mortality at a given level as compared to events with no deaths. Analyses were performed using Stata Statistical Software, Version 11.0 11

Systematic Literature Review

Key word searches in MEDLINE (Ovid Technologies, humans), EMBASE (Elsevier, B.V., humans), SCOPUS (Elsevier B.V., humans), and Web of Knowledge, Web of Science (Thomson Reuters) were performed to identify articles published in July 2007 or earlier that described natural hazards and their impact on human populations. Following the systematic review, a hand search was conducted to identify relevant articles published after the initial search thru October 2012. One search was done for all the five natural hazards described in this set of papers. This paper describes the results for earthquakes. The systematic review is reported according to the PRISMA guidelines. The key word search included natural hazard(s), natural disaster(s), volcano(s), volcanic, volcanic eruption, seismic event, earthquake(s), cyclone(s), typhoon(s), hurricane(s), tropical storm(s), flood(s), flooding, mudslide(s), tsunami(s), and tidal wave(s). Key words included for impact on human populations were affected, damage(d), injury, injuries, injured, displaced, displacement, refugees, homeless, wounded, wound(s), death(s), mortality, casualty, casualties, killed, died, fatality, fatalities in either the title, abstract or as a subject heading/key word. The search resulted in 2,747 articles from MEDLINE, 3,763 articles from EMBASE, 5,219 articles from SCOPUS, and 2,285 articles from ISI Web of Knowledge. Results from the four databases were combined and duplicates excluded to yield a total of 9,958 articles.

Title screening was performed to identify articles that were unrelated to natural disasters or human populations. Each title was screened by two reviewers and was retained if either or both reviewers established that inclusion criteria were met. Percent agreement was assessed across reviewers, and title screening began after 80% agreement was achieved. A total of 4,873 articles were retained for abstract review. During abstract screening articles that met one or more of the following criteria were excluded: language other than English; editorial or opinion letter without research-based findings; related to environmental vulnerability or hazard impact but not human populations; individual case report/study; focus on impact/perceptions of responders; and not related to human or environmental vulnerabilities or impacts of hazards. Each abstract was screened by two reviewers and was retained if either or both reviewers established that inclusion criteria were met. Again, 80% agreement between reviewers was achieved prior to screening. During the abstract review, included abstracts were coded for event type, timeframe, region, subject of focus, and vulnerable population focus. A total of 3,687 articles were retained for full article review. Articles discussing the impacts of natural disasters on human populations in terms of mortality, injury, and displacement were prioritized for review. From this general review of 395 articles specific to earthquake events meeting the aforementioned subject focus criteria were identified for full review. Upon full review, 150 articles were retained 143 that underwent standard data abstraction; seven that were identified as review articles (Figure 1). Articles that focused on risk factors for specific types of injuries (primarily crush injuries and renal failure) or deaths were excluded because they did not provide insight on overall risk factors for mortality or injury. In total, 70 articles relating to risk factors for mortality, injury or displacement were identified; summaries of articles with primary data (n=60) and review articles (n=10) are presented in Tables 1 and 2, respectively.

Overview of the systematic literature review process for earthquakes

Table 1: Articles included in the earthquake systematic literature review related to mortality and injury risk (N=60)*

* Displacement is excluded from the table because primary data on displacement in earthquake events was collected in only six studies: Daley, 2001; Parasuraman, 1995; Roces, 2002, Chun 2010; Kun 2010; and Milch, 2010. ** Additional articles identified in the hand search conducted through October, 2012.

Table 2: Review articles relating to earthquake mortality and injury (N=10)

* Additional articles identified in the hand search conducted through October 2012

Historical Event Review

Overall, 74.1% of events in the database were reported by EM-DAT, 60.8% by NOAA and 25.8% by USGS; reporting by USGS improved dramatically from 2000 onwards. An average of 24.6 (range 13-43) earthquakes affected human populations annually between 1980 and 2009 (figure 2). The frequency of events increased over time, which is attributable to improvements in reporting. The average magnitude was 6.2 (range 4-9; n=493, 66.8% reporting) and focal depth 27.1km (median 19.0, range 0-235.8; n=493; 66.8% reporting). Earthquake mortality increased in parallel with the frequency of events from the 1980s onwards (Figure 3). A rapid increase in earthquake-affected populations was observed after 2000, which is likely a result of both improved reporting and population growth (Figure 3). Earthquakes were most frequent in the Americas, South-East Asia and the Eastern Mediterranean with each region accounting for 20-25% of events; however earthquake impact was greatest in the Western Pacific, which accounted for 44% of deaths and Americas, which accounted for 60% of the affected population (Figure 4). The overall impact of earthquakes on human populations is summarized in Table 3. Of the 738 identified events, the databases recorded 687 (96.9%) causing deaths, 420 (56.9%) causing injuries and 359 (51.4%) leading to homelessness.

Earthquakes affecting human populations by decade, 1980-2009 (n=738)

Table 3: Summary measures for the impact of earthquakes on human populations, 1980-2009 (n=738)

Notes: Best estimate figures are based on the average reported number of deaths or injuries in an event; homeless and affected populations were rarely reported by sources other than EM-DAT thus ranges are not presented.

Affected Population and Homelessness. An estimated 61.5 million people were affected by earthquakes between 1980 and 2009, including 16 million rendered homeless. These figures are likely to underestimate the true impact of earthquakes because the total affected and homeless populations were reported in only 95.5% and 51.4% of events, respectively. There were an average of 200,783 affected (median 3,7215, range 1-46,000,000) and 46,594 homeless (median 0, range 0-4,000,000) per event [where data were reported] and distributions were highly skewed.

Mortality and Injury.When mortality data from the three sources were combined, information on deaths (inclusive of events with no reported deaths) was recorded in 93.1% (n=687) of earthquakes, with fatalities occurring in 71.0% (n=524). Overall, an estimated 372,634 total deaths (range: 314,531-412,599) were reported; for events with mortality, there were an average of 604 deaths (median=3, range=0-87,652) per event when using the highest reported death toll. Deaths were concentrated in the Western Pacific (190,955 deaths, 44.6%) and Americas (103,679, 24.2%). When assessed by country, the greatest earthquake mortality was observed in China (n=90,106, 21.0%), Pakistan (n=88,314, 20.6%), and Iran (n=86,254, 20.1%). The two most deadly earthquakes (Sichuan China, 2008 and Kashmir Pakistan, 2005) accounted for 40% of all earthquake mortality.

Injuries were reported in only 56.9% (n=420) of events with estimated total of 995,219 reported injuries (range: 845,345-1,145,093). When injuries were reported, there were an average of 3,499 (median=100, range 1-374,171) injuries per event using the highest reported number for the event. To better estimate the total number of injuries, it was presumed that injuries would occur in events where deaths were reported. Among the 687 earthquakes with fatalities reported, injuries were reported in only 420 (61%) events. When the median and mean for injuries were applied to the remaining 267 events, between 29,392 and 1,267,864 additional unreported earthquake related injuries may have occurred between 1980 and 2009.

Bivariate associations between country-level characteristics and earthquake-related mortality are presented in Table 4. All predictors except for earthquake focal depth were significantly associated with mortality. In the adjusted multinomial logistic regression model (Table 5), only magnitude was significantly associated with earthquake mortality. World Bank development level, the Gini Index coefficient, and focal depth were not statistically associated with earthquake-related mortality. The odds of a high mortality event as compared to an event with no deaths increased by 11.93 (95 CI: 5.35-26.57) per additional point on the magnitude scale.

Table 4. Earthquake Mortality by Select Country Characteristics, 1980-2009 (N=738)

*GINI coefficient scores for income distribution range from 0 to 100 with 0 representing a perfect equality and 100 perfect inequality.

Table 5: Multinomial Logistic Regression: Relative Risk Ratios (RRR) of earthquake mortality* (N=288)

*Reference is ‘no deaths’ for all categories (n=55) **Model includes both magnitude and focal depth; focal depth is measured on a log (base 10) scale ***p-values reported for each category with Wald test p-values for the variable.

Systematic Literature Review

Mortality. Of the articles reviewed, 27 reported on causes of death (n=17) and/or risk factors including sex (n=8), age (n=15), building or location (n=17) and other risk factors (n=11) (Table 6). The primary cause of death in the majority of studies was building collapse 16^-20^,22^,23^,25^,29^,31^,33^,36^,40^,46. Females faced a significantly increased risk of death in three studies 19^,36^,41 while several others found no significant difference in mortality by sex 18^,33^,38^,66 none reported that males faced a significantly increased mortality. Of the 14,709 earthquake deaths where sex was reported in the articles reviewed, 45% (n=6649) and 55% (n=8,060) of deaths were among males, yielding a ratio of 1.0:1.2 for male to female mortality. Age was a risk factor for mortality in many studies. Older populations consistently had higher rates of death 13^,18^,20^,26^,29^,33^,36^,38^,41^,66 and in several studies children also faced increased mortality 19^,29^,33^,44.

Table 6: Articles Reporting Detailed Information on Mortality (n=29)

Article	Event	Mortality Rate	Cause	Sex	Age	Building and Other Risk Factors
Angus, 199722	Turkey, 1992	Not reported	48% (n=26) instant/building collapse. Of protracted deaths, 50% (n=13) hemorrhaged and 42% (n=11) asphyxiated.	Not reported	Not reported	92% of indoor deaths occurred in mid-level unreinforced masonry buildings; deaths were more likely among those on the ground floor. Prior first-aid or rescue training of lay, uninjured survivors was associated with a higher likelihood of rescue and resuscitation.
Aoki, 200440	Japan, 1995	Not reported	Asphyxia/pressure, 74% (n=3551); contusion injury, 17% (n= 828); head/neck injury, 8% (n=286); indirect, 3% (n=121).	Not reported	Not reported	Not reported
Armenian, 199713	Armenia, 1988	254/10,000	Trauma due to building collapse.	Not reported	Increased deaths among >60yrs.	Building height and upper floor location were important predictors of death; odds of death were 9.8 times greater for those inside compared witho those outside.
Bisselll, 199416	Costa Rica, 1991	Not reported	Entrapment and crush injury.	Not reported	Not reported	Most fatalities occurred in homes; wood-frame houses with lateral bracing were less likely to collapse than those without bracing.
Chan, 200336	Taiwan, 1999	134/10,000	77% (n=1,441) instant/building collapse; causes asphyxiation (32%), intracranial inj (29%), trauma/ trunk/extremity inj (16%), internal inj (7%), crush inj (6%), and fractures (6%).	Male: 122/10,000; Female: 144/10,000. Ratio: 0.85:1.0	Increased risk w/ age; death ratio of >45yrs to adults <45yrs of 3.3:1.	Complete collapse was a better predictor of death than partial collapse; a 1% increase in completely collapsed home was associated with a 5% increase in the crude death rate.
Chou, 200441	Taiwan, 1999	Not reported	Not reported	Increased female risk: OR 1.2 (CI: 1.1-1.3)	Higher mortality in older age groups.	People with lower socioeconomic status and the physically disabled were at increased risk of mortality.
Doocy, 200954	Peru, 2007	1.4/1000	Not reported	Not reported	Sample size too small for analysis	Not reported
Eberhart-Phillips,199418	California, 1989	Not reported	Elevated freeway collapse; 81% (46/57) of direct deaths vehicle /roadway related. Indirect deaths due to CO poisoning, heart attacks, falls and GI bleeding.	Victims more likely to be female (NS)	Victims more likely to be older (NS)	Elevated freeway collapse
Ellidokuz, 200542	Turkey, 2002	1.6/10,000	Not reported	Not reported	Median age = 51 yrs (range 4-74)	Collapsed (11 deaths) and severely damaged (2 deaths) buildings.
Hatamizadeh, 200646	Iran, 2003	19.7% (41/2086 patients)	Trauma (n=11), cardiac arrest (n=6), septicemia (n=5), DIC (n=3), hypovolemic shock (n=2), and ARDS (n=3)	Not reported	Mean age = 32.3 yrs (SD=16.3)	Patients with acute renal failure were significantly more likely to die than those with other diagnoses.
Kuwagata, 199725	Japan, 1995	6.6%(178 /2702 injuries)	Crush syndrome (n=50, 28%), vital organ injuries (n=36, 20%), 7 (1%); fractures of the pelvis or spine (n=7, 1%); others (n=18, 1.3%); and unknown (n=67, 59%)	Not reported	Not reported	The most life-threatening injuries, crush syndrome and vital organ injuries, occurred indoors.
Laverick, 200749	Pakistan, 2007	Adults: 4.3% (118/ 2721) Children 3.5% (50/ 1449 patients)	Tetanus (n=22) deaths and neonatal causes (n=4); no other causes reported	Not reported	Not reported	Not reported
Liang, 200133	Taiwan, 1999	14.82/100,000	Body compression, including head injury (32%), shock (29%) and asphyxiation (29%). Other causes included organ injury, spinal cord injury, burns and CO poisoning.	Male:14.0/100,000 Female:15.6/100,000 Ratio:1.11 (NS)	>80yrs 80/100,00070-79yrs 50/100,000 20-29yrs 6.9/100,000 0-9yrs 12.7/100,000.	Distance to epicenter; earthquake intensity, age, population density, and physicians and hospital beds per 10,000 population were all significant predictors of mortality.
Liao, 200338	Taiwan, 1999	Not reported	Not reported	Male:10.7/100,000 Female:10.1/100,000 Ratio: 1.05(NS)	<15yr:8.5/100,00015-64:8.4/100,000 65+: 34.8/100,000	Overall building collapse rate was a better predictor of mortality than partial building collapse. Intensity and distance to the epicenter were positively associated with mortality.
Mulvey, 200852	Pakistan, 2008	0.2% (2/1502 patients)	Head injuries	Not reported	Not reported	Not reported
Parasuraman, 199519	India, 1993	Not reported	Building collapse	More females than males died in all adult age groups.	By age grp: <14, 50%; 15-24, 13%; 25-59, 28%; 60+, 11%.	Homes with mud/stone walls suffered the most damage (~90% collapsed); fewer deaths occurred in mud/thatch homes and in stone/mud/concrete homes.
Pawar, 200544	India, 2001	Not reported	Not reported	Not reported	By age group: 0-14, n=171 (62%); 14-19, n=41 (15%), adults, n=45 (16%); older adults, n=19 (7%).	The death rate was significantly associated with distance to epicenter.
Peek-Asa, 199826	California, 1994	19.3% (33/ 171 injured)	Asphyxia and body compression from building collapse (n=22, 71%); vehicle accidents (n=5, 15%); falls (n=4, 12%).	Not reported	31% of the deceased were >65 yrs.	Most fatalities were caused by a structural failure (n=25, 76%); >66% of fatalities involved a structural failure of the home. Earthquake related motor vehicle injuries were 5 times more likely to result in fatality than a hospitalized injury.
Peek-Asa, 200031	California, 1994	22.6% (30/ 133 injured patients)	Not reported	Not reported	Not reported	Fatal injuries were concentrated near the epicenter and in areas with higher peak ground acceleration.
Pointer, 199214	California, 1989	1.3/100,000 (CMR)	Not reported	Not reported	Not reported	Not reported
Pretto,199417	Costa Rica, 1991	4/10,000	92% (n=45) instant deaths due building collapse/crush syndrome	Not reported	Not reported	People inside wood frame buildings had a higher risk of injury and death than people in other building types (OR 22.5, p<.001).
Roces, 199215	Philippines, 1990	19% among the injured (68/363)	Not reported	Not reported	Not reported	Cases were more likely to be inside concrete/mixed materials rather buildings as compared to wood (OR 2.6, CI 1.7-4.1) and on a middle or upper floor (OR 3.4, CI:2.2-5.5 and OR 1.9, CI 1.3-2.9, respectively). Chance of survival decreased as time of rescue increased: 84% of the survivors were rescued within the first hour.
Sullivan, 201066	Pakistan, 2005	1.7-5.4% in camps/ communities (708 deaths)	Not reported	Higher Death rate among females (NS)	Children <5 (1.2-10.6% CMR) and adults >50 (3.2-9.9% CMR) had highest risk	Not reported
Tanaka, 199929	Japan, 1995	8.6% (527/ 6107 patients)	Crush injuries (n=50). Indirect causes included respiratory (n=110) and cardiovascular (n=56).	Not reported	Increased with age in patients with prior injuries and illness.	Not reported
Tanida, 199620	Japan, 1995	Not reported	Crush injuries (77%); also penetrating injuries and burns.	Among those >60yrs, female fatalities were 2 times greater than males.	>50% of deaths among those >60; the death rate of 80+yrs was 6 times that of <50yrs.	Not reported
Wen, 200957	China, 2008	NA – case control study	Not reported	Not reported	Not reported	Traumatic brain injury, multiple system organ failure, prior disease, and infection significantly associated w/ increased death risk
Yasin, 200960	Pakistan, 2005	1.9% (17/862 patients)	Tetanus (n=7), trauma/ sepsis (n=5), spinal injury n=(2), crush syndrome (n=2), head injury (n=1)	Not reported	Not reported	Not reported
Zhao, 201169	China, 2008	7 deaths	4 patients with open-head injury, 3 had severe crush injury.	Not reported	Not reported	Not reported
Kang, 201270	China, 2010	0.2% (7/3255)	Four patients died from earthquake-related injuries and three from other illnesses.	Not reported	Not reported	Not reported

A majority of deaths occurred indoors 13^,16^,19^,22^,25^,29^,42 often at home, and the rate of complete building collapse was a good predictor of crude mortality rates 36^,38 Construction materials were associated with increased mortality risk, including unreinforced masonry 22, mud and stone walls19, concrete 15, panel construction 13 and wood construction 16^,17^,42; however no clear trend was observed across studies. Location on the ground floor 20^,22 and upper floors 15^,23 of multistory buildings were associated with increased risk of death. Other mortality risk factors included earthquake intensity and distance to epicenter 31^,33^,38^,44 physical disability 41 prior injury or illness 29, low socioeconomic status 41, and being in a car 31. Response and health systems characteristics associated with mortality risk included time to rescue15, per capita availability of physicians and hospital beds 33, and prior first-aid or rescue training of lay, uninjured survivors 22; better availability of rescue and early emergency care could prevent a substantial portion of deaths 17.

Injury. Detailed information on injury was reported in 51 articles among which 42 included data on injury type, 30 on gender risk, and 31 on age risk (Table 7). Soft tissue injuries (including lacerations and contusions) and fractures were the most common types of injury reported 15^,16^,23^,25^,27^,29^,43^,47^,51^,52^,53^,56^,58^,60^,62^,67^,69^,70^,71, and the extremities were the most likely areas of the body to be affected 26^,46^,50^,51^,59^,61. Crush injuries/syndrome were reported as the most common injury in several in-patient studies, and there was a substantial body of literature on this topic (articles focusing on a specific injury type were not abstracted for this review) 16^,32^,45^,55 . The proportion of injured by sex and, when combined, suggests a similar injury risk among males in females- Males accounted for the majority in eleven studies 13^,32^,43^,46^,48^,50^,51^,52^,53^,71^,73 and females in sixteen 23^,26^,28^,32^,34^,35^,39^,45^,47^,54^,56^,58^,59^,62^,63^,65^,70^,72 . However statistically significant differences were observed in a few cases, all of which suggested increased female risk 28^,39^,45^,55 . Many articles reported descriptive age data, however information on age-related injury risk was reported in fewer articles and included decreased risk among children 30^,46, and increased risk among young and/or working age adults 50^,52^,56^,62 , the elderly 30, and with increasing age 26^,29^,34^,39^,54, Building characteristics and other related risk factors included being indoors 13^,15^,16^,23^,25, or on a middle or upper floor 13^,15^,23^,25, construction type and/or quality 15^,16^,23^,26^,34^,37^,39 and low socioeconomic status 54^,56.

Table 7: Articles Reporting Detailed Information on Earthquake-Related Injuries (n=50)*

Notes: Peek-Asa 2000 and Laverick, 2007 reported detailed information on injury but are excluded from the table because no information was reported on factors included in the table. In many cases reporting by injury type, age, and/or sex was incomplete which is why numbers reported for each outcome may not sum to the total number of deaths reported.

Main findings

In the 30 year period between 1980 and 2009, approximately 372,634 people died and nearly one million were injured as a result of earthquakes, with potentially an additional 29,392 to 1,267,864 unreported injuries. In this same period, 61.5 million people were affected by earthquakes, including at least 16 million left homeless. While mortality estimates in this study are consistent with those reported by other sources 2 the numbers injured and homeless populations are likely gross underestimates given the low frequency with which these figures are reported. Prior review articles either focused on specific regions 69^,71^,73^,74^,78, a limited time period 70^,74 mitigation strategies 75 mortality only 75, or individual injury and treatment 77. Only one prior review used data from multiple sources 81.

Findings from this review, including descriptive statistics of and factors associated with earthquake mortality, are consistent with previous observations that earthquake mortality varies as a function of severity 74^,79, place 12^,77^,79^,80, time 12, and development level of the affected area 79^,80. With respect to severity, greater focal depth was inversely associated with mortality, whereas greater magnitude (moment scale) was positively associated with mortality. In terms of place, earthquakes were relatively evenly distributed across the Western Pacific, American and European regions, whereas the plurality of deaths occurred in the Western Pacific, followed by the Eastern Mediterranean region. The largest numbers affected by earthquakes were in the Western Pacific followed by the South East Asia. As observed in previous studies, these findings are skewed by large events, such as the 2005 Pakistan earthquake that resulted in approximately 75,000 deaths 79^,80 ^,81. The Haiti earthquake in 2010, one of the deadliest on record, which falls just outside the scope of the review period, is illustrative of how an occasional high-impact event can drastically change regional impact distributions and study conclusions.

In terms of time trends, the number of earthquakes has increased steadily since the 1980s and a greater number of people have been affected over time. While improved reporting may partly explain an increase in the number of earthquake events, the increases in mortality and the size of affected populations may also be attributable to population growth, urbanization and migration 80 and changes in land use patterns 76. Similar to other reviews lower economic development level, measured by per capita GDP, was associated with increased mortality which suggests that poorer countries face increased risk due to a variety of characteristics of the built environment 79^,80 .

Findings from the systematic literature review of studies examining earthquake-related mortality and injury contribute to an improved understanding of the primary causes of death and types of injury as well as factors that may place certain populations at increased risk. Consistent with prior review articles, this review identified the most common cause of earthquake-related death as building collapse 13^,74^,75^,78^,80. In addition, multiple studies highlighted that building type, the rate of collapsed buildings and construction materials were significantly associated with injury and mortality risk. This highlights that building improvements, especially in the design and construction and the enforcement of zoning and building codes, should be central to earthquake prevention and mitigation strategies.

Recurrent characteristics associated with increased risk for both mortality and injury were extremes of age, socioeconomic status and location of individuals at the time of the event. Consistent with the ecological study using the historical event database, individuals and households of lower socioeconomic status were at increased mortality and injury risk. Location, including distance from epicenter, being inside or outside a building, and type of building and location within the building were also strong predictor of earthquake mortality and injury risk. Timing of the event was also associated with mortality and injury risk where earthquakes occurring at night had higher mortality levels than those occurring during the day 74^,77 .The relationship between sex and mortality and injury was less straightforward. While it is tempting to draw conclusions from these findings, it is important to highlight that 70% and 44% of the 27 mortality studies did not report deaths by sex and age, respectively. In addition, few studies performed significance tests, and an even smaller number controlled for other risk factors in the analyses. When considering the extent to which age and sex may interact with other important risk factors, such as location during the event or characteristics of the built environment, accurately characterizing factors that contribute to mortality and injury risk becomes especially challenging.

The important role of the emergency response and health care systems in reducing mortality and injury in the immediate aftermath of an earthquake was highlighted in a number of studies 18^,22^,33^,81, it is clear that such systems remain inadequate in many earthquake prone countries that are less developed. Health facilities are especially vulnerable from earthquakes due to direct and indirect damage (losses in utilities and infrastructure) that affect that affect their emergency response capacity. The extensive body of literature on earthquake related mortality and injuries could inform response planning for future earthquakes in high risk areas.

An historical event review such as this can elucidate patterns over place and time as well as factors associated with increased mortality risk, but cannot identify more specific associations. For instance, a number of country-specific studies have highlighted significant differences in mortality risk by population density, rural/urban area and across diverse geographic regions 77^,78^,79. Particularly in earthquake prone regions or countries, additional research is needed to identify specific characteristics that may place populations at increased risk for mortality or injury during or in the immediate aftermath earthquakes. Nonetheless, statistical models to predict earthquake mortality, can be useful tools for estimating the relative contribution of geographic characteristics and population sociodemographics to earthquake mortality 79. Compared to other natural disasters a wealth of data and peer review articles on earthquakes exists and there is a comparatively strong evidence base for drawing conclusions on earthquake impact at global, regional, and in some cases national levels.

Limitations

The effects of earthquakes are the subject of gross approximations and aggregations with a great deal of imprecision. The availability and quality of data has likely improved over time and the use multiple data sources increased reporting. However, underestimation of the impacts of earthquakes is substantial because in many events outcomes such as injured and affected are unreported. In addition, inconsistencies and errors were common in data files from different sources. Several challenges were encountered when attempting to model earthquake mortality including a non-normal distribution, which necessitated analysis with a categorical outcome. Information on 2007-2009 GDP, 2009 World Bank development classification and 2009 GINI index were used for the analysis regardless of event year, and it is possible that many of these values were substantially different in prior decades and some countries are new or have merged with other nations. Many of the island-countries in the Caribbean are territories of European countries, which necessitated the use of GDP, GINI, and development levels representative of the actual earthquake affected areas. Systematic literature reviews are not without their limitations. The articles identified and included in this review is not an exhaustive list, as articles that were not written in English were excluded, and a number of studies meeting inclusion criteria during the abstract review could not be found. Additionally, findings from the included studies are difficult to aggregate because of differences in design, reporting, and study population. Another important series of articles not included in this review is those which report on specific types of injuries and their outcomes; future reviews with an in-depth focus on injury, and to the extent possible, relationships between built environment, injury and outcomes could make an important contribution to the literature.

In the last 30 years, almost 400,000 deaths and 1 million earthquake-related injuries were reported, with an estimated 61.5 million people affected. Approximations of the numbers injured and those made homeless are likely gross underestimates of the true values given low reporting levels. The distribution of earthquake related deaths and injuries vary greatly by region and economic development level with greater magnitude and lower economic development of affected areas associated with increased mortality. Globally, earthquake impact was concentrated in Asia, which had the greatest number of deaths and the largest affected population.

The primary cause of earthquake-related mortality was building collapse most frequently leading to soft tissue injuries, fractures and crush injuries/syndrome. Risk factors for earthquake-related death and injury included very young and very old age, poor socioeconomic status, being indoors and being in a poorly constructed building during the time of the event. Earthquake losses are likely to increase in future years due to population growth of in high-risk seismic areas and in the case low and medium development areas, inadequate construction quality. Increased attention to earthquake prevention and mitigation strategies, with a focus on the built environment in particular, is necessary. Strategies that are specific to the development level and country context are essential. For instance, improved building construction is not a reasonable short term objective for a country like Haiti. Other interim short term strategies need to be adopted in settings where changes in building codes, their enforcement, construction methods, and other characteristics of the built environment may take decades to achieve.

The authors have declared that no competing interest exist.

Shannon Doocy, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe St, Suite E8132, Baltimore, MD 21230. Tel: 410-502-2628. Fax: 410-614-1419. Email: sdoocy@jhsph.edu.