A new metric shows which countries experience disproportionate earthquake casualties

A new system for cataloguing earthquake fatalities suggests that five countries have suffered the greatest loss of life over the past 500 years.
 

By Rebecca Owen, Science Writer (@beccapox)
 

Citation: Owen, R., 2024, A new metric shows which countries experience disproportionate earthquake casualties, Temblor, http://doi.org/10.32858/352
 

Even though there are many seismically active regions throughout the world, each with the potential to host damaging quakes, some countries are especially vulnerable to seeing high numbers of earthquake-related casualties. As unaffected people elsewhere watch fatalities tick up higher and higher in the aftermath of a major earthquake, the lives lost can be hard to comprehend.

To better understand how a country’s population can be affected by an earthquake, the authors of a February 2024 study crafted a new type of measurement: the Earthquake Fatality Load (or EQFL). This number is the ratio of the number of fatalities to a country’s entire population estimate at the time of an earthquake. It can provide a more comprehensive view of the possible loss of life that could result from future quakes. In doing so, it can also focus the world’s attention on vulnerable countries before an earthquake strikes.
 

Studying earthquake records

In the new study, researchers analyzed records from the last 500 years in countries that each had a cumulative number of earthquake-related deaths of 10,000 or more. That collection totaled 97% of all earthquake-oriented fatalities recorded since 1500, which, according to the researchers’ determination, is the furthest back in history that records could be relatively reliable.

The catalog of these fatalities includes those caused by building collapse or other related hazards like landslides, fire, and liquefaction, but did not include people killed by earthquake-sourced tsunamis. A different equation is needed to calculate the death and damage from tsunamis than from shaking, says Max Wyss, retired seismologist with the International Center for Earth Simulation and one of the study’s authors.
 

 

The study ranked 35 seismically at-risk countries and regions in order of EQFL, with the top locations including Ecuador, Lebanon, Haiti, Turkmenistan, and Portugal. These are not necessarily countries with the most frequent, most recent, or the largest tremors — but if they were to experience an earthquake, the expected loss of life would be significantly higher in these five countries than in other nations.
 

Factors influencing EQFLs

Several factors influence a country’s EQFL, including its population size, tectonic setting and overall disaster readiness.

Though every casualty is tragic, a death toll of a given size hits much harder in a smaller country, Wyss explains. The human impact of the earthquake is much greater in a smaller country because the number of lives lost in smaller countries may encompass a significant part of the population. China, for instance, ranks first in the sheer number of earthquake-related fatalities over the last 500 years, but it sits at number 23 on the EQFL list because its population is so large. Meanwhile, Lebanon and Turkmenistan, two countries on the top of the EQFL list, have reported populations below 10 million.

Tectonic setting provides another risk factor, says James Dalziel, earth risk research lead at WTW Research Network, who was not a part of the study. “Major faults on plate boundaries like the Anatolian Fault Zone [in Türkiye], for example, will be at high risk of large magnitude events and susceptible to cascading hazards like liquefaction, subsidence, slope failure and landslide.”

Ecuador and Haiti both have a significantly long fault rupture distance — meaning their faults can rupture for greater lengths, producing large earthquakes that can easily overwhelm a small population. Greece “has many, many earthquakes,” says Wyss. “But it’s never a big, big earthquake because the country’s chopped up in short faults.” In other words, Greece’s smaller but more frequent earthquakes drop it to number 20 on the EQFL list.

One more factor affecting the EQFL is a country’s disaster readiness. The West Coast of the United States is well known for its earthquakes, yet it ranks second-to-last on the study’s EQFL list. That score reflects the fact that the United States is a country with scientific resources, enforced building codes, and awareness of seismic hazards, with alert systems in place to give residents warning as a quake is occurring. All of these preparations can help keep fatalities low.

For similar reasons, other countries with well-known earthquake hazards—like Japan and Mexico—rank low on the list (numbers 28 and 32, respectively). Both places have modern or reinforced infrastructure and rapid emergency response systems. Meanwhile, Türkiye, which is ranked at number 11 on the EQFL list, has seismic building codes, but they are not always enforced, Wyss says.
 

The evolving EQFL

The news isn’t all grim. For all 35 countries that Wyss and colleagues included in their analysis, fatalities from earthquakes have decreased over time. What’s more, that decrease was observed even though large earthquakes have occurred over the past 500 years. This trend could be due to faster aid arrival and more efficient emergency services. It could also be the result of populations shifting from rural to urban settings in which buildings may be better suited to withstand strong shaking. In the past 500 years, Mexico, Columbia, Ecuador and the state of California have shown the strongest decrease in EQFL. Italy has seen the lowest decrease because of its aging buildings.

The ranking of countries on the EQFL list isn’t static; it’s not meant to be a permanent prediction of future fatalities or earthquakes. Wyss points out India’s low ranking at number 33 despite its location along the active Himalayan plate boundary. Its low placement comes from a lack of reliable historical records for fatalities and few recent major earthquakes, instead of truly low risks of societal impacts from earthquakes. When the next earthquake occurs there, if the fatalities climb to relatively high numbers based on its population size, it will move up the list, Wyss says.

Although Wyss is retired, he offers his seismic expertise to the public by operating the QLARM alert system. QLARM provides real-time loss estimates for earthquakes around the world. Each event is given a green, yellow, or red indication within half an hour, with the colors providing an estimated range of fatalities and injuries for each reported event based on the size, depth and location of the earthquake as well as the population affected in that particular region. Red represents the highest estimated levels of fatalities and injuries, yellow represents middle values, while green represents the lowest estimated values.

Alongside resources like QLARM, as well as the USGS’s PAGER system, the EQFL list can become another tool to bring awareness to regions that are likely to incur disproportionate fatalities from an earthquake. “Someone in those smaller countries could use this information to get their governments to pay attention to the problem and fund earthquake readiness,” Wyss says.

“When looking at seismic risk we tend to examine not only the hazard but also exposure and vulnerability,” says Dalziel. “This includes infrastructure and the potential for things like business interruption, but also the potential for fatalities. This is an important metric for knowing where resilience measures are going to be of greatest importance.”
 

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