Nov 01, 2024

Did the 2017 Pohang earthquake affect the mental health of residents?

Tags: Thoughts, Research

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Photo of Pohang after the 2017 Pohang Earthquake, Source: Ministry of the Interior and Safety

2017 Pohang Earthquake

On November 15, 2017, an earthquake occurred 7.5 km north of Pohang City [KMA Report]. The magnitude of the earthquake was 5.4, the second largest on record in South Korea, with a maximum seismic intensity of VI recorded in North Gyeongsang Province. Lesser tremors were felt in neighboring provinces such as Gangwon, South Gyeongsang, Daegu, Busan, Ulsan, and North Chungcheong, with an intensity of IV. A significant aftershock with a magnitude of 4.6 hit Pohang on February 11, 2018. According to the Korea Meteorological Administration (KMA), as of May 2018, a total of 615 aftershocks were reported, including 100 with a magnitude of 2.0 or higher [KMA Report].

Due to the Pohang earthquake, the national college entrance exam was postponed for a week, and the government declared Pohang as a special disaster area, initiating recovery and relief measures. The earthquake and aftershocks resulted in 135 injuries across Busan, Daegu, Ulsan, and North Gyeongsang, with estimated property damages reaching 85 billion KRW, including 56,622 private properties and 417 public facilities [2017 Pohang Earthquake White Paper]. Even by April 2019, over 100 victims were reportedly still residing in temporary housing facilities. [Research Article].

Compensation for Induced Earthquake Damage

On March 20, 2019, a government investigation team announced that a geothermal power development project near northern Pohang had triggered the 2017 Pohang earthquake and subsequent aftershocks in 2018 [News Article]. The team explained that micro-earthquakes were induced by water injection at the geothermal plant, impacting a critical stress fault that eventually triggered the Pohang earthquake. Multiple studies have also confirmed that Pohang earthquake was not natural but rather human-induced due to geothermal activities [Research Article 1] [Research Article 2].

Unlike typical natural disasters, the Pohang earthquake had a clear cause (the geothermal project) and a direct impact (damage to residents), leading Pohang residents to file a lawsuit seeking compensation from the government. On November 16, 2023, a ruling awarded 2,000,000–3,000,000 KRW per person in compensation for mental stress caused by the earthquake. Following this ruling, 490,000 residents—approximately 96% of Pohang’s population in 2017—are now participating in a new lawsuit [News Article].

However, aside from the tangible property damage or physical injuries, how can we quantify the invisible mental impact of earthquake on Pohang residents? If Pohang residents experienced anxiety and stress-related disorders after the earthquake, how can we be sure that these disorders were solely caused by the earthquake? Determining causality between the earthquake and health impacts remains a socially important challenge.

Limitations of Past Health Impact Studies on Earthquakes

Various epidemiological studies have shown that earthquakes can affect cardiovascular, respiratory, and mental health in residents of affected communities [Research Article 1] [Research Article 2]. Due to the sudden and threatening nature of earthquakes, affected residents may experience significant anxiety-related mental health issues. However, past studies faced limitations in establishing causality between earthquake exposure and health outcomes, as they recruited study participants after the earthquake and lacked appropriate control groups [Research Article]. Especially without pre-earthquake health data, it is challenging to determine whether observed health changes (e.g., an increase in anxiety or stress) were due to the earthquake or other prior factors.

Limitations in Causal Interpretation in Disaster Research

Assumptions for Evaluating the Health Impact of the Pohang Earthquake

1. Many disaster studies face the limitation of not having pre-event health data on study participants. However, since all South Korean residents are covered under a single National Health Insurance system, medical service utilization information is available in a central database. Utilizing data provided by the National Health Insurance Service, we can indirectly assess pre- and post-earthquake health data for individuals. If anxiety and stress-related disorders increased post-earthquake, we would expect an increase in healthcare utilization for these disorders among Pohang residents, while such an increase would not be observed in unaffected regions.


2. The seismic intensity distribution map indicates that the 2017 Pohang earthquake occurred near the geothermal power plant located in Northern Pohang. Given that residents closer to the epicenter are likely to experience greater stress due to stronger tremors, it can be hypothesized that residents in Northern Pohang were more affected psychologically than those in Southern Pohang.

Seismic Intensity Distribution, Source: KMA Pohang Earthquake Report

3. If there is indeed a causal relationship between earthquakes and the incidence of mental disorders, this relationship would not be unique to the Pohang earthquake alone. For example, the 2016 Kyungju earthquake, the most intense earthquake recorded in South Korea (intensity 5.8), would also have led to a similar increase in mental disorders among residents of affected areas.


4. We anticipate that anxiety and stress-related mental disorders increased in Pohang following the earthquake but that no significant changes occurred in unaffected areas. Additionally, even for Pohang residents, there should be no changes in the incidence of these disorders if we compare an arbitrary pre- and post-earthquake period unrelated to the actual earthquake event.

Health Impacts on Residents Following the 2017 Pohang Earthquake

Based on the assumptions outlined above, this research sought to analyze the causal impact of the 2017 Pohang earthquake on the incidence of anxiety and stress-related mental disorders among Pohang residents. For this study, data from the National Health Insurance Service (NHIS) were used. Gimhae, a city with a similar population size to Pohang, and Kyungju, the nearest city to Pohang, were used as control groups to compare the incidence of anxiety and stress-related disorders before and after the Pohang earthquake. The study aimed to test the following five hypotheses:

1. The incidence of anxiety and stress-related mental disorders among Pohang residents will increase following the 2017 Pohang earthquake.
2. This increase will not be observed in Gimhae, a city unaffected by the earthquake.
3. Residents in Northern Pohang, closer to the earthquake’s epicenter, will experience a greater increase in mental health issues compared to those in Southern Pohang and Kyungju.
4. The association between earthquake exposure and increased mental health disorders will also be observed among residents affected by the 2016 Kyungju earthquake.
5. There will be no significant change in the incidence of anxiety and stress-related mental disorders among Pohang residents at an arbitrary time point unrelated to the 2017 Pohang earthquake.

Affected areas by the 2017 Pohang and 2016 Kyungju Earthquakes

The above map, adapted from the 2017 Pohang Earthquake White Paper, shows the affected areas from the 2016 Kyungju earthquake and 2017 Pohang earthquake. The map indicates that the Pohang earthquake primarily impacted Northern Pohang, with limited damage in nearby cities like Kyungju and Gimhae. In contrast, the Kyungju earthquake caused widespread damage, impacting heavily populated regions of Pohang as well.

For this study, residents of Pohang and control areas from 2014 were randomly sampled based on age and gender, and 50% of the total population were selected. Among these, 515,750 individuals with no change in residence until death or the end of 2019 were selected. The incidence of anxiety and stress-related disorders (ICD-10 code: Neurotic, stress-related, and somatoform disorders, F40-F48) was defined by the first-ever hospital visit for these conditions since 2010. The 42-day period before and after the Pohang earthquake was divided into three-week intervals (-42 to -22 days; -21 to -1 days; 0 to 20 days; 21 to 41 days), with the interval -42 to -22 days set as the baseline. Differences in the incidence of anxiety and stress-related disorders between Pohang and the control areas were evaluated using a difference-in-differences model, adjusting for population size and time trends.

Changes in Daily Incidence of Anxiety and Stress-related Mental Disorders before and after the 2017 Pohang Earthquake

Before the Pohang earthquake, the average daily incidence of anxiety and stress-related mental disorders in Pohang was 7.14 cases (-42 to -22 days) and 6.57 cases (-21 to -1 days), but this increased to 15.62 cases (0 to 20 days) after the earthquake, with a more pronounced increase among women. A difference-in-differences analysis revealed that the incidence of anxiety and stress-related mental disorders among Pohang residents increased significantly, by about two times compared to residents in control areas, with a particularly greater increase observed among residents in Northern Pohang.

Weekly Incidence of Anxiety and Stress-related Mental Disorders by Region before and after the 2016 Kyungju and 2017 Pohang Earthquakes

After the 2017 Pohang earthquake, an increase in anxiety and stress-related mental disorders was observed only among Pohang residents. In contrast, following the 2016 Kyungju earthquake, both Kyungju and Pohang residents experienced an increase in anxiety and stress-related mental disorders. Additionally, when evaluating changes at a random time point set at 90 days before the Pohang earthquake, no significant changes in incidence were observed in either Pohang or the control areas.

Few studies in South Korea have assessed the health impacts of earthquakes, but most have used conventional samples with small sample sizes and lacked appropriate controls. This study utilized customized data from the NHIS and applied quasi-experimental methods, specifically a difference-in-differences analysis, to infer causality between specific events (earthquakes) and their health impacts on local residents. By comparing control areas, the study confirmed the specificity of the association between earthquake exposure and health outcomes on Pohang residents. Regional-level analysis also revealed a dose-response relationship, and applying the same data and methods to the 2016 Kyungju earthquake replicated the findings, increasing the possibilities for causal interpretation.

Summary

• On November 15, 2017, an earthquake struck Northern Pohang, resulting in the largest property damage caused by a natural disaster in South Korea.
• However, a government investigation concluded that the Pohang earthquake was a man made disaster induced by activities at a geothermal power plant. Consequently, Pohang residents filed for compensation for mental distress caused by the earthquake, and a court ruled that the government should provide compensation of 2,000,000–3,000,000 KRW per person.
• Analysis using NHIS data revealed that the incidence of anxiety and stress-related mental disorders among Pohang residents increased significantly, about twofold compared to residents in control areas. This increase was particularly notable among Northern Pohang residents, who live near the epicenter.
  
  

Related Article

Information on this study is as follows:

Han, C. (2022). Induced Seismicity and Acute Development of anxiety and stress-related Mental disorders: findings from the 2017 Pohang Earthquake. Environmental Health Perspectives, 130(6), 067701.

Related Presentation

The presentation on this research can be viewed in the video below.

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