Natural disasters have physical and psychological impacts on individuals and their surrounding community. The psychological effects of such catastrophes on a person include depression, anxiety, and stress-related illnesses (1). Post-traumatic stress disorder (PTSD) is one of the stress-related disorders that may develop following exposure to a major traumatic event. PTSD sufferers experience episodes of recurrent intrusion symptoms such as distressing memories of traumatic events, nightmares, and dissociative reactions, as well as avoidance, negative changes in cognition and mood, and hyperarousal (2).

The risk factors for the development of PTSD include extreme age (children, adolescents, and elderly), female gender, low socioeconomic status, low level of education, and aspects of trauma severity (direct and indirect exposure to disaster, witnessing destruction of property, worry about others, witnessing death and injuries of others and physical injury to self during an event of a natural disaster) (3, 4). A study in Indonesia by Marthoenis et al. (5) found that 58.3% of adolescents showed clinical symptoms of PTSD 6 months after the 2016 Aceh Earthquake. The high prevalence of post-traumatic stress (PTS) symptoms in adolescents is worrying as this may affect their daily functioning and cognition. The worse scenario was PTS symptoms that persisted until adulthood resulting in the need for PTSD treatment secondary to childhood trauma (6). Maladaptive cognitive processes experienced during traumatic events may contribute to the long-lasting PTS symptoms. Meiser-Stedman et al. (7) observed that cognitive processes play crucial in the development and persistence of PTS symptoms in both children and adolescents. In the study, all the perceived threats, overwhelming feelings, and confusion during the traumatic event contributed to the onset of acute PTS symptoms. Poorly elaborated, sensory-based memories, dissociation, rumination, and negative appraisals were closely associated with persistent PTS symptoms.

A recent cohort study conducted by Altamore et al. (8) postulated that repeated exposure to earthquakes increased the prevalence of developing psychological distress and PTSD, in which 0.5% prevalence of probable PTSD assessed in 2015 spiked to 16.9% in 2017 after the second earthquake. Although the cohort samples experienced a low level of distress for 8 years after the first earthquake, a second exposure to the earthquake had led to a higher level of psychological and PTS symptoms. Even after the natural disaster has subsided, visiting or being at the place of incidence may still trigger trauma and negative memories that can affect a person's mental and physical health (9). Therefore, the frequency of exposure to earthquakes may influence the development of PTSD and the resilience of adolescents exposed to natural disasters.

Also, resilience is fundamental for people to positively function after a disaster. Resilience was strongly associated with reduced PTS symptoms 3 months after a hurricane (10) and improved quality of life after earthquake exposure (11). Moreover, Smith et al. (12) revealed that a high level of resilience was associated with lower probabilities of developing mental health issues such as depression, anxiety, and stress. Adolescents who experienced the 2016 Fort McMurray wildfire also showed that those who had high resilience showed higher self-esteem and quality of life scores (13).

Several factors that increased resilience in the post-disaster population included self-efficacy, having coping strategies, and good social support (14). Positive thinking and self-motivation were among the strategies used in self-efficacy by the population. Coping strategies such as turning to God and religious activities had helped them to remain hopeful in adversities. Social support given by government and non-government organizations also proved to be helpful in building resilience in the population (14).

Developing countries have started integrating mental health and psychosocial support in their disaster preparedness and response (15–17). However, recent studies showed that mental health problems especially PTSD, depression, and anxiety were still relatively high in these countries (18, 19). Adolescents are vulnerable to their surroundings and may not have adequate knowledge of how to cope with mental health issues and what to do in response to natural disasters. There are limited studies on the effects of repeated trauma exposures on adolescents' mental health. If no prompt identification and treatment, PTSD may persist for a long period of time and impair the children's or adolescents' function and development (20, 21). Therefore, this study aimed to determine the relationship between PTS symptoms, maladaptive trauma-related cognition, and resilience in adolescents exposed to the earthquakes in Lombok, Indonesia.

This cross-sectional study was part of an intervention under a student mobility program conducted by the Student Council of the National University of Malaysia in a state high school located at Lombok, Indonesia from July 15 to 21, 2019. The aim of the program was to provide humanitarian aid and psychosocial support, including interventions such as relaxation and coping techniques, for the local adolescents exposed to multiple earthquakes. Lombok is well known as a disaster-prone area due to the island's location in the Pacific Ring of Fire characterized by active movement of tectonic plates resulting in frequent natural disasters. Multiple earthquakes occurred within 9 months: a strong magnitude earthquake (6.4) on July 29, 2018, followed by a major earthquake of 7.0 magnitude on August 5, 2018, and a moderate magnitude earthquake (5.8) on March 17, 2019. The current study involved a group of adolescents in Lombok who survived the earthquakes.

The final participants included were 409 with 158 (38.6%) males and 251 (61.4%) females. One subject was removed from the study as it was an outlier for the CPTCI questionnaire, identified with scatter plot and interquartile range method. A suggested cut-off of 30 was used and the prevalence of probable PTSD was 69.9% for the CRIES questionnaire. The proportion of exposure to the earthquake at least once, twice, and three times were 21.3, 28.4, and 50.4%, respectively. Table 1 presents the questionnaire responses.

As predicted, results of independent t-test showed a significant difference in the PTS symptoms across gender, in which females [M = 39.99, SD = 11.46, t₍₄₀₇₎ = −7.48, p < 0.001] had higher PTSD scores than males. Besides, adolescents with mothers of lower educational level [M = 37.56, SD = 12.42, t₍₃₉₉₎ = 2.02, p = 0.04] scored significantly higher in PTS symptoms; in comparison with adolescents whose mother had education of at least secondary level. There were also significantly higher PTS scores among adolescents who had witnessed injury or death [M = 37.96, SD = 12.36, t₍₄₀₇₎ = −3.02, p = 0.003] compared with those who did not; and among adolescents who had family, guardian, or acquaintance who died during earthquake [M = 38.87, SD = 13.07, t₍₄₀₇₎ = −2.55, p = 0.01] in comparison with those who did not have deceased proxy during earthquake. In addition, PTS scores were significantly higher among adolescents whose parents reacted excessively during earthquake (e.g., loud wailing, loud prayers) [M = 39.23, SD = 12.24, t₍₄₀₇₎ = −4.33, p ≤ 0.001], in contrast to those whose parents did not react this way. In comparison with the differences in PTS scores, adolescents who were trapped or experienced difficult escape during earthquake [M = 39.90, SD = 11.95, t₍₄₀₇₎ = −2.46, p = 0.01] scored significantly higher than those who did not experience this. The adolescents who have higher level of resilience were found to have higher PTS scores [M = 38.71, SD = 12.34, t₍₄₀₇₎ = −2.69, p = 0.01] than those with lower level of resilience. Details are tabulated in Table 2.

The results of zero-order correlation are shown in Table 3. This bivariate analysis was primarily used to guide the selection of variables into the regression model. Findings show that when compared with males, females had a positive but weak PTS score (r_pb = 0.35). Maternal education level had a negative but negligible correlation with PTS symptoms (r_pb = −0.10). In contrast, maladaptive trauma-related cognition (higher score indicating more negative trauma-related cognition) and resilience had statistically significant weak, positive correlation with PTS symptoms (r = 0.12 and r = 0.21). In addition, the variables of trauma exposure listed in Table 3 also correlated positively and significantly with PTS symptoms (r = 0.12–0.21), indicating weak relationships.

According to the regression analysis results (Table 4), the model explained 17% of the variance and was a significant predictor of PTS symptoms [F_(4,404) = 22.06, p ≤ 0.001]. The female gender contributed most significantly to the model (β = 7.350, p < 0.001), followed by excessive reaction of parents during earthquake (β = 3.283, p = 0.005), maladaptive trauma-related cognition (β = 0.224, p = 0.002), and resilience (β = 0.192, p < 0.001). Simple linear regression demonstrated that the statistical significance of adolescents who witnessed injury or death during earthquake (p = 0.003), had a proxy died during earthquake (p = 0.01), and those who were trapped or had a difficult escape (p = 0.01) may potentially predict the occurrence of PTS symptoms.

The prevalence of PTS symptoms among adolescents post-earthquake was 69.9% in this study, which was higher compared with other studies. The prevalence of PTSD among adolescents 6 months after Aceh earthquake and 12 months post-Wenchuan earthquake were 47 and 17.5%, respectively (5, 30). Furthermore, Rahmadian et al. (31) reported that 19.9% of children and adolescents who were survivors of natural disasters in Indonesia fulfilled the criteria of PTSD diagnosis. The prevalence may be affected by differences in the study population, method of assessments, time-lapse after earthquake, and the severity of the event. A few factors may contribute to the high prevalence of PTS symptoms in this study. Older children were found to be more susceptible to the development of PTSD compared with younger children (32). Other than that, recurrent exposures to disasters can potentially bring a negative additive effect on mental health (33). Moreover, the purposive sampling method of this study may also contribute to the high prevalence.

This study found a significant difference between gender with regards to severity of PTS symptoms. According to the study results, female adolescents had higher PTS symptoms score compared with males. This result is consistent with the meta-analysis by Furr et al. (34) that suggested females are more vulnerable to the development of PTS symptoms. Derivois et al. (35) and Cadichon et al. (36) also concluded that female gender is an important PTSD risk factor among the study's population. Several explanations including stronger apprehension of threat, higher extent of peritraumatic dissociation, poor social support, and gender differences in acute subjective responses to trauma were suggested by a research review (37). Witnessing injury or death during earthquakes and excessive response from parents during and after earthquakes were significantly associated with higher PTS symptoms scores. Kilic et al. (38) reported that negative effect on children was more significant when fathers became more irritable and detached. Ekşi et al. (39) and Ma et al. (40) also reported that witnessing death and suffering as well as extreme reactions from parents or other adults during and following earthquake are significant risk factors for the development of PTS symptoms. These reactions include wailing, crying, and praying loudly, which may raise children's fright, insecurity, and helplessness. As parents or adults are coping models, the children may perceive the event as frightening or even threatening after observing the adults' reactions. This finding suggests that the subjective element of disaster experience contributes to an adolescent's post-trauma response, which should be made aware and recognized in psychological interventions.

In addition, maladaptive trauma-related cognitions measured by CPTCI was found to be one of the predictors that was positively associated with PTS symptoms. A meta-analysis showed cognitive deficits regarding working memory, executive function, verbal learning and memory, visual learning and memory, information processing speed, and visuospatial function play important roles in PTS symptoms and are associated with the disorder (41). Stallard et al. (42) supported that negative trauma appraisal and cognitive coping style lead to permanent PTS symptoms. This is because the ongoing negative trauma appraisal contributes as a factor that causes the traumatic event to be experienced as a current threat even though the traumatic event happened in the past. A significant difference in cognitive style between adolescents with high risk of PTSD and low risk of PTSD was also reported in research conducted following the Wenchuan earthquake in China (40). Thus, adolescents with negative and maladaptive trauma-related cognitions require careful screening and monitoring for PTSD development.

The findings of the study revealed that resilience was significantly and positively associated with PTS symptoms among adolescents exposed to Lombok earthquakes. A study done among street children in Haiti showed that those with severe PTS symptoms possessed higher level of resilience (43). On the contrary, other studies showed adolescents with higher resilience level had lower risk of developing PTS symptoms (4, 44–46). Resilience was also shown to be a predictor of PTSD in a recent study (47). While resilience has been an established protective factor that modulates response toward trauma, the study results showed that adolescents with higher resilience level were significantly associated with higher PTS scores. We postulated that the high scoring of PTS symptoms in these participants may be contributed by repeated exposures to earthquakes within a 9-month period. In this study, as high as 50.4% of participants experienced earthquakes three times in Lombok, Indonesia. Previous studies have observed dose gradients of trauma, in which more intense, more prolonged, and more cumulative traumas were associated with more symptoms (48, 49). Adolescents who experienced additional trauma after an earthquake exposure were also shown to be more likely to develop delayed or chronic PTS symptoms (50). Moreover, a longitudinal study over 17 years among child survivors of dam collapse found that PTSD remained present at a higher-than-normal rate; however, resilience and recovery were observed in most exposed individuals (51).

Also, resilience is not merely a personality trait, but it has been broadening to a more ecological context that can be developed at any age based on individual relationships and environments (52–54). It is conceivable that in the study, the measure of current resilience level captured both effects of existing resilience and growth following trauma exposures. The high level of resilience in this population may be contributed by various external resources including good social support from caregivers and community, religion, spirituality, and cultural resources, not solely associated with the experiences from repeated earthquakes. Different dimensions of social support from family members, peers, teachers, and community were identified as resources of resilience in previous studies (55–57). The study participants scored high with regards to relational resilience, which also suggested that family members and peers were important resources for adolescents to show resilience. Besides, our participants are all Muslims. While religion and spirituality were shown to promote resilience (58–60), a study conducted in Islamic population pointed out that religion was a key factor in facing the tragedy of tsunami in their communities and reinforcing social ties (61).

Several potential predictors of PTS symptoms were ascertained in this study, including adolescents who witnessed injury or death during earthquake, had a proxy died during earthquake, and those who were trapped or had a difficult escape. These exposures to traumatic events during earthquake were significantly associated with higher PTS scores, which were consistent with other studies (62–64). The results may imply that adolescents who had higher degree of physical exposure to a disaster portrayed a larger impact on their reactions or coping in post-trauma adjustment. However, these findings must be cautiously interpreted due to the weak association in the study results. The potential of these exposure indicators as predictors of PTS symptoms warrants future research to gain further insight.

More importantly, the study results demonstrated that there was a negative correlation between maladaptive trauma-related cognitions and resilience. Limited studies have adequately answered the relationship between these two salient indicators of PTS symptoms. This finding will add value to and consolidate the holistic interventions among adolescents exposed to disasters as cognitive functioning is one of many aspects that is often disregarded in post-traumatic psychopathology. Our growing understanding of negative trauma-related appraisals and resilience will hopefully help with the development of more strategies for PTSD management. The psychological therapy of PTSD is deemed to focus on the key role of various predictors in overcoming the adversity and trauma response among adolescents, for instance, avoidance, intrusion, and arousal. Intervention designs should be based on the unique gender differences in responding to traumatic events as females exhibited higher PTS scores compared with males. Also, it is necessary to be aware that proxy's reaction in adverse situations may influence children's stress responses. Thus, family-based therapy is recommended as the importance of proxy's response in preventing stress reactions of adolescents needs to be emphasized. Moreover, in the situation of family members who were affected during earthquakes, the vulnerable adolescents should be screened vigorously and provided intervention, if necessary, even though they appeared physically or mentally well.

This study has some limitations. A cross-sectional study design was used and hence, the relationship between the exposures and outcomes could not be well explained. Thus, further longitudinal studies on the same population may produce more valuable results. Besides, the collection of data took place a year after the earthquake incidents. The results may not explain the direct acute effects of the earthquakes and may not be applicable to other time frames after earthquakes. The cognition and resilience of the samples might be affected by other confounding variables such as social support in this period. Furthermore, the back-translated questionnaires in Indonesian language have not been validated in the local population. The questionnaires were administered by self-reporting method, which carried the risk of information bias and led to less accuracy. Future studies may employ other information sources such as caregivers' and teachers' reports, as well as clinical interviews to enhance the accuracy and reliability of the findings.

The findings of this study revealed that the natural disaster, namely earthquakes, brought notable psychological impacts on adolescents in Lombok, Indonesia. This was discernible by the high prevalence of PTS symptoms in the participants. Several predictors of PTS symptoms among adolescents post-earthquakes were identified in this study, including maladaptive trauma-related cognitions, resilience, and excessive reactions of proxy during earthquakes. These are worth targeting and prioritizing in future post-disaster interventions. Adolescents who witnessed injury or death, had a proxy died, and had difficulty in escaping or being trapped during earthquakes were identified as the potential predictors of PTS symptoms, which warrant further studies. Early identification of vulnerable adolescents is essential to offer preventive measures and to provide effective psychological support if necessary. The negative association between maladaptive trauma-related cognition and resilience further emphasized the role of cognition in post-traumatic psychopathology and should be further investigated in future studies.

The datasets presented in this article are not readily available because data cannot be shared due to confidentiality issues. Requests to access the datasets should be directed to Suzaily Wahab, suzailywhb@yahoo.com.

The study involving human participants was reviewed and approved by Secretariat of Research and Innovation, Faculty of Medicine, The National University of Malaysia and Ethical Committee of Medical Research, Faculty of Medicine, The University of Mataram. Written informed consent to participate in this study was provided by the participants' legal guardian/next of kin.

SW and HD conceptualized and contributed to the study design. LY, WC, MY, NS, NA, CM, and SMW collected the data. RI, HD, WC, LY, and AO performed the data analysis and interpretation. SW, LY, WC, MY, NS, and HD wrote the draft of the article. Finally, SW, RI, and HD critically revised the article. All authors have made substantive intellectual contributions to the manuscript, read, and approved the final article.

This is an independent research funded and supported by the Ministry of Higher Education, Malaysia and Universiti Kebangsaan Malaysia Medical Centre.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer CN declared a shared affiliation, with no collaboration, with the authors SW, LY, WC, MY, NS, RI, AO, and HD at the time of the review.

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