The observed proportion of Google search episodes originating in Oklahoma and focused on anxiety increased over the test period (Figures 2B, 3). These Google searches in Oklahoma appeared significantly positively associated with similar search episodes nationwide (Table 1, base model). The coefficient for the Oklahoma toothache search episodes did not indicate an association with Oklahoma anxiety Google searches, but we nevertheless elected to include this covariate in our test equation.
We conducted several robustness checks. We repeated the test but deleted the Oklahoma “toothache” search variable given that its coefficient did not differ from 0 in the counterfactual or test models. Results remained unchanged with this removal. We applied the methods of Chang et al.42 to the full test model to identify and control outliers in our dependent variable that may have distorted our results. We detected no outliers. We estimated a falsification test in which we replaced earthquakes ≥ M 4 with those ≤ M 2.5 (eFigure 2; http://links.lww.com/EE/A10, available as a supplement). Oklahomans likely did not sense earthquakes of this small magnitude. Our theory, therefore, would predict no association with anxiety from Google searches. We repeated the steps in our test model and found no association (coefficient = −0.0001; SE = 0.0002).
We also assessed the robustness of our findings with two less-conventional approaches. Oklahoma experienced a marked increase in M 4 earthquakes beginning in 2015; therefore, we hypothesized that the proportion of Oklahoma-based Google search episodes concerned with anxiety would outpace the proportion nationwide (Figure 3). We tested this prediction by applying outlier detection methods to residuals from a regression of the Oklahoma anxiety variable on that for the United States. We found evidence of a significant (P < 0.005, single-tailed test) divergence between Oklahoma and the rest of the nation that began in September 2015, indicating that starting in autumn of 2015, the proportion of anxiety-focused search episodes in Oklahoma increased more than the proportion nationwide.
Second, we grouped our data into weeks rather than months. We did not use weekly data in our main test because they often exhibit week-of-month and moveable holiday effects that complicate the detection and specification of autocorrelation by interacting with other patterns in monthly and weekly data (e.g., seasonality).43 Despite this difficulty, we found increases in the proportion of Oklahoma Google search episodes concerned with anxiety 3 weeks after M 4 earthquakes (coefficient = 0.0175; SE = 0.0103), a finding consistent with our main test results. The weekly analysis also controlled for US anxiety search episodes and Oklahoma toothache search episodes.
Finally, we estimated a “binary-X” exposure model in which we replaced the continuous > M 4 earthquake variable with a binary variable scored 1 for months with more than one M 4 earthquake and 0 for all other months. Repeating the steps above with this variable, we observed a significant 5.8% increase in the proportion of Google anxiety search episodes in months with > 1 M 4 earthquake (Table 1). The persistence parameter (i.e., 0.57) implied that 57% of that increase carried in the following month. Therefore, we estimated that the proportion of Google search episodes concerned with anxiety increased by about 9.1% over a 2-month period when > 1 earthquake ≥ M 4 struck Oklahoma.
In this quasi-experimental, time-series analysis, we found that the proportion of Google search episodes concerned anxiety increased in months with ≥ M 4 earthquakes in Oklahoma. This elevation of interest in anxiety on the internet persisted into the following month. With weekly search data, we discovered a peak in anxiety queries 3 weeks after ≥ M 4 quakes. Neither state-specific trends in health-related queries nor nationwide trends in anxiety queries explained these relationships.
Many factors contribute to earthquakes. In Oklahoma, however, scientists have linked a large proportion of ≥ M 3 quakes to high-rate fluid injection.8 Wastewater disposal appears to have caused the two largest and most destructive earthquakes in the state’s history, the 2011 Prague M 5.7 and the 2016 Pawnee M 5.8 earthquakes.6,7,44,45 Over 60,000 people self-reported sensing the 2016 Pawnee quake on the USGS “Did you feel it?” website.10 On the same website, Oklahomans reported feeling every ≥ M 4 quake in our analysis. Earthquakes that result from wastewater injection may elicit a more pronounced psychological response than earthquakes with no specified cause.21 As the result of induced earthquakes, perceptions of the oil and gas industry in Oklahoma have shifted over time from fully supportive to various narratives of alarm, concern, and acceptance.46 These perceptions may influence psychological responses to Oklahoma tremblors.
Data from the Behavioral Risk Factor Surveillance System (BRFSS) suggest that Oklahomans experience more poor mental health days than the national average.47 Because BRFSS data are only collected annually, we could not use them to assess short-term response to frequent Oklahoma earthquakes as we could with real-time Google search data. Still, BRFSS data suggest Oklahomans may represent a high-risk group for adverse mental health outcomes. Oklahoma also has higher rates of poverty and lower levels of health insurance coverage than the national average.47 These factors may make Oklahomans more likely to live in older and earthquake-susceptible housing, more vulnerable to mental health consequences of earthquakes,18,48 and more apt to seek information online regarding mental health.49
Exposure to earthquakes may trigger anxiety through complex physiological pathways, including activation of the hypothalamic–pituitary–adrenal system, alterations to neural circuits such as the amygdala and insular cortex, and heightened reactivity of the nervous system (e.g., heart rate).50,51 Evolution has conserved these pathways, underscoring the important role of anxiety as an adaptive response to stress that helps organisms defend against a variety of threats.52 Excessive anxiety, however, may disable individuals and has long-term implications for health and functioning.24–28 Such excessive symptoms of anxiety occur more readily in response to a recurrent and unpredictable stressor,53 such as the Oklahoma earthquakes included in our study.
Previous research has documented adverse mental health effects among survivors of single major earthquake events using survey data of limited sample size.54–56 One study from China found that fear and psychological response dampened after the first of two major earthquakes.57 We present a novel finding that multiple more moderate earthquakes (M 4 to M 5.8), mostly manmade, may increase anxiety across a state’s population. Two studies have documented psychological morbidity and post-traumatic stress disorder among survivors of single M 5.6 and M 5.9 earthquakes.58,59 Other research implies that coping with the damage caused by earthquakes could induce psychological distress. Survey respondents living in an area with induced earthquakes in the Netherlands named property damage and reduced value of homes as their primary concern and a cause of anger and worry.22 The value of homes in Oklahoma—where builders have not constructed earthquake-resistant structures—appears to drop after moderate earthquakes.60,61 Governor Mary Fallin has also twice declared a state of emergency after earthquakes in 2016.62 These events may result in concerns about safety and economic loss perhaps causing, in turn, the anxiety gauged by Google searches.
We chose to examine queries related to anxiety because, of all psychiatric disorders, anxiety has been the most frequently associated with disaster exposure.18 While online searches for depression appear to correlate with positive screening for major depression,63 we could not assess concordance between upticks in internet searches for anxiety and clinical mental health outcomes. Individuals may search for information about anxiety unrelated to health (e.g., “test anxiety”), on the behalf of others, or out of general interest in the topic. As noted above, however, Google identifies queries as health-relevant based on associated queries and internet “clicks.”64 Moreover, many searches may be provoked by subthreshold symptoms that would not meet clinical diagnostic criteria. Nevertheless individuals with these symptoms can experience emotional distress and functional impairment in work, school, and interpersonal relationships that can develop into full-blown disorder over time.65
Recent research suggests that the prevalence of serious psychological distress (a construct that includes anxiety as well as related psychological disorders, such as depression) has increased significantly in the United States during the past decade.66,67 This increase appears to be more pronounced among low-income individuals67 who may be overrepresented in Oklahoma relative to the broader US population. Treatment seeking for mental health conditions also appears to be rising,66 perhaps due to gradually decreasing stigma related to mental health problems, as well as federal legislation mandating expansion of mental health insurance benefits. It is possible, therefore, that the increasing health-related anxiety Google searches in the United States overall reflect both true increases in the prevalence of anxiety and psychological distress, as well as increased willingness among individuals suffering from symptoms of distress to search for help. We note, however, that our finding of increased health-related anxiety Google searches in Oklahoma after earthquakes adjusted for levels of such searches in the United States as a whole.
Data collection through Google searches may bias our sample. We only captured searches in English, and certain groups—younger, more educated individuals—report using the internet more often for health information.68 Within Oklahoma, specific subgroups—females, those with history of trauma or preexisting psychological disorders or a high degree of disaster exposure—may have particular susceptibility to adverse effects of earthquakes, including post-traumatic stress disorder.55,57,69 Due to the ecologic nature of our study, we cannot specifically track these groups that may be under-represented among online searches. In 2013, however, most households in Oklahoma (71.1%) had high-speed internet access.70 In addition, the majority of Americans seek health information online and most use the internet as their first source of health information.68 Despite limitations, the use of Google search data allowed us to include timely, spatially comprehensive data in our study. Our results highlight the importance of real-time mental health syndromic surveillance at state and local levels.71
The decision to allow, deny, or further modify the wastewater injection linked to earthquakes in Oklahoma72 likely reflects cost/benefit analyses that include accounting of associated health effects. We posit that better estimates of the suspected mental health consequences of induced earthquakes could improve the regulation of oil and gas extraction. We suggest that the application of time series methods to real-time Google search data would contribute to these estimates. Herein, we demonstrated such an application using data from Oklahoma. Google search data holds particular utility for the study of mental health outcomes,33 for which many do not immediately, or perhaps ever, seek medical care. We found increased anxiety-related Google search episodes following earthquakes of ≥ magnitude 4. Such searches may indicate elevated rates of anxiety among Oklahomans. Our analyses have illustrated the potential contribution of internet search data to mental health surveillance and, in turn, to the regulation of environmental hazards at the state and local level.
The authors declare that they have no conflicts of interest with regard to the content of this report.
We thank G. Stocking and A. Mitchell at Pew Charitable Trusts for help in accessing and downloading the Google search data and for valuable comments on the manuscript, as well as Google’s data experts for providing access to and assistance in understanding the structure of the data.
3. Silva TLS, Morales-Torres S, Castro-Silva S, Figueiredo JL, Silva AMT. An overview on exploration and environmental impact of unconventional gas sources and treatment options for produced water. J Environ Manage 2017; 200511–529
5. Vengosh A, Jackson RB, Warner N, Darrah TH, Kondash A. A critical review of the risks to water resources from unconventional shale gas development and hydraulic fracturing in the United States. Environ Sci Technol 2014; 48(15)8334–48
6. Keranen KM, Savage HM, Abers GA, Cochran ES. Potentially induced earthquakes in Oklahoma, USA: Links between wastewater injection and the 2011 Mw 5.7 earthquake sequence. Geology 2013; 41(6)699–702
7. Keranen KM, Weingarten M, Abers GA, Bekins BA, Ge S. Induced earthquakes. Sharp increase in central Oklahoma seismicity since 2008 induced by massive wastewater injection. Science 2014; 345(6195)448–51
8. Weingarten M, Ge S, Godt JW, Bekins BA, Rubinstein JL. Induced seismicity. High-rate injection is associated with the increase in U.S. mid-continent seismicity. Science 2015; 348(6241)1336–40
11. Howell EL, Li N, Akin H, Scheufele DA, Xenos MA, Brossard D. How do US state residents form opinions about ‘fracking’in social contexts? A multilevel analysis. Energy Policy 2017; 106345–355
12. McLaughlin DK, Corra J, Hagedorn AD, Wang D. Does Marcellus Shale natural gas extraction affect how much youth in rural Pennsylvania like their community? Rural Sociol 2017; 82(4)772–799
13. Evensen D, Stedman R. Beliefs about impacts matter little for attitudes on shale gas development. Energy Policy 2017; 10910–21
14. Lai P-H, Lyons KD, Gudergan SP, Grimstad S. Understanding the psychological impact of unconventional gas developments in affected communities. Energy Policy 2017; 101492–501
15. Maguire K, Winters JV. Energy boom and gloom? Local effects of oil and natural gas drilling on subjective well-being. Growth Change 2016; 48(4)590–610
16. Sangaramoorthy T, Jamison AM, Boyle MD, Payne-Sturges DC, Sapkota A, Milton DK, Wilson SM. Place-based perceptions of the impacts of fracking along the Marcellus Shale. Soc Sci Med 2016; 15127–37
17. Thomas M, Partridge T, Harthorn BH, Pidgeon N. Deliberating the perceived risks, benefits, and societal implications of shale gas and oil extraction by hydraulic fracturing in the US and UK. Nat Energy 2017; 2(5)17054
18. North CS, Pfefferbaum B. Mental health response to community disasters: a systematic review. JAMA 2013; 310(5)507–18
19. Slovic P, Finucane ML, Peters E, MacGregor DG. Risk as analysis and risk as feelings: some thoughts about affect, reason, risk, and rationality. Risk Anal 2004; 24(2)311–322
20. Siegrist M, Sütterlin B. Human and nature-caused hazards: the affect heuristic causes biased decisions. Risk Anal 2014; 34(8)1482–1494
21. McComas KA, Lu H, Keranen KM, Furtney MA, Song H. Public perceptions and acceptance of induced earthquakes related to energy development. Energy Policy 2016; 9927–32
22. Perlaviciute G, Steg L, Hoekstra EJ, Vrieling L. Perceived risks, emotions, and policy preferences: a longitudinal survey among the local population on gas quakes in the Netherlands. Energy Res Soc Sci 2017; 291–11
23. Vos T, Barber RM, Bell B, et al. Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013. The Lancet 2015; 386(9995)743–800
24. Haller H, Cramer H, Lauche R, Gass F, Dobos GJ. The prevalence and burden of subthreshold generalized anxiety disorder: a systematic review. BMC Psychiatry 2014; 14(1)128
25. Lambiase MJ, Kubzansky LD, Thurston RC. Prospective study of anxiety and incident stroke. Stroke 2014; 45(2)438–43
26. Roest AM, Martens EJ, de Jonge P, Denollet J. Anxiety and risk of incident coronary heart disease: a meta-analysis. J Am Coll Cardiol 2010; 56(1)38–46
27. Ding XX, Wu YL, Xu SJ, Zhu RP, Jia XM, Zhang SF, Huang K, Zhu P, Hao JH, Tao FB. Maternal anxiety during pregnancy and adverse birth outcomes: a systematic review and meta-analysis of prospective cohort studies. J Affect Disord 2014; 159103–10
28. Subbaraman M, Goldman-Mellor S, Anderson E, Lewinn K, Saxton K, Shumway M, Catalano R. An exploration of secondary sex ratios among women diagnosed with anxiety disorders. Hum Reprod 2010; 25(8)2084–2091
30. Ayers JW, Althouse BM, Allem J-P, Childers MA, Zafar W, Latkin C, Ribisl KM, Brownstein JS. Novel surveillance of psychological distress during the great recession. J Affect Disord 2012; 142(1)323–330
31. Ayers JW, Althouse BM, Allem J-P, Rosenquist JN, Ford DE. Seasonality in seeking mental health information on Google. Am J Prev Med 2013; 44(5)520–525
32. Tefft N. Insights on unemployment, unemployment insurance, and mental health. J Health Econ 2011; 30(2)258–264
33. Ayers JW, Althouse BM, Dredze M. Could behavioral medicine lead the web data revolution? JAMA 2014; 311(14)1399–1400
37. Aatamila M, Verkasalo PK, Korhonen MJ, Suominen AL, Hirvonen M-R, Viluksela MK, Nevalainen A. Odour annoyance and physical symptoms among residents living near waste treatment centres. Environ Res 2011; 111(1)164–170
38. Eversole LR, Stone CE, Matheson D, Kaplan H. Psychometric profiles and facial pain. Oral Surg Oral Med Oral Pathol 1985; 60(3)269–74
39. Catalano R, Serxner S. Time series designs of potential interest to epidemiologists. Am J Epidemiol 1987; 126(4)724–31
40. Zeger SL, Irizarry R, Peng RD. On time series analysis of public health and biomedical data. Annu Rev Public Health 2006; 2757–79
41. Box G, Jenkins G, Reinsel G. Time Series Analysis: Forecasting and Control 2008. 4th edHoboken, NJWiley
42. Chang I, Tiao GC, Chen C. Estimation of time series parameters in the presence of outliers. Technometrics 1988; 30(2)193–204
43. Bell WR, Hillmer SC. Modeling time series with calendar variation. JASA 1983; 78(383)526–534
44. Kroll KA, Cochran ES, Murray KE. Poroelastic properties of the Arbuckle Group in Oklahoma derived from well fluid level response to the 3 September 2016 Mw 5.8 Pawnee and 7 November 2016 Mw 5.0 Cushing earthquakes. Seismol Res Lett 2017; 88(4)1–8
46. Drummond V, Grubert E. Fault lines: Seismicity and the fracturing of energy narratives in Oklahoma. Energy Res Soc Sci 2017; 31128–136
48. Fothergill A, Peek LA. Poverty and disasters in the United States: a review of recent sociological findings. Nat Hazards 2004; 32(1)89–110
49. Amante DJ, Hogan TP, Pagoto SL, English TM, Lapane KL. Access to care and use of the internet to search for health information: results from the US National Health Interview Survey. J Med Internet Res 2015; 17(4)e106
50. Pitman RK, Rasmusson AM, Koenen KC, Shin LM, Orr SP, Gilbertson MW, Milad MR, Liberzon I. Biological studies of posttraumatic stress disorder. Nature Rev Neurosci 2012; 13(11)769
51. Shin LM, Liberzon I. The neurocircuitry of fear, stress, and anxiety disorders. Neuropsychopharmacology 2010; 35(1)169–91
52. Chrousos GP. Stressors, stress, and neuroendocrine integration of the adaptive response: The 1997 Hans Selye Memorial Lecture. Ann NY Acad Sci 1998; 851(1)311–335
53. Katz R, Wykes T. The psychological difference between temporally predictable and unpredictable stressful events: Evidence for information control theories. J Pers Soc Psychol 1985; 48(3)781–790
54. Goenjian AK, Steinberg AM, Najarian LM, Fairbanks LA, Tashjian M, Pynoos RS. Prospective study of posttraumatic stress, anxiety, and depressive reactions after earthquake and political violence. Am J Psychiatry 2000; 157(6)911–916
55. Galea S, Nandi A, Vlahov D. The epidemiology of post-traumatic stress disorder after disasters. Epidemiol Rev 2005; 2778–91
56. Zhang Z, Wang W, Shi Z, Wang L, Zhang J. Mental Health Problems among the Survivors in the Hard-Hit Areas of the Yushu Earthquake. PLoS ONE 2012; 7(10)e46449
57. Xie Z, Xu J, Wu Z. Mental health problems among survivors in hard-hit areas of the 5.12 Wenchuan and 4.20 Lushan earthquakes. JMH 2017; 26(1)43–49
58. Carr VJ, Lewin TJ, Webster RA, Kenardy JA, Hazell PL, Carter GL. Psychosocial sequelae of the 1989 Newcastle earthquake: II. Exposure and morbidity profiles during the first 2 years post-disaster. Psychol Med 1997; 27(1)167–78
59. Livanou M, Kasvikis Y, Basoglu M, Mytskidou P, Sotiropoulou V, Spanea E, Mitsopoulou T, Voutsa N. Earthquake-related psychological distress and associated factors 4 years after the Parnitha earthquake in Greece. Eur Psychiatry 2005; 20(2)137–44
60. Cheung R, Wetherell D, Whitaker S. Induced earthquakes and housing markets: evidence from Oklahoma. Reg Sci Urban Econ 2018; 69153–166
61. Metz NE, Roach T, Williams JA. The costs of induced seismicity: a hedonic analysis. Economics Letters 2017; 16086–90
63. Leykin Y, Munoz RF, Contreras O. Are consumers of Internet health information “cyberchondriacs”? Characteristics of 24,965 users of a depression screening site. Depress Anxiety 2012; 29(1)71–7
65. Karsten J, Hartman CA, Smit JH, Zitman FG, Beekman AT, Cuijpers P, van der Does AW, Ormel J, Nolen WA, Penninx BW. Psychiatric history and subthreshold symptoms as predictors of the occurrence of depressive or anxiety disorder within 2 years. Br J Psychiatry 2011; 198(3)206–212
66. Mojtabai R, Jorm AF. Trends in psychological distress, depressive episodes and mental health treatment-seeking in the United States: 2001–2012. J Affect Disord 2015; 174556–61
67. Weinberger AH, Gbedemah M, Martinez AM, Nash D, Galea S, Goodwin RD. Trends in depression prevalence in the USA from 2005 to 2015: widening disparities in vulnerable groups. Psychol Med 2017. 1–10
68. Jacobs W, Amuta AO, Jeon KC, Alvares C. Health information seeking in the digital age: an analysis of health information seeking behavior among US adults. Cogent Social Sciences 2017; 3(1)1302785
69. Smid GE, van der Velden PG, Lensvelt-Mulders GJLM, Knipscheer JW, Gersons BPR, Kleber RJ. Stress sensitization following a disaster: a prospective study. Psychol Med 2011; 42(8)1675–1686
71. Goldman-Mellor S. JY, Kwan K., Rutledge J. Syndromic surveillance of mental and substance use disorders: a validation study using emergency department chief complaints. Psych Serv 2017; 691–6
72. Pollyea RM, Mohammadi N, Taylor JE, Chapman MC. Geospatial analysis of Oklahoma (USA) earthquakes (2011–2016): quantifying the limits of regional-scale earthquake mitigation measures. Geology 2018; 46(3)215–218