Increased motor vehicle crashes following induced earthquakes in Oklahoma, USA.

Anxiety-inducing life events increase the risk of motor vehicle crashes. We test the hypothesis that earthquakes, known to increase anxiety in the population, also increase the incidence of motor vehicle crashes. Our study took place in Oklahoma, USA where wastewater injection resulted in increased induced seismicity between 2010 and 2016. We identified dates of earthquakes ≥ magnitude 4 (a level felt by most people) with data from the U.S. Geologic Survey. The Oklahoma Highway Safety Office provided county-level monthly vehicle crash counts. We defined high, medium, and low earthquake exposure counties based on the location of earthquake epicenters. Using time-series analyses, we evaluated the association between monthly counts of ≥magnitude 4 earthquakes and motor vehicle crashes by exposure group. Earthquakes ≥ magnitude 4 took place in 38 of 84 study months, and a monthly average of 5813 (SD = 384) crashes occurred between 2010 and 2016. In high-exposure counties, we observed an additional 39.2 motor vehicle crashes per each additional ≥ magnitude 4 earthquake in the prior month (SE = 11.5). We found no association between the timing of ≥magnitude 4 earthquakes and motor vehicle crashes in the medium or low exposure counties. With a binary earthquake exposure variable, we found a 4.6% (SE = 1.4%) increase in motor vehicle crashes in the high exposure counties in the month following 1 or more ≥magnitude 4 earthquakes. Consistent with our hypothesis, there was no association between earthquakes of magnitude ≤ 2.5 and motor vehicle crashes in the high-exposure counties. This novel evidence of an association between induced earthquakes in Oklahoma and motor vehicle crashes warrants future research given the high economic and social costs of such vehicle crashes.