EXAMINATION OF USAGE RATES FOR THE MULTI-HAZARDS SAN DIEGO COUNTY EMERGENCY APP TO IMPROVE EARTHQUAKE EARLY WARNING

One of the seven global targets of the Sendai Framework for Disaster Risk Reduction 2015-2030 is to ‘substantially increase the availability of and access to multi-hazard early warning systems and disaster risk information and assessments to people by 2030’. Increased availability and access for early warning requires systems to be tailored to user specific needs, have a broad scope of communication channels, and dissemination of critical and timely hazard information to potentially affected communities, such as through smartphone applications. The efficacy of these systems, including earthquake early warning, requires integrating ideas from a range of stakeholders, including governments, academics, and industry. A recent study identified a key problem in that a smartphone application specifically designed for earthquake early warning experienced high attrition rates, losing 38% of users within a day of install, 69% within a month, and 95% within a year. In this study, we investigated the increases and decreases in usage over time of the multi-hazard early warning smartphone application SD Emergency, developed by the San Diego County Office of Emergency Services with Peraton, the IT provider for San Diego County. As the only multi-hazard smartphone application in the United States that delivers ShakeAlert-powered earthquake early warning alerts, we hypothesized the SD Emergency app would have lower attrition rates that would increase the efficacy of alerting. By comparing install and uninstall data for Android and iOS, we found that the SD Emergency app maintained a retention rate above 50% over the past 5 years. This was accomplished by fairly stable uninstall rates which we interpret as due to regular alerting (40 alerts per year). In addition, there were frequent spikes in install rates during both natural (e.g., earthquake, fire, weather) and anthropogenic (e.g., boil water notice, oil spill) hazard events. We found that the largest install increases mainly occurred associated with wildfires, which is the greatest natural hazard to regularly affect San Diego County. These findings indicate app providers should favor multi-hazard alerting strategies to improve the efficacy of alerting and maintain critical communication pathways.