The European Mediterranean Seismological Centre (EMSC), one of the top global earthquake information centers, has been empirically developing a multichannel rapid information system comprising websites, a Twitter quakebot, and a smartphone app for global earthquake eyewitnesses. At the intersection between seismology, citizen science, and digital communication, its aim is twofold: to offer timely, appropriate information in regions where an earthquake is felt and to collect high numbers of eyewitnesses' direct and indirect observations about the degree of shaking being felt and possible damage incurred. This, in turn, will improve rapid situation awareness and augment data at a relatively low cost. Engagement with eyewitnesses is based on the rapid provision of tremor detection (between few tens of seconds to a couple of minutes from when the earthquake strikes) which is derived from the analysis of indirect information, i.e., digital footprints of Internet and social media searches by eyewitnesses eager to find out the cause of the tremor. This detection generally precedes detection by seismic networks. Eyewitness' behavior is comparable to real-time seismic sensors when using EMSC websites or LastQuake smartphone app. The hit times on our websites and launch times of our app closely follow seismic wave propagation. Crowdsourced data (felt reports, geo-located pictures, and open comments) is then fed back into the ongoing information product improvement and situation awareness which, in turn, attracts more eyewitnesses through a viral spread, thus creating a positive feedback loop. The use of visual communication for felt report collection, where traditional online questionnaires have been replaced by cartoons depicting different degrees of shaking and damage levels, has proven to be fast and efficient on a global scale with, on average, half of the felt reports being collected within 10 min. Following requests by Nepalese users after the devastating 2015 Gorkha, Nepal earthquake, the LastQuake app now includes timely geo-targeted safety checks to inform loved ones that one is safe and safety tips communicated using cartoons to describe behaviors to be encouraged or avoided after violent tremors. We argue that this simple and affordable system, based on standard Internet technologies and social media, can reduce anxiety by offering timely information and services to eyewitnesses and possibly contribute to immediate global seismic risk reduction by complementing well-established long-term strategies built around improving the seismic performance of the existing buildings by raising situation awareness and limiting potentially dangerous behaviors after violent ground shaking. Short abstract: The EMSC, one of the top global earthquake information centers, has been empirically developing a multichannel rapid information system comprising websites, a Twitter quakebot and a smartphone app for global earthquake eyewitnesses. At the intersection between seismology, citizen science, and digital communication, its aim is twofold: to offer timely, appropriate information in regions where an earthquake is felt and to collect high numbers of eyewitnesses' direct and indirect observations to improve rapid situation awareness. Engagement with eyewitnesses is based on the rapid provision of tremor detection (between few tens of seconds to a couple of minutes) which is derived from the analysis of indirect information, i.e., Internet and social media searches by eyewitnesses eager to find out the cause of the tremor. Eyewitness' behavior is comparable to real-time seismic sensors when using EMSC websites or LastQuake smartphone app. Crowdsourced data is then fed back into the ongoing information product improvement and situation awareness which, in turn, attracts more eyewitnesses through a viral spread. The use of visual communication for felt report collection has proven to be fast and efficient on a global scale with, on average, 50% of felt reports being collected within 10 min. The LastQuake app now includes timely geo-targeted safety checks and safety tips to describe behaviors to be encouraged or avoided after violent tremors. We argue that this simple,affordable system, based on Internet technologies and social media, can reduce anxiety by offering timely information to eyewitnesses and possibly contribute to immediate global seismic risk reduction.
