From Tight Coupling to Flexibility: A Digital Twin Middleware Layer for the ShakeAlert System.

ShakeAlert is an earthquake early warning (EEW) system that detects significant earthquakes so quickly that alerts can reach many people before shaking arrives. The current ShakeAlert system has been developed incrementally over the past decade, following an old-fashioned system design. The system's tight coupling between physical sensors and data processing modules has made it difficult to expand new sensors, adopt novel networking technology advances, or change the system's behavior at runtime, thus hindering the system's extensibility, scalability, and reliability. To address these limitations, this paper proposes to expand the existing system design by adding a “digital twin” middleware layer as virtual representations of physical sensor stations, which provides a standardized software interface for running distributed data processing applications and conceals the hardware/software differences in physical sensors. These virtual stations are placed at the edge of the network near physical stations, acting as a middleware layer between sensors and the ShakeAlert system. By incorporating digital twins, we can leverage cutting-edge networking technologies (such as edge/fog computing) to improve scalability, accept trust-worthy sensor data from diverse sources to enhance extensibility, and move data processing functions closer to the sensor stations to reduce response time during large earthquakes when network throughput is impacted. Ultimately, this will enhance the reliability of the ShakeAlert system and help keep communities safe during earthquakes.