The Web-enabled Awareness Research Network (WARN) project

The Web-enabled Awareness Research Network (WARN) implements the data acquisition, event detection and correlation aspects of an integrated geohazard alert system. The intent of the project is to lead to the delivery of early warning to urban areas, coastal communities and key infrastructure operators. Figure 1 provides the overview of a generic alert system top-level architecture and situates WARN in this context. WARN relies on the existence of sensors installed both underwater and on land. WARN also relies on data acquisition performed by Ocean Networks Canada's Oceans 2.0 data management system. Event detection/correlation are the key parts of WARN. The Ocean Networks Canada (ONC) infrastructure is host to the various sensors required to perform the detections. The sensors include, but are not limited to, accelerometers (installed off- and on-shore), coastal radars to detect incoming near-field tsunami waves, and bottom pressure recorders to complete the network. This infrastructure can be expanded geographically both on land and underwater. Earthquake detection is performed by detecting the initial P-wave that is disseminated by the earthquake and which arrives before the destructive S-waves. By correlating the P-wave detection at 3 or more accelerometers, the epicentre location can be estimated. The magnitude of the earthquake is also estimated. Both the epicentre and magnitude solutions undergo automatic quality checks to help prevent false alarms. Tsunami detection is performed by analyzing the water pressure readings from highly sensitive Bottom Pressure Recorders (BPRs). The residual and tidal pressure is removed from the data and then it is analyzed by various software filters to detect changes in pressure within a range of frequencies that might be attributed to a tsunami wave. Another filter helps to avoid false alarms caused by seismic waves that cause the sensors to vibrate. An event is declared only if a tsunami is detected on 3 BPRs. Earthquake and tsunami events are reported to those users who have subscribed to these events. Notification methods include e-mail, push notification to a special ONC WARNAlert iPhone app, and push notification to the client's computer via HTTP. This paper describes the earthquake and tsunami detection algorithms used by Ocean Networks Canada, explains how event notifications are sent out and how they are interpreted by the client software, and gives examples of actual detections.