To assist users of earthquake early warning, we have developed a UserDisplay, which visualizes alert information from ShakeAlert (Böse et al., 2012). The UserDisplay runs on a user’s computer, receives XML messages from ShakeAlert and displays their content in a simple and easily understandable way. The application is written in Java and is thus platform-independent. The UserDisplay has the following features:
- calculation & display of remaining warning time for a given user
- calculation & display of expected MMI intensity at this site (the user can specify a Vs30 value for site characterization if desired)
- description of expected MMI intensity at user site (e.g., “Moderate Shaking expected”)
- display of estimated magnitude
- display of the probability of correct alarm
- calculation & display of P/S-wavefronts
- display of user site
- display of a 30-km radius blind-zone around the user for education purpose
- siren and audio announcement
The UserDisplay pops up automatically whenever an alert message is received (Figure 1). The user can set thresholds for intensities, magnitudes and probability values to reduce the number of reports (Böse et al., 2011). Multiple map layers showing, e.g., fault lines or infrastucture can be added. XML messages received by the UserDisplay are stored locally in a history folder and can be replayed. A log-file summarizes the key information for each received report. Network Time Protocol (NTP) is used for time synchronization. Further features include password-protection, encryted communication, and the capability to receive and display heartbeats from the ShakeAlert system to ensure robust communication. The UserDisplay is currently tested by a group of individuals, emergency responders, and companies throughout California.
Simulated performance of UserDisplay during 2008 M5.4 Chino Hills earthquake. Blue house marks user location; yellow and red circles show P- and S-wavefronts.
Simulated performance of UserDisplay during 1933 M6.4 Long Beach earthquake. Blue house marks user location; yellow and red circles show P- and S-wavefronts.
Real-time performance of UserDisplay during 2012 M3.5 Aromas earthquake. Epicenter is close to 1989 M6.9 Loma Prieta earthquake. Blue house marks user location; yellow and red circles show P- and S-wavefronts.
Click here to view the latest ShakeAlert: UserDisplay – Operations Guide V2.6.0.