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Earthquake detection is done using a number of accelerometers located on land and on the seafloor west of Vancouver Island. Normally they only output a characteristic amplitude value, the Japanese Meteorological Agency's (JMA) instrumental intensity, which is not used at the moment. Instead, WARN's driver software, which runs on a computer collated co-located with the accelerometer, analyzes the accelerometer data on all three axes and looks for the signature of a "P-wave", which is the initial compression wave emanated by the earthquake. This P-wave does not cause damage but travels much faster than the "S-wave" that comes later and causes the damage. If a P-wave is detected the driver outputs the time of detection of the P-wave. Then the driver analyzes the first few seconds of motion and determines the maximum displacement of the vertical component of the acceleration, which we call Pd, and the maximum period of the vertical component, which we call Tau. The Pd and Tau are then sent out by the driver computer to the Oceans 2.0 software running at the University of Victoria.
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Software in the device receiving the message (eg. client application or WARNAlert iPhone application) can further process this information. By knowing the GPS coordinates of the client the software can determine the distance to the epicenter and hence predict the arrival time of the S-waves at that location. The client software can also predict the level of shaking at the client location.
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Licencing
No licencing is required to become a subscriber of WARN events. However at the present time subscription to earthquake and tsunami events is only possible by invitation and only to those with an account to Oceans 2.0.