Real‐time Global Navigation Satellite Systems (GNSS) data are on their way to being well integrated into earthquake early warning (EEW) systems. The strength of GNSS data lies in the resolution of large dynamic and static displacements. Because of the limits in precision, GNSS data alone cannot resolve small ground displacements due to, for instance, P waves. Therefore, their use is currently limited to refining early warnings with more precise earthquake characteristics, such as magnitudes or ground‐motion predictions.
Here, we analyze 1‐Hz Global Positioning System (GPS) data from the 24 January 2016 7.1 Iniskin earthquake, which ruptured 125 km under Cook Inlet in Alaska, to motivate the inclusion of GNSS‐derived S‐wave measurements into the trigger algorithms of EEW systems in regions lacking dense early‐warning instrumentation networks. We derive a relationship between earthquake depth and distance to help determine whether GNSS S‐wave observations could expedite warnings to specific locations.
Because the Iniskin earthquake was deep, by the time the S wave reached the surface, the P wave had already been observed over a wide region, limiting the potential for unique contributions from GNSS data to this event. For the same earthquake occurring near the surface, however, S waves derived from GNSS data have the potential to increase the warning time. Regardless of the depth, the Iniskin earthquake is an excellent example of the utility of GNSS in rapidly assessing the magnitude, improving predictions of ground shaking, and estimating the area of impact for the earthquake.