We explore the use of real-time high-rate GPS displacement data for earthquake early warning using 1 Hz displacement waveforms from the April 4, 2010, Mw 7.2 El Mayor-Cucapah earthquake. We compare these data to those provided by the broadband velocity and accelerometer instrumentation of the Southern California Seismic Network. The unique information provided by the GPS-based displacement timeseries is the permanent/static displacement. Using a simple algorithm that can be applied in real-time, we extract the static offset shortly after the S-wave arrival, around the time of the observed peak shaking at the same site, and before shaking at more distant locations. These data can be used, as they become available, to provide a robust estimate of the earthquake magnitude, which ranges from 6.8 to 7.0 in this case. We therefore conclude that real-time high-rate GPS can provide a useful and independent assessment of earthquake magnitude for the purpose of earthquake early warning and real-time earthquake information systems in general including tsunami warning systems.