Calculating California's Tsunami Risk
Andreas Hoechner from the German Research Centre for Geosciences (GFZ) led the research, which looked at data from the 2011 earthquake in Japan. His team showed that a close look at the GPS data would have allowed geoscientists to get the word out three minutes after the shaking on the sea floor started - maybe less.
The scientists used data from the Japanese GPS Earth Observation Network (GEONET) recorded between March 10 and March 12, 2011, just before and after the 9.0-magnitude temblor. There are 1,200 GEONET stations in Japan, but to simplify the calculations they only used data from 50 that were in the area where the tsunami hit.
This scheme works because most tsunamis happen in subduction zones, where the crust is getting pushed down into the mantle. These zones are common in the Pacific, and it's why Japan and California are so quake-prone. That sea floor movement also affects coastal regions, and GPS can measure the small changes in say, the height of hills in the San Francisco Bay area.