Tsunamis can’t be stopped, but if you can warn people that one is coming you can save a lot of lives, even if it’s only an extra few minutes.
Currently, tsunami alerts are generated from seismic data, but even the fastest response based on the magnitude, location, and depth of the earthquake can be up to five minutes or more — too slow for the immediate at-risk vicinity. Buoy’s developed to measure sea pressure changes from tsunami waves can communicate the speed and size of a tsunami as it travels across an ocean basin and provide advanced warnings for those in its path, but again not for those who got hit by the wave before it hit the buoy.
Which is why using the global positioning system (GPS) may be the best tool for getting the information about a tsunami out the fastest. How exactly? By measuring the ground deformation to the neighboring shoreline caused by a large underwater earthquake. Those measurements can be used to figure out how much the seafloor has moved, and once you know that, it’s possible to calculate how big the tsunami will be and where it’s going, and do so in less than three minutes.
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.
The next step is to see how the system works in a real quake. Several GPS stations were installed in places like Indonesia after the 2004 earthquake and they will be part of the warning system the next time it happens.
The results are in the May 17 issue of the journal Natural Hazards and Earth System Sciences.
Image: Wikimedia Commons / U.S. Navy photo by Mass Communication Specialist 1st Class Matthew M. Bradley