The 2011 Tohoku earthquake toppled buildings, fractured roads, and set off a tsunami—a disaster that cost nearly 16,000 lives and roughly $220 billion in damage. But the larger story of the quake lies far below the Earth’s surface, in the slow movement of tectonic plates that rub shoulders off the coast of Japan.
As the Pacific Plate subducts under the Japanese islands, strain accumulates at the plate’s edge, and this pent-up energy gets released through earthquakes. Scientists can look at the subduction rate to analyze potential seismicity, and recent studies suggest that subduction may accelerate after a quake. To test this hypothesis, Tomita et al. used a new technique called GPS/A (which combines GPS and marine acoustic ranging) to look at seafloor crustal deformation.
The team observed that after the earthquake, the displacement rate accelerated. They suggested a number of geophysical mechanisms that might be to blame. Possibilities include simple acceleration in plate subduction, or after slip, the slow creep that occurs along a fault after an earthquake. Another contributor could be viscoelastic relaxation, in which materials gradually release the sudden stress change excited by the quake and stress decreases even though subduction rates stay the same.
The researchers suggest that this viscoelastic response may be the culprit behind the apparent high displacement rate following the 2011 Tohoku quake. They also conclude that there was no significant acceleration in the subduction rate itself, at least not during the study period, between September 2012 and 2014. These insights—and the success of the new GPS/A technique—contribute to the growing scientific knowledge of these ongoing seismic hazards. (Geophysical Research Letters, doi:10.1002/2015GL065746, 2015)
—Lily Strelich, Freelance Writer
Citation: Strelich, L. (2016), Plate displacement rate offers insight into 2011 Tohoku quake, Eos, 97, doi:10.1029/2016EO044947. Published on 4 February 2016.