Science 358, 1164–1168 (2017)

In this era of gravitational-wave detection, our imagination is routinely captured by astronomical events of colossal magnitude. But one need not travel far to encounter phenomena capable of shaking the gravitational field — it's enough to consider what happened in Japan seven years ago. Using data from the 2011 Tohoku earthquake, Martin Vallée and co-workers have demonstrated that perturbations to the gravitational field generated by elastogravity waves leave a detectable signal in distant seismometers.

Acting as additional sources of elastic deformation, these gravitational disturbances are difficult to isolate, as seismographs are attached to the ground, and thus detect both gravity's pull and the acceleration of the ground. A careful computation allowed the authors to derive the difference between these two quantities, obtaining the actual detected signal, and revealing that it contains information about both the earthquake and its magnitude. Travelling at the speed of light, the gravitational perturbation might allow a much earlier detection of the strength of larger seismic events, which is notoriously difficult to establish near the epicentre.