Earthquake Early Warning: Gravity changes beat seismic signals
Posted on November 30, 2017 by Temblor
By Jean Paul Ampuero, Caltech Seismological Laboratory; Université Côte d’Azur, IRD, Géoazur
This story starts a few years ago, when astrophysicists in search for gravitational waves from the distant universe crossed paths with seismologists starving for new clues about how earthquakes work beneath our feet. Someone’s noise soon became someone else’s signal, indeed a very unique signal: the earliest harbinger of earthquake shaking that nature and physics have to offer.
Earthquakes move mass around, in enormous quantities. This is obvious to anyone who has been mesmerized by the view of fault offsets of several meters left at the Earth’s surface after a large earthquake. But mass is also redistributed temporarily by seismic waves, even before the earthquake is over. For example, P waves compress and dilate the rock they travel through, perturbing the rock’s density momentarily. These static and dynamic mass perturbations are natural sources of gravity changes … and gravity changes travel remotely at the speed of light!
http://temblor.net/earthquake-insights/earthquake-early-warning-gravity-changes-beat-seismic-signals-5743/
