金曜日セミナー (2019年11月8日) Dr. Jean-Paul MONTAGNER (IPGP)

Detection of prompt gravity signals for earthquakes- Speed-of-light Seismology


Jean-Paul MONTAGNER (IPGP)

Abstract:
The recent finding of prompt elastogravity signals (PEGS) before the arrival of P-waves, associated with the M9.1 2011 Tohoku earthquake (Montagner et al., Nat. Comm., 2016; Vallée et al., Science, 2017) and a few earthquakes of magnitude larger than 8.5(Vallée and Juhel, JGR, 2019) opens the new field of speed-of-light seismology. The systematic detection of PEGS on real-time might help saving a few seconds before the arrival of destructive seismic waves and to obtain an accurate determination of the magnitude of the earthquake at the end of rupture. So the potential application to earthquake early warning is obvious. However, the use of classical broadband seismometers for detecting PEGS has severe limitations for detecting earthquakes of magnitude smaller than 8.5: first of all, the background seismic noise and second of all,  the partial cancellation of the gravitational perturbation by the inertial induced acceleration recorded by
seismometers (Heaton, Nature Comm., 2017).
Two different approaches can be explored for detecting PEGS for earthquakes of magnitude smaller than 8.5. Either, by using a dense array of broadband seismometers  (more than 100 receivers) or by designing completely new instruments such as gravity strainmeters. These new detectors must be able to measure the difference in gravity acceleration between two masses, making this instrument isolated from the seismic noise. A sensitivity of 10^-15 Hz^-1/2 at 0.1 Hz is required for detecting earthquakes of M>7 (Juhel et al., JGR, 2019) and the technology developed by the gravitational wave physicists can be used for reaching such a sensitivity.