Detecting earthquakes at the speed of light the

Detecting earthquakes « at the speed of light » the E-GRAAL / PEGASEWS project Matteo Barsuglia for the E-GRAAL/PEGASEWS team 1

History of the project at APC Mission of a « exploratory project » : Explore synergies between Geophysics and GW detectors • How geophysics experience and instrumentation can contribute to GW science? GEO GW • How GW experience and instrumentaiton can contribute to geosciences and to geophysical applications? GW GEO • collaboration APC, IPGP, U Nice (initially Caltech), INFN + U Florida, U Tokyo 2

Goal • Can we detect the gravity perturbation due to an earthquake before the arrival of the seismic waves? • Can we use the gravity perturbation to improve the current earthquake early-warning systems ? • Can we use the gravity perturbation to improve our knowledge of earthquakes? « speed-of-light seismology » 3

Early-warning systems 4

Gravity-based early warning system 5

Gravity-based early warning system • Increase of available time for warning • Reduction of the blind zone • Quicker estimation of the magnitude 6

Is it useful? Is it feasible? Working program and a few results • Computation/simulation of gravity signals due to the fault rupture • Transient gravity perturbations induced by earthquake rupture, Harms J. et al, Geophys. J. Int. 201, 1416 (2015) • Normal mode simulation of prompt elastogravity signals induced by an earthquake rupture, Juhel et al. , Geophys. J. Int. (2019) 216, 935– 947 • Search of gravity signals in the existing seismometer’s data • Observation and modeling of the elasto-gravity signal preceeding the direct seismic waves, Vallée et al. , Science 358, 1164– 1168 (2017) • Prompt gravity signal induced by the 2011 Tohoku-Oki earthquake, J. -P. Montagner et al. , Nature Communications 7, 133349 (2016) • Feasibility of a gravity-based detector • Impact of infrasound atmospheric noise on gravity detectors used for astrophysical and geophysical applications, Donatella Fiorucci, Jan Harms, Matteo Barsuglia, Irene Fiori, and Federico Paoletti, Phys. Rev. D 97, 062003 (2018) • Design and noise analysis of a prompt earthquake gravity signal detector, in preparation • Study of the detection pipeline and implementation strategy • Ph. D thesis of K. Juhel (tutors: J. -P. Montagner and M. Barsuglia) • Earthquake early warning using future generation gravity strainmeters, K. Juhel et al. JGR, solid Earth, 2018 7

A gravity signal from the Tohoku 2011 earthquake: “First act” 8

Detection of the gravity signal from the Tohoku earthquake: second act Published in Science, 1/12/2017 9

Results • Stronger signal • More accurate modelling • Assessment of the magnitude 10

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Tohoku analysis: lessons learned • Seismometers • Can detect gravity signals for M=8 -9 in ~ 100 of seconds • Signals limited by seismic noise • Important role of the gravity induced inertial acceleration in the modeling • For Tohoku the gravity signal would have given the magnitude in ~ 3 minutes • To detect M<9 in 5 -10 seconds new instruments are necessary strainmeters with seismically isolated test masses 12

Strainmeters with seismically isolated test masses 1014 First proposed by Ando et al. TOBA Prototypes in Japan (TOBA) and TORPEDO (Australia) 13

Sensitivity of strainmeters with seismically isolated test masses Earthquake early warning using future generation gravity strainmeters, K. Juhel et al. JGR, solid Earth, 2018 14

Earthquake detection with a torsion bar detector Earthquake early warning using future generation gravity strainmeters, K. Juhel et al. JGR, solid Earth, 2018 15

Earthquake detection with a torsion bar detector Earthquake early warning using future generation gravity strainmeters, K. Juhel et al. JGR, solid Earth, 2018 16

Earthquake detection with a network of 3 torsion bar detectors Earthquake early warning using future generation gravity strainmeters, K. Juhel et al. JGR, solid Earth, 2018 17

Estimation of the magnitude with a network of 3 torsion bar detectors 18

Detector design 19

Summary • Exploratory projects: synergies between GW and geophysics • Gravity signals prior to seismic waves • Detected recently for the first time (as the GW!) • first detectable messengers of earthquake occurrence • New instruments are necessary: seismometers limited by seismic (inertial effects) • Strainmeters with isolated seismic masses with h~ 10 -15 Hz/sqrt(Hz) @ 100 m. Hz • Possibility to detect M>7 in 10 sec at 100 km • Use of technologies developed in the context of GW detection • Interesting synergies with GW (Einstein Telescope, LISA, detection of Newtonian noise) • PEGASEWS: conceptual design and data-analysis 20