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Can we do Earthquake Early Warning with high-precision gravity strain meters?

Can we do Earthquake Early Warning with high-precision gravity strain meters?. Pablo Ampuero (Caltech Seismolab )

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Can we do Earthquake Early Warning with high-precision gravity strain meters?

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  1. Can we do Earthquake Early Warning with high-precision gravity strain meters? Pablo Ampuero (Caltech Seismolab) Collaborators: J. Harms (INFN, Italy), M. Barsugliaand E. Chassande-Mottin (CNRS France), J.-P. Montagner (IPG Paris), S. N. Somala (Caltech), B. F. Whiting (U. Florida)

  2. A multi-disciplinary, international collaboration: J. Harms (INFN, Italy) M. Barsuglia(CNRS France) E. Chassande-Mottin (CNRS) J.-P. Montagner (IPG Paris) S. N. Somala (Caltech) B. F. Whiting (U. Florida)

  3. Overview • Earthquake Early Warning Systems: current principles and limitations • Gravity perturbations induced by earthquakes • Gravitational Wave detectors: current and future capabilities • Potential capabilities of an EEWS based on gravity sensors Mainly based on: Harms, Ampuero, Barsuglia, Chassande-Mottin, Montagner, Somalaand Whiting(2014), Prompt earthquake detection with high-precision gravity strain meters, manuscript submitted to J. Geophys. Res., available at http://web.gps.caltech.edu/~ampuero/publications.html

  4. Why do we need Early Warning ? Expected ground shaking in the Los Angeles basin, if we had an earthquake of Probabilities of events that would cause at least strong shaking(MMI≥VI) in the Los Angeles basin magnitude M6.5 magnitude M7.0 Los Angeles Böse et al., in prep.

  5. P-Wave S-Wave S-P time What is Earthquake Early Warning ? ability to provide a few to tens of seconds of warning before damaging seismic waves arrive San Andreas Fault

  6. Where is Early Warning used ? Operational systems Systems under development Japan Taiwan Romania Mexico Turkey Italy California Greece India Earthquake Early Warning Demonstration System

  7. How can we use Early Warning ? • Public Alert • warn people to take protective measures (drop-cover-hold on) • move people to safe positions • prepare physically and psychologically for the impending shaking • Trigger Automatic Responses • slow down/stop trains • control traffic by turning signals red on bridges, freeway entrances • close valves and pipelines • stop elevators • save vital computer information • Limitations: • chance of false/wrong alerts: need to account for finite rupture size • no warning in blind zone (~30 km around epicenter)

  8. Arrays Networked to Track Sources a network of high-frequency seismic arrays that will image large earthquakes with 10-fold better resolution than current seismic networks Multiple small-aperture arrays with overlapping fields of view covering a set of faults Exploit high-frequency waves (10 Hz) to achieve high resolution of rupture processes Fault ANTS - Pablo Ampuero - Caltech Seismo Lab

  9. The blind zone of an EEWS Blind zone size in California (Kuyuk and Allen, 2013) • Blind zone = region close to the earthquake epicenter where damaging waves arrive before the warning is declared • Size of the blind zone = distance travelled by S waves at the time the 4th seismometer detects shaking + signal processing time + communication delays • Can we use geophysical signals that travel faster than seismic waves?

  10. Static gravity changes induced by earthquakes • GRACE / GOCE satellite mission have measure gravity changes after vs before large earthquakes • Those are STATIC gravity changes • Mention Kamioka superconducting gravimeter Matsuo and Heki (2011)

  11. Dynamic gravity changes induced by earthquakes: theory Gravity perturbation (acceleration) is related to a potential that satisfies a Poisson’s equation The density perturbation induced by the seismic deformation is Assume point-source earthquake in an infinite elastic medium (ignore free surface effects): use known analytical solutions for the induced seismic displacement field

  12. Dynamic gravity changes induced by earthquakes: theory We find that the perturbation of the gravity potential is Distance Radiation pattern Double integral of seismic moment  Gravity strain acceleration:

  13. Verification: comparison to numerical simulation We implemented finite kinematic sources and computation of gravity field in the 3D spectral element program SPECFEM3D We find that errors are smaller than 5% http://geodynamics.org/cig/software/specfem3d/

  14. Verification: comparison to numerical simulation We implemented finite kinematic sources and computation of gravity field in the 3D spectral element program SPECFEM3D The signal decays as , as predicted, even for dipping faults http://geodynamics.org/cig/software/specfem3d/

  15. Earthquake spectra compared to gravity sensitivity Epicentral distance = 70 km Gravity strain acceleration: Relation to moment rate function:

  16. Gravitational wave detectors Devices designed to measure gravitational waves, minute distortions of space-time that are predicted by Einstein's theory of general relativity GW: new way to study the universe Ex: VIRGO, LIGO projects to observe GW of cosmic origin (Laser Interferometer Gravitational-Wave Observatory)

  17. Gravitational wave detectors Devices designed to measure gravitational waves, minute distortions of space-time that are predicted by Einstein's theory of general relativity Ex: TOBA TOBA concept (torsional bar antenna)

  18. Gravitational wave detectors Devices designed to measure gravitational waves, minute distortions of space-time that are predicted by Einstein's theory of general relativity Ex: TOBA TOBA concept (torsional bar antenna)

  19. Earthquake spectra compared to gravity sensitivity Epicentral distance = 70 km Gravity strain acceleration: Relation to moment rate function:

  20. Signal to noise ratio

  21. Shortest period resolved

  22. Optimal matched filter detection (with prewhitening) Preliminary

  23. Conclusions • Multidisciplinary research, from fundamental to applied, from paper-and-pen to high-performance-computing and instrument design • Next generation GW detector technology can be useful in Earth science: potential contribution to Earthquake Early Warning Systems • Advantage over other EEWS approaches: reduces the blind zone  Earthquake warning sooner and for all • To do: • develop signal detection pipeline and demonstrate its capabilities • Propose an optimal system • Theory: incorporate free surface effects, etc

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