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

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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)

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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, Somala and 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.htmlhttp://web.gps.caltech.edu/~ampuero/publications.html

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

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

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

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1.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 How can we use Early Warning ? 2.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) 7

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ANTS - Pablo Ampuero - Caltech Seismo Lab Fault Arrays Networked to Track Sources 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 a network of high-frequency seismic arrays that will image large earthquakes with 10-fold better resolution than current seismic networks

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The blind zone of an EEWS 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 4 th seismometer detects shaking + signal processing time + communication delays Can we use geophysical signals that travel faster than seismic waves? Blind zone size in California (Kuyuk and Allen, 2013)

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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)

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Dynamic gravity changes induced by earthquakes: theory

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We find that the perturbation of the gravity potential is DistanceRadiation patternDouble integral of seismic moment Gravity strain acceleration:

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Verification: comparison to numerical simulation http://geodynamics.org/cig/software/specfem3d/ 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%

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Verification: comparison to numerical simulation http://geodynamics.org/cig/software/specfem3d/ We implemented finite kinematic sources and computation of gravity field in the 3D spectral element program SPECFEM3D

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

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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)

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

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

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

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Signal to noise ratio

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Shortest period resolved

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Optimal matched filter detection (with prewhitening) Preliminary

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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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The following figures show three modeled measures of network capability 1) Minimum magnitude threshold 2) Network detection time 3) Earthquake Location.

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