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)

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)

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

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

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

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

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

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

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)

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)

Dynamic gravity changes induced by earthquakes: theory

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

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%

Verification: comparison to numerical simulation We implemented finite kinematic sources and computation of gravity field in the 3D spectral element program SPECFEM3D

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

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)

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

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

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

Signal to noise ratio

Shortest period resolved

Optimal matched filter detection (with prewhitening) Preliminary

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