Adv. Grant Whisper

"Application of ambient noise analysis in at regional and global scales"

Michel Campillo

ISTerre Université Joseph Fourier and CNRS,38041 Grenoble, France

Imagerie sismique industrielle: Valhall 2400 capteurs sources acves: canons à air avec la permission de J. Virieux (projet Seiscope) Large networks – connuous recordings

Huge data sets consisng for a large part of ‘ambient noise’ Availability: ORFEUS, IRIS RESIF,… Computers for massive processing

A long history of noise studies…. including aempts of using noise for retrieving Earth properes (Aki 1957+, Toksoz, Claerbout,..)

Global ‘noise’ sources in the band (extended ≈2-50s) seismological observaons oceanographic modeling

Strong contribution from oceanic waves

Example of a global comparison (secondary microseism- Miche/Longuet-Higgins mechanism)

Longer periods: infragravity waves, e.g. Fukao et al. 2010 Hillers et al., 2012

+ high frequency: industrial noise, local characteriscs + : direct paths and coda (scaered waves)

Long range correlaons

()*&#"()*&#"' ' !"#"$%"&!"#"$%"&'' Source in A ⇒ the signal recorded in B characterizes the propagation between A and B. ! ! !!!!!!!!!!!!""!! ##!! ➡ Green function between A and B: GAB

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!"#"$%"&!"#"$%"&' ' !"#"$%"&!"#"$%"&'' GAB can be reconstructed by the correlation (CAB) of ‘noise’ from randomly distributed sources !!!!!!!!!!!!""!! ##!! or « diffuse » (equipartitioned) fields recorded at A and B

A way to provide new data with control on source location and origin time

Experimentally verified with seismological data: Coda waves: Campillo and Paul, 2003,….. Ambient noise: Shapiro and Campillo, 2004,…… Mathemacal basis

Arbitrary medium: an integral representaon wrien in the

Volume term Surface term FT of G(-t)

Absorpon coefficient

FT of G(t) 2 1 Surface term: κ =0 (no attenuation)

and we obtain a widely used integral relation:

èDerode et al., 2003: Analogy with Time reversal mirrors èWapenaar 2004

For surface waves: distant sources of noise at the surface of the sphere (2D problem)

Surfave wave reconstruction within a large array (Boué et al. 2014)

Noise correlaon=GF(t)-GF(-t) (Rayleigh waves) Several hundreds of applicaons in the last 10 years!

An issue for tomography:

In practice, the noise sources are not evenly distributed and the field is not made fully isotropic by scattering.

We can study the effect of non isotropy of the intensity of the field incident on the receivers.

It results in a bias on the measurements of direct path travel times.

Correlaon of direct waves: Bias in the travel time

Increasing anisotropy of the source intensity B

Azimuthal distribuon of source intensity B(θ) = 1+ B2 cos(2θ)

Travel me 1 d 2B(θ) error wrt the δt = observed Green 2tω 2B(0) dθ 2 funcon 0 θ =0

valid with t (travel me) > T (period)

From Froment, Campillo, Roux, Gouédard, Verdel and Weaver 2011. Multiple scattering and equipartition

Equipartion principle for a completely randomized (diffuse) wave-field: in average, all the modes of propagation are excited to equal energy.

Implication for diffuse elastic waves (Weaver, 1982, Ryzhik et al., 1996): P to S energy ratio stabilizes at a value independant of the details of scattering.

Observations (Hennino et al., 2001)

Numerical simulation (Margerin et al.2000)

RTE Monte Carlo Diffusion equation An argument independant of the representation theorems Multiple scattering and equipartition: the simplest case (finite body)

equipartion

correlation

Compare with:

1 derivative 2 causality

è Long range correlaon in seismic coda= Green funcon (Campillo and Paul, Science 2003) In presence of scaering: Correlaon of coda waves -isotropy provided by mulple scaering Increasing anisotropy of the source intensity B

B(θ) = 1+ B2 cos(2θ) (a)

(b) No bias in the correlation of coda waves!

Noise records contain direct and scaered waves:

è the biases of direct wave travel mes are generally small enough for imaging purpose è Importance of processing strategies From Froment, Campillo, Roux, Gouédard, Verdel and Weaver 2011. Fault zone structures

-fault segments, complexity (rupture speed) -bi-material interfaces: preferenal direcon of rupture propagaon -amplificaon effects

-lack of resoluon for shear wave in the first kilometers for tradional tomography

From Zigone, Ben-Zion, Campillo and Roux, 2014 Surface wave tomography with noise correlaon 9-component correlaons

Rayleigh wave

8 measurements

From Zigone, Ben-Zion, Campillo and Roux, 2014 Group velocity maps at different periods

From Zigone, Ben-Zion, Campillo and Roux, 2014 3D shear velocity

-Damaged fault zone -Flower-like paerns -Diffuse seismicity associated with low- velocity (damaged) area between SAF and SJFZ

From Zigone, Ben-Zion, Campillo and Roux, 2014 Surface wave tomography è body waves (deep reflecons)

Comparison of high frequency (1Hz) 1-year noise correlaon with data

POLENET/LAPNET array in Finland Z-Z noise correlaons Z comp. actual earthquake

From Poli, Pedersen , Campillo and LAPNET WG, 2012 Comparison with synthec Green funcons

CZZ (data) GFZZ (theory) CRR (data) GFRR (theory)

From Poli, Pedersen , Campillo and LAPNET WG, 2012 GLOBAL TELESEISMIC CORRELATIONS (periods 25-100s vertical components)

Noise correlaons PREM synthecs

From Boué, Poli, Campillo, Pedersen , Briand, and Roux, 2013 Numerous phases can be idenfied

Vercally incident S waves on the vercal component??

From Boué, Poli, Campillo, Pedersen , Briand, and Roux, 2013 Long periods (25-100s): dominance of coherent earthquake signals Processing: separang EQ and their long lasng reverberaons from ambient noise

Low daily coherence High daily coherence (EQs)

AXISEM synthecs

High amplitude spurious

From Boué, Poli, Campillo, Pedersen , Briand, and Roux, 2013 Long periods (25-100s) Spurious arrivals and simulaon

CC (ambient noise) CC(EQ days) PREM synth (no scaering!) Synth EQ CC

From Boué, Poli, Campillo, Pedersen , Briand, and Roux, 2013 Short periods 5-10 s è stronger scaering

P and PcP 12

11.5 Japan to Finland 11 (P-PcP) 10.5

10

9.5 −9.5 time (min) −10

−10.5 Finland to Japan −11 (P-PcP)

−11.5

−12 58 60 62 64 66 68 θ (°)

Standard pre-processing (Shapiro and Campillo, 2004; Sabra et al. 2005) eliminates the contaminaon by EQ ballisc waves.

èEarth’s mantle transion zone disconnuies from ambient seismic noise ( phase transion è (P,T))

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      

                               

           In agreement with receiver funcons (Alinaghi et al. 2003)  From Poli, Campillo, Pedersen and LAPNET WG, 2012    Going deeper:

invesgang the core with records of the ambient noise Core phases PcP and PdP

D’’: - different hypotheses for the nature of the layer - PdP difficult to observe - lack of earthquake data

From Poli, Thomas, Campillo and Pedersen 2014 Advantage of noise vs earthquake records: -surface to surface -impulsive wavelet -double beam forming Stacked vespagrams for:

Earthquakes Noise

0.5 0.5 B) A)

0 0 P −0.5 P −0.5

−1 −1

−1.5 −1.5

−2 −2 PcP Slowness to P wave [s/deg] Slowness to P wave [s/deg] PdP −2.5 PdP PcP −2.5

−3 −3 −10 0 10 20 30 40 50 −10 0 10 20 30 40 50 Time to P wave [s] Time to P [s]

A 5% increase of velocity at 2530 km depth…. From Poli, Thomas, Campillo and Pedersen 2014 Tradional Seismic velocity tomography

Local seismic velocity (V) = D/(travel me)

Seismic velocity is a proxy for sffness (high velocies) and compliance (low velocies) of rocks Tradional Seismic velocity New Seismic suscepbility tomography tomography

Dynamic stress (Δσ)

ΔV Local seismic velocity (V) = D/(travel me) Nonlinear ΔV elascity, slow dynamics

Seismic velocity is a proxy velocity for sffness (high velocies) and compliance me (low velocies) of rocks

Seismic suscepbility (ΔV/Δσ) is sensive to fractured, damaged or pressurized rocks Noise based seismic velocity temporal changes

Because seismic noise is connuous in me, it is possible to reconstruct repeang virtual seismic sources and perform connuous monitoring of seismic velocies.

ΔV Monitoring seismic velocies before and aer the M9 Tohoku-oki earthquake

600 seismic staons (Hi-net)

For each seismic staon, we obtain a connuous seismic velocity change me series

ΔV

Tohoku-oki earthquake

From Brenguier, Campillo, Takeda, Aoki, Shapiro, Briand, Emoto and Miyake 2014 Seismic suscepbility tomography of Japan

We use seismic waves caused by the 2011 Tohoku-oki earthquake as dynamic stress perturbaons

Ozawa et al. 2011

Furumura et al. 2011 Tomography of seismic suscepbility (velocity change/dynamic stress)

¥ Delineates volcanic regions characterized by high volcanic fluid pressure (low effecve pressure) and sedimentary basins

¥ Maximizes below Mt Fuji volcano where a M6 earthquake occurred 4 days aer the Tohoku-oki earthquake

¥ Minimizes in sff old plutonic regions

Feasibility of imaging new parameters relevant for the dynamics of erupons and earthquakes From Brenguier, Campillo, Takeda, Aoki, Shapiro, Briand, Emoto and Miyake 2014 Conclusions

Ambient noise provides reliable travel me measurements for surface and deep waves, including the core phases

A careful consideraon of reconstrucon condions is required for body waves

Coverage for all staon-to-staon paths (different from EQ-to staon!) è new data

Dense arrays allow for beam-forming

Wide possibilies of improvement of the processing

Time dependent elasc properes: monitoring of the deformaon and mechanical condions at depth?