The Detection of Time-Varying Crustal Properties: Diving into the Seismic Dumpster for Treasure

Transcription

1 The Detection of Time-Varying Crustal Properties: Diving into the Seismic Dumpster for Treasure Matthew M. Haney U.S. Geological Survey, Alaska Volcano Observatory

2 Why are small changes important? Changes in the Earth usually subtle and spatially limited Seismic deployments often sparse Bulk seismic velocity varies ~1% in response to tectonic and volcanic processes Small changes invisible to tomography May be the only way to seismically detect aseismic processes Monitoring for early signs of unrest

3 Imaging the crust with seismic noise Shapiro et al. (2005) Science Brenguier et al. (2007) GRL

4 Types of change detected Co- and post-seismic changes Poupinet et al. (1984) Volcanic unrest Temperature and precipitation Aseismic processes Where are we going? Imagine... it s easy if you try

5 Doublet method in an nutshell

6 One without and one with sleeves a Δa

7 Wrapping a short cable

8 Wrapping a long cable

9 Difference ΔL Δa/a = -ΔL/L or Δv/v = -Δt/t

10 Co- and post-seismic changes Coyote Lake Eq - Poupinet et al. (1984) Parkfield Eq - Brenguier et al. (2008) L Aquila Eq - Duvet et al. (2010) Tohoku Eq - Nakata and Snieder (2011) Tohoku Eq - Minato et al. (2012) Many more studies Strong shaking modifies the near-surface Healing occurs over months

11 Nakata and Snieder (2011) GRL

12 Volcanic unrest Piton de la Fournaise - Brenguier et al. (2008) Montserrat - Baptie (2010) Merapi - Poupinet and Ratdompurbo (1996) Vesuvius - Pandolfi et al. (2006) Asama - Nagaoka et al. (2010) Pavlof - Haney et al. (2009)

13 Brenguier et al. (2008) Nat. Geosci. Duputel et al. (2009) JVGR

14 Time delay in coda at Pavlof Volcano Haney et al. (2009) TLE

15 2009 eruption of Redoubt Volcano

16 Figure by S. de Angelis

17 Redoubt s magmatic system Grapenthin et al. (2012) JVGR

18 Temperature and precipitation Merapi - Sens-Schonfelder and Wegler (2006) Japan - Nakata and Snieder (2011) The Moon - Sens-Schonfelder and Larose (2008) Infrasound - Haney (2009)

19 Infrasound monitoring Haney (2009) GRL

20 Inversions occur between 1-7am Inversion 1 Inversion 2 Inversion 3 No inversion Inversion 4 No inversion Inversion 5

21 Aseismic processes Guerrero, Mexico - Rivet et al. (2011) Velocity changes due to Slow Slip Event (SSE) Velocity change occurred during peak strain rate Gofar Fault, EPR - McGuire et al. (2012) Velocity changes during a foreshock swarm Velocity change correlated with seismicity rate Nonlinear elasticity

22 McGuire et al. (2012) Nat. Geosci.

23 Imaging versus change detection Ambient noise tomography (ANT) susceptible to artifacts or ghosts ANT also requires a minimum offset between stations Both issues irrelevant for change detection Only stable noise sources are needed

24 2 stations

25 Derivation of traveltime change 1. v = d/t 2. v+δv = d/(t+δt) changes in v & t v+δv = d/t (dδt)/t 2 Taylor series Δv = (vδt)/t Using Eq 1. Δv/v = Δt/t Poupinet et al.

26 θ

27 Taking oblique angle into account 1. v/cosθ = d/t (v+δv)/cosθ = d/(t+δt) (v+δv)/cosθ = d/t (dδt)/t 2 1. Δv/cosθ = (vδt)/(t cosθ) Δv/v = Δt/t Same result!

28 ... changes in the medium can be observed even if the Green's function of the medium is not reconstructed... the Green's function reconstruction in the correlations is not a necessary condition: The only condition to monitoring with correlation passive experiment is the relative stability of the background noise structure. Hadziioannou et al. (2009) JASA

29 Stable tremor visible in correlations Haney (2010) JGR

30 Dawson et al. (2010) GRL

31 VLP tremor at Kilauea May/June 2007 Differen$al distance to Pu u O o Sta$on distance Feb/Mar 2008 Differen$al distance to Halema uma u Ballmer, et al. (2012) In prep

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33 Possible dirty sources Anthropogenic Traffic Machinery Drilling Active sources Stable volcanic and tectonic tremor Tremor location and characterization

34 Time-varying anisotropy New observable in addition to dt/t Parkfield Eq - Durand et al. (2010) Polarization direction Tohoku Eq - Nakata and Snieder (2012) 60% change in anisotropy parameter Large changes due to greater sensitivity

35 Future New observables besides dt/t Anisotropy changes New processes Glaciers and ice-sheets? Marsan et al. (2012) State-of-the-art networks and instruments De-emphasizing Green s functions and instead seeking stable noise sources Continued integration into monitoring

36 Considering a new research direction? I hope someday you ll join us...

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38 Grand challenges addressed How do faults slip? How does the near-surface environment affect natural hazards and resources? What is the relationship between stress and strain in the lithosphere? How do processes in the ocean and atmosphere interact with the solid earth? How do magmas ascend and erupt?

39 Lack of seismicity prior to eruption

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41 Time-lapse time delay time (s) time (s) Haney et al. (2009) TLE

42 Increasing delay during the eruption Haney et al. (2009) TLE

43 Figure by S. de Angelis

44 Figure by S. de Angelis

45 Figure by S. de Angelis

46 One (approach to volcano monitoring) is to track the volcano s changes in response to known, repeating natural signals such as earth tides. Newhall (2007) Volcanology 101 for Seismologists

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