Haijiang Zhang University of Science and Technology of China Outline Seismic tomography between different time periods Repeating earthquakes Coda wave interferometry Ambient noise Different ray distribution on velocity models ID: 366824
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Slide1
Detecting temporal velocity changes using various methods
Haijiang Zhang
University of Science and Technology of ChinaSlide2
Outline
Seismic tomography between different time periods
Repeating earthquakes
Coda wave
interferometry
Ambient noiseSlide3Slide4Slide5Slide6
Different ray distribution on velocity models
Same theoretical models but with different ray distribution.
Separately Inverted models are differentSlide7
Different ray distribution on velocity models
Same theoretical models but with different ray distribution.
Jointly Inverted models are differentSlide8
Regularization in timeSlide9Slide10
Scattering
:
Scattering occurs when there are velocity heterogeneities in the medium with wavelengths on the order of
λ
of the wave. Slide11
Snieder et al., Science, 2002
A simulation of 100 randomly-perturbed scatterers…
Moving the scatterers (here, 1/40th of the distance shown,
so the perturbation is visible) mostly changes the shapes
and amplitudes of the waveforms…Slide12
Snieder et al., Science, 2002
Waveforms
measured in a
granite sample
at temperatures
of 45°C (blue)
and 50°C (red).
Changing the matrix velocity, by contrast, introduces a shift
(delay or advance) that increases with coda time.Slide13Slide14Slide15
Near- and far-field effects of stress changes on cracks Slide16
3-m separation between two wellsSlide17Slide18
Near- and far-field effects of stress changes on cracks Slide19Slide20Slide21
Repeating events
-with (almost) the same waveformsSlide22Slide23Slide24Slide25
Seismic velocity imaging and monitoring of volcanic areas using ambient seismic noise
F.
Brenguier
(2008)
Slide26
Noise sources
Shapiro et al.
(2005)
sensor
Virtual seismic source reconstructionSlide27
A case study: Piton de la Fournaise volcano, La Réunion island
S 21°
E 55°30Slide28
Synthetic velocity decrease
Temporal changes of seismic velocities using cross-correlations of seismic noiseSlide29
Velocity changes on Piton de la FournaiseSlide30
Brenguier
et al.,
Nature
Geoscience
, 2008
Velocity drops preceding eruptionsSlide31
Seismic velocity changes as a proxy for magma
forcing
O'Connell, R. J., and B. Budiansky (1974), Seismic Velocities in Dry and Saturated Cracked Solids,
J. Geophys. Res.
, 79(35), 5412–5426
Seismic velocities are strongly sensitive to crack density.Slide32
These velocity changes are linked to dilatation induced by stress changes
Magmatic intrusive complex
Link between temporal changes and structure