seismic tremors: the rock physic interpretation. · 2017-04-04 · non-volcanic tremor and...
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Seismic tremors:the rock physic interpretation.
Luigi Burlini
ETH Zurich
Collaboration with: Non volcanic tremors: Ph. Meredith (UCL), A. Feenstra (GFZ),
G. DiToro (Uni-PD), C. DellePiane (ETH).Volcanic tremors: S. Vinciguerra (INGV), L. Caricchi (ETH),
G. DeNatale (INGV)
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SCIENCE v. 296 – 31 May 2002
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Episodic Tremor and Slip on the Cascadia Subduction Zone:The Chatter of Silent Slip
Garry Rogers & Herb Dragert
8 May 2003
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SCIENCE v. 300 – 20 June 2003
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Journal of Geophysical Research v. 108 – 2003
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SCIENCE v. 303 – 9 Jan. 2004
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Tectonophysics v. 417 – 2006
Nature v. 442 – July 2006
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Geophysical Research Lettersv. 34 - 2007
Scaling relationship between the duration and the amplitude of non-volcanic deep low-frequency tremors Watanabe, Tomoko; Hiramatsu, Yoshihiro; Obara, Kazushige
Seismic interferometry using non-volcanic tremor in Cascadia
Chaput, J. A.; Bostock, M. G.
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SCIENCE v. 315 - January 2007
The mechanism of deep low frequency earthquakes: Further evidence that deep non-volcanic tremor is generated by shear
slip on the plate interfaceSatoshi Ide, David R. Shelley and Gregory C. Beroza
Geophysical Research Lettersv. 34 - 2007
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Non-volcanic tremor and low-frequency earthquake swarms
David R. Shelly, Gregory C. Beroza & Satoshi Ide
NATURE v. 446, 15 March 2007
Slow earthquake coincident with episodic tremors and slow slip events
Y. Ito, K. Obara, K. Shiomi, S. Sekine, H. Hirose
SCIENCE v. 315, 26 January 2007
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Outline
1. Non volcanic tremors and LFEs
2. Rock-physics interpretation
2a. Methods
2b. Results
3. Conclusions
4. Volcanic tremors
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Seismograms from the Nankai Through (JPN) subd. zone: tremor + Low Frequency EQs (LFE)
Red indicates time with LFE detectionson 3 stations (courtesy of D. Shelly)
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Nankai Through, Japan
LFE (red dots)
Shelly et al., Nature, 2006
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LFE
Temperature at a depth of 30Temperature at a depth of 30--40 km is 50040 km is 500ooC, but uncertainty of C, but uncertainty of ±±5050--100100ooC C (Peacock & Wang, Science, 1999)(Peacock & Wang, Science, 1999)
LFE and tremor localization: depth 30-40 km (0.75 - 1 GPa), oceanic subducting lower crust, HFP.
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Origin of tremors (Shelly et al., 2006):
a) Slip and fluid flowFluid released by dehydration reactions lowers the effective normal stress, triggers slip, LFEs and fluid flow.
b) Superposition of LFEsLFEs generated by local slip accelerations at geometric or frictional heterogeneities during large slow slip events.
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Outline
1. Non volcanic tremors, LFEs and AEs
2. Rock-physics interpretation
2a. Methods
2b. Results
3. Conclusions
4. Volcanic tremors
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Experimental approach to address this problem:
recording of microseismicity (AEs) during rock testing
Acoustic Emissions = small events related to microcracking.
Originally measured on triaxial tests to record damage prior and during faulting.
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Burlini et al., Geology, Feb 2007
Extend AEs investigation to HT (gas apparatus) and analysis of dehydration reactions.
dnatx fnat = dlabx flab
d = crack length
f = frequency
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Dehydration underTriaxial conditions
The experimental approachDehydration underHydrostatic conditions
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Paterson rig equipped with AE instrumentation
Rocks:Gypsum, Diasporite,Serpentinites
Exp. conditions:HydrostaticPc = 220 - 340 MPaT up to 1000 oCDrained &undrained
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Sample assembly
Furnace
Specimen
Pressurevessel
AE trasducer
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AEs trasducer (works up to 200 oC)
Zirconia rods (therm. insulation)
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Outline
1. Non volcanic tremors, LFEs and AEs
2. Rock physics interpretation
2a. Methods
2b. Results
3. Conclusions
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Dehydration reactions on
• Gypsum
• Diasporite
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Fine-grained granoblastic gypsum rock from Volterra, Italy.
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Gypsum sample – before & after dehydration
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Gypsum (drained)
Temperature (0C)
80 100 120 140 160 180
AE e
nerg
y
Gypsum 2 (undrained)
Temperature (0C)
60 80 100 120 140 160 180
AE e
nerg
y
AE during Gypsum dehydration
Gypsum dehydrates to bassanite + H2O
around 100oC at 200 MPa
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Two waveform types captured above 100°C
thermal cracking event ? dehydration event ?
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0
0.4
0.8
0
10
20
Freq
uenc
y, M
Hz
Am
plitu
de, V
Thermal cracking: 0-25 MHz
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Dehydrated Gypsum microstructures
Bassanite with minor anhydrite (bright fibrous phase).
Note: homogeneous porous structure.
Bassanite with minor anhydrite (bright fibrous phase).
Note: large voids filled with platy anhydrite.
drainedundrained
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DIASPORITE
Metamorphosed karst- bauxite from the southern margin of the MenderesMassif, south-west, Turkey.
Metamorphosed at 350 – 400oC and about 500 MPa.
Composition: diaspore 78%, Ti-hematite 20%, with minor rutile, muscovite and paragonite.
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AE during Diasporite dehydration
Diasporite dehydrates to Corundum + H2O
around 400oC at 200 MPa
Diasporite (undrained)
Temperature (0C)
300 350 400 450 500 550
AE e
nerg
y
Diasporite (drained)
Temperature (0C)
300 350 400 450 500 550
AE e
nerg
y
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Dehydrated Diasporite microstructures
drained undrained
Grey – diaspore + corundumWhite – Ti-hematiteBlack – porosityNote: cross-cutting fractures
– fluid conduits?
Grey – corundumWhite – Ti-hematiteBlack – porosityPorosity results from 28% decrease in volume during dehydration
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Tempearture vs Time and AE for Diasporite
Diasporite (drained)
Time (minutes)
30 50 70 90 110 130
Tem
pera
ture
(0 C)
360
380
400
420
440
460
480
AE
ene
rgy
0
2000
4000
6000
8000
Temporary temperature drop due to evaporation of H2O from dehydration (drained conditions)
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Results 4: AE waveforms - undrained Diasporite experiment
thermal cracking event ? dehydration event ?
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Preliminary conclusions. 2 types of events:
• short– single isolated event– spread of frequency
• thermal cracking?
• Long– cascade of events – Coincided with dehydration– Constant frequency from 3 to 15 MHz with peak at 5
• pore collapse, crack propagation, fluid migration?
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Serpentine dehydration reactions in nature and experiments.
Ulmer and Trommsdorf, Science, 1995
EXPERIMENTS
NATURE (tremors)
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X-Ray Powder Diffr. composition after experimentsS5 600ºC
S6 700ºC
S3 900ºC
S1 1000ºC
Serpentine
Talc
Enstatite
Forsterite + enstatite + hematite(+monticellite + calcite)
T
incr.
Magnetite
Talc Olivine
Olivine
Olivine
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Serpentinite – before & after dehydration
BEFOREBEFORE AFTERAFTER
5 mm
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0
50
100
150
200
250
0 20 40 60 80 100
Time (minutes)
N o
f Eve
nts
450
500
550
600
650
700
750
Tem
pera
ture
(C)
Cumulative number of eventsCumulative EnergyTemperature (C)
AEs at 550oC: first dehydration (endothermic) reaction (Srp = Ol + Tlc + H2O)
Exp. S6: Pc = 323 MPa
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Freq
uenc
yM
Hz
Am
plitu
de, V
Time, s x 10-4
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Freq
uenc
yM
Hz
0
10
20
Dehydr. Reaction: 1-12 MHz, max ampl. 3 MHz
Time, μs0 200 400
0
0.15
-0.15
Am
plitu
de, V
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SEM BSE SEM BSE ImageImage of of SerpentiniteSerpentinite beforebefore experimentsexperiments
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After After experimentexperiment at 700at 700ººCC
serpentineserpentine
talctalc
olivineolivine
hematitehematite
20 20 μμmmPorePore
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0
50
100
150
200
250
0 20 40 60 80 100
Time (minutes)
N o
f Eve
nts
450
500
550
600
650
700
750
Tem
pera
ture
(C)
Cumulative number of eventsCumulative EnergyTemperature (C)
At higher temperature (650ºC):
Exp. S6: Pc = 323 MPa
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0
50
100
150
200
250
0 20 40 60 80 100
Time (minutes)
N o
f Eve
nts
450
500
550
600
650
700
750
Tem
pera
ture
(C)
Cumulative number of eventsCumulative EnergyTemperature (C)
Exp. S6: Pc = 323 MPa
At higher temperature (660ºC):
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Freq
uenc
yM
Hz
Am
plitu
de, V
Time, s x 10-4
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X-Ray Powder Diffr. composition after experimentsS5 600ºC
S6 700ºC
S3 900ºC
S1 1000ºC
Serpentine
Talc
Enstatite
Forsterite + enstatite + hematite(+monticellite + calcite)
T
incr.
Magnetite
Talc Olivine
Olivine
Olivine
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Serpentine dehydration reactions in nature and experiments.
Ulmer and Trommsdorf, Science, 1995
EXPERIMENTS
NATURE (tremors)
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0
100
200
300
400
500
600
700
800
900
1000
0:00:00 0:14:24 0:28:48 0:43:12 0:57:36 1:12:00 1:26:24300
400
500
600
700
800
900
1000Cumulative number of events
Cumulative Energy
Temperature (C)
Exp. S3 Pc= 224 MPa
1
6
3
45
8
AEs at 700-800 oC: second dehydration reaction (Srp = Ol + En + H20)
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Dehydr. reaction 2: max ampl. 5 MHz, gap 10-20 MHz
200
10
5
20
0Freq
uenc
yM
Hz
0.8
0.4
0.0
Am
plitu
de, V
0 400 800Time, μs
Background noise
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SEM BSE SEM BSE ImageImage
olivineolivine
20 20 μμmm
enstatiteenstatite
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Cracking Srp=Ol+Tlc+H2O Srp=Ol+En+H2O
5
25
0 5
Time, μsTime, μs Time, μs0 100 0 8000 400
550-650 oC 700-800 oC500-530 oC
SummarizingSummarizing
3
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Natural tremor beneath Shikoku
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Courtesy of D. Shelly
Natural tremor beneath Shikoku
Experimental tremor beneath our rig
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Courtesy of D. Shelly
Natural tremor beneath Shikoku
Experimental tremor beneath our rig
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3. Conclusions II3. Conclusions IIDehydration reactions produces excess fluid Dehydration reactions produces excess fluid pressure that generate microseismicity (AEs) even pressure that generate microseismicity (AEs) even under hydrostatic conditions.under hydrostatic conditions.
• pore collapse, crack propagation, fluid migration?
Water dehydration produces a cascade of events Water dehydration produces a cascade of events characterised by low frequency and long duration, characterised by low frequency and long duration, very similar to natural tremors under subduction very similar to natural tremors under subduction zones.zones.
By analogy, we propose that dehydration reactions By analogy, we propose that dehydration reactions and water flow are the primary source of tremors in and water flow are the primary source of tremors in subduction zones. subduction zones.
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X-Ray Powder Diffr. composition after experimentsS5 600ºC
S6 700ºC
S3 900ºC
S1 1000ºC
Serpentine
Talc
Enstatite
Forsterite + enstatite + hematite(+monticellite + calcite)
T
incr.
Magnetite
Talc Olivine
Olivine
Olivine
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Oficalcite – up to 1000°C (decarbonatation)
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Serpentinite S1
0
200
400
600
800
1000
1200
0:00:00 0:14:24 0:28:48 0:43:12 0:57:36 1:12:00
time
Tem
pera
ture
(C
)
0
50
100
150
200
250
Sum
. N. o
f eve
nts
Temperature CN. of eventsCumulative absolute energy
First dehydration reaction
Second dehydration reaction
Decarbonatation
225 MPa
Ol+
Dio
psid
e+
Cal
cite
Mon
ticel
lite
+ C
O2
Serp
entin
e
Ol+
ens
tatit
e+
H2OSe
rpen
tine
Ol+
talc
+ H
2O
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Decarbonation : 5-25 MHz, max ampl. 5 and 22 MHz
10
5
0Freq
uenc
yM
Hz
0.8
0.4
Am
plitu
de, V
20
0.0
22
0 400 800Time, μs
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monticellite
olivineenstatite
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Decarbonation of Dolomite (850 oC)
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A failure
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A failure
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3. Conclusions III3. Conclusions IIIWater dehydration from different rock type produces Water dehydration from different rock type produces similar types of AEs, characterized by a similar types of AEs, characterized by a monochromatic frequency (3 to 5 MHz at laboratory monochromatic frequency (3 to 5 MHz at laboratory scale).scale).
Also Also decarbonatationdecarbonatation produces similar long lasting produces similar long lasting AEsAEs made of a cascade of events.made of a cascade of events.The processes producing The processes producing AEsAEs should be similar. should be similar.
We propose that from the spectrogram we can infer We propose that from the spectrogram we can infer if water or CO2 were involved.if water or CO2 were involved.
Could it be a difference in fluid viscosity?Could it be a difference in fluid viscosity?And of so, what about magmas?And of so, what about magmas?
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Volcanic tremor
Burlini et al., Geology, Feb. 2007
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Sample assembly
Dunite
Dunite
Basalt
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Dunite microstructure
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Measurements of AE during melting reaction and melt flow
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Glass transition
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HT thermal cracking
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Volcanic tremor
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Intrusion ?
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PP133 – AE 30 – 1470 K, 350 MPa
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The dyke within the peridotite sandwich after testing
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Conclusions
• Different type of AE (events) produces different waveforms.
• Is it possible to extrapolate frequencies and lengths to natural earthquakes?
• The examples from the active volcanoes seem to support this hypothesis.
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Towards geological geometries
Before After
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Melt propagation trough conduit and diffusion into porous spacer with time
-5
-4
-3
-2
-1
0
1
2
3
0 5 10 15 20 25 30 35 40 45 50
time (0.01*sec)
Posi
tion
(mm
)
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Towards geological geometries
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Towards geological geometries
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Thank You