Seismic tremors: the rock physic interpretation. · 2017-04-04 · Non-volcanic tremor and...

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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)


At higher temperature (650ºC):


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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)



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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S6 700ºC

S3 900ºC

S1 1000ºC

Serpentine

Talc

Enstatite


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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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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S6 700ºC

S3 900ºC

S1 1000ºC

Serpentine

Talc

Enstatite


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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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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Thank You

Seismic tremors: the rock physic interpretation. · 2017-04-04 · Non-volcanic tremor and...

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