on the nature of fault slip: from the field to the lab f.x. … · 2020-05-04 · on the nature of...
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On the Nature of Fault Slip: From the Field to the Lab
F.X. Passelègue1
Michelle Almakari2, Pierre Dublanchet2, Fabian Barras3, Marie Violay1
1 Laboratoire Expérimental de Mécanique des roches, EPFL, Lausanne2 MINES ParisTECH, Centre de Géosciences, Fontainebleau
3 The Njord Centre for Studies of the Physics of the Earth, Oslo, Norway
Acknowledgments: Federica Paglialunga, Mateo Acosta, Alexandre Schubnel, Harsha Bhat
Raul Madariaga, Soumaya Latour…
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𝑀0 ∝ ∆𝜎 𝐿3
𝑀0 ∝ 𝜇 𝐷 𝐿2
∆𝜎 ∝ 𝜇𝐷
𝐿
𝛿 ∝ 𝐿/ 𝑉𝑟
Various types of seismic ruptures
Scaling relationsPasselègue et al., submitted
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𝑉𝑟 ∝ ∆𝜎
Same physic
Various types of seismic ruptures
𝑀0 ∝ ∆𝜎 𝐿3
𝑀0 ∝ 𝜇 𝐷 𝐿2
∆𝜎 ∝ 𝜇𝐷
𝐿
𝛿 ∝ 𝐿/ 𝑉𝑟
Scaling relationsPasselègue et al., submitted
Ph.D. of F. Paglialunga
Work in progress
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Organisation in this complexity
Passelègue et al., submitted
Various types of seismic ruptures
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Which parameter(s) control(s) the nature of seismicity?
Something that:
• changes spacially along faults
Fault jogs can present both slow and fast ruptures
• Is variable with time
A same asperity can break seismically and aseismically
• Dominates at shallow depth or close to BDT,affected by fluid pressure
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Reproduce earthquakes in the laboratory: controlled conditions!
𝜎𝑥𝑦 𝑖, 𝑗 & 𝜎𝑦𝑦 𝑖, 𝑗 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
Here
Regular triaxial experiments
𝜎𝑥𝑦0 𝑖, 𝑗 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝜎𝑦𝑦
𝑒𝑓𝑓𝑖, 𝑗 vary spacially
y
Fluid injection at the edge of the faultLow fault permeability, no bulk diffusion
𝑉𝑟x
Measurement of stress along the fault Inversion of the fluid pressure (Almakari et al, in prep)
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Reproduce earthquakes in the laboratory: controlled conditions!
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Experimental results: From fast to transient slow slip events
Slip rate and stress drop decrease with decreasing τ0 Rupture speed also: transition from fast to slow rupture
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What about the control of the rupture speed?
𝑉𝑟 = 𝐶𝑅 1 −(𝜎𝑛 − 𝑃𝑓)
𝜏0 − 𝜏𝑟2
Ω𝐸∗
𝜋𝑙/2
𝑉𝑟 ↘ 𝑃𝑓 ∝ 𝐿𝑐?
𝐿𝑐 < 𝐿𝑓
From LEFM (Freund, 1990)
𝑉𝑟 = 𝐶𝑅 1 −𝐺𝑐
Γ
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What about the control of the rupture speed?
Initial stress 𝝉𝟎& Energies are keys!
𝑉𝑟 ↘ 𝑃𝑓
𝑉𝑟 ↗ ∆𝜏𝑑
Passelègue et al., 2016
Passelègue et al., 2016
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On going work and perspectives
Ph.D. of Federica Paglialunga
She is closing the energy budget in the lab: Eg, Eh, Er
She compare the estimates of EG (LEFM, Sismo, Stress-slip)
Study deceleration and rupture arrest (control on τ0)
Wednesday
TS2.5/EMRP1.12
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Conclusions and Take home message
Rupture speed, i.e. nature of the seismicity, depends of
the stress acting along the fault ahead of the rupture tip, the energy available
• Explain slow rupture phenomena at shallow depth and in fluid over-pressurized area
• What about rupture length? Also predictable from LEFM!
• Low stress level inhibits radiation damping terms → 𝑉𝑟 remains slow (Barras et al., 2019)
Small rupture of high stressed patches trigger slow rupture front?