Heat Signature on the Chelungpu Fault Associated with the 1999 - - PowerPoint PPT Presentation

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Heat Signature on the Chelungpu Fault Associated with the 1999 - - PowerPoint PPT Presentation

Oct 19, 2022 27 likes •348 views

Heat Signature on the Chelungpu Fault Associated with the 1999 Chi-Chi, Taiwan Earthquake Yasuyuki Kano, Jim Mori, Ryo Fujio, Takashi Yanagidani, Setsuro Nakao (DPRI, Kyoto Univ.), Hisao Ito (JAMSTEC), Osamu Matsubayashi (AIST), Kuo-Fong Ma

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RCEP, DPRI, KYOTO UNIV.

Heat Signature on the Associated with the 1999 Chi-Chi, Taiwan Earthquake Chelungpu Fault

Yasuyuki Kano, Jim Mori, Ryo Fujio, Takashi Yanagidani, Setsuro Nakao (DPRI, Kyoto Univ.), Hisao Ito (JAMSTEC), Osamu Matsubayashi (AIST), Kuo-Fong Ma (NCU)

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RCEP, DPRI, KYOTO UNIV.

Energy budget for an earthquake W = EH + W0 W0 = ER + EG DS W 2

1

σ σ + =

D

DS W 2

1

σ σ − = DS EH

1

σ =

D

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RCEP, DPRI, KYOTO UNIV.

Goal of the talk

Target: Temperature (heat) signature of the earthquake We observed temperature signature around the fault zone along the Chelungpu fault (September, 2005) The signature can be interpreted as the frictional heat caused by fault slip at the time of the 1999 Chi-Chi earthquake Evaluate other cause of the temperature anomaly (1) Spatial variation of material thermal conductivity Estimate “noise level” and obtain upper bound of heat strength (2) Water flow Calculate the temperature anomaly affected by 1-dimensional water flow

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RCEP, DPRI, KYOTO UNIV.

Shallow borehole (Tanaka et al., 2006) Deeper and stable measurement!

Relatively broad anomaly: affected by shallow ground water flow? Mesurement right after drilling: drilling effect

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RCEP, DPRI, KYOTO UNIV.

1999 Chi-Chi earthquake and TCDP site

[Ma et al, 2002] TCDP (大坑，台中)

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RCEP, DPRI, KYOTO UNIV.

Measurement

900 m

1.0 m/min 0.4 m/min

1200 m

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RCEP, DPRI, KYOTO UNIV.

Quartz thermometer

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RCEP, DPRI, KYOTO UNIV.

Temperature profile using Quartz thermometer

(Kano et al., 2006, GRL)

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RCEP, DPRI, KYOTO UNIV.

Spatio-temporal variation of the temperature signature

One-dimensional heat conduction

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛− = t x t S t x T α πα 4 exp 2 ) , (

2

(Officer, 1974)

S： strength of source, ºCm α ： thermal diffusivity, Temperature anomaly Transient: Friction, …. Stable: Geothermal gradient + thermal property Plane Heat Source = S

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RCEP, DPRI, KYOTO UNIV.

Temperature anomaly

~ 50 m Remove linear temperature gradient Average of 4 profiles 4 m slip, 6 years, α = 3.4 x 10-7 m2/s (Kano et al., 2006, GRL)

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RCEP, DPRI, KYOTO UNIV.

Estimated parameters

  • Heat diffusivity α ~ 0.3 x 10-6 m2/s

(k ~ 0.9 Wm-1K-1)

  • Strength of source S ~ 1 oCm

↓ (Q ~ 4 x 106 J/m2) Shear stress τ ~ 0.6 MPa ↓ Frictional coefficient μ ~ 0.04

  • Upper limit of shear stress τ ~ 1.7 MPa

↓ Frictional coefficient μ ~ 0.1

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RCEP, DPRI, KYOTO UNIV.

Pt-RTD thermometer

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RCEP, DPRI, KYOTO UNIV.

Temperature anomaly using another thermometer (Pt-RTD )

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RCEP, DPRI, KYOTO UNIV.

Shear stress and frictional heat q : Heat flow κ : Thermal conductivity T : Temperature z : depth

dz dT q κ =

Temperature gradient (-> temperature structure) is affected by variation of thermal conductivity under constant heat flow.

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RCEP, DPRI, KYOTO UNIV.

Temperature observation and core measurement

Observed temperature variation Predicted temperature variation from core thermal conductivity [Matsubayashi, T145-P003] Hole-B Hole-A LPF: 40 m 60 mA/m2

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RCEP, DPRI, KYOTO UNIV.

Effect of water flow

t T x T ∂ ∂ = − ∂ ∂ α

2 2

x T v c c n

w w

∂ ∂ ρ ρ

(Domenico and Schwartz, 1997)

v : flow rate n : porosity ρw: density of water cw : specific heat of water.

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RCEP, DPRI, KYOTO UNIV.

Effect of water flow fault

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RCEP, DPRI, KYOTO UNIV.

Effect of waster flow

(Kano et al., 2006, GRL) t T x T v c c n x T

w w

∂ ∂ = ∂ ∂ − ∂ ∂ ρ ρ α

2 2

The effect of the water flow: (1) move the anomaly downstream in position (2) broaden its shape

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RCEP, DPRI, KYOTO UNIV.

Temperature anomaly

(Kano et al., 2006, GRL) ~ 50 m Remove linear temperature gradient Average of 4 profiles Observed temperature signature is located right at the location of the fault

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RCEP, DPRI, KYOTO UNIV.

Summary (1) Spatial variation of material thermal conductivity may cause noise in data

Our observation gives upper bound of heat strength (still low friction)

(2) Minimal effects from fluid flow in our observed temperature signature (3) Small heat signature indicates a low level friction

  • n the fault during earthquake

Shear stress: 2 MPa

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RCEP, DPRI, KYOTO UNIV.

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RCEP, DPRI, KYOTO UNIV.

Temperature observation and core measurement

Observed temperature variation (Hole-A) – Predicted temperature variation (Hole-B) LPF: 40 m Correct background temperature gradient

  • Depth correction (Hole-A vs Hole-B)
  • Appropriate filter

Our estimate give upper bound of temperature anomaly

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RCEP, DPRI, KYOTO UNIV.

Upper limit of the shear stress α = 0.34 m2/s, c =1140 J/kgK, ρ = 2600 kg/m3

1 3 2 4 0.00 0.10

α = 2.00 m2/s c =300 J/kgK, ρ = 2200 kg/m3

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RCEP, DPRI, KYOTO UNIV.

Motivation

Find the temperature signature associated with the 1999 Chi-Chi, Taiwan earthquake Amount of frictional heat (~ Level of shear stress) Key unknown values of important parameter for understanding the physics

  • f earthquake rupture

Cannot be determined by seismic observation Residual heat Can be observed as temperature anomaly along the fault

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RCEP, DPRI, KYOTO UNIV.

Precise temperature measurements

Development of thermometers Quartz thermometer (0.003 °C) Pt-RTD thermometer (0.001 °C) No water flow in the borehole Cased borehole No drilling disturbance A half year from the end of drilling

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RCEP, DPRI, KYOTO UNIV.

Quartz thermometer

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RCEP, DPRI, KYOTO UNIV.

Pt-RTD thermometer

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RCEP, DPRI, KYOTO UNIV.

Estimation

Assumption – Transferred to frictional heat – One-dimensional heat conduction – Constant background thermal gradient

p

n −

= σ τ µ u c S ρ τ ⋅ = ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛− ∆ = ∆ t x t S t x T α πα 4 exp 2 ) , (

2

σn：normal stress (Sibson, 1974) p：pore pressure hydrostatic

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RCEP, DPRI, KYOTO UNIV.

Summary Precise temperature measurement reveals

Temperature anomaly of ~ 0.05°C Temperature distribution at depth comparable to core measurement

Low shear stress

Low dynamic friction Mechanism such as super-hydrostatic pore pressure or lubrication Future works Temperature anomaly caused by spatial variation of thermal property Sensor calibration (transfer function of instruments) Repeated measurement (Hole-B ?)

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RCEP, DPRI, KYOTO UNIV.

Shear stress and frictional heat

ρ τ ⋅ ⋅ = c u S

DS EH

1

σ = S : Strength of source, °Cm τ : Shear stress, MPa u : Slip, m c : Heat capacity, 1140 J Kg-1 oC-1 ρ : Density, 2600 Kg/m3

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RCEP, DPRI, KYOTO UNIV.

Expectation

Depth 1 km, Slip 8 m, frictional coefficient 0.6 (S ~50 °Cm) 5 years 5.5 years α = 1.2 x 10-6 m2/s α = 0.6 x 10-6 m2/s α = 0.9 α = 1.2 5 years

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RCEP, DPRI, KYOTO UNIV.

Temperature anomaly

Remove linear temperature gradient Average of 4 profiles