Energetics of chemical alteration in fault zones and its relationship to the seismic cycle

Jacobs, Joseph R.; Evans, James P.; Kolesar, Peter T.

doi:10.1029/170gm18

Cited by 5 publications

(6 citation statements)

References 48 publications

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“…We propose that seismic energy and fluids may play a role in initiating the smectite-illite reaction at shallow depths in the fault core (Jacobs et al 2006;Vrolijk and van der Pluijm 1999). Preliminary results from TCDP core show the same mineralogical trends in the footwall as in the hanging wall (L. W. Kuo, pers.…”

Section: Variations With Depthmentioning

confidence: 90%

“…Phyllosilicates in the fault core have been identified by many workers as an important mechanism for fault weakening (Wu 1978;Chester et al 1993;Evans and Chester 1995;Wintsch et al 1995;Schleicher et al 2006;Solum et al 2006). Smectite has been documented as a major constituent of fault gouge (Wu 1978;Chester and Logan 1986;Solum et al 2003;Jacobs et al 2006) as has illite (Vrolijk and van der Pluijm 1999;Solum et al 2005) and other clays including chlorite and kaolinite (Solum et al 2003; this study).…”

Section: Fault Zone Structure and Compositionmentioning

confidence: 99%

“…The damage zone records deformation inherited from past fault motion, presumably by repeated earthquakes (Chester and Logan 1986;Caine et al 1996;Schulz and Evans 1998). The damage zone can further be divided into the primary damage zone (PDZ) and the secondary damage zone (SDZ; Jacobs et al 2006). The primary damage zone surrounds the fault core and can have a dense network of fractures and secondary faults that may obscure the original rock structure.…”

Section: Fault Zone Structure and Compositionmentioning

confidence: 99%

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Structural, Mineralogical, and Geochemical Characterization of the Chelungpu Thrust Fault, Taiwan

Isaacs¹,

Evans²,

Song³

et al. 2007

Terr. Atmos. Ocean. Sci.

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The Chelungpu fault, Taiwan, produced a northward propagating rupture on 21 September 1999 resulting in a M w 7.6 earthquake with a ~90 km long N-S trending fault scarp. The mineralogic and physical character of the fault-related rocks within the Chelungpu fault zone, as measured at 9 sites along 70 km of the 1999 rupture trace, changes significantly along strike and with depth. The northern section of the Chelungpu fault has a 10 -30 m-wide primary damage zone that is characterized by increased fracture density and alteration, but little microstructural damage to within 1 m from the main fault. The southern section of the Chelungpu fault has a 25 -70 m wide primary damage zone that is characterized by increased fracture density and alteration, the presence of intensely sheared rock, and numerous secondary faults and gouge zones as far as 240 m from the main fault. The complexity of the damage zone, geochemistry, and clay mineralogy of the southern fault zone may reflect its relative maturity (~1 Ma) compared to the northern fault zone (~46 -100 Ka). The major down-dip mineralogic variation is a transition from a significant amount of smectite in exhumed fault cores to little or no smectite in the fault core at sampled depths of 200 to 1000 m. This transition may be influenced by weathering processes at the surface, however co-seismic fluid flow may have a role in illite-smectite reactions. The composition of clays has important seismologic implications as clays play a role in fault weakening.

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Section: Variations With Depthmentioning

confidence: 90%

Section: Fault Zone Structure and Compositionmentioning

confidence: 99%

Section: Fault Zone Structure and Compositionmentioning

confidence: 99%

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Structural, Mineralogical, and Geochemical Characterization of the Chelungpu Thrust Fault, Taiwan

Isaacs¹,

Evans²,

Song³

et al. 2007

Terr. Atmos. Ocean. Sci.

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“…They propose that this may explain the lack of a frictionally generated heat flow anomaly. Similarly, Jacobs et al [2006] demonstrated that endothermic reactions resulting in authigenic mineral formation in fault zones might account for as much as 20% of the total energy budget.…”

Section: Frictional Heat Generationmentioning

confidence: 97%

Effect of thermal refraction on heat flow near the San Andreas Fault, Parkfield, California

Fulton¹,

Saffer²

2009

J. Geophys. Res.

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[1] Heat flow data near the San Andreas Fault (SAF) do not reveal a near-fault anomaly as expected from frictional heat generation, an observation interpreted to indicate that the fault slips at a depth-averaged shear stress <20 MPa. The data also contain large unexplained scatter, which has been a separate major issue in the analysis of heat flow within the California Coast Ranges. Here we use numerical models of heat conduction to evaluate the hypothesis that thermal refraction, due to contrasts in thermal conductivity in the subsurface, both produces the observed scatter in heat flow and as a result obscures the thermal signature from frictional heating on a fault that supports large shear stress during slip. Our study focuses on the region around the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, California. Our results show that surface heat flow is most sensitive to the contrast between Tertiary sediments and basement rocks and to wavelengths of basement topography of $10 km. With realistic thermal conductivity contrasts and a reasonable interpretation of this geologic contact, we show that thermal refraction is a plausible explanation for the observed heat flow scatter. However, refraction effects are unable to mask frictional heat generation in a manner consistent with observations. We show that even with large refraction effects, low background heat flow, a regional NW-SE decrease in heat flow, or nonsteady state heat conduction, the data are most consistent with a fault that produces little to no frictional heat.

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“…Coseismic fluid movement in the fault zone [Sibson, 2001] will also require energy. Mineral alteration in the fault core and damage zone [Evans and Chester, 1995;Schulz and Evans, 1998;Jacobs et al, this volume] may consume energy (though on timescales of the entire seismic cycle). Although there is no simple relationship between slip and damage zone thickness [Shipton et al, this volume], damage zone deformation will tend to accumulate during the lifetime of a fault and therefore larger faults tend to have more complex damage zones.…”

Section: What Structural Processes Exist To Provide Dissipative Energmentioning

confidence: 99%

The missing sinks: Slip localization in faults, damage zones, and the seismic energy budget

Shipton

Evans

Abercrombie

et al. 2006

Earthquakes: Radiated Energy and the Physics of Faulting

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The majority of work done during an earthquake may be consumed by dissipative processes that occur within geometrically and mechanically complex fault zones, rather than radiated as seismic waves. Many processes are likely to act as dissipative energy sinks in a three-dimensional faulted volume: slip along the principal slip zone is likely to be accompanied by deformation in the surrounding damage zone volume. Examination of exhumed fault zones in granite, which are meters to tens of kilometers long, shows thin principal slip zones developing on the smallest faults. As slip is accumulated on progressively larger faults, the principal slip zones remain less than 10 cm wide, but there is increasing complexity in the damage zone of the larger faults. By considering the amount of energy required to crush fine-grained gouge in the principal slip zone, and the grain size of gouge reported from other (seismogenic) faults, we conclude that principal slip zones must remain relatively thin for all sizes of rupture. Any energy consumed by dissipative processes in the damage zone will therefore tend to make the principal slip zone thinner, and will reduce the energy available to propagate the rupture.

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Energetics of chemical alteration in fault zones and its relationship to the seismic cycle

Cited by 5 publications

References 48 publications

Structural, Mineralogical, and Geochemical Characterization of the Chelungpu Thrust Fault, Taiwan

Structural, Mineralogical, and Geochemical Characterization of the Chelungpu Thrust Fault, Taiwan

Effect of thermal refraction on heat flow near the San Andreas Fault, Parkfield, California

The missing sinks: Slip localization in faults, damage zones, and the seismic energy budget

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