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| Titel |
In situ coseismic stiffness of fault rocks calculated using pseudotachylyte injection veins |
| VerfasserIn |
W. Ashley Griffith, Tom M. Mitchell, Giulio Di Toro |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053742
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| Zusammenfassung |
| Elastic stiffness of fault zone rocks is expected to be highly variable during the seismic cycle
due to complicated damage and healing processes. In addition to longer-term alteration which
may take place during exhumation, it is impossible to assess how well rock stiffness as
measured in the laboratory represents in situ, coseismic rock stiffness at seismogenic (5-15
km) depths. Here we calculate the in situ, coseismic rock stiffness of fault rocks from the
pseudotachylyte-bearing Gole Larghe Fault Zone of the Adamello Batholith, Italian Southern
Alps, using aspect ratio measurements of pseudotachylyte injection veins and numerical
Displacement Discontinuity Method simulations. Aspect ratios of over 100 pseudotachylyte
injection veins which cut across tonalite, cataclasite, or aplite show that maximum vein
thickness is linearly related to vein length. For modeling of vein opening, the fault and
the injection vein are assumed to be filled with melt that has a fluid pressure P .
Consistent with recent results from modeling of melt lubrication we assume that the
magnitude of the fluid pressure P is exactly the same as the normal stress (ÏăyyR) such
that the fault vein approximately maintains constant thickness (i.e. melt extrusion
exactly balances melt production). This model assumes that an array of tensile cracks
orthogonal to the fault vein have been left in the wake of the earthquake rupture tip,
allowing fluid to inject into the sidewall without significant fluid overpressures.
These assumptions are in contrast to previous models of injection vein development
which assume that vein opening is driven by melt fluid overpressure. Numerical
simulations of injection vein opening due to fluid pressure of frictional melt indicate
that in situ coseismic stiffness of the fault rocks ranged from 5-50 GPa, about a
factor of two less than typical laboratory measurements of the same rocks, and
the coseismic stiffness of tonalite, cataclasite, and aplite are markedly different. |
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