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| Titel |
A new three-dimensional method of fault reactivation analysis : Application to the 2011 Tohoku-Oki earthquake sequence |
| VerfasserIn |
Henri Leclere, Olivier Fabbri |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250084552
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| Zusammenfassung |
| The determination of the state of stress around fault is of fundamental importance to
understand fault reactivation and earthquake triggering. During the last decades,
the determination of the stress state in the crust has been improved thanks to deep
borehole stress measurements and the development of stress inversion methods.
However, the influence of the stress tensor on the ability of faults to be reactivated
remains unclear. The use of the reduced stress tensor given by most stress inversion
methods to estimate the ability of fault to be reactivated is possible with only a few
methods.
We developed a new 3-D fault reactivation method to evaluate the reactivation
potential of fault planes. The method is based on the Mohr-Coulomb theory and can be
applied to cohesive or noncohesive faults whatever their orientations and without
any conditions on the regional stress field. It allows computation of the effective
stress ratio Ïă3’/Ïă1’ required to reactivate any fault plane and to determine whether
the plane is favorably oriented, unfavorably oriented or severely misoriented with
respect to the ambient stress field. The method also includes a graphical sorting tool
that involves plotting poles of fault planes on stereoplots for which the boundaries
separating the three domains corresponding to favorable orientations, unfavorable
orientations and severe misorientations cases are shown. The delineation of these domains
is based on the value of the Ïă3’/Ïă1’ ratio that depends on the orientation of the
fault plane with respect to the principal stress axis orientations, the stress ellipsoid
shape ratio, the coefficient of static friction μs of the fault, and the fault cohesion
C0.
The method is then applied on 145 focal mechanisms of the 2011 March 11th
Tohoku-Oki (Japan) earthquake sequence. This application delineates, along or in the
vicinity of the Pacific-Okhotsk plate interface, three types of domains characterized
by favorable orientations, unfavorable orientations or severe misorientations of
mainshock/aftershock fault planes. Aftershock focal mechanisms that plot in the ’severe
misorientation’ domains are interpreted to have occurred because of pore fluid
pressures exceeding the regional minimum principal stress at those locations. The
distribution of these ’severe misorientation’ domains partly overlaps the asperities or
the low-velocity anomalies mapped on the plate interface off NE Japan. The 3-D
fault reactivation analysis appears complementary to geophysical investigations. |
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