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| Titel |
Mechanical analysis of fault activation in southern Longmen Shan fold-and- thrust belt |
| VerfasserIn |
Zhen Zhang, Huai Zhang, Liangshu Wang, Yaolin Shi, Yves M. Leroy |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250154187
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| Publikation (Nr.) |
 EGU/EGU2017-19255.pdf |
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| Zusammenfassung |
| A mixed fault activation mode with obvious hinterland rupture in the southern
Longmen Shan, the eastern margin of Tibetan Plateau, is revealed by recent 2008
Mw7.9 Wenchuan and 2013 Mw6.6 Lushan earthquakes together with GPS
measurements. How to systematically understand the coexistence and competition
mechanisms of fault activation, especially the principal-subordinate relationship on
deformation absorption, in essence, involves mechanical onset analysis of this fold-
and-thrust belt. However, due to the two-décollement- level thrust system with active
‘flat-ramp- flat’ geometry décollement, the predication of fault activation in the LMS
has beyond the scope of Critical Coulomb wedge theory, not to mention the
synchronous listric-type splay fault rupturing in the Beichuan fault (BCF) and
Pengguan fault (PGF). For that purpose, we adopted maximum strength theorem, the
kinematic approach of limit analysis, to deal with mechanical analysis of fault
activation. Four end-member failure modes, or collapse mechanisms (CMs) in
classical limit analysis, are proposed corresponding to the rupture of BCF, PGF,
Range Frontal Blind Fault (RFBF) and the rupture of the flat-ramp- flat décollement
into Sichuan Basin via RFBF. By selecting the available CMs via finite element limit
analysis, the listric geometry of BCF and PGF is demonstrated to the dominant factor
in trapping deformation in the hinterland. To activate the high-angle Beichuan splay
fault, low cohesion and low friction angle on the BCF are combined effects on the
rupturing of BCF. The change in cohesion and friction on BCF eventually forms the
transition state between high angle BCF and low-angle PGF. Besides, due to the
existence of low frictional upper décollement layer in Sichuan Basin (the Triassic
evaporate layer), small amount of deformation is attracted into the Sichuan Basin
forming small-scale thrusting folding. Moreover, favorable deformation migration
toward Sichuan Basin is jointly influenced by larger upper décollement layer rock
strength, the vergence of thrusting fold in the deformation front, the low density and
small bulk rock strength of the overlying strata in Sichuan Basin since Mesozoic.
Hence, present-day mixed fault activation mode of the LMS region is a combined
effect on fault geometry and frictional properties. |
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