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| Titel |
Theory of mechanically heterogeneous critical-taper wedges with application to Barbados |
| VerfasserIn |
E.-C. Yeh, J. Suppe  , M. H. Huang |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024723
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| Zusammenfassung |
| Many well-imaged accretionary wedges are mechanically heterogeneous based on spatial
variations in wedge taper. For example, the toes of active accretionary wedges such as
the Nankai trough and Barbados display deceasing surface slope α away from the
toe, with no associated variation in the detachment dip β. Likely sources of this
heterogeneity in taper are spatial variations in fluid pressure, density, cohesion, and fault
strength. We parameterize these in-situ observables from the active accretionary
wedges and evaluate the influences of spatial variations of these observables on
the development of heterogeneous wedges. We show that the spatial gradients in
pore-fluid pressure can be approximated by a single easily observable parameter, the
fluid-retention depth zFRD below which compaction is strongly diminished. The
Hubbert-Rubey weakening (1 - λ) is a simple function of fluid-retention depth
(1 -λ) = (1 -λh)[zFRD/ z] . We find that the heterogeneous critical taper wedge theory of
Dahlen (1990) can be recast in terms of the ratio of fluid-retention depth zFRD to the
detachment depth H, which leads to more concise and easily applied critical-taper wedge
equations.
The analysis results of the Barbados wedge show that the fluid-retention depth
ratiozFRD-H dramatically decreases in the toe area and slightly declines into the back of
wedge. This leads that both wedge and fault strengths follow the similar trend as
fluid-retention depth ratio does. For example, wedge strength of 0.4 significantly lessens in
the first 30km of toe area and reaches 0.1 into the wedge interior. Fault strength has the
similar reduction from 0.03 to 0.01, indicating a noticeable weak fault in general. The lateral
gradients of mean physical properties only contribute small influence to develop this
heterogeneous wedge. Compared with the CORK measurement of fluid pressure within the
detachment, the fault strength is contributed from either extremely weak basal friction
coefficient of 0.15 with the static fluid pressure at the wedge base or the high transient fluid
pressure pulse of 0.97 with the basal friction coefficient of 0.45. Our results strongly
indicate that temporal-spatial variations of fluid pressure play an important role of
developing heterogeneous wedges. The detailed analysis on both co-variations of surface
slope-detachment dip and fault strength-wedge strength displays that the entire wedge and
detachment are completely heterogeneous, even in the apparently homogeneous interior. |
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