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Displacement fields and finite strains in a sandbox model simulating a fold-thrust-belt
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
2007 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 169, no 3, 1341-1355 p.Article in journal (Refereed) Published
Abstract [en]

A sandbox model consisting of two adjacent mechanically different decollements (frictional and viscous) loosely simulated the southeastern part of the Zagros fold-thrust-belt. Digital images of the model surface are used to coordinate passive markers on the surface and quantify displacement fields and estimate 2-D finite strains. These analyses show that, mapped in a fixed coordinate system, the deformation front propagates at different rates above the two decollements. Strain analysis of the model surface at different stages of deformation also shows that cumulative strain is more heterogeneous above the viscous decollement where strain domains are separated by fault zones. Maps of displacement fields, finite strain ellipses and dilatation also differ in character above the two decollements. Displacements above a viscous decollement decrease gradually towards the foreland, whereas they decrease sharply in front of the frontal thrust above the frictional decollement. Our analyses also show that the estimated finite strain depends not only on the density of the marker points chosen for the analysis, but also their initial distribution relative to the structures. This comparison shows that marker density limits measuring the actual strains in a heterogeneously deforming fold-thrust-belt and marker density and distribution have a strong impact on the strain analysed in nature. The similarity of our model with nature is examined with recent GPS study in the Zagros fold-thrust-belt (SW Iran) and shows, similar to the model results, that a weak salt decollement causes divergent movement in the sedimentary cover in SE Zagros.

Place, publisher, year, edition, pages
2007. Vol. 169, no 3, 1341-1355 p.
Keyword [en]
analogue modelling, decollement, fold-thrust-belt, strain, Zagros
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-96014DOI: 10.1111/j.1365-246X.2007.03341.xISI: 000247205400040OAI: oai:DiVA.org:uu-96014DiVA: diva2:170419
Available from: 2007-05-07 Created: 2007-05-07 Last updated: 2011-11-17Bibliographically approved
In thesis
1. Ground Movements in the Zagros Fold-Thrust Belt of SW Iran Measured by GPS and InSAR Compared to Physical Models
Open this publication in new window or tab >>Ground Movements in the Zagros Fold-Thrust Belt of SW Iran Measured by GPS and InSAR Compared to Physical Models
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis uses geodetic satellite data to measure present-day crustal deformation in the Zagros fold-thrust belt (SW Iran). Geodetic-type measurements are also used in down-scaled models that simulate the surface deformations seen in convergent settings like the Zagros fold-thrust belt.

Global Positioning System (GPS) measurements of three surveys between 1998 and 2001 indicate 9 ± 3 mm/yr and 5 ± 3 mm/yr shortening across the SE and NW Zagros respectively. GPS results show that in addition to the different rates and directions of shortening on either side of the NS trending Kazerun fault, local along-belt extension occurs to the east.

Differential SAR interferograms of ERS1 & 2 images between 1992 and 1999 detect 8 ± 4 mm/yr uplift rate across a newly recognized fault in SW Qeshm Island. This can be attributed to a steep imbricate thrust that may still represent the local Zagros deformation front.

The salt diapirs in the Zagros rise from a source layer that acts as a low-frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern Zagros whereas the cover to the west deforms above a high-friction decollement. Physical models were prepared to simulate cover deformation in the Zagros by shortening a sand pack above adjacent high- and low-frictional decollements (represented by a ductile layer). The strain distributions differed above the two types of decollements; it was more heterogeneous above the salt where local extension in the shortening direction was dominant. A separate work also investigated systematically the role of basal friction on cover deformation in convergent settings. Accurate height measurements of the model surface by laser-scanner indicated a deformation front more distal than usual, particularly in the low-basal frictional models. The volume reduction in our shortened sand models correlated directly with their basal friction.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 38 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 318
Earth sciences, Zagros fold-thrust belt, deformation, GPS, InSAR, Physical modeling, tectonics, convergent settings, basal friction, Geovetenskap
urn:nbn:se:uu:diva-7928 (URN)978-91-554-6918-4 (ISBN)
Public defence
2007-06-01, Axel Hansrambergsalen, Geocentrum, Villavägen 16, SE75236, Uppsala, 10:00
Available from: 2007-05-07 Created: 2007-05-07Bibliographically approved

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Nilforoushan, FaramarzKoyi, H.
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