Physical models of normal-fault relays between variably offset grabens

Journal Article · Tue Aug 01 04:00:00 EDT 1995 · AAPG Bulletin

OSTI ID:127725

Vendeville, B C ^[1]; Le Calvez, J ^[2]

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1. Univ. of Texas, Austin, TX (United States)
2. Universite de Nice (France)

We conducted a series of scaled models in which two grabens initially offset along the direction of regional extension subsequently propagated freely along strike while synkinematic sediments were added. Models comprised a thick layer of dry sand overlying a thin lubricating layer of viscous silicone. The experiments are applicable to both crustal scale and to the scale of a brittle sedimentary cover above a salt or shale decollement. Results show that fault orientation and linkage vary with graben offset ({Delta}L) and model thickness (h). Grabens with small offset (O < {Delta}L< h/2) propagated along strike while remaining perpendicular to the direction of regional extension; the grabens eventually linked. Fault traces were initially jagged but straightened after further extension and sedimentation. Grabens with moderate offsets (h/2 < {Delta}L < 2h) widened as they propagated toward each other. Soft fault linkage created ramps of strained overburden blocks between faults. Later, ramps were cut by hard-linked faults. Hour-glass structures formed where faults of opposite vergence intersected. Fault slip progressively decreased along strike. Where graben offset was large ({Delta}L > 2h), a transtensional graben was generated oblique to the direction of regional extension, providing hard linkage with each initial graben. Fault-slip gradients along fault strike remained low. We infer that formation of a new oblique graben reflects a size threshold above which the rock volume between the grabens (proportional to graben offset) cannot rotate or deform by soft linkage to accommodate deformation.

• OSTI ID: 127725
• Report Number(s): CONF-950995--
• Journal Information: AAPG Bulletin, Journal Name: AAPG Bulletin Journal Issue: 8 Vol. 79; ISSN 0149-1423; ISSN AABUD2
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
EXPERIMENTAL DATA
GEOLOGIC FAULTS
GEOMETRY
MATERIALS TESTING
SEDIMENTS