--> --> Fault Locking and Alternate Fault Activity in Outcrop and Subsurface, a Transfer Mechanism, Jean-Yves Chatellier, #40368 (2009).
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PSPrevious HitFaultNext Hit Locking and Alternate Previous HitFaultNext Hit Activity in Outcrop and Subsurface, a Transfer Mechanism*

 

Jean-Yves Chatellier1

 

Search and Discovery Article #40368 (2009)

Posted January 26, 2009

 

*Adapted from poster presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008

 

1Talisman Energy Inc., Calgary, AB, Canada ([email protected])

 

Abstract 

A series of observations from outstanding outcrops in Sarawak and in Ecuador led to a concept of Previous HitfaultNext Hit lock and alternate Previous HitfaultNext Hit activity that can explain numerous geometric anomalies encountered in the subsurface.  

The Previous HitfaultNext Hit locking mechanism takes place when the interface of two contrasting lithologies on the hanging wall of a Previous HitfaultNext Hit become aligned with another such interface on the footwall. Compressional, transpressional or oblique stress then create a microdetachment along the lithological interfaces on both sides of the Previous HitfaultNext Hit. The displacement along the major Previous HitfaultNext Hit is thus interrupted/locked and the strain is transferred to a neighboring Previous HitfaultNext Hit.  

In the Western Canadian Basin, numerous formations with dramatic vertical lithological changes have confirmed the validity of the proposed mechanism. The lithological contrasts relate to their rheology and invoke the interface between shales and massive sandstones, massive siltstones or competent grain-supported carbonates. The Mississippian Pekisko Formation in West Central Alberta will be used to demonstrate the mechanisms invoked and the resulting geometries.  

Previous HitFaultNext Hit locking is best recognized with either a perfect repeat (superposition) of a very competent unit or when all of the tops and bases of the same formation occur at exactly the same TVDss depth.  

The same mechanism of Previous HitfaultNext Hit locking and alternating Previous HitfaultNext Hit activity can be evoked at basin scale, 1) in map view when dealing with conjugate Previous HitfaultTop sets, 2) in cross section when dealing with triangle zones or when there is interference between horizontal detachments and subduction zones (tsunami of December 26th 2004).