--> ABSTRACT: New Geometrical Techniques to Infer Listric Normal Fault Shapes, by Bill Kilsdonk and J. H. Spang; #91030 (2010)
[First Hit]

Datapages, Inc.Print this page

New Geometrical Techniques to Infer Listric Normal Previous HitFaultNext Hit Shapes

Bill Kilsdonk, J. H. Spang

Two new geometric methods infer listric normal Previous HitfaultNext Hit shape with both area and bed-length balances. These two new methods are significantly better than older published methods. Balancing errors with these methods are generally less than 5% and are often close to 1%. The first method assumes constant layer thickness and constant line length. The second method projects displacement vectors from the rollover down between dipping Previous HitplanesNext Hit. Results from the two methods are virtually identical. Both assume no extension of the marker bed that defines the rollover, but either can be modified to accommodate marker beds with known extension.

The horizontal displacement on the Previous HitfaultNext Hit is the difference between the lengths of the deformed marker bed and the undeformed marker bed, both measured from the Previous HitfaultNext Hit to a point where the deformed bed assumes regional dip. In the first method, an undeformed marker line is drawn at regional dip to intersect the Previous HitfaultNext Hit above the rollover toe. The distance between the marker line and the regional dip line that intersects the footwall cutoff is the layer thickness. A deformed marker line is drawn below the known rollover assuming horizontal displacement constant layer thickness, and constant line length. The end of the deformed marker line must lie on the Previous HitfaultNext Hit, and the Previous HitfaultNext Hit is drawn to meet it. The procedure is repeated with subsequently lower marker lines to yield the Previous HitfaultNext Hit shape.

In the second method, displacement vectors are found by connecting points on the rollover with corresponding points on the appropriate regional dip line. The vectors are projected down between Previous HitplanesNext Hit whose dips are determined by both the horizontal displacement and the rollover shape. The Previous HitplanesNext Hit are vertical where the marker bed has regional dip, but are inclined where the marker bed rolls over. The change in inclination is continuous along the length of the rollover. The projected displacement vectors connect with one another at projection Previous HitplanesNext Hit to infer the Previous HitfaultTop shape.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.