Scaled Experimental Modeling of Gravitational Collapse Structures
E. R. Poorvin
Department of Earth and Planetary Sciences, Rutgers University
Gravitational collapse, the non-catastrophic failure of an unstable slope,
commonly produces coherent domino-style fault
blocks. Scarp-creation and
scarp-retreat, produced by faulting and/or erosion, are the main mechanisms for
creating the unstable slope. Gravitational collapse structures may
compartmentalize hydrocarbon traps and influence hydrocarbon recovery (e.g.,
Sirikit field, onshore Thailand).
To document the geometry and evolution of gravitational collapse
structures, I conducted a series of scaled experimental models with wet clay. The
modeling variables included clay strength (i.e., clay density, 1.60 g/cm3 and 1.68
g/cm3) and scarp height (4 to 8 cm). These two variables are related – as
strength increases, the potential scarp height increases. Each model had two
phases: an initial scarp-creation phase followed by a scarp-retreat phase. Scarpcreation
involved vertical clay removal (2 mm every 2 minutes). Scarp-retreat
involved horizontal clay removal (1.67 mm every minute). During scarp-creation,
collapse began as small normal faults parallel to the scarp. As scarp height
increased, the displacement on these faults increased, and they began to link.
Most faults dipped moderately to steeply toward the scarp. Smaller secondary
faults formed within the fault
blocks to accommodate
fault
-block rotation. During
scarp-retreat, displacement on the major linked normal faults continued to
increase, and new normal faults formed behind the first
fault
set. Displacement
on the major linked faults increased until the scarp retreat reached a critical
distance. At this point the first
fault
set became inactive, and collapse
concentrated along the second
fault
set.
AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas