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