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	Extensional sandbox model helps to investigate fault system connectivity.
	The cross section through sandbox model above shows offset of colored sand layers by normal faults; scale is in 5-cm increments.

Physical analog modeling is a well-established laboratory technique for reproducing the developmental sequence and overall geometry of geologic structures. In the models, rock strata are represented by table-top scale analog layers such as:

• Sand

• Claycake

• Silicon putty

Analog models can be constructed and deformed in a number of ways to simulate real-world structures and test tectonic hypotheses. Construction of digital terrain models (DTMs) at different time steps, photography, and horizontal and vertical slicing of models enables in-depth characterization and quantification of model results.

The analog materials and deformation styles are selected to reproduce, at small scale, geometric and kinematic features of natural geologic structures. To simulate development of the geologic structures, the analog layers are deformed consistent with the observable geology.

Extensional sandbox model		Adding growth (syn-kinematic sedimentary) layers to the sandbox model

Physical Modeling Laboratory

The Southwest Research Institute (SwRI) Physical Modeling Laboratory, built in 1995, is a state-of-the-art facility designed to emulate a variety of tectonic settings. The modeling apparatus is periodically updated and modified to increase the range of simulated geologic environments and also maintain SwRI capabilities as an innovator in the field. Displacements are imparted to the models by gravity or programmable motor drives. The apparatus can be configured to represent most tectonic deformation style or combinations of these styles, for example:

	Right-lateral strike-slip system with right-stepping major fault. Sand deforming above  thick ductile substratum
	Cross section of strike-slip fault system above
	Pull-apart basin developed between right-stepping, right-lateral strike-slip faults
	Elliptical dome developing in claycake during regional extension; clay deforming over active dome
	Detail of breaching relay ramp between two en echelon normal faults in sandbox model; grid squares initially 1.5-cm square

• Extension

• Contraction

• Strike slip

• Localized uplift

• Localized doming

• Normal faulting

• Reverse faulting

• Deformation of a brittle layer over a ductile substratum

Physical Analog Model Applications

Physical analog models:

• Allow seismic interpreters to see three-dimensional (3D), kinematically and geometrically realistic simulations of geologic structures. Physical analog models are particularly useful for exploring fault system kinematics where real world analogs are not accessible

• Provide quantitative data for input to seismic interpretation and numerical models, including finite element modeling and reservoir simulation

• Can be configured at a range of scales: crustal, basin, field, and outcrop, including structures below the detection limits of seismic methods

• Show geometric development of complex structures (data vital for modeling the petroleum system through maturation, migration, and reservoir charge stages)

• Can be used to test a variety of tectonic histories. By calibrating model results against natural structures, tectonic history can be incorporated into the interpretation of complex structures

• Aid in the interpretation of fractured reservoirs, including information on fracture density and fracture orientation

• Provide understanding of fault geometry in faulted reservoirs or faulted aquifers.

Photography

Still photographs are used to document the pre-, syn-, and post-kinematic stages of the experiments. While deformation is active, models are photographed from above at set intervals and with a variety of illumination angles. Photographs are also taken from various angles and magnifications throughout the experiment and are keyed to displacement magnitude. Vertical and horizontal slicing after model deformation allows analysis and photography of the internal structure of the model.

	Digital terrain model (DTM) created using dynamic structured light (DSL), plan view
	DTM as above, oblique view
	Photograph of model surface used to create the DTM above; extensional clay model

Digital Terrain Models

Mapping of 3D seismic reflection surveys, availability of 3D digital topographic data for Earth's surface (and Mars), and development of computer software for 3D visualization and geologic framework modeling have led to rapid growth in 3D analysis of geologic structures. Detailed measurement of the 3D geometry of physical analog models, however, has lagged behind.

To close this data analysis gap, we are using a new SwRI-developed technique to produce digital terrain models (DTMs) of the deformed model upper surface using patterned light. Digital images of the model upper surface are collected throughout the model deformation and processed near real time to construct 3D DTMs that represent the topography of the model upper surface. These 3D DTMs are used for:

• Visualization

• Extraction of fault cutoff lines

• Export to finite element models

• Extraction of topographic slope

• Extraction of slope aspect information

• Quantitative evaluation of topomorphic evolution

• Production of digital shaded relief models

• Quantitative comparison with real-world examples from digital topographic data, 3D seismic reflection surveys, and geologic framework modeling

For more information about the physical analog modeling capabilities at SwRI or how you can contract with SwRI, please contact Darrell Sims at dsims@swri.org or (210) 522-6829, or David Ferrill, Ph.D. at dferrill@swri.org or (210) 522-6082.

| Department of Earth, Material and Planetary Sciences | Geosciences and Engineering Division | SwRI Home |

Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

March 29, 2009