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Physical models have been widely used to study geological structures for more than one hundred years. The greatest benefit of physical models is that with proper scaling of model dimensions and materials, researchers can directly observe structural or tectonic processes that take millions of years to occur naturally. Despite this benefit, however, use of physical models is not widespread because their construction and analysis is commonly labor-intensive work that yields largely qualitative information on structural geometry and limited quantitative information on displacement and strain. This paper describes how close-range photogrammetry can be used to obtain quantitative information on the geometry, displacement, and strain patterns in an evolving physical model. The technique is an inexpensive, high-resolution, noninvasive, and efficient method that uses standard commercial software and a digital camera to determine the x, y, z positions of high-contrast markers placed on the model surface. The model geometry at any given time is defined by the positions of all the markers, whereas strain and displacement are obtained by comparing, or tracking, the positions of the markers at different times during an experiment. We present as an example application of the technique, an analysis of scaled physical models of monoclimes that form above basement-involved reverse faults with differing displacement distributions. Using close-range photogrammetry, we are able to link fault displacement and lateral propagation history to unique, evolving, three-dimensional (3-D) geometries and deformation patterns that are unlikely to be revealed by other analysis techniques. [ABSTRACT FROM AUTHOR]

Presents results of models for fracture evolution in folds that form when sedimentary strata drape over basement-involved reverse faults. Use of fault-bend in predicting the characteristics of joint networks; Impact of the timing of jointing during folding on spatial variation in joint orientations; Characteristics of fold-related joint sets.

Argues that poroelastic behavior is responsible for the unusually high horizontal stress (Sh) in the overpressured parts of sedimentary basins. Correlation between Sh and pore pressure (Pp); Definition of the theory of poroelasticity; Demonstration of poroelastic behavior.

Comments on the research `Heterogeneous Hydrofracture Development and Accretionary Fault Dynamics' by Kevin M. Brown by pointing out the appropriate method for analysis of natural hydraulic fracturing. Debate on the orientation of principal stresses near the bases of accretionary wedges.

The fluid system within a critically tapering orogenic wedge is governed by complex interactions between topographic drive, thermal gradients, prograde dehydration reactions, internal structure, and regional tectonic compaction. Despite this complexity, topography is widely known to be the primary driving potential responsible for basin-scale fluid migration within the upper 7-10 km of an orogenic wedge. In recent years, investigators have revisited the problem of basin-scale fluid flow with an emphasis on depth-decaying permeability, which is a geologic phenomenon that is seldom accounted for in regional flow models. These recent investigations have shown that depth-dependent permeability at the basin scale strongly influences the relationship between local- and regional-scale flow paths. Here we investigate topography driven fluid flow within an orogenic wedge using a numerical modeling experiment designed to assess first-order fluid system behavior when permeability decreases systematically with depth. Critical taper theory is invoked to define two-dimensional basin geometry, and three subaerially exposed orogenic wedge models are presented with critical taper angles of 2°, 4°, and 10°. To assess the combined influence of topographic slope and depth-dependent permeability, a constant rate infiltration is applied at the wedge surface and a transient simulation is performed within each model for 20 m.y. Our results suggest that (1) depth-dependent permeability severely limits the penetration depth of infiltrating water within broadly tapering orogenic wedge systems, (2) fluid system evolution within a narrowly tapering orogenic wedge (i.e., ≤2°) is governed by local-scale topography superimposed on the regional gradient, (3) the influence of subbasin topography on local-scale fluid circulation is suppressed as the regional topographic gradient increases, and (4) the spatial distribution of groundwater residence time is fundamentally different when topographic slope exceeds 3°. [ABSTRACT FROM AUTHOR]

Oxygen, carbon, and strontium isotope variations in vein-filling calcite and quartz Cements and their host rocks are used to elucidate the origin, spatial and temporal evolution, and migration pathways of fluids in the detachment Nuncios fold complex, northeastern Mexico. The folded Mesozoic sedimentary sequence contains two regional paleohydrostratigraphic units separated by a unit of low permeability. Two main generations of cements are present in both paleohydrostratigraphic units. Distinct differences exist between δ18O, δ13C, 87Sr/86Sr, and fluid-inclusion temperatures of early vein-filling cements in the lower and the upper units. These differences, together with a strong correspondence between early cement and host-rock δ18O and δ13C values, suggest that early diagenetic fluids were compartmentalized between the two units. Late vein-filling cements have isotopic compositions and fluid-inclusion temperatures that converge to similar values, indicating a change to open fluid flow between the lower and upper units. We hypothesize that the fluid history of the Nuncios fold complex evolved in two main stages: (1) burial diagenesis and early folding, during which fluids were confined within individual units, and (2) late-stage folding, during which increased deformation associated with fold tightening caused the expulsion of fluid from the lower unit into the upper unit. [ABSTRACT FROM AUTHOR]