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Given the wealth of data concerning the kinematics of deforming fold-thrust belts (FTBs), first-order generalizations about
how the major strain components vary within a deforming thrust wedges are considered. These generally observed strain patterns
are used to constrain a general, kinematics-based, FTB-wedge model. We considered five strain components within a deforming
thrust sheet: (1) thrust-parallel simple shear, (2) horizontal contractional strain, (3) thrust-normal reaction strain, (4)
gravitational strain, and (5) a lateral confining boundary condition. After making assumptions about how these strain components
vary within a model FTB-wedge, the incremental deformation matrix can be calculated for any given point within the deforming
wedge. Thus, the material path of a given marker can be determined and an initially spherical marker’s strain path can be
calculated as it moves through the deforming wedge. Furthermore, by illustrating various kinematic parameters of many initially
spherical markers (for example, Flinn’s k-value, incremental octahedral shear strain, transport-perpendicular stretch), we have assembled representations of the kinematic
properties of the entire model wedge. By including a flat-ramp-flat fault surface geometry for the model wedge, we are able
to examine the kinematic effects of this relatively common structural geometry. Within the fault ramp segment there are greater
incremental strain magnitudes, out-of-the-plane motion, and flattening strains. Additionally, data from this model suggests
that gravitational strains potentially have a significant effect on the strain distribution within a deforming thrust wedge.
M. Mookerjee is formerly Matthew Strine. 相似文献
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Lake Houston is a man-made reservoir located northeast of Houston, Texas. The purpose of this investigation was to document
suspended sediment transport, sedimentation, and resuspension in the lake with a view towards estimating the influence of
sedimentation on water quality. Sediment traps were placed in strategic locations in the lake to collect suspended sediments.
Samples were analyzed for bulk density, grain size, organic carbon, and a number of trace elements. These data were analyzed
along with meteorological data to examine those factors which regulate suspended sediment input and dispersal, and the role
of suspended sediments in controlling water quality within the lake.
Sediment input to the lake depends primarily on the intensity of rainfall in the watershed. Sediment movement within the lake
is strongly influenced by wave activity, which resuspends sediments from shallow areas, and by wind-driven circulation. The
increased residence time of suspended sediments due to resuspension allows greater decomposition of organic matter and the
release of several trace elements from sediments to the water column.
Virtually all samples from sediment traps suspended between 1 and 5 m above the lake bottom contain medium to coarse silt,
and even some very fine sand-sized material. This implies that circulation in Lake Houston is periodically intense enough
to transport this size material in suspension. During winter, northerly winds with sustained velocities of greater than 5
m/sec provide the most suitable condition for rapid (<1 d) transport of suspended sediment down the length of the lake.
Fluctuations in current velocities and the subsequent suspension/deposition of particles may explain variations in the abundance
of coliform bacteria in Lake Houston. 相似文献
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