In Situ Monitoring of Free-Phase Gas Accumulation and Release in Peatlands Using Ground Penetrating Radar (GPR)

We tested a set of surface common mid-point (CMP) ground penetrating radar (GPR) surveys combined with elevation rods ( to monitor surface deformation) and gas flux measurements to investigate in-situ biogenic gas dynamics and ebullition events in a northern peatland ( raised bog). The main findings are: ( 1) changes in the two-way travel time from the surface to prominent reflectors allow estimation of average gas contents and evolution of free-phase gas (FPG); ( 2) peat surface deformation and gas flux measurements are strongly consistent with GPR estimated changes in FPG content over time; ( 3) rapid decreases in atmospheric pressure are associated with increased gas flux; and ( 4) single ebullition events can induce releases of methane much larger ( up to 192 g/m(2)) than fluxes reported by others. These results indicate that GPR is a useful tool for assessing the spatial distribution, temporal variation, and volume of biogenic gas deposits in peatlands.

Along-Strike Differences in the Southern Alps of New Zealand: Consequences of Inherited Variation in Rheology

Long- and short-term strain variations along the Australian-Pacific plate boundary through the South Island of New Zealand, including a 300% increase in orogen width, coexistence of oblique thrusting on orthogonal structures, and variability in the locus of orogenic gold deposits, coincide with rheologically relevant geological variation. Our model investigates the consequences of thin, strong lower crust in the north and thick, weak lower crust in the south. Solution of the full 3-D mechanical equations reproduces the larger wavelength strain patterns of the orogen. A 3-D perturbation-based analytical solution leads to the identification of the sensitivity of displacement type to minor stress changes. Transition from boundary-normal thrusting to boundary-parallel thrusting occurs at the transition from strong to weak lower crust and is related to an increase in either tau(yz) (shear stress in the yz plane) or the ratio of the coordinate normal stresses, (sigma(yy)/sigma(xx)), where x and y are in the horizontal and z is vertical. Both mechanisms are compatible with the geologically dependent rheological variation employed in our model. Citation: Upton, P., P. O. Koons, D. Craw, C. M. Henderson, and R. Enlow (2009), Along-strike differences in the Southern Alps of New Zealand: Consequences of inherited variation in rheology, Tectonics, 28, TC2007, doi:10.1029/2008TC002353.