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41.
42.
The GIS approach to evaporite-karst geohazards in Great Britain 总被引:2,自引:0,他引:2
A. H. Cooper 《Environmental Geology》2008,53(5):981-992
Evaporite karst in Great Britain has formed in Permian and Triassic gypsum, and in Triassic salt. Active dissolution of these
deposits can occur on a human rather than a geological timescale causing subsidence and building damage. The British Geological
Survey has taken two approaches towards understanding and advising on hazards caused by dissolution of these soluble rocks.
At a detailed level, a national database and GIS of karstic features is being populated. Information gathered includes dolines,
springs, stream sinks, caves and building damage. At a national level, the soluble rocks in Great Britain have been identified
and digital-map polygon information relating to them was extracted from the British 1:50,000-scale digital geological map.
These areas have been assessed, and in places their margins extended to include some overlying rocks where subsidence features
are known to penetrate upwards through the overlying sequence. The national areas have then been assessed using detailed local
information to assign a susceptibility rating from A (extremely low) to E (high), depending on the nature and regularity of
the subsidence events that occur. This national zonation of the soluble rocks can be used for planning, construction and in
the insurance businesses. This has proved useful for assessing the potential stability of linear routes, such as roads and
pipelines or for other important structures such as bridges and buildings. The information can also be used to delineate zones
of karstic groundwater flow. 相似文献
43.
The halite-bearing Barbastro Formation crops out in the core of the Barbastro Anticline (Ebro Tertiary Basin). This anticline
is traversed perpendicularly by some of the most important Pyrenean drainages such as the Cinca and Noguera-Ribagorzana Rivers.
The terrace sequences of these fluvial systems have been used as markers to identify and assess dissolution-induced subsidence
and salt tectonics. In the limbs of the anticline, terrace deposits underlain by detrital bedrock do not show any evidence
of deformation and have a consistent thickness of less than 10 m. The deposits of certain terrace levels of the Noguera-Ribagorzana
River and its tributary, the Lo Reguer Creek, are locally thickened filling basins generated by dissolution-induced synsedimentary
subsidence up to several kilometers long and more than 100 m deep. Conversely, terraces of the Cinca River do not show anomalously
high thicknesses, but local uplifts related to differential upward flow of the halite-bearing bedrock. Locally, a minimum
uplift rate of 0.3 mm/year has been estimated from a 64-ka terrace tilted away from the valley. The subsidence hazards occur
chiefly in areas where the ground receives artificial water recharge. Serviceability of some canals has been notoriously affected
by evaporite karstification. The problem has been mitigated to acceptable levels by grouting. Numerous buildings of Ivars
de Noguera are severely damaged by dissolution subsidence, and possibly, by hydrocompaction of gypsiferous silts. The pipe
network has been replaced to ameliorate the subsidence risk. In the Cinca River valley, cavities with a total volume of about
180,500 m3 have been created by solution mining at depths greater than 500 m. No investigation methods are applied in the brine field
to monitor the distribution and evolution of artificial voids. Substantial increase in salinity of the Cinca River is another
evidence of subjacent evaporite dissolution. 相似文献
44.
A genetic classification of sinkholes illustrated from evaporite paleokarst exposures in Spain 总被引:2,自引:0,他引:2
This contribution analyses the processes involved in the generation of sinkholes from the study of paleokarst features exposed
in four Spanish Tertiary basins. Bedrock strata are subhorizontal evaporites, and in three of the basins they include halite
and glauberite in the subsurface. Our studies suggest that formation of dolines in these areas results from a wider range
of subsidence processes than those included in the most recently published sinkhole classifications; a new genetic classification
of sinkholes applicable to both carbonate and evaporite karst areas is thus proposed. With the exception of solution dolines,
it defines the main sinkhole types by use of two terms that refer to the material affected by downward gravitational movements
(cover, bedrock or caprock) and the main type of process involved (collapse, suffosion or sagging). Sinkholes that result
from the combination of several subsidence processes and affect more than one type of material are described by combinations
of the different terms with the dominant material or process followed by the secondary one (e.g. bedrock sagging and collapse
sinkhole). The mechanism of collapse includes any brittle gravitational deformation of cover and bedrock material, such as
upward stoping of cavities by roof failure, development of well-defined failure planes and rock brecciation. Suffosion is
the downward migration of cover deposits through dissolutional conduits accompanied with ductile settling. Sagging is the
ductile flexure of sediments caused by differential corrosional lowering of the rockhead or interstratal karstification of
the soluble bedrock. The paleokarsts we analysed suggest that the sagging mechanism (not included in previous genetic classifications)
plays an important role in the generation of sinkholes in evaporites. Moreover, collapse processes are more significant in
extent and rate in areas underlain by evaporites than in carbonate karst, primarily due to the greater solubility of the evaporites
and the lower mechanical strength and ductile rheology of gypsum and salt rocks. 相似文献
45.
Numerical Simulation of Bed Separation Development and Grout Injecting into Separations 总被引:2,自引:0,他引:2
In this paper, the Cosserat theory that has been incorporated into a three dimensional finite element code COSFLOW, is applied
to analyze the development of bed separations in the layered overburden and grout injection into the bed separations. The
mechanism of bed separation development during the longwall mining is investigated. A parametric study is carried out to investigate
the effect of major factors including hard rock grade, panel height and panel weight on bed separation development. Based
on the modeling, a conceptual model to describe the development process of bed separation is proposed. The effect of grout
injecting into the bed separations on subsidence reduction is also studied and the conclusion agrees well with the common
realization. 相似文献
46.
47.
The differential interferometric synthetic aperture radar (DInSAR) remote sensing technique has proven to be invaluable in the remote monitoring of earth surface movements associated with the extraction and geostorage (subsurface injection) of natural resources (water, oil, gas). However, a significant limitation of this technique is the low density and uneven coverage that may be achieved over vegetated rural environments. The Intermittent Small Baseline Subset (ISBAS) method, an amended version of the established SBAS algorithm, has been designed to improve coverage over rural, vegetated, land cover classes by allowing for the intermittent coherence that is predominant in such areas. In this paper we perform a validation of the ISBAS method over an area of gas production and geostorage in North Holland, the Netherlands. Forty-two ERS-2 (SAR) C-band images (1995–2000) and 63 ENVISAT (ASAR) C-band images (2003–2010) were processed using the ISBAS technique and the derived measurements enabled the identification of subsidence patterns in rural and urban areas alike. The dominant feature was an area of subsidence to the west of Alkmaar, attributed to natural gas production from the Bergermeer reservoir, where subsidence rates in the region of 3 mm/year were measured. Displacements derived using linear and non-linear surface deformation models were validated with respect to the first order system of levelling benchmarks which form the Amsterdam Ordnance Datum (NAP). It was established that ISBAS products were accurate to within 1.52 mm/year and 1.12 mm/year for the ERS and ENVISAT data sets respectively. Errors achieved were comparable to results using persistent scatterers interferometry (PSI) during a validation activity carried out in the European Space Agency Terrafirma project. These results confirm the capability of the ISBAS method to provide a more regular sampling of land motion measurements over gas fields that may be critically used in future to infer the properties of buried, fluid-filled, porous rock. 相似文献
48.
D. Praeg M.S. Stoker P.M. Shannon S. Ceramicola B. Hjelstuen J.S. Laberg A. Mathiesen 《Marine and Petroleum Geology》2005,22(9-10):1007
The North Atlantic margins are archetypally passive, yet they have experienced post-rift vertical movements of up to kilometre scale. The Cenozoic history of such movements along the NW European margin, from Ireland to mid-Norway, is examined by integrating published analyses of uplift and subsidence with higher resolution tectono-stratigraphic indicators of relative movements (including results from the STRATAGEM project). Three episodes of epeirogenic movement are identified, in the early, mid- and late Cenozoic, distinct from at least one phase of compressive tectonism. Two forms of epeirogenic movement are recognised, referred to as tilting (coeval subsidence and uplift, rotations <1° over distances of 100s of Kilometres) and sagging (strongly differential subsidence, rotations up to 4° over distances <100 km). Each epeirogenic episode involved relatively rapid (<10 Ma) km-scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity-bounded stratigraphic units. Early Cenozoic tilting (late Paleocene to early Eocene, c. 60–50 Ma) caused the basinward progradation of shelf-slope wedges from elongate uplifts along the inner continental margin and from offshore highs. Mid-Cenozoic sagging (late Eocene to early Oligocene, c. 35–25 Ma) ended wedge progradation and caused the onset of contourite deposition in deep-water basins. Late Cenozoic tilting (early Pliocene to present, <4±0.5 Ma) again caused the basinward progradation of shelf-slope wedges, from uplifts along the inner margin (including broad dome-like features) and from offshore highs. The early, mid- and late Cenozoic epeirogenic episodes coincided with Atlantic plate reorganisations, but the observed km-scale tectonic movements are too large to be accounted for as flexural deflections due to intra-plate stress variations. Mantle–lithosphere interactions are implied, but the succession of epeirogenic episodes, of differing form, are difficult to reconcile with the various syn-to post-rift mechanisms of permanent and/or transient movements proposed in the hypothetical context of a plume beneath Iceland. The epeirogenic movements can be explained as dynamic topographic responses to changing forms of small-scale convective flow in the upper mantle: tilting as coeval upwelling and downwelling above an edge-driven convection cell, sagging as a loss of dynamic support above a former upwelling. The inferred Cenozoic succession of epeirogenic tilting, sagging and tilting is proposed to record the episodic evolution of upper mantle convection during ocean opening, a process that may also be the underlying cause of plate reorganisations. The postulated episodes of flow reorganisation in the NE Atlantic region have testable implications for epeirogenic movements along the adjacent oceanic spreading ridge and conjugate continental margin, as well as on other Atlantic-type ‘passive’ margins. 相似文献
49.
The present-day basement depth of the seafloor in the absence of sediment loading was inferred along a traverse crossing the
Southern Tyrrhenian Basin. A correction for sediment loading was proposed on the basis of density, seismic velocity and porosity
data from selected deep boreholes. The empirical relation between sediment correction and seismic two-way travel time was
extrapolated downward by applying the Nafe–Drake curve and a specific porosity–depth relation. The sediment loading response
of the basement calculated for flexural isostasy is on average about one hundred meters lower than results for local isostasy.
A pure lithosphere extensional model was then used to predict quantitatively the basement subsidence pattern on the margins
of the basin. The basement depth is consistent with uniform extension model predictions only in some parts of the margins.
The observed variability in the region of greatest thinning (transition from continental to oceanic crust) is attributable
to the weakening effect caused by diffuse igneous intrusions. Subsidence of the volcanic Calabrian–Sicilian margin is partly
accounted for by magmatic underplating. The comparison of the calculated subsidence with an oceanic lithosphere cooling model
shows that subsidence is variable in some areas, particularly in the Marsili Basin. This argues for a typical back-arc origin
for the Tyrrhenian Basin, as a result of subduction processes. By taking into account the geodynamic setting, stratigraphic
data from the deepest hole and the terrestrial heat flow, we reconstructed the paleotemperatures of cover sediments. The results
suggest that low temperatures generally have prevailed during sediment deposition and that the degree of maturation is expected
not to be sufficient for oil generation processes. 相似文献
50.
Katja K. Hirsch Magdalena Scheck-Wenderoth Jan-Diederik van Wees Gesa Kuhlmann Douglas A. Paton 《Marine and Petroleum Geology》2010
The Orange Basin offshore southwest Africa appears to represent a classical example of continental rifting and break up associated with large-scale, transient volcanism. The presence of lower crustal bodies of high seismic velocities indicates that large volumes of igneous crust formed as a consequence of lithospheric extension. 相似文献