Quantifying subaqueous slope stability during seismic shaking: Lake Lucerne as model for ocean margins     

Michael Strasser  Sylvia Stegmann  Felix Bussmann  Flavio S. Anselmetti  Beat Rick  Achim Kopf 《Marine Geology》2007,240(1-4):77-97

Lakes can be used as model basins to investigate subaqueous slope stability under static and dynamic loading conditions. This study combines geophysical, sedimentological and in situ geotechnical methods with limit equilibrium calculations in order to discuss (i) the geological and sedimentological processes acting on submerged non-deltaic lateral slopes in perialpine, fjord-type Lake Lucerne (Central Switzerland); (ii) their control on physical and geotechnical properties that eventually affect the subaqueous stability conditions and slope failure initiation, and (iii) the quantitative assessment of subaqueous slope stability. Three detailed case studies are presented to describe and quantitatively reconstruct stability conditions of slopes that failed during a well-documented historic earthquake in 1601 A.D. and during a prehistoric Late Holocene earthquake around 2220 cal yr BP (both M_w > 6).

Glacio-lacustrine sedimentation dominated by suspension settling from meltwater plumes and slight overconsolidation from ice-grounding during small readvances of a generally retreating glacier lead to a peculiar glacial-to-postglacial lithologic slope succession that eventually was buried by the Holocene sediment drape. During past earthquake shaking, the slopes that were stable under static loading conditions (factor of safety of 1.5–2) failed along planar sliding surfaces that developed at the lithological boundary between fine-grained, thinly-laminated, slightly underconsolidated cyclic plume deposits with low undrained shear strength values above and overconsolidated, glacially-deformed, glacio-lacustrine deposits with excessive formation pore pressure below. Measured in situ shear strength characteristics and sediment geometries were implemented into limit equilibrium models that allow for quantitative reconstruction of critical ground accelerations of past earthquakes in Central Switzerland. Results reveal seismic peak ground acceleration (PGA) of  0.08 g and  0.14 g for the historic 1601 A.D. M_w  6.2 earthquake and the prehistoric,  2220 cal yr B.P. earthquake, respectively. Additionally, results reveal that stability conditions change over relative short geological time scales because the postglacial sedimentation rate, which mainly controls the static weight of the slope sediment acting on the critical lithological boundary, turns out to be a key parameter in “charging” slopes susceptible to sliding.  相似文献   

Hawaii Cyclonic Eddies and Blue Marlin Catches: The Case Study of the 1995 Hawaiian International Billfish Tournament   总被引：6，自引：0，他引：6  

Michael P. Seki  Rick Lumpkin  Pierre Flament 《Journal of Oceanography》2002,58(5):739-745

The combination of prevailing northeasterly tradewinds and island topography results in the formation of vigorous, westward propagating cyclonic eddies in the lee of the Hawaiian Islands on time scales of 50–70 days. These mesoscale (∼10² km) features are nowhere more conspicuous or spin up more frequently than in the Alenuihaha Channel between the Island of Maui and the Big Island of Hawaii. Cyclonic eddies in subtropical waters such as those around Hawaii vertically displace the underlying nutricline into the overlying, nutrient-depleted euphotic zone creating localized biologically enhanced patches. Insight into how these eddies may directly influence pelagic fish distribution is provided by examination of recreational fish catch data coinciding with the presence of eddies on the fishing grounds. We highlight the 1995 Hawaii International Billfish Tournament in which a cyclonic eddy dominated the ocean conditions during the weeklong event and the fish catch distribution differed significantly from the average historical tournament catch patterns. On the tournament fishing grounds, well-mixed surface layers and strong current flows induced by the eddy's presence characterized the inshore waters where the highest catches of the prized Pacific blue marlin (Makaira mazara) occurred, suggesting possible direct (e.g., physiological limitations) or indirect (e.g., prey availability) biological responses of blue marlin to the prevailing environment. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Parental effects on early life history traits of haddock Melanogrammus aeglefinus     

Nikolaus Probst  W.; Kraus  Gerd; Rideout  Rick M.; Trippel  Edward A. 《ICES Journal of Marine Science》2006,63(2):224-234

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Vertical cross-spectra of horizontal velocity components at the Boulder observatory     

Rick Soucy  Robert Woodward  H. A. Panofsky 《Boundary-Layer Meteorology》1982,24(1):57-66

Cross-spectra between horizontal wind components at different levels of the Boulder Atmospheric Observatory (BAO) tower lead to the following conclusions:

1. Davenport's hypothesis is satisfied that coherence decays exponentially with the ratio of vertical separation to horizontal wave length, at least to very small values of coherence.
2. The decay coefficients increase with z/L for z/L < 0.5. For larger stabilities, irregular fluctuations with periods of order 10–20 min have considerable vertical coherence. Results at BAO are quite consistent with those elsewhere.
3. Eddy slopes in vertical planes increase with wind shear up to a point where the slope (horizontal delay over vertical separation) is just above 2. Beyond that point, the systematic increase of slopes with shear ceases. Since wind shear decreases upward, slopes tend to decrease upward. Slopes for lateral components are significantly larger than those for u-components.

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Strontium isotopic geochemistry of the volcanic rocks and associated megacrysts and inclusions from Ross Island and vicinity,Antarctica     

John S. Stuckless  Rick L. Ericksen 《Contributions to Mineralogy and Petrology》1976,58(2):111-126

Twelve whole-rock samples of volcanic rocks and a composite of 11 basanitoid samples from Ross Island and vicinity, Antarctica show a narrow range of ⁸⁷Sr/⁸⁶Sr ratios from 0.7030₅ to 0.7033₉. This range is consistent with a model of differentiation from a single parent magma, but the data allow a 30% variation in the ⁸⁷Rb/⁸⁶Sr ratio in the source region if the average ratio is less than 0.057 and if the source region has existed as a closed system for 1.5 b.y. Megacrysts of titaniferous augite, kaersutite, and anorthoclase are isotopically indistinguishable from the host volcanic rocks and therefore are probably cogenetic with the volcanic sequence. A single trachyte sample is isotopically distinct from the rest of the volcanic rocks and probably was contaminated with crustal strontium.Ultramafic and mafic nodules found in association with basanitoids and trachybasalts have ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7027₅ to 0.7057₅. Several of these nodules exhibit evidence of reaction with the melt and are isotopically indistinguishable from their hosts, but data for seven granulite-facies nodules show an apparent isochronal relationship. Although this isochron may be fortuitous, the resulting age of 158±22 m.y. is similar to ages reported for the voluminous Ferrar Dolerites, and suggests isotopic re-equilibration within the lower crust and upper mantle. These nodules are not genetically related to the Ferrar Dolerites, as evidenced by their lower initial ⁸⁷Sr/⁸⁶Sr ratios.Three ultramafic nodules are texturally and isotopically distinct from the rest of the analyzed nodules. These are friable, have larger ⁸⁷Sr/⁸⁶Sr ratios, and may represent a deeper sampling of mantle rock than the granulite-facies nodules. They were, however, derived at a shallower depth than the alkalic magma. Thus they are not genetically related to either the magma or the granulite-facies nodules.  相似文献   

Monitoring Wells: Self-Contamination and Cross Contamination     

Rick Jacoby 《Ground Water Monitoring & Remediation》1990,10(4):77-78

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Are cladoceran fossils in lake sediment samples a biased reflection of the communities from which they are derived?     

G. R. Kattel  R. W. Battarbee  A. Mackay  H. J. B. Birks 《Journal of Paleolimnology》2007,38(2):157-181

A study on the taphonomy of Cladocera was carried out in a small (9 ha), oligotrophic mountain loch, Loch Coire Fionnaraich (LCFR) in northwest Scotland. Four approaches were used. First, the fossil assemblage of Cladocera in the core-top sample taken from the deepest basin (14 m) of the loch were compared with the fossil assemblages of Cladocera in surface sediments along eight depth transects with samples taken at 2, 5, 8 and 11 m, respectively. The results of the deposition of remains of individual Cladocera and of the PCA ordination showed that littoral Cladocera were dominant in the 2 m-depth samples, while the planktonic Cladocera dominated the deeper water (8, 11 m and core-top) samples. Second, the fossil assemblages of Cladocera in the core-top sample were compared with the assemblages in a sediment trap sample. The core-top sample showed a better representation of the cladoceran taxa present in the loch than the trap sample, but rare taxa were missing in the core sample. Third, the fossil assemblages of Cladocera in the core sample were compared with the contemporary assemblages in the source samples derived from seasonal sampling across all habitats (macrophyte, sand, boulder) over 2 years. Only a small proportion of Cladocera in the source samples was represented by the fossil assemblages in the core sample. Finally, ‘integrated’ approach samples (spatial, trap, source and core together) were compared using PCA. The Cladocera in the core-top sample were closely related to the trap and surface sediment samples, but weakly related to the source samples. The overall results indicate that biases may occur whilst reconstructing the past environmental change based on the fossil assemblages of Cladocera in the core sample taken from the deepest basin of the lake.  相似文献   

The Cornubian Batholith: an Example of Magmatic Fractionation on a Crustal Scale     

Bruce W. Chappell  Rick Hine 《Resource Geology》2006,56(3):203-244

Abstract. The Cornubian Batholith comprises six major and several smaller bodies of S‐type granite in southwestern England. These late‐Variscan granites comprise two‐mica granites, and much less abundant Li‐mica granites that are restricted to one of the major bodies (St Austell) and smaller bodies. Some of these intrusive rocks are associated with major Sn mineralization. This paper is concerned with the geochemistry of the two‐mica granites, which are felsic, strongly peraluminous, and have a high total alkali content and low Na:K. Rocks with very similar compositions to these granites occur elsewhere, including the Variscan granites of continental Europe, and in southeastern Australia. In detail all of the major plutons of this batholith have distinctive compositions, except for Bodmin Moor and Carnmenellis which cannot be discriminated from each other compositionally. A comparison with experimental data shows that the granites attained their major element composition under conditions of crystal‐liquid equilibrium, with the final melt being saturated in H₂O, at temperatures close to 770d?C and pressures about 50 MPa. That temperature estimate is in good agreement with values obtained from zircon saturation thermometry. The specific minimum‐temperature composition excludes the possibility of widespread transfer of elements during hydrothermal alteration. Minor elements that are relatively very abundant are Li, B, Cs and U, while F, Ga, Ge, Rb, Sn, Ta, W and Tl are quite abundant and P is high for felsic rocks. Sr, Ba, and the trace transition metals Sc to Zn, are low, but not as low as they commonly are in very felsic granites. These trace element abundances, and the EL₂O‐saturation, resulted from the fractional crystallization of a melt derived by the partial melting of feldspathic greywackes in the crust. The Cornubian granites have compositions very similar to the more felsic rocks of the Koetong Suite of southeastern Australia, where a full range of granites formed at the various stages of magmatic fractionation postulated for the Cornubian granites, can be observed. The operation of fractional crystallization in the Cornubian granites is confirmed by the high P abundances in the feldspars, with P contents of the plagioclase crystals correlating with Ab‐con‐tent Most of the granites represent solidified melt compositions but within the Dartmoor pluton there is a significant component of granites that are cumulative, shown by their higher Ca contents. The Cornubian plutons define areas of high heat flow, of a magnitude which requires that fractionated magmas were transported laterally from their sources and concentrated in the exposed plutons. The generation of these granite plutons therefore involved magmatic fractionation during the stages of partial melting, removal of unmelted material from that melt, and fractional crystallization. During the later stages of those processes, movement of those magmas occurred on a crustal scale.  相似文献   

Use of drones to analyse sedimentary successions exposed in the foreshore     

Julie E.G. Harrald  Angela L. Coe  Rick M. Thomas  Murray Hoggett 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(3):253-268

Drones have revolutionised the gathering of geoenvironmental data over the last decade. To date, the majority of drone studies of sedimentary rock successions have focussed on well-exposed vertical to subvertical cliff sections. Here, we describe a fundamental method to obtain new data and perspectives on sedimentary successions exposed in partially-obscured foreshore or other horizontal to subhorizontal outcrop surfaces using drones. We illustrate the technique using an example from foreshore exposures of Jurassic strata near Helmsdale, Scotland, UK. Our method aims to make the process of safely collecting drone footage accessible and covers practical considerations from pre-field preparation to data processing. Capturing drone imagery in a foreshore setting involves trade-offs between the time of day which constrains the lighting, the time of year which determines algal cover and tidal range, and the flight time available which indirectly governs image resolution. We show how: (1) orthomosaic images can be used to view sedimentary deposits at different scales and angles enabling identification of large-scale sedimentary features marked by small-scale changes in orientation and lateral variability; (2) production of digital elevation models permits differentially weathered features covered by water or algae to be distinguished, and (3) drones can be used for close up photography of inaccessible features.  相似文献   

A Reservoir–Geomechanical Model to Study the Likelihood of Tensile and Shear Failure in the Caprock of Weyburn CCS Project with Regard to Interpretation of Microseismic Data     

Cyrus Khazaei  Rick Chalaturnyk 《Geotechnical and Geological Engineering》2017,35(6):2571-2595

According to poroelastic theory and also field observations, an increase in reservoir pore pressures can result in a decrease in horizontal stresses in the seal layers. This reduction is in favor of hydrofracture initiation and reactivation of weak planes and has to be studied in caprock integrity analyses. In this paper, a field scale reservoir–geomechanical (GEM-FLAC3D) model is developed for the Phase IB area of the Weyburn (Canada) CCS project that is located in Williston sedimentary basin. A one-way coupling has been conducted between the two codes for the period of CO₂ injection in Phase IB area from 2000 to 2010. Therefore, the reservoir pore pressures at selected timesteps are unidirectionally fed to the FLAC3D. In order to study the likelihood of tensile and shear failure in the seal layer on top as a result of stress transfer due to poroelastic effects, two margin ratios are defined for tensile and shear failure and their variations are studied above the reservoir upon changes in pore pressures within the reservoir. The results show that overall; the likelihood of shear failure has been about 25% greater than that of tensile failure in Weyburn. However, between 2008 and 2009, the pressures were high enough to trigger both tensile and shear mechanisms above the reservoir. A discussion is also presented on relevance of this study for interpretation of microseismic data with regard to failure margin ratios, magnitudes and distribution of events recorded in each year.  相似文献