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341.
Mass movement-induced fold-and-thrust belt structures in unconsolidated sediments in Lake Lucerne (Switzerland) 总被引:2,自引:0,他引:2
MICHAEL SCHNELLMANN FLAVIO S. ANSELMETTI DOMENICO GIARDINI† JUDITH A. McKENZIE 《Sedimentology》2005,52(2):271-289
High-resolution seismic imaging and piston coring in Lake Lucerne, Switzerland, have revealed surprising deformation structures in flat-lying, unconsolidated sediment at the foot of subaqueous slopes. These deformation structures appear beneath wedges of massflow deposits and resemble fold-and-thrust belts with basal décollement surfaces. The deformation is interpreted as the result of gravity spreading induced by loading of the slope-adjacent lake floor during massflow deposition. This study investigated four earthquake-triggered lateral mass-movement deposits in Lake Lucerne affecting four sections of the lake floor with areas ranging from 0·25 to 6·5 km2 in area. Up to 6 m thick sediment packages draping the subaqueous slopes slid along the acoustic basement. The resulting failure scars typically lie in water depths of >30 m on slopes characterized by downward steepening and inclinations of >10°. From the base-of-slope to several hundred metres out onto the flat plains, the wedges of massflow deposits overlie deeply (10–20 m) deformed basin-plain sediment characterized by soft sediment fold-and-thrust belts with arcuate strikes and pronounced frontal thrusts. The intensity of deformation decreases towards the more external parts of the massflow wedges. Beyond the frontal thrust, the overridden lake floor remains mostly undisturbed. Geometrical relationships between massflow deposits and the deformed basin-plain sediment indicate that deformation occurred mainly during massflow deposition. Gravity spreading induced by the successive collapse of the growing slope-adjacent massflow wedge is proposed as the driving mechanism for the deformation. The geometry of fjord-type lakes with sharp lower slope breaks favours the deposition of thick, basin-marginal massflow wedges, that effectively load and deform the underlying sediment. In the centre of the basins, the two largest massflow deposits described are directly overlain by thick contained (mega-)turbidites, interpreted as combined products of the suspension clouds set up by subaqueous mass movements and related tsunami and seiche waves. 相似文献
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After careful analyses of the popular Monte Carlo method and geometric method in reliability analysis, the misuse of Monte Carlo method with several non-uniform distribution random variables is pointed out. As a result, a correct procedure sampling procedure of Monte Carlo method is presented. Meanwhile, in order to satisfy the needs of practice in reliability analysis, an extended geometrical optimized method(EGOM) is proposed, its procedure under conditions of correlation and non-normal distribution variable is also presented. Furthermore, several examples from others’ reliability analysis practice with the proposed EGOM prove its correctness and effectiveness. 相似文献
344.
Flexural response of piles under liquefied soil conditions 总被引:1,自引:1,他引:1
The paper pertains to the development of a generalized procedure to analyze and predict the flexural behavior of axially and
laterally loaded pile foundations under liquefied soil conditions. Pseudo-static analysis has been carried out taking into
consideration the combined effect of axial load and lateral load. Based on the available literature effect of degradation
on the modulus of subgrade reaction due to soil liquefaction has been incorporated in the analysis. The developed program
was calibrated and validated by comparing the predicted behavior of the pile with theoretical and experimental results reported
in literature. The predicted behavior has been found to be in excellent to very good agreement with the theoretical and observed
values in the field, respectively. The present study highlights the importance of considering the axial load from the superstructure
along with the inertia forces from the superstructure and the kinematic forces from the liquefied soil in the design of pile
foundations in liquefiable areas. The significance of densification of the soil in the liquefiable areas and presence of an
adequate top non-liquefied soil cover causing appreciable reduction in deflection and bending moment experienced by the piles
has been highlighted. 相似文献
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346.
Integrating GIS and DSS for identification of suitable areas for artificial recharge,case study Meimeh Basin,Isfahan, Iran 总被引:12,自引:0,他引:12
Jafar?GhayoumianEmail author B.?Ghermezcheshme S.?Feiznia A.?A.?Noroozi 《Environmental Geology》2005,47(4):493-500
Flood spreading is an inexpensive method for flood mitigation and artificial recharge of aquifers that results in a large budget return for relatively small investment.It is necessary to study some regional characteristics in order to determine the appropriate areas for artificial groundwater recharge by flood spreading in Meimeh Basin, Isfahan Province, Iran. Necessary regional characteristics to be studied are: slope, infiltration rate, sediment thickness, transmissivity, and water quality. In this research to identify suitable areas for artificial recharge several thematic layers were prepared, assigning each layer to one of the mentioned characteristics. The thematic layers were classified to several classes based on the existing criteria. All of the classes of the thematic layers were integrated and analyzed using a decision support system (DSS) in a geographical information system (GIS) environment. Finally suitability of the integrated classes for artificial recharge was identified in which the following classes were separated:(i) Very suitable, (ii) suitable, (iii) moderate suitability, and (iv) unsuitable.The validity of the generated model was verified by applying the model to a number of successful floodwater spreading stations throughout Iran. The verified model showed satisfactory results for all of the stations. The results for Meimeh Basin showed that about 70% of the Quaternary sediments in the studied area are suitable and moderately suitable for artificial recharge by flood spreading. 相似文献
347.
Morpho-tectonic study on late-stage spreading of the Eastern Subbasin of South China Sea 总被引:4,自引:0,他引:4
Three NE-trending linear structural zones with different strikes are present in the Eastern Subbasin of the South China Sea. They are distributed in the 350-km-wide central region of both sides of the Scarborough seamount chain, representing a morphological indication of the basement faulting. These three zones correspond respectively to three spreading episodes: the magnetic anomalies 6c -6a (24-21 Ma), 6a - 5e (21 - 19 Ma) and 5e - 5d (5c) (19 - 16 Ma). Instability, subsection and asymmetry characterize the seafloor spreading of the subbasin. The spreading directions change in a continuous way in each of the zones, but abrupt changes by 3°-5° occur when crossing the boundary between the zones, reflecting that the spreading direction has evolutionary characteristics of both gradual and sudden changes. NW-trending transform faults of the spreading become progressively densely distributed from the east to the west, cutting the NE-trending zones into several segments, between which the strikes of the NE-trending zones have marked changes. Such features indicate that the spreading axis is associated with subsection along the strike. Around 21 Ma (magnetic anomaly 6a), there was an important event of spreading acceleration, with the full rate rapidly increasing from 30.54 km/Ma to 42.88 km/Ma. This rate increment event corresponds to the sudden changes in the spreading characteristics of basement faulting, sedimentation, volcano activities, etc. The asymmetry of spreading over the eastern part of the Eastern Subbasin is generally larger than that over the western part, and the spreading rate is markedly larger on the southern side than on the northern side. As a result, the oceanic basin is wide in the east and narrow in the west, forming a significantly asymmetric pattern. 相似文献
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