High-resolution seismic reflections have been used effectively to investigate sinkholes formed from the dissolution of a bedded salt unit found throughout most of Central Kansas. Surface subsidence can have devastating effects on transportation structures. Roads, rails, bridges, and pipeliues can even be dramatically affected by minor ground instability. Areas susceptible to surface subsidence can put public safety at risk. Subsurface expressions significantly larger than surface depressions are consistently observed on seismic images recorded over sinkholes in Kansas. Until subsidence reaches the ground surface, failure appears to be controlled by compressional forces evidenced by faults with reverse orientation. Once a surface depression forms or dissolution of the salt slows or stops, subsidence structures are consistent with a tensional stress environment with prevalent normal faults. Detecting areas of rapid subsidence potential, prior to surface failure, is the ultimate goal of any geotechnical survey where the ground surface is susceptible to settling. Seismic reflection images have helped correlate active subsidence to dormant paleofeatures, project horizontal growth of active sinkholes based on subsurface structures, and appraise the risk of catastrophic failure. 相似文献
Liquidus relations in the four-component system Na2OAl2O3SiO2F2O1were studied at 0· 1 and 100 MPa to define the locationof fluoridesilicate liquid immiscibility and outlinedifferentiation paths of fluorine-bearing silicic magmas. Thefluoridesilicate liquid immiscibility spans the silicaalbitecryoliteand silicatopazcryolite ternaries and the haplogranite-cryolitebinary at greater than 960°C and 0· 1100 MPa.With increasing Al2O3 in the system and increasing aluminum/alkalication ratio, the two-liquid gap contracts and migrates fromthe silica liquidus to the cryolite liquidus. The gap does notextend to subaluminous and peraluminous melt compositions. Forall alkali feldsparquartz-bearing systems, the miscibilitygap remains located on the cryolite liquidus and is thus inaccessibleto differentiating granitic and rhyolitic melts. In peralkalinesystems, the magmatic differentiation is terminated at the albitequartzcryoliteeutectic at 770°C, 100 MPa, 5 wt % F and cation Al/Na =0· 75. The addition of topaz, however, significantlylowers melting temperatures and allows strong fluorine enrichmentin subaluminous compositions. At 100 MPa, the binary topazcryoliteeutectic is located at 770°C, 39 wt % F, cation Al/Na 0·95, and the ternary quartztopazcryolite eutecticis found at 740°C, 32 wt % F, 30 wt % SiO2 and cation Al/Na 0· 95. Such location of both eutectics enables fractionationpaths of subaluminous quartz-saturated systems to produce fluorine-rich,SiO2-depleted and nepheline-normative residual liquids. KEY WORDS: silicate melt; granite; rhyolite; fluorine; liquid immiscibility相似文献
Dipping anisotropic clastic strata are ubiquitous in fold and thrust belts. Geological structures below these strata will be mispositioned laterally and vertically on seismic images if we do not properly correct for seismic anisotropy during migration. The magnitude of this lateral mispositioning of a target structure varies with source‐receiver offset, so reflection points will be smeared in the final stacked image. Raytracing demonstrates the lateral‐position and smear phenomena when imaging structures below tilted transversely isotropic media. Analysis of the raytracing results predicts the quantity of lateral‐position error and reflection‐point smear on a seismic image. We created numerical‐model seismic data to show reflection‐point smear on synthetic seismic images and to evaluate the accuracy of the predictions from raytracing. 相似文献
For certain porous media and initial conditions, constant flux infiltrations show a saturation profile which exhibits overshoot. This overshoot is the cause of gravity driven fingering, cannot be described by standard models of unsaturated flow, and is likely controlled by the exact nature of the pore filling at the initial front. Here we report synchrotron X-ray micro-tomography measurements of the porous medium and measure which pores are filled by water and air at the initial wetting front as a function of flux. We find that at high fluxes all the pores are filled with water; for intermediate fluxes, the pores along the edge of the column remain unsaturated; and for low fluxes the pores in the bulk of the experimental column remain unsaturated. This suggests that the unsaturated overshoot conditions observed at higher fluxes are primarily an edge effect of the column. The results can help delineate the correct continuum models that can capture overshoot and gravity driven fingering. 相似文献
The August 1, 1975 earthquake near Oroville, California, occurred along the Sierra foothills in a region characterized by occasional moderate earthquakes. Several earthquakes in the general region, including those in 1869, 1875, and 1909, appear to have had significant aftershock sequences. The general character of the aftershock sequence of the Oroville earthquake thus does not appear to be anomalous when measured against the known seismic history of this area.
Four smoked-paper micro-earthquake recorders were deployed immediately following the occurrence of the main earthquake to attempt to define the structural associations of the principal earthquake by location and analysis of aftershocks. Focal locations for 243 micro-earthquakes in the magnitude range of 1–3 were selected from the 30-day period (August 2–September 1), during which monitoring was continued. The aftershocks clearly define a planar surface striking north–south and dipping west at 62° from the surface to a depth of about 12 km. Aftershocks during the first two days of monitoring defined a surface of active faulting of approximately 100 km2. Extension of this surface both to the north and south began on August 5 at focal depths of 5–10 km, resulting in a total ruptured area of approximately 125 km2. The number of aftershocks per day decreased at the rate oft−1.1, but the decay curve was punctuated by several secondary aftershock sequences. No. direct relationship between the aftershock sequence and the presence of Oroville Reservoir was observed. 相似文献
The investigation of the angular momentum vs mass relation for binary stars is completed with a study of the 847 systems contained in theFourth Catalog of Orbits of Visual Binary Stars. Because bothJ andM of a visual binary depend steeply on the distance to the system (5th and 3rd powers, respectively), and many of the distances are not well known, the study makes use of an auxiliary parameterR which is independent of distance and proportional toJM–5/3.R appears to be uncorrelated withM for the 789 systems for which both can be determined. The non-correlation implies thatJM5/3, expected from Kepler's third law, provides a better fit to the visual binaries than doesJM2, predicted by some more complex considerations.The distribution functionf(q=M2/M1) of mass ratios for the visual binaries results as a byproduct of the investigation. It peaks extremely sharply towardq=1.0 (much more so than for spectroscopic binaries). Because most visual binaries are wide enough to consist of stars that condensed independently (and so that can be thought of as chosen at random from an initial mass function), one expects the realf(q) to rise toward low ratios. Observational selection against the discovery and study of systems with large magnitude differences between the components must be very large indeed to account for the discrepancy between expectation and observation. The alternative is a mechanism for formation of wide binaries that favours equal components. The distribution of mass ratios for eclipsing binaries is given in an appendix. It peaks strongly atq=0.6–0.75 and largely reflects processes of angular momentum, mass, and energy exchange between the stars in contact systems. 相似文献
Wireline logs and vertical seismic profile data were acquired in two boreholes intersecting the main mineralized zone at the Cu–Au New Afton porphyry deposit, Canada, with the objectives of imaging lithological contacts, fault zones that may have acted as conduits that channelled the mineralization, and alteration zones. Log data provide physical rock properties for the main lithologies and alteration zones. Calliper logs reveal many faults and caved-in zones generally indicating rocks with low integrity at the borehole wall. The preponderance of these zones, as indicated by the logs, suggests that their response may dominate the seismic-reflection wavefield. Outside fault zones, compressional and shear-wave velocities exhibit significant variability due to porosity, the heterogeneity of volcanic fragmental rocks and alteration. Distributed acoustic sensing was used to acquire vertical seismic profiling data in the two boreholes surveyed with wireline logs. Straight and helically wound fibre-optic cables housed standard fibres and a fibre engineered to increase the intensity of backscattering at the distributed acoustic sensing interrogator. Standard and engineered optical fibres placed in the two boreholes were daisy-chained together to form two 5-km-long continuous fibres that were interrogated at once with two interrogators. A new generation of interrogator connected to the engineered fibres provided field data with lower noise level and higher signal-to-noise ratio. These data with higher signal-to-noise ratio from straight fibre-optic cable were processed and used for depth imaging. Depth images benefitted from new migration weights that account for the directional sensitivity of the straight fibre-optic cable and limit the extent of migration artefacts. Migration results show several reflectors with shallow dips to the northwest, some explained by faults intersecting the surveyed boreholes. The main sub-vertical lithological and alteration contacts at New Afton generated downgoing reflections that were not considered in the migration. 相似文献