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Thomas C. Hanks 《地震工程与结构动力学》1976,4(5):473-488
While the accurate estimation of ground-motion amplitudes across the entire frequency band of engineering interest is not possible at the present time, the excitation and propagation of long-period strong-ground motion can be understood with existing seismological methodology. In the Los Angeles Basin, the long-period strong ground motion excited by the San Fernando earthquake is dominated by the presence of surface waves, whose gross amplitude and frequency content are easily attributable to physical properties of the earthquake source and source-station propagation paths. Observed measures of the long-period strong ground motion of the Kern County earthquake relative to the San Fernando earthquake at two sites in the Los Angeles Basin which recorded both shocks can be predicted with considerable accuracy by a simple earthquake source model. This source model is extrapolated to represent the maximum credible earthquake likely to affect the Los Angeles area, taken to be a repeat of the Fort Tejon (1857) earthquake along the San Andreas fault. The measures of long-period strong ground motion in the Los Angeles Basin estimated for it agree well with the comparable measures of Earthquake A-2, intended to represent the same situation. For the purpose of aseismic design of long-period structures, Earthquake A-2 is a reasonable, if not all inclusive, estimate of the long-period strong ground motion in the Los Angeles Basin generated by a magnitude 8+ earthquake along the San Andreas fault north and east of Los Angeles. 相似文献
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The Colorado River system in southern Utah and northern Arizona is continuing to adjust to the baselevel fall responsible for the carving of the Grand Canyon. Estimates of bedrock incision rates in this area vary widely, hinting at the transient state of the Colorado and its tributaries. In conjunction with these data, we use longitudinal profiles of the Colorado and tributaries between Marble Canyon and Cataract Canyon to investigate the incision history of the Colorado in this region. We find that almost all of the tributaries in this region steepen as they enter the Colorado River. The consistent presence of oversteepened reaches with similar elevation drops in the lower section of these channels, and their coincidence within a corridor of high local relief along the Colorado, suggest that the tributaries are steepening in response to an episode of increased incision rate on the mainstem. This analysis makes testable predictions about spatial variations in incision rates; these predictions are consistent with existing rate estimates and can be used to guide further studies. We also present cosmogenic nuclide data from the Henry Mountains of southern Utah. We measured in situ 10Be concentrations on four gravel‐covered strath surfaces elevated from 1 m to 110 m above Trachyte Creek. The surfaces yield exposure ages that range from approximately 2·5 ka to 267 ka and suggest incision rates that vary between 350 and 600 m/my. These incision rates are similar to other rates determined within the high‐relief corridor. Available data thus support the interpretation that tributaries of the Colorado River upstream of the Grand Canyon are responding to a recent pulse of rapid incision on the Colorado. Numerical modeling of detachment‐limited bedrock incision suggests that this incision pulse is likely related to the upstream‐dipping lithologic boundary at the northern edge of the Kaibab upwarp. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Earthquake stress drops,ambient tectonic stresses and stresses that drive plate motions 总被引：1，自引：0，他引：1
Thomas C. Hanks 《Pure and Applied Geophysics》1977,115(1-2):441-458
A variety of geophysical observations suggests that the upper portion of the lithosphere, herein referred to as the elastic plate, has long-term material properties and frictional strength significantly greater than the lower lithosphere. If the average frictional stress along the non-ridge margin of the elastic plate is of the order of a kilobar, as suggested by the many observations of the frictional strength of rocks at mid-crustal conditions of pressure and temperature, the only viable mechanism for driving the motion of the elastic plate is a basal shear stress of several tens of bars. Kilobars of tectonic stress are then an ambient, steady condition of the earth's crust and uppermost mantle. The approximate equality of the basal shear stress and the average crustal earthquake stress drop, the localization of strain release for major plate margin earthquakes, and the rough equivalence of plate margin slip rates and gross plate motion rates suggest that the stress drops of major plate margin earthquakes are controlled by the elastic release of the basal shear stress in the vicinity of the plate margin, despite the existence of kilobars of tectonic stress existing across vertical planes parallel to the plate margin. If the stress differences available to be released at the time of faulting are distributed in a random, white fasbion with a mean-square value determined by the average earthquake stress drop, the frequency of occurrence of constant stress drop earthquakes will be proportional to reciprocal faulting area, in accordance with empirically known frequency of occurrence statistics. 相似文献
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Two major construction projects of ancient times in China involved what todaywould be considered engineering geology. We describe an ancient canal system in Gaotai County, Gansu province that was possibly begun in the Han dynasty (206 BC–220 AD). The canal system heads at the Dasha River and extends northwestward for about 55 km to the City of Camels and Xusanwan village. Four parallel canals are present at the local site we examined. The canals were likely built primarily to transport water but may also have served as defensive military barriers. A second project involves trenches and berms along the north side of the Great Wall, dearly part of the Great Wall defensive system. This site is in Ningxia Autonomous Region near the town of Shizuishan. 相似文献
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Pascal Umekwe Joanna Mongrain Mohabbat Ahmadi Catherine Hanks 《Natural Resources Research》2013,22(1):45-58
The capacity of 21 major fields containing more than 95% of the North Slope of Alaska’s oil were investigated for CO2 storage by injecting CO2 as an enhanced oil recovery (EOR) agent. These fields meet the criteria for the application of miscible and immiscible CO2-EOR methods and contain about 40 billion barrels of oil after primary and secondary recovery. Volumetric calculations from this study indicate that these fields have a static storage capacity of 3 billion metric tons of CO2, assuming 100% oil recovery, re-pressurizing the fields to pre-fracturing pressure and applying a 50% capacity reduction to compensate for heterogeneity and for water invasion from the underlying aquifer. A ranking produced from this study, mainly controlled by field size and fracture gradient, identifies Prudhoe, Kuparuk, and West Sak as possessing the largest storage capacities under a 20% safety factor on pressures applied during storage to avoid over-pressurization, fracturing, and gas leakage. Simulation studies were conducted using CO2 Prophet to determine the amount of oil technically recoverable and CO2 gas storage possible during this process. Fields were categorized as miscible, partially miscible, and immiscible based on the miscibility of CO2 with their oil. Seven sample fields were selected across these categories for simulation studies comparing pure CO2 and water-alternating-gas injection. Results showed that the top two fields in each category for recovery and CO2 storage were Alpine and Point McIntyre (miscible), Prudhoe and Kuparuk (partially miscible), and West Sak and Lisburne (immiscible). The study concludes that 5 billion metric tons of CO2 can be stored while recovering 14.2 billion barrels of the remaining oil. 相似文献
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