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71.
准时间可预报复发行为与断裂带分段发震概率估计 总被引:7,自引:0,他引:7
反不确定性引入“时间可预报模式”,可将一次地震之后的平静时间表示成与这次地震位错量在小呈正相关的随机变量。称这种带有不确定性的地震原地复发行为为“准时间可预报行为”。对于历史地震资料,准时间可预报复发行为可由地震后平静时间的对数与地震烈度的回归方程。文中给出了估计一条枯断裂带不同段落以上一次地震烈度值为背景的平均复发时间间隔的方法,以及可用 于对未来地震潜势进行不确定评价的实时概率模型,并以鲜水河 相似文献
72.
布朗族使用傣历(祖葛历),以月份结合物候变化指导生产,生活中使用7d(天)为1轮的纪日制度,并将7个日名赋予不同寓意。这种状况可能距今只有200余年的历史,在此以前的历法,由于没有文字记录而被完全淡忘了,但从其先民的崖画和口头流传的传说中,有阴阳并重、同时崇拜太阳和月亮的内容看,是处于阴阳合历初期的“物候历”,其内容应与佤族(清朝时分化)的阴阳历相似。 相似文献
73.
74.
Significant population growth over the last three decades, as well as efforts to improve surface-water quality mandated by the Clean Water Act, potentially have had opposing influences on aquatic ecosystems in the U.S. Because historical data on water-quality trends are limited over this time period, we developed a diatom-based transfer function to reconstruct chloride, color, acid neutralizing capacity (ANC), total phosphorus (TP), and pH in 55 Minnesota lakes. The lakes span three different ecoregions, as well as the Twin Cities metropolitan area, and differ in their history of settlement and land use, and in surficial geology, climate, and vegetation. Lakes in the Northern Lakes and Forest ecoregion are nearly pristine, whereas those in the other regions likely are strongly affected by urban or agricultural pollutants. Reconstructions of water-chemistry trends since 1970 suggest that recent human activities have had substantial impacts in both urban and rural areas. Chloride concentrations have increased in many Metro lakes, which may be due to road salts, and phosphorus levels have been steady or rising in agricultural regions. The majority of Metro lakes show some decline in TP, although many of the changes are not statistically significant based on our reconstruction techniques. There is no evidence that atmospheric deposition of sulfate or nitrate has caused acidification or changes in trophic state for remote lakes in the northeastern part of the state. 相似文献
75.
Solute recycling from irrigation can be described as the process that occurs when the salt load that is extracted from irrigation wells and distributed on the fields is returned to the groundwater below irrigated surfaces by deep percolation. Unless the salt load leaves the system by means of drains or surface runoff, transfer to the groundwater will take place, sooner or later. This can lead to solute accumulation and thus to groundwater degradation, particularly in areas where extraction rates exceed infiltration rates (semi-arid and arid regions). Thus, considerable errors can occur in a predictive solute mass budget if the recycling process is not accounted for in the calculation. A method is proposed which allows direct simulation of solute recycling. The transient solute response at an extraction well is shown to be a superposition of solute mass flux contributions from n recycling cycles and is described as a function of the travel time distribution between a recycling point and a well. This leads to an expression for a transient ‘recycling source’ term in the advection–dispersion equation, which generates the effect of solute recycling. At long times, the ‘recycling source’ is a function of the local capture probability of the irrigation well and the solute mass flux captured by the well from the boundaries. The predicted concentration distribution at steady state reflects the maximum spatial concentration distribution in response to solute recycling and can thus be considered as the solute recycling potential or vulnerability of the entire domain for a given hydraulic setting and exploitation scheme. Simulation of the solute recycling potential is computationally undemanding and can therefore, for instance, be used for optimisation purposes. Also, the proposed method allows transient simulation of solute recycling with any standard flow and transport code. 相似文献
76.
Selection of ground motion time series and limits on scaling 总被引:4,自引:0,他引:4
Jennie Watson-Lamprey Norman Abrahamson 《Soil Dynamics and Earthquake Engineering》2006,26(5):477-482
A procedure to select time series for use in non-linear analyses that are intended to result in an average response of the non-linear system is proposed that is not based simply on magnitude, distance, and spectral shape. A simple model of a yielding system is used as a proxy for the non-linear behavior of a more complicated yielding system. As an example, Newmark displacements are used as a proxy for more complex slope-stability models. The candidate scaled time series are evaluated to find those that yield a response of the simple non-linear system that is near the expected response for the design event. Those scaled time series with responses near the expected value are selected as the optimum time series for defining average response even if the scale factors are larger than commonly accepted (e.g. scale factors >factor of 2). 相似文献
77.
78.
A large number of studies have documented the structural and sedimentary architecture of the Corinth Gulf, especially the major E–W trending normal faults important in accommodating the main extensional strain and associated growth of the Gilbert fan deltas. However, the role of several N–S oriented structures that crop out at the surface and are detectable at depth by seismic reflection and gravity surveys are not clearly understood. Based on new geological data, collected near Xylokastro, we describe the N–S oriented tectonic activity of this area. The mapped inland faults correspond to off-shore structures identified in re-interpreted seismic lines and appear to have acted as a major transfer zone during the opening of the Corinth Gulf. Reconstruction of the paleo-topography based on sedimentary facies and the environment of clay mineral formation suggest these transfer zones played an important role in controlling both local structural relief and depositional conditions of the Gilbert fan deltas. 相似文献
79.
On the link between GPS pseudorange noise and day-boundary discontinuities in geodetic time transfer solutions 总被引:1,自引:3,他引:1
When neglecting calibration issues, the accuracy of GPS-based time and frequency transfer using a combined analysis of code
and carrier phase measurements highly depends on the noise of the GPS codes. In particular, the pseudorange noise is responsible
for day-boundary discontinuities which can reach more than 1 ns in the time transfer results obtained from geodetic analysis.
These discontinuities are caused by the fact that the data are analyzed in daily data batches where the absolute clock offset
is determined by the mean code value during the daily data batch. This pseudorange noise is not a white noise, in particular
due to multipath and variations of instrumental delays. In this paper, the pseudorange noise behavior is characterized in
order to improve the understanding of the origin of the large day-boundary discontinuities in the geodetic time transfer results.
In a first step, the effect of short-term noise and multipath is estimated, and shown to be responsible for only a maximum
of 150 ps (picoseconds) of the day-boundary jumps, with only one exception at NRC1 where the correction provides a jump reduction
of 300 ps. In a second step, a combination of time transfer results obtained with pseudoranges only and geodetic time transfer
results is used to characterize the long-term evolution of pseudorange errors. It demonstrates that the day-boundary jumps,
especially those of large amplitude, can be explained by an instrumental effect imposing a common behavior on all the satellite
pseudoranges. Using known influences as temperature variations at ALGO or cable damages at HOB2, it is shown that the approach
developed in this study can be used to look for the origin of the day-boundary discontinuities in other stations. 相似文献
80.
太阳常数的变化与太阳软x射线辐射流量及低频天波时延的关系 总被引:1,自引:0,他引:1
本文对1982年在陕西临潼接收的美国罗兰-C西北大平洋链Y台发射的100kHz低频一跳天波时延的实测资料及SMS-GOES测量的太阳1~8A软x射线的每日辐射流量与SMM/ACRIMI测量的太阳常数之间的关系进行了分析。结果表明:太阳1~8A软x射线辐射流量与太阳常数之间存在较强的负相关;低频一跳天波时延与太阳常数之间存在着较强的正相关。并对此进行了讨论。 相似文献