FURTHER STUDY ON THE PROPERTIES OF OPERATORS OF ATMOSPHERIC EQUATIONS AND THE EXISTENCE OF ATTRACTOR

The equivalent operator equation is derived from the full primitive nonlinear equations of theatmospheric motion and the properties and physical senses of the operators are studied.In theinfinite dimensional Hilbert space,the global asymptotic behavior of the atmosphere system withthe non-stationary external forcing is studied under the assumption of the bounded externalforcing.The existence theorems of the global absorbing set and the global attractor are obtained.Thus,the conclusions deduced from the large-scale atmosphere(Li and Chou 1996 a;1996 b)areextended to the general atmosphere.     

THE EFFECTS OF EXTERNAL FORCING,DISSIPATION AND NONLINEARITY ON THE SOLUTIONS OF ATMOSPHERIC EQUATIONS*

Based on the primitive equations of the atmosphere,we study the effects of external forcing.dissipation and nonlinearity on the solutions of stationary motion and non-stationary motion.The results show that the asymptotic behavior of solutions of the forced dissipative nonlinear system is essentially different from that of the adiabatic non-dissipative system,the adiabatic dissipative system,the diabatic non-dissipative system and the diabatic dissipative linear system,and that the joint action of external forcing,dissipation and nonlinearity is the source of multiple equilibria.From this we can conclude that the important actions of diabatic heating and dissipation must be considered in the models of the long-term weather and the climate.     

垂直切变基流中东西向地形对惯性重力波稳定性的影响

利用分层浅水波方程和小参数(WKB)方法，考虑具有垂直切变的基流和地形的作用，求得惯性重力波的局地频率方程，并根据此方程分析讨论了在多种环境条件下波动的稳定性情况。     

Ar/Ar ages of tephras intercalated in astronomically tuned Neogene sedimentary sequences in the eastern Mediterranean

We present new ⁴⁰Ar/³⁹Ar data for sanidine and biotite derived from volcanic ash layers that are intercalated in Pliocene and late Miocene astronomically dated sequences in the Mediterranean with the aim to solve existing inconsistencies in the intercalibration between the two independent absolute dating methods. ⁴⁰Ar/³⁹Ar sanidine ages are systematically younger by 0.7-2.3% than the astronomical ages for the same ash layers. The significance of the discrepancy disappears except for the upper Ptolemais ashes, which reveal the largest difference, if an improved full error propagation method is applied to calculate the absolute error in the ⁴⁰Ar/³⁹Ar ages. The total variance is dominated by that of the activity of the decay of ⁴⁰K to ⁴⁰Ar (∼70%) and that the amount of radiogenic ⁴⁰Ar_p in the primary standard GA1550 biotite (∼15%). If the ⁴⁰Ar/³⁹Ar ages are calculated relative to an astronomically dated standard, the influence of these parameters is greatly reduced, resulting in a more reliable age and in a significant reduction of the error in ⁴⁰Ar/³⁹Ar dating.Astronomically calibrated ages for Taylor Creek Rhyolite (TCR) and Fish Canyon Tuff (FCT) sanidine are 28.53±0.02 and 28.21±0.04 Ma (±1 S.E.), respectively, if we start from the more reliable results of the Cretan A1 ash layer. The most likely explanation for the large discrepancy found for the younger Ptolemais ash layers (equivalent to FCT of 28.61 Ma) is an error in the tuning of this part of the sequence.     

考虑应力水平的软土固结系数计算与试验研究

在固结度计算中通常将固结系数视为常数,实际上并非如此.通过研究软土固结系数在压缩过程中随应力水平变化的规律,推导出正常固结和超固结状态下固结系数与有效应力之间的表达式.在正常固结状态下,当应力水平小于在前期固结压力时,固结系数随应力水平的增加而增加;当超过前期固结压力后,固结系数随应力水平的增加而减小;在超固结状态下,固结系数随应力水平的增加而增加,在一定程度后趋于平稳.室内试验结果进一步说明了和验证固结系数这一特点.推导的固结系数与固结应力水平关系表达式是可行的,其计算值与试验结果的变化趋势一致,大小基本吻合,将其用于计算变形速率和固结度中,可提高准确性.     

The effective number of cycles of earthquake ground motion

The seismic response of any system that accumulates damage under cyclic loading is dependent not only on the maximum amplitude of the motion but also its duration. This is explicitly recognized in methods for estimating the liquefaction potential of soil deposits. Many researchers have proposed that the effective number of cycles of the ground motion is a more robust indicator of the destructive capacity of the shaking than the duration. However, as is the case with strong‐motion duration, there is no universally accepted approach to determining the effective number of cycles of motion, and the different methods that have been proposed can give widely varying results for a particular accelerogram. Definitions of the effective number of cycles of motion are reviewed, classified and compared. Measurements are found to differ particularly for accelerograms with broad‐banded frequency content, which contain a significant number of non‐zero crossing peaks. The key seismological parameters influencing the number of cycles of motion and associated equations for predicting this quantity for future earthquakes are identified. Correlations between cycle counts and different duration measures are explored and found to be rather poor in the absence of additional parameters. Copyright © 2004 John Wiley & Sons, Ltd.     

Penny-shaped fractures revisited

All methods of seismic characterization of fractured reservoirs are based on effective media theories that relate geometrical and material properties of fractures and surrounding rock to the effective stiffnesses. In exploration seismology, the first-order theory of Hudson is the most popular. It describes the effective model caused by the presence of a single set of thin, aligned vertical fractures in otherwise isotropic rock. This model is known to be transversely isotropic with a horizontal symmetry axis (HTI). Following the theory, one can invert the effective anisotropy for the crack density and type of fluid infill of fractures, the quantities of great importance for reservoir appraisal and management.Here I compute effective media numerically using the finite element method. I deliberately construct models that contain a single set of vertical, ellipsoidal, non-intersecting and non-interconnected fractures to check validity of the first-order Hudson’s theory and establish the limits of its applicability. Contrary to conventional wisdom that Hudson’s results are accurate up to crack density e ≈ 0.1, I show that they consistently overestimate the magnitudes of all effective anisotropic coefficients ε^(V), δ^(V), and γ^(V). Accuracy of theoretically derived anisotropy depends on the type of fluid infill and typically deteriorates as e grows. While the theory gives | ε^(V)|, |δ^(V)|, |γ^(V)| and close to the upper bound of the corresponding numerically obtained values for randomly distributed liquid-filled fractures, theoretical predictions of ε^(V), δ^(V) are not supported by numerical computations when the cracks are dry. This happens primarily because the first-order Hudson’s theory makes no attempt to account for fracture interaction which contributes to the final result much stronger for gas- than for liquid-filled cracks. I find that Mori-Tanaka’s theory is superior to Hudson’s for all examined crack densities and both types of fluid infill.The paper was presented at the 11th International Workshop on Seismic Anisotropy (11IWSA) held in St. John’s, Canada in 2004.     

Did Paleogene North Atlantic rift-related eruptions drive early Eocene climate cooling?

The delivery of volcanogenic sulphur into the upper atmosphere by explosive eruptions is known to cause significant temporary climate cooling. Therefore, phreatomagmatic and phreatoplinian eruptions occurring during the final rifting stages of active flood basalt provinces provide a potent mechanism for triggering climate change.

During the early Eocene, the northeast Atlantic margin was subjected to repeated ashfall for 0.5 m.y. This was the result of extensive phreatomagmatic activity along 3000 km of the opening northeast Atlantic rift. These widespread, predominantly basaltic ashes are now preserved in marine sediments of the Balder Formation and its equivalents, and occur over an area extending from the Faroe Islands to Denmark and southern England. These ash-bearing sediments also contain pollen and spore floras derived from low diversity forests that grew in cooler, drier climates than were experienced either before or after these highly explosive eruptions. In addition, coeval plant macrofossil evidence from the Bighorn Basin, Wyoming, USA, also shows a comparable pattern of vegetation change. The coincidence of the ashes and cooler climate pollen and spore floras in northwest Europe identifies volcanism as the primary cause of climate cooling. Estimates show that whilst relatively few phreatomagmatic eruptive centres along the 3000 km opening rift system could readily generate 0.5–1 °C cooling, on an annual basis, only persistent or repeated volcanic phases would have been able to achieve the long-term cooling effect observed in the floral record. We propose that the cumulative effect of repeated Balder Formation eruptions initiated a biodiversity crisis in the northeast Atlantic margin forests. Only the decline of this persistent volcanic activity, and the subsequent climatic warming at the start of the Eocene Thermal Maximum allowed the growth of subtropical forests to develop across the region.     

关于岩石圈有效弹性厚度的地质理解

简要回顾了岩石圈均衡理论的发展及岩石圈区域均衡和挠曲理论在岩石圈动力学研究中起的作用,阐述岩石圈有效弹性厚度(Te)的概念和特征。强调Te的研究是地质学和地球物理学的紧密结合,即通过岩石圈挠曲理论和区域均衡原理,对地形和重力资料进行谱分析计算,来获取岩石圈的物理性质信息。计算的Te(和相应的挠曲刚度)是岩石圈等效的强度,与爆破地震、地震层析成像和大地电磁测深等方法观测到的岩石圈和地壳厚度不同,它们之间只有通过岩石圈的屈服刚度包络面(YSE)才能比较。大洋和大陆岩石圈YSE的理论计算,表明Te值显著小于地震学的地壳和岩石圈厚度。尤其对于大陆岩石圈,地壳厚度、热年龄和应变率均可显著影响岩石圈的强度。本文还以滇西为实例介绍了对相干值曲线计算的新认识和当前岩石圈Te研究的最新趋势。