圆弧形凹陷地形表面覆盖层对入射平面SV波的影响

利用Fourier Bessel级数展开法，给出了表面具有覆盖层的圆弧形凹陷地形对入射平面SV波散射问题的一个解析解，并利用该解分析了不同深宽比凹陷地形表面覆盖层刚度和厚度对入射SV波的影响．结果表明，凹陷地形表面覆盖层的存在，即使厚度很薄，也会显著增加对入射SV波的放大作用，该放大作用可达到单一凹陷地形的2.5倍以上．覆盖层刚度和厚度的变化对入射平面SV波也具有很大影响．      

High precision glacial–interglacial benthic foraminiferal Sr/Ca records from the eastern equatorial Atlantic Ocean and Caribbean Sea

Glacial–interglacial variation in the marine Sr/Ca ratio has important implications for coral Sr thermometry [J.W. Beck et al., Science 257 (1992) 644–647]. A possible variation of 1–3% was proposed based on ocean models [H.M. Stoll and D.P. Schrag, Geochim. Cosmochim. Acta 62 (1998) 1107–1118]. Subsequently, studies have used fossil foraminifera to test this prediction [P.A. Martin et al., Geochem. Geophys. Geosyst. 1 (1999); H.M. Stoll et al., Geochim. Cosmochim. Acta 63 (1999) 3535–3547; H. Elderfield et al., Geochem. Geophys. Geosyst. 1 (2000)]. But whether some component of foraminiferal Sr/Ca variation can be uniquely ascribed to seawater Sr variation is still not clear. To address this question, we developed cleaning and analysis techniques and measured Sr/Ca ratios on individual shells of the modern benthic foraminifer Cibicidoides wuellerstorfi. We showed that different size shells have different Sr/Ca ratios; however, samples with shell sizes of 355–500 μm appear to have normally distributed Sr/Ca ratios (1σ=1.8%). For multi-shell measurements (with estimated errors of 0.12–0.39%), the ratio varied by as much as 7.2±0.5% during the last glaciation for two Caribbean records at the same site and by 3.7±0.5% over the past 40,000 yr for one record from the Sierra Leone Rise in the eastern equatorial Atlantic. The two Caribbean records are very similar indicating that the behavior of shell Sr uptake was identical locally and that the shell Sr/Ca ratio faithfully reflects the local environment. The Atlantic record differs from the Caribbean records by as much as several percent. Thus, the foraminiferal Sr/Ca changes cannot be solely due to changes in seawater Sr/Ca unless the glacial deep ocean had spatial variation in Sr/Ca well in excess of the modern ocean. Certain similarities between the three records do exist. Notably, the rate of change of Sr/Ca is similar between 9 and 0 ka (−0.25%/kyr) and between 25 and 16 ka (+0.16%/kyr). This suggests that during these intervals, benthic foraminiferal Sr/Ca was affected by similar large-scale variables. One of these variables may be the average marine Sr/Ca ratio; however, comparison with model predictions [H.M. Stoll and D.P. Schrag, Geochim. Cosmochim. Acta 62 (1998) 1107–1118] suggests other factors must also be considered. The discrepancies between the two sites may be related to the different water mass histories for the Caribbean and eastern Atlantic. Our results suggest that variation of the seawater Sr budget only partially contributed to C. wuellerstorfi Sr/Ca records, while other significant factors still need to be quantified. At present we cannot confidently determine past seawater Sr/Ca variation from our foraminiferal records.     

Neuro‐control of seismically excited steel structure through sensitivity evaluation scheme

The neuro‐controller training algorithm based on cost function is applied to a multi‐degree‐of‐freedom system; and a sensitivity evaluation algorithm replacing the emulator neural network is proposed. In conventional methods, the emulator neural network is used to evaluate the sensitivity of structural response to the control signal. To use the emulator, it should be trained to predict the dynamic response of the structure. Much of the time is usually spent on training of the emulator. In the proposed algorithm, however, it takes only one sampling time to obtain the sensitivity. Therefore, training time for the emulator is eliminated. As a result, only one neural network is used for the neuro‐control system. In the numerical example, the three‐storey building structure with linear and non‐linear stiffness is controlled by the trained neural network. The actuator dynamics and control time delay are considered in the simulation. Numerical examples show that the proposed control algorithm is valid in structural control. Copyright © 2001 John Wiley & Sons, Ltd.     

The natural enrichment of ferruginous weathering products and its implication for water quality in the Hunchun Basin, China

In order to evaluate the extent of a natural enrichment of Fe and Mn over the whole of the Hunchun Basin, the stability of Fe-Mn mineral phases, their status, the weathering rate of source materials, and soil characteristics were determined. A variety of samples were collected from sediments, soil profiles, and surface soils. In the solutions after a sequentially selective dissolution using sodium pyrophosphate (p), acid oxalate (o), and dithionite-citrate-bicarbonate (d), Si, Al and Fe were dominant in the d and p fractions, and Mn in the o and p fractions. The results showed that the existing phases and status of Fe and Mn were distinctly different, and that the abundance of amorphous Mn phases made thermodynamic calculation difficult. An application of these ferruginous weathering products was therefore made to understand basin development. The first terrace of the Hunchun River is more active than the second terrace, which can be inferred from it having a higher value in Fe_d/Fe_t. Amorphous Fe phases such as Fe(OH)₃ and Fe₃(OH)₈ were controlling factors of Fe in the thermodynamic calculations. The transformation of the amorphous Fe phases to more stable phases was hindered by high contents of smectite and gibbsite, amorphous opaline produced from rice roots, and organic phosphate pesticides or fertilizers in soils. Source-rock deduction using water samples suggested granitic weathering. Precipitation around the Hunchun Basin is gradually becoming more acidic. Therefore, in the future it is inevitable that ecological and environmental problems related to the Fe phases mentioned above will occur in the drinking water supply for this area, especially in that of the first terrace.     

Zinc-rich Pyrite from the TAG Active Mound, the TAG Hydrotherma Field, Mid-Atlantic Ridge

Abstract: Pyrite rich in Zn, up to 3.1 wt%, was found in the TAG active mound of the TAG hydrothermal field, the slow-spreading Mid-Atlantic Ridge at 26°08'N and 44°49'W. The Zn-rich pyrite is characterized by an optical homogeneity, a homogeneous distribution of Zn in the back-scattered electron images, both at a magnification of about 500, a negative correlation between Fe and Zn contents of the pyrite and a rather small unit cell edge (a₀ = 5.4117 ± 0.0008Å), strongly indicating that the detected Zn is present in the pyrite in solid solution. Such Zn concentrations are observed exclusively in dendritic pyrite, suggesting that the Znrich pyrite grew from hydrothermal fluids of a high degree of supersaturation due to quenching on the seafloor.     

Frequency–volume relation and prediction of rainfall-induced landslides

Rainfall-induced landslides constitute a major public concern in Hong Kong. This paper investigates two aspects of critical importance to landslide hazard and risk assessment and management: magnitude–cumulative frequency relationship for landslides, and relationship between rainfall and the occurrence of landslides. The results indicated that landslides with a failure volume of not less than 4 m³ have a cumulative frequency–size distribution with a power-law dependence on volume of failure. Analysis of rainfall/landslides showed that the 12-hour rolling rainfall is most important in predicting the number of landslides. Failure volume dependency in the relationships between rainfall and the number of landslides is also presented. However, with an increase in failure volume of landslides, the most important rainfall variable may vary from rainfall of short duration (12-h rolling rainfall) to that of relatively long duration (24-h rolling rainfall).     

How do long-term patterns affect time-limited environmental monitoring programmes?

A five year Environmental Monitoring Programme (EMP) was set up in east-Australian coastal waters to determine the environmental effects of diverting most of Sydney's primary treated sewage from cliff face outfalls to diffuser outfall systems some 3 km offshore in 60–80 m of water. Many component EMP studies adopted Before and After Control Impact (BACI and ‘beyond BACI’) designs, to isolate outfall impacts on the marine ecosystem from background variability. Although seasonal patterns dominated ambient conditions in coastal waters, long-term climatic signals, such as the El Nino Southern Oscillation (ENSO), were apparent during the EMP. The Southern Oscillation Index (SOI) indicated the two year post-commissioning study period of 1991–1993 was dominated by an El Nino episode, while the 1989–1990 pre-commissioning period experienced a La Nina episode. Anomalous rainfall conditions and ocean temperature structure were associated with these episodes with respect to long-term records. Rainfall patterns suggested that the pre-commissioning period experienced high rainfall causing an increased incidence of stormwater pollution in coastal waters. Effects of the lower rain levels during post-commissioning phase were, however, outweighed by the dramatic improvements due to the commissioning of the deepwater outfalls. Decreased thermal stratification was experienced during the winter months of the 1992–1993 El Nino episode, and promoted increased dilutions associated with a greater frequency in sewage plume surfacing. There was, however, no apparent short-term effect of this change in plume behaviour on the marine environment as measured by EMP indicators.     

The impact of doubled CO2 on the energetics and hydrologic processes of mid-latitude transient eddies

The Northern Hemisphere winter (DJF) stationary eddy response of a general circulation model (GCM) to a doubling of atmospheric CO₂ is simulated with a linear steady state model as a response to anomalies in diabatic heating (latent, sensible and radiative), mountain and transient eddy effects. For this analysis the doubled CO₂ experiment performed by Wilson and Mitchell (1987) is used. The linear simulations of the control and perturbation climate capture most of the important features of the GCMs stationary eddies. The simulation of the anomalous stationary eddy pattern in the Northern Hemisphere captures only some of the important features of the GCMs anomalies. The climate anomalies in the Southern Hemisphere are poorly simulated. In the Northern Hemisphere the climate anomalies are dominated by the effect of transient eddies and mountains. In low latitudes also the contribution of latent heating is important. The contributions of sensible and radiative heating are small.     

Thermal evolution of the Tertiary Shimanto Belt, Muroto Peninsula, Shikoku, Japan

Abstract The Shimanto accretionary complex on the Muroto Peninsula of Shikoku comprises two major units of Tertiary strata: the Murotohanto Sub-belt (Eocene-Oligocene) and the Nabae Sub-belt (Oligocene-Miocene). Both sub-belts have been affected by thermal overprints following the peak of accretion-related deformation. Palaeotemperatures for the entire Tertiary section range from ～ 140 to 315°C, based upon mean vitrinite reflectance values of 0.9–5.0%R_m. Values of illite crystallinity index are consistent with conditions of advanced diagenesis and anchimetamorphism. Illite/mica b₀ lattice dimensions indicate that burial pressures were probably no greater than 2.5kbar. In general, levels of thermal maturity are higher for the Murotohanto Sub-belt than for the Nabae Sub-belt. The Eocene-Oligocene strata also display a spatial decrease in thermal maturity from south to north and this pattern probably was caused by regional-scale differential uplift following peak heating. Conversely, the palaeothermal structure within the Nabae Sub-belt is fairly uniform, except for the local effects of mafic intrusions at the tip of Cape Muroto. There is a paleotemperature difference of ～ 90°C across the boundary between the Murotohanto and Nabae Sub-belts (Shiina-Narashi fault), and this contrast is consistent with approximately 1200 m of post-metamorphic vertical offset. Subduction prior to Middle Miocene probably involved the Kula or fused Kula-Pacific plate and the background geothermal gradient during the Eocene-Oligocene phase of accretion was ～ 30–35°C/km. Rapid heating of the Shimanto Belt evidently occurred immediately after a Middle Miocene reorganization of the subduction boundary. Hot oceanic lithosphere from the Shikoku Basin first entered the subduction zone at ～ 15 Ma; this event also coincided with the opening of the Sea of Japan and the rapid clockwise rotation of southwest Japan. The background geothermal gradient at that time was ～ 70°C/km. Whether or not all portions of the inherited (Eocene-Oligocene) palaeothermal structure were overprinted during the Middle Miocene remains controversial.