地表探槽断裂岩岩石磁学揭示汶川地震断裂带不同滑移机制

岩石磁学能揭示岩石的磁性矿物组合,通过断裂岩不同的磁性矿物组合可揭示地震过程中磁性矿物变化、地震摩擦温度及地震滑移机制等基础地震地质问题。2008年Mw 7.9级汶川地震使两条断裂带同时发生地表破裂,包括映秀-北川和灌县-安县断裂地表破裂带,破裂带上地震断裂岩为岩石磁学提供了大量的研究对象。本研究主要以汶川地震地表破裂带上两个探槽内断裂岩为对象,包括映秀-北川地表破裂带上的八角庙探槽和灌县-安县地表破裂带上的九龙探槽,结合目前已发表的地表及WFSD-1孔的研究成果,从岩石磁学角度探讨汶川地震断裂带经历的地震滑移机制:1综合映秀-北川地震断裂带上八角庙探槽和其它位置的断裂岩岩石磁学研究,结果显示该地震断裂带附近断层泥的高磁化率源于新生的亚铁磁性矿物,如磁铁矿和磁赤铁矿等,故映秀-北川地震断裂曾经历高温快速热增压地震滑移机制;2灌县-安县地震断裂带上九龙探槽内断层泥略低的平均磁化率源于其铁的硫化物含量比断层角砾及侏罗纪砂岩多,铁的硫化物可能源于地震过程或断裂岩抬升到地表后的地表作用,如果断层泥中铁的硫化物多含量源于地震过程,则灌县-安县地震断裂带曾经历低温慢速机械润滑地震滑移机制;3两条断裂经历的不同地震滑移机制可能受控于断裂深部结构,如断层产状,映秀-北川地震断裂带的陡倾角易产生高温快速地震滑移,而灌县-安县地震断裂带的缓倾角更易产生低温慢速地震滑移。     

The impact of ecosystem functional type changes on the La Plata Basin climate

In this paper, the effects of land cover changes on the climate of the La Plata Basin in southern South America are investigated using the Weather and Research Forecasting (WRF) Model configured on a 30/10km two-way interactive nested grid. To assess the regional climate changes resulting from land surface changes, the standard land cover types are replaced by time-varying Ecosystem Functional Types (EFTs), which is a newly devised land-cover classification that characterizes the spatial and interannual variability of surface vegetation dynamics. These variations indicate that natural and anthropogenic activities have caused changes in the surface physical parameters of the basin, such as albedo and roughness length, that contributed to regional climate changes. EFTs are obtained from functional attributes of vegetation computed from properties of the Normalized Difference Vegetation Index (NDVI) to represent patches of the land surface with homogeneous energy and gas exchanges with the atmosphere. Four simulations are conducted, each experimental period ranging from September to November in two contrasting years, 1988 and 1998. The influence of an identical EFT change on the surface heat fluxes, 2-m temperature and humidity, 10-m winds, convective instabilities and large-scale moisture fluxes and precipitation are explored for 1988 (a dry year) and 1998 (a wet year). Results show that the surface and atmospheric climate has a larger response to the same EFT changes in a dry year for 2-m temperature and 10-m wind; the response is larger in a wet year for 2-m water vapor mixing ratio, convective available potential energy, vertically integrated moisture fluxes and surface precipitation. For EFTs with high productivity and a weak seasonal cycle, the nearsurface temperature during the spring of 1988 and 1998 increased by as much as 1℃ in the central and western portions of La Plata Basin. Additionally, for higher productivity EFTs, precipitation differences were generally positive in both dry and wet years, although the patterns are not uniform and exhibit certain patchiness with drier conditions.     

The pre-Landnám fauna of Iceland: a palaeontological contribution

The origins of the Icelandic biota are discussed with particular reference to recent work on Coleopteran (beetle) and Trichopteran (caddis fly) fossils from deposits which are earlier than the arrival of man (Landnám) in the country. The hypothesis of survival through Pleistocene glaciations in refugia is discounted in favour of immigration on ice floes during Late Glacial/Early Holocene deglaciation. Consideration of the nature of the insect fauna and the extent of Late Glacial ice sheets, with the evidence from ocean circulation patterns, suggests a source area in the fjords of south-west Norway. The model is applicable to the origins of the biota on all the North Atlantic islands, east of the Davis Strait.     

THE FREE-WILSON PARADIGM REDUX:SIGNIFICANCE OF THE FREE-WILSON COEFFICIENTS,INSIGNIFICANCE OF COEFFICIENT ‘UNCERTAINTIES’ AND STATISTICAL SINS

The Free-Wilson paradigm is an established and powerful tool for quantitatively relating activity withchemical structure.Current implementations of the paradigm,however,are flawed both conceptually andin execution.As part of an attempt to more fully realize the promise of the paradigm,it was necessaryto examine these limitations in detail.This report introduces a robust,theory-founded Free-Wilson implementation:stepwise principalcomponents regression analysis(SPCRA).SPCRA is computationally superior to previousimplementations but does not in itself correct their conceptual flaws.The development of SPCRA did,however,facilitate derivation of a simple and chemically significantinterpretation of the Free-Wilson structure-activity model.A number of statistical aspects of this modelcommonly misused in previous applications are discussed at length.These discussions provide criticalbackground for the development of an alternative implementation of the Free-Wilson paradigm.     

Vertical profiles of biospheric and fossil fuel-derived CO2 and fossil fuel CO2 : CO ratios from airborne measurements of Δ14C, CO2 and CO above Colorado, USA

Measurements of  Δ¹⁴C  in atmospheric CO₂ are an effective method of separating CO₂ additions from fossil fuel and biospheric sources or sinks of CO₂. We illustrate this technique with vertical profiles of CO₂ and  Δ¹⁴C  analysed in whole air flask samples collected above Colorado, USA in May and July 2004. Comparison of lower tropospheric composition to cleaner air at higher altitudes (>5 km) revealed considerable additions from respiration in the morning in both urban and rural locations. Afternoon concentrations were mainly governed by fossil fuel emissions and boundary layer depth, also showing net biospheric CO₂ uptake in some cases. We estimate local industrial CO₂:CO emission ratios using in situ measurements of CO concentration. Ratios are found to vary by 100% and average 57 mole CO₂:1 mole CO, higher than expected from emissions inventories. Uncertainty in CO₂ from different sources was ±1.1 to ±4.1 ppm for addition or uptake of −4.6 to 55.8 ppm, limited by  Δ¹⁴C  measurement precision and uncertainty in background  Δ¹⁴C  and CO₂ levels.     

Do the anomalous fluctuations of Sólheimajökull reflect ice-divide migration?

Ice-divide migration may explain the pattern of Holocene glacier fluctuations around the Mýrdalsjökull ice cap in southern Iceland. On at least three occasions Sölheimajokull, the principal outlet glacier on the southwest flank of the ice cap, has exceeded the Little Ice Age limits of recent centuries that mark the maximum extent of neighbouring glaciers in the Holocene. Bedrock divides beneath the Mýrdalsjökull ice cap do not coincide with present ice divides. It is suggested that the ice divide migrated during the course of ice-cap growth. At various stages during the Holocene (7000-4500, c. 3100, 1400-1200 BP) Sólheimajokull could have drained more of the ice cap than today, so becoming more advanced than neighbouring glaciers. In the Little Ice Age ( c. AD 1600–1900) the glacier could have had a smaller catchment as a result of ice-divide migration, resulting in a more inhibited advance compared with neighbouring glaciers which reached their Holocene maximum at that time. Identification of ice-divide migration is important for palaeoclimatic reconstructions because of the need to recognize different responses of glaciers to climate if one is to use their fluctuations as indicators of change.     

Lake Boksehandsken's earliest postglacial sediments and their palaeoenvironmental implications, Jameson Land, East Greenland

Lake Boksehandsken, the largest lake on Jameson Land, central East Greenland, is situated 54 m a.s.l. and holds a long (6.3 m) and complex stratigraphy. It was analysed with respect to lithology, carbon content, ¹⁴C, micro- and macrofossils. The diamict material in the bottom is overlain by a fining-upwards sequence, possibly deposited close to a receding ice margin in a glaciomarine environment. These deposits are interpreted to have been formed at the time of the marine limit ( c . 70 m) in the area. In spite of a large series of ¹⁴C datings, very few of the obtained dates were considered reliable. This is because the sediments contain coal fragments and old redeposited plant remains. Based on a set of arguments and correlations to the surrounding glacial stratigraphy it is implied that the marine limit and deglaciation cannot be much older than 10,000 BP. The lithology of the lake sediments, in combination with occurrence of marine macrofossils. shows that deglaciation was succeeded by a (glacio)marine depositional environment. The lake was isolated from the sea at c . 9000 BP. followed by a short transgression and a final isolation at c . 8400 BP. This sequence of events is demonstrated by both litho-and biostratigraphy and possible causes are discussed. A later oscillation some time between 8000 and 7500 BP. evidenced by litho-, carbon-, pollen- and Pecliastrum stratigraphy, is interpreted as a regional climatic cooling possibly correlatable to a distinct δ¹⁸O minima in the Greenland ice cores.     

Quaternary changes in level of the upper Taylor Glacier, Antarctica: implications for paleoclimate and East Antarctic Ice Sheet dynamics

Glacial drifts perched alongside outlet glaciers that drain through the Transantarctic Mountains constrain inland polar plateau ice elevations. The Taylor Glacier, which heads in the Taylor Dome (a peripheral dome of the East Antarctic Ice Sheet), drains East Antarctic ice into the Dry Valleys sector of Transantarctic Mountains and terminates in central Taylor Valley, about 24 km west of the Ross Sea. Five gravel-rich drifts (including 39 distinct moraine ridges) fringe a lateral lobe of the Taylor Glacier in the lower Arena Valley, Quartermain Mountains, southern Victoria Land. ³He and ¹⁰Be exposure age dating (from Brook et al . 1992), together with Arena Valley stratigraphy and soil morphologic data, provide chronologic control for these drifts and constrain maximum Quaternary thickening of the inland Taylor ice dome to less than 160 m. These minor Quaternary expansions of Taylor Glacier were out-of-phase with outlet glaciers that pass through the Transantarctic Mountains and terminate in the Ross Sea north and south of the Dry Valleys region. Textural analyses suggest that drift deposition occurred from cold-based ice, even though Taylor Glacier advances most likely occurred during global interglaciations. The thermal regime of former Taylor Glacier ice lobes, the character of geomorphic features superimposed on individual drifts, the chemical composition of soils developed on Taylor drifts, and the stability of in situ moraine ridges on steep valley walls suggest that the present cold-desert climate in Arena Valley has persisted for at least the last 2.2 Ma.