Greece, in particular the western and southern parts close to the subduction zone of the Hellenic Trench, experiences strong earthquakes and subsequent tsunamis. Nevertheless, field evidence of tsunamis from the late Holocene is extremely rare. Our research along the coastlines of the western and southern Peloponnesus resulted in new findings of tsunami impacts in the form of clusters and ridges of large boulders and thick tsunamigenic sand layers encountered in vibracores. Many boulders contained attached marine organisms, which prove that they were transported from the foreshore environment against gravity by extreme wave events. The attached organisms, which have been dated by 14C-AMS, suggest that historical tsunami events of great energy occurred around 1300 cal AD. A wood fragment found at the base of tsunami deposits in a vibracore from Cape Punta was dated to ~ 250 cal AD. 相似文献
Studies were done on new geomorphological and quaternary-geological profiles through representative reliefs of Tibet from
the Central Himalaya as far as the Kuenlun. Thus, further detailed investigations on the prehistoric glaciation could be carried
out. Youngest historical to neoglacial ice margin positions could be recorded. Their mapping took place in a downward direction
from the modern glacier margins. They confirm snow line (ELA) depressions from decametres up to ca. 100–250 m. At distances
of several kilometres to many decakilometres (depending on the relief) from the modern glaciers, névé shields and perennial
snow fields, end moraines and later just remnants of lateral moraines and kame complexes of the Late Glacial (ca. Stadia IV-II)
have been localized in an increasing disrupted succession and samples have been taken. The recorded, inter- and extrapolated
lowest ice margin positions allowed the reconstruction of accompanying depressions of the snow line which, due to the altitude
of the Tibetan plateau plains, attained a maximum of 400–700 m. Accordingly, the early Late Glacial (Stadia I to II) and High
Glacial glacier traces (Riss or pre-LGM and Würm or LGM = Stadia −I and/or 0) occurred over a horizontal distance of 1620
km across the plateau with an average height of 4700 m asl without showing the key forms of ice margin positions. From the
profiles introduced here, running from Mt. Everest/Cho Oyu (Central Himalaya) in the SE via Gertse (Kaitse; Central Tibet)
as far as the Lingzi Thang and Aksai Chin and from there into the Kuenlun, as well as from a parallel section of the Gurla
Mandhata (central S Tibet) to the currently very arid Nako Tso, located centrally in the W, sediment samples have been analysed
which provide evidence for a ground moraine genesis. Thus, the macroscopic field observations are confirmed. Only the relatively
small basin of Shiquanha (Ali) – like the Indus valley chamber of Leh – may have been free of ice during the High Glacial
(LGM). Forms of glacial horns, as well as roches moutonnées and large, several metres-high round-polished mountain ridges
with slight debris covers, flank polishings, abraded mountain spurs at intermediate valley ridges and high-lying erratics
document the widespread ice cover. Important ice thicknesses of at least 1300–1400 m have been recognized by means of transfluences.
Especially by and in the Nako Tso (lake) the limnic undercutting of roches moutonnées provides evidence only of a postglacial
filling into a primary glacial relief. The glacial ice cover (with the LGM at the end) testified here for a further area of
Tibet, is the foundation of the relief-specific hypothesis on the development of the Ice Ages, based on the global radiation
geometry: accordingly, the last great geological event, the early Pleistocene plate-tectonically induced uplift of Tibet above
the snow line, has brought about a glaciation which, owing to its high albedo, reflected the subtropical radiation energy
into space, so that it could not be exploited for the heating of the atmosphere. This may have triggered the Ice Ages. The
repeated interglacial warming-up is to be reduced to the positive radiation anomalies by the variations of the parameters
of the earth's orbit – which take place rhythmically – and the overlying glacio-isostatic lowering of Tibet and the other
inland ice areas.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
We use three-integral models to infer the distribution function (DF) of the boxy E3–E4 galaxy NGC 1600 from surface brightness and line-profile data on the minor and major axes. We assume axisymmetry and that the mass-to-light ratio is constant in the central ∼1 R e. Stars in the resulting gravitational potential move mainly on regular orbits. We use an approximate third integral K from perturbation theory and write the DF as a sum of basis functions in the three integrals E , L z and K . We then fit the projected moments of these basis functions to the kinematic observables and deprojected density, using a non-parametric algorithm. The deduced dynamical structure is radially anisotropic, with σ θ σ r ≈ σ φ σ r ≈0.7 on the major axis. Both on the minor axis and near the centre the velocity distribution is more isotropic; thus the model is flattened by equatorial radial orbits. The kinematic data are fitted without the need for a central black hole; the central mass determined previously from ground-based data therefore overestimates the actual black-hole mass. The mass-to-light ratio of the stars is M L V =6 h 50. The anisotropy structure of NGC 1600 with a radially anisotropic main body and more nearly isotropic centre is similar to that found recently in NGC 1399, 2434, 3379 and 6703, suggesting that this pattern may be common amongst massive elliptical galaxies. We discuss a possible merger origin of NGC 1600 in the light of these results. 相似文献
Micrometeorological measurements (including eddy-covariance measurements of the surface fluxes of sensible and latent heat) were performed during the LITFASS-2003 experiment at 13 field sites over different types of land use (forest, lake, grassland, various agricultural crops) in a 20 × 20 km2 area around the Meteorological Observatory Lindenberg (MOL) of the German Meteorological Service (Deutscher Wetterdienst, DWD). Significant differences in the energy fluxes could be found between the major land surface types (forest, farmland, water), but also between the different agricultural crops (cereals, rape, maize). Flux ratios between the different surfaces changed during the course of the experiment as a result of increased water temperature of the lake, changing soil moisture, and of the vegetation development at the farmland sites. The measurements over grass performed at the boundary-layer field site Falkenberg of the MOL were shown to be quite representative for the farmland part of the area. Measurements from the 13 sites were composed into a time series of the area-averaged surface flux by taking into account the data quality of the single flux values from the different sites and the relative occurrence of each surface type in the area. Such composite fluxes could be determined for about 80% of the whole measurement time during the LITFASS-2003 experiment. Comparison of these aggregated surface fluxes with area-averaged fluxes from long-range scintillometer measurements and from airborne measurements showed good agreement. 相似文献
An overview of the Energy Balance Experiment (EBEX-2000) is given. This experiment studied the ability of state-of-the-art
measurements to close the surface energy balance over a surface (a vegetative canopy with large evapotranspiration) where
closure has been difficult to obtain. A flood-irrigated cotton field over uniform terrain was used, though aerial imagery
and direct flux measurements showed that the surface still was inhomogeneous. All major terms of the surface energy balance
were measured at nine sites to characterize the spatial variability across the field. Included in these observations was an
estimate of heat storage in the plant canopy. The resultant imbalance still was 10%, which exceeds the estimated measurement
error. We speculate that horizontal advection in the layer between the canopy top and our flux measurement height may cause
this imbalance, though our estimates of this term using our measurements resulted in values less than what would be required
to balance the budget.
The National Center for Atmospheric Research is supported by the National Science Foundation 相似文献
Field observations of area-averagedturbulence characteristics were conducted in a densely built-up residential neighbourhood in Tokyo, Japan. In addition to eddy-correlation (EC) sensors a scintillometer was used for the first time in a city. Significant results include: (1) Scintillometer-derived sensible heat fluxes, QH, obtained at a height 3.5 times the building height agree well with those using the EC technique; (2) source areas for the scintillometer fluxes are larger than for the EC sensors, so that at low heights over inhomogeneous terrain scintillometry offers advantages; (3) new similarity relationships for dissipation rates are proposed for urban areas; (4) a new technique that uses simultaneous scintillation measurements at two heights to directly estimate area-averaged zero-plane displacement height, zd, is proposed. zd estimated in this way depends slightly on atmospheric stability (lower zd under more unstable conditions). 相似文献
One-dimensional Lagrangian dispersion models, frequently used to relate in-canopy source/sink distributions of energy, water
and trace gases to vertical concentration profiles, require estimates of the standard deviation of the vertical wind speed,
which can be measured, and the Lagrangian time scale, TL, which cannot. In this work we use non-linear parameter estimation to determine the vertical profile of the Lagrangian time
scale that simultaneously optimises agreement between modelled and measured vertical profiles of temperature, water vapour
and carbon dioxide concentrations within a 40-m tall temperate Eucalyptus forest in south-eastern Australia. Modelled temperature
and concentration profiles are generated using Lagrangian dispersion theory combined with source/sink distributions of sensible
heat, water vapour and CO2. These distributions are derived from a multilayer Soil-Vegetation-Atmospheric-Transfer model subject to multiple constraints:
(1) daytime eddy flux measurements of sensible heat, latent heat, and CO2 above the canopy, (2) in-canopy lidar measurements of leaf area density distribution, and (3) chamber measurements of CO2 ground fluxes. The resulting estimate of Lagrangian time scale within the canopy under near-neutral conditions is about 1.7
times higher than previous estimates and decreases towards zero at the ground. It represents an advance over previous estimates
of TL, which are largely unconstrained by measurements. 相似文献
We present the results of a finite-element modelling study of pull-apart basin formation related to left-stepping left lateral strike-slip faults. The modelling quantifies the relationship between fault geometry (i.e., fault overlap and separation) and pull-apart basin formation. Two depocentres (subbasins) separated by a broad zone of relative uplift in between may develop if the strike-slip domain is characterized by fault underlap. For overlapping faults migration of the subbasins is predicted by the models. Deep subbasins in a large area of subsidence which spans the entire inner fault zone may form if fault overlap is about three times the fault separation.
The models suggest that a topographic asymmetry within the fault zone may arise due to a different displacement ratio of the strike-slip faults. The modelling results show that this asymmetry in topography becomes more pronounced towards the more active fault. Thus, basin deepening occurs progressively towards the fault characterized by the largest amount of lateral displacement. Moreover, the results indicate that the smaller the fault separation (less than basin length) the less pronounced the topographic asymmetry.
The models provide quantitative estimates for the effects of changes in elastic material properties, the magnitude of the compressive far-field stress and the coefficient of friction of the faults on the resulting topography.
Comparison of the modelling results with field observations from the Cerro Blanco-El Barranquete (CBB) subbasin located in the Internal Zone of the Betic Cordillera, southeastern Spain support an interpretation in which the interplay of major faults has formed the CBB subbasin. 相似文献