Ice-lubricated gravity spreading of the Olympus Mons aureole deposits     

Kenneth L. Tanaka 《Icarus》1985,62(2):191-206

Gravity sliding and spreading at low strain rates can account for the general morphology and structure of the aureoles and basal scarp of Olympus Mons. Detachment sliding could have occurred around the volcano if either pore-fluid pressures were exceptionally high (greater than 90%) or the rocks had very low resistance to shear (about 1 × 10⁵ Pa or 1 bar). Because of the vast areal extent and probable shallow depth of the detachment zone, development of ubiquitous, high pore-fluid pressures beneath aureole-forming material was unlikely. However, a zone of sufficiently weak material consisting of about 10% interstitial or interbedded ice could have been present. If so, a simple rheologic model for the aureole deposits can be applied that consists of a thin ductile layer overlain by a thicker brittle layer. According to this model, extensional deformation would have occurred near the shield and compressional deformation in its distal parts. Proximal grabens and distal corrugations on aureole surfaces support this model. A submarine slide at Kitimat Arm, British Columbia, is a valid qualitative analogy for the observed features and inferred emplacement style of the aureole deposits. Ground-ice processes have been considered the cause of many geologic features on Mars; a 3% average concentration of ground ice in the regolith is predicted by theoretical models for the ice budget and cryosphere. Ice may have been deposited in higher concentrations below the aureole-forming material; the source of the ice could have been juvenile water circulated hydrothermally by Olympus Mons volcanism. The basal scarp of Olympus Mons apparently demarcates the transition between the upper, stable part of the shield and its lower part that decoupled and formed the aureole deposits. This transition may reflect a change in the bulk shear strength of the shield, caused either by a radial dependence in the abundance of ice or fluid in the shield materials or by the concentration of intrusive dikes within the volcano. Other Martian volcanoes exhibit virtually no evidence of similar large-scale gravity spreading and basal scarps. Perhaps such evidence, if it existed, has been buried by lava flows, or perhaps the smaller size of other volcanoes did not permit the development of these features.  相似文献   

The 1984 Round Valley, California Earthquake Sequence     

Keith F. Priestley  Kenneth D. Smith  Robert S. Cockerham 《Geophysical Journal International》1988,95(2):215-235

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Seismic scattering and shallow structure of the moon in oceanus procellarum   总被引：1，自引：0，他引：1  

Anton M. Dainty  M. Nafi Toksöz  Kenneth R. Anderson  P. Jacques Pines  Y. Nakamura  G. Latham 《Earth, Moon, and Planets》1974,9(1-2):11-29

Long, reverberating trains of seismic waves produced by impacts and moonquakes may be interpreted in terms of scattering in a surface layer overlying a non-scattering elastic medium. Model seismic experiments are used to qualitatively demonstrate the correctness of the interpretation. Three types of seismograms are found, near impact, far impact and moonquake. Only near impact and moonquake seismograms contain independent information. Details are given in the paper of the modelling of the scattering processes by the theory of diffusion.Interpretation of moonquake and artificial impact seismograms in two frequency bands from the Apollo 12 site indicates that the scattering layer is 25 km thick, with a Q of 5000. The mean distance between scatterers is approximately 5 km at 25 km depth and approximately 2 km at 14 km depth; the density of scatterers appears to be high near the surface, decreasing with depth. This may indicate that the scatterers are associated with cratering, or are cracks that anneal with depth. Most of the scattered energy is in the form of scattered surface waves.Communication presented at the Lunar Science Institute Conference on Geophysical and Geochemical Exploration of the Moon and Planets, January 10–12, 1973.  相似文献   

Observations and discussions concerning ‘high’ polarization features in the solar corona     

Serge Koutchmy  Kenneth H. Schatten 《Solar physics》1971,17(1):117-128

Photographic observations were obtained of the radial and tangential polarization of the solar corona for the 1970, March 7, solar eclipse. The corona was photographed using a neutral density filter and rotating linear polaroid sectors to allow the polarization structure to be seen from 1 to 6 solar radii. Anomalously high polarizations were found for structures with the E-tangential intensity being predominantly larger than the E-radial intensity. These structures are generally filamentary in nature and radial in direction. One case with a high radial polarization was also found. The photographs were calibrated accurately against the Earth shine from the Moon. Possible source mechanisms are discussed that may explain this new component in the solar corona. Most sources may be ruled out on physical grounds. One possibility appears to be synchrotron radiation from 10 GeV electrons in a 0.4 G field. The existence of these electrons, however, is unlikely in that spacecraft observations at 1 AU do not confirm their presence.  相似文献   

The acquisition of post-depositional detrital remanent magnetization in a variety of natural sediments     

Michael A. Payne  Kenneth L. Verosub 《Geophysical Journal International》1982,68(3):625-642

Summary. Post-depositional detrital remanent magnetization (pDRM) is the primary means whereby many sediments acquire their palaeomagnetic signal. We have studied the acquisition of this magnetization in a variety of natural sediments. Our technique involves determining the magnetic direction recorded by a sediment as a function of the water content present in the sediment when the sediment experiences a change in the direction of the applied magnetic field. Most of the sediments used in this study were collected wet from natural environments and were preserved in their original state until they were used in the experiments. Grain sizes were measured by the settling tube method which led to the determination of the clay, silt and sand fractions in each sediment. Isothermal remanent magnetization acquisition studies indicated that the predominant magnetic carriers were magnetite. In the pDRM acquisition studies two distinct modes of behaviour were found. For sediments with a sand content less than 60 per cent, the original direction of magnetization was preserved regardless of the water content. Such behaviour is not consistent with a theoretical model which assumes that at high water contents the magnetic carriers remain mobile within fluid-filled voids and hence are able to realign along a new magnetic field direction. For sediments with a sand content in excess of 60%, remagnetization along a new magnetic field direction occurred as expected, provided the sediments were sufficiently wet. Studies of natural sediments and corresponding samples of dried and reconstituted sediments have demonstrated that the magnetic characterization of a sediment can be reliably determined even for older, desiccated sediments.  相似文献   

Analysis to Extended Periods of Rayleigh and Love Wave Dispersion across Australia     

John H. Goncz  Anton L. Hales  Kenneth J. Muirhead 《Geophysical Journal International》1975,41(1):81-105

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Metallothioneins and trace metals in the dogwhelk Nucella lapillus (L.) collected from Icelandic coasts     

Leung KM  Dewhurst RE  Halldórsson H  Svavarsson J 《Marine pollution bulletin》2005,51(8-12):729-737

Different sizes of the dogwhelk Nucella lapillus were collected from eight locations along the southwest and north coasts of Iceland. Concentrations of total metallothioneins (MTs) and heavy metals (Cd, Cu, Cr, Mn, Ni, and Zn) were analysed using the silver saturation method and inductively coupled plasma-atomic emission spectrometry. The level of tributyltin (TBT) contamination was also assessed using imposex indices, the vas deferens stage index (VDSI) and relative penis size index (RPSI). Gufunes N. lapillus presented the highest values of VDSI (4.0) and RPSI (11.1), followed by Grenivík individuals (VDSI = 3.0; RPSI = 0.9), while the Strandakirkja population showed the lowest VDSI (0.3) and zero RPSI. At a standardised size (0.25 g dry soft-body weight), Grenivík N. lapillus exhibited significantly higher concentrations of all metals whereas overall metal concentrations were significantly lower in individuals from Strandakirkja and Garðskagi compared to other study sites. Partial correlation analyses with size correction indicated that MT concentrations were better correlated with Cd and Cu concentrations than with other metals. At the standard size, the pattern of MT concentrations in N. lapillus from different sites was, however, very different from those of metal profiles. Such discrepancies between the patterns of MT and metals in N. lapillus might be explained by the fact that MT induction could be influenced by various factors such as temperature, dietary metal intake, growth rate and co-existence of other MT-inducing chemicals.  相似文献   

Clay mineralogical,geochemical and isotopic tracing of the evolution of the Woodleigh impact structure,Southern Carnarvon Basin,Western Australia     

I.?Tongu? UysalEmail author  Arthur?J.?Mory  Suzanne?D.?Golding  Robert?Bolhar  Kenneth?D.?Collerson 《Contributions to Mineralogy and Petrology》2005,149(5):576-590

Chaotically structured diamictite from the inner ring syncline surrounding the central uplift of the Woodleigh impact structure contains shocked metamorphic and impact melt-rock fragments, largely derived from Ordovician and Devonian target sandstones. Coarse illite fractions (<2 m) from the sandstones containing no K-feldspar yield K–Ar ages of around 400 Ma, whereas the K–Ar ages of authigenic clays of >0.2 m fractions from the diamictite without smectite and K-feldspar cluster around 360 Ma, consistent with Rb–Sr data. Crystallisation of newly formed illite in the impact melt rock clasts and recrystallisation of earlier formed illite in the sandstone clasts preserved in the diamictite, are attributed to impact-induced hydrothermal processes in the Late Devonian. The illitic clays from the diamictite and from the sandstones have very similar trace element compositions, with significantly enriched incompatible lithophile elements, which increase in concentrations correlatively with those of the compatible ferromagnesian elements. The unusual trace element associations in the clays may be due to the involvement of hot gravity-driven basinal fluids that interacted with rocks of the Precambrian craton to the east of the study area, or with such material transported and reworked in the studied sedimentary succession.  相似文献   

Evidence for a coronal magnetic bottle at 10 solar radii     

Kenneth H. Schatten 《Solar physics》1970,12(3):484-491

The Faraday rotation of a radio source (Pioneer 6) occulted by the solar corona has been measured by Levy et al. (1969). During the course of these measurements, three large-scale transient phenomena were observed. These events were preceded by subflares and class 1 flares. These transient events are interpreted as evidence for a coronal magnetic bottle at 10 R _⊙. The velocity of propagation for the disturbance is set at 200 km/sec; the dimension of the region, 10 R _⊙; field strength at 10 R _⊙, 0.02 G; particle density, 2.0 × 10⁴/cm³; Alfvén speed, 320 km/sec. From the nature of the observations and the lack of related effects from similar flares on the interplanetary sector pattern observed at 1 AU, it is suggested that such coronal magnetic bottles expand to perhaps 10–30 R _⊙ and then contract to a few solar radii. Such a phenomena is evidence for an expansion of the corona with a sub-Alfvénic velocity. It is further suggested that such magnetic bottles may be important in the storage and diffusion of solar generated cosmic ray particles. NAS-NRC Postdoctoral Resident Research Associate.  相似文献   

Are toxic contaminants accumulating in Massachusetts coastal sediments following startup of the Massachusetts Bay outfall: a comprehensive comparison of baseline and post-diversion periods     

Dahlen D  Hunt C  Emsbo-Mattingly S  Keay K 《Marine pollution bulletin》2006,52(11):1372-1388

The Massachusetts Water Resources Authority (MWRA) conducts monitoring to address concerns related to the 2000 diversion of secondarily treated effluent discharge into Massachusetts Bay. Baseline data (1992-2000) showed multiple regions defined by physical and chemical composition. Near the Massachusetts Bay outfall, there is a series of heterogeneous sediments in relatively close proximity to the primary historic source of contaminants (Boston Harbor). Farfield sediments exhibited greater compositional definition from one another, which was attributed to the greater spatial separation of the sampling locations. Factors that influence contaminant variability include local and distributed sources, and are primarily related to gradients in depositional environments. Post-diversion sediment data suggest that 4 years of treated effluent discharge has not increased contaminant concentrations to the bay system. However, abundance of the sewage tracer, Clostridium perfringens, has increased variably in sediments located within 2 km of the outfall, providing a distinct effluent signal near the outfall.  相似文献