Patterns in the sand: From forcing templates to self-organization   总被引：2，自引：0，他引：2  

Giovanni Coco  A. Brad Murray   《Geomorphology》2007,91(3-4):271

The nearshore region exhibits many striking morphological patterns with a variety of spatial and temporal scales. The formation of these rhythmic features has been initially ascribed, depending on the pattern in question, to spatial structures in the flow or geological constrains. These forcing templates have been hypothesized to provide the spatial structure that becomes imprinted on the shoreline or seabed morphology. More recently, new explanations for rhythmic patterns have involved interactions between fluid flow and sediment transport that create morphological feedbacks and lead to pattern self-organization. While forcing-template models do not explicitly treat transport of the sediment that makes up the pattern, self-organization models focus on the strong couplings within flow/sediment systems, and on interactions between emergent structures. We illustrate the sweeping shift from template explanations to self-organization by discussing four nearshore patterns: beach cusps, surfzone crescentic sandbars, inner-shelf sorted bedforms, and large-scale cuspate shorelines. Models involving self-organization show that local interactions between flow and sediment transport can collectively give rise to patterns with large-scale coherence and that the driving feedbacks can be associated with either topographical or grain-size composition instabilities. An approach based on self-organization also allows researchers to establish limitations in the predictability of the occurrence of rhythmic patterns and characteristics as well as to study mechanisms leading to the observed variability of pattern or lack of regularity.  相似文献   

美国国家级干旱监测业务产品介绍     

王涓力 《干旱气象》2006,24(1):90-94

美国需要改进干旱监测与评估方法。干旱是代价昂贵的自然灾害(联邦应急管理局(FEMA),1995;W ilhite,2000),但经常被评估和预报产品的开发者忽略。相比于其他灾害,干旱表现得更模糊并且不适合用传统的评估或预报方法,它相对缓慢的发生以及其影响的复杂性,需要有一套新的方法来对它进行评估。干旱监测和预报技术的提高会使我们为应对干旱灾害做更好的准备工作,进行更好的应对实践,从而减少社会对干旱及其影响的脆弱性。为追踪和展示全美国干旱的程度、空间范围以及其影响,开发了新的干旱监测工具,研发了每周发布的国家级干旱监测业务产品(th…  相似文献   

Kinematics of the Galactic halo from horizontal branch stars in the Hamburg/ESO survey     

Christopher Thom  Chris Flynn  Michael S. Bessell  Jyrki Hänninen  Timothy C. Beers  Norbert Christlieb  Dionne James  Johan Holmberg  Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2005,360(1):354-359

Large samples of field horizontal branch (FHB) stars make excellent tracers of the Galactic halo; by studying their kinematics, one can infer important physical properties of our Galaxy. Here we present the results of a medium-resolution spectroscopic survey of 530 FHB stars selected from the Hamburg/ESO survey. The stars have a mean distance of ∼7 kpc and thus probe the inner parts of the Milky Way halo. We measure radial velocities from the spectra in order to test the model of Sommer-Larsen et al., who suggested that the velocity ellipsoid of the halo changes from radially dominated orbits to tangentially dominated orbits as one proceeds from the inner to the outer halo. We find that the present data are unable to discriminate between this model and a more simple isothermal ellipsoid; we suggest that additional observations towards the Galactic Centre might help to differentiate them.  相似文献   

From Strange Attractors to Real-World Data: Evaluating a Bedform Model by Measuring the Distance Between State-Space Plots     

A. Brad Murray 《Mathematical Geology》2001,33(3):293-300

A new nonlinear data-analysis technique compares the typical sequences in different time or spatial series. The method quantitatively compares delay-coordinate embedded state-space plots by treating them plots as probability distributions. Thus its application is not limited to data generated by deterministic systems, and does not require knowledge of a system's dimension. In a preliminary application, comparing state-space plots of natural and model-generated eolian ripples suggests that the interactions in them have similarities with those in nature, and that this method can be of use as an additional model evaluation tool.  相似文献   

Interpretation of discordant ⁴⁰Ar/³⁹Ar age-spectra of mesozoic tholeiites from antarctica     

Robert J Fleck  John F Sutter  David H Elliot 《Geochimica et cosmochimica acta》1977,41(1):15-32

Conventional K-Ar ages of tholeiitic basalts of the Ferrar Group in the central Transantarctic Mountains indicate significant loss of radiogenic ⁴⁰Ar from this unit over much of its outcrop area. Argon loss varies inversely with amount of devitrified matrix in the basalts, which have not been thermally or tectonically disturbed since extrusion. ⁴⁰Ar/¹⁹Ar age-spectra of these tholeiites are generally discordant and indicate significant inhomogeneity in the distribution of radiogenic ⁴⁰Ar with respect to ³⁹Ar, but are distinctly different from release patterns of thermally disturbed samples. Amounts of argon redistribution vary directly with amounts of devitrification and are reflected in progressive modification of the age spectra. A model of redistribution of radiogenic ⁴⁰Ar by devitrification of originally glassy matrix is suggested that is consistent with disturbance of the conventional K-Ar systematics as well as the ⁴⁰Ar/³⁹Ar age-spectra. Samples with substantial redistribution but minor loss of radiogenic argon yield age spectra whose apparent ages decrease from low-temperature to high-temperature steps, similar to those reported for some lunar basalts, breccias, and soils. Modification of all the age spectra is attributed to redistribution of radiogenic ⁴⁰Ar during progressive devitrification, although ³⁹Ar-recoil effects suggested by Turner and Cadogan (1974) may be a factor in some cases. Where devitrification involves most potassium sites within the basalt, ⁴⁰Ar/³⁹Ar age-plateaux may be formed that have no geologic significance.  相似文献   

Manufactured home building regulations and the February 2, 2007 Florida tornadoes     

Kevin M. Simmons  Daniel Sutter 《Natural Hazards》2008,46(3):415-425

The Department of Housing and Urban Development (HUD) and the state of Florida implemented new wind load and tie-down regulations for manufactured homes following Hurricane Andrew. This article examines the effect of the new regulations on the likelihood that occupants of mobile homes would survive a tornado. On February 2, 2007, three tornadoes struck central Florida, resulting in 21 deaths in Lake County, all in manufactured homes. The deaths occurred almost exclusively in homes rated as leveled by the county tax appraiser. Manufactured homes built to the new regulations, however, were significantly less likely to be leveled. Regression analysis finds that manufactured homes built to the post-Andrew requirements were 79% less likely to be leveled than homes built prior to the HUD Code in 1976, and 68% less likely to be leveled than homes built after 1976 but before the 1994 wind load regulations. Construction of all manufactured homes in the tornado paths to the wind load and tie-down requirements could have reduced fatalities by 70%.

Daniel Sutter (Corresponding author)Email:

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Geochemistry and argon thermochronology of the Variscan Sila Batholith,southern Italy: source rocks and magma evolution     

Robert A. Ayuso  Antonia Messina  Benedetto De Vivo  Selma Russo  Laurel G. Woodruff  John F. Sutter  Harvey E. Belkin 《Contributions to Mineralogy and Petrology》1994,117(1):87-109

The Sila batholith is the largest granitic massif in the Calabria-Peloritan Arc of southern Italy, consisting of syn to post-tectonic, calc-alkaline and metaluminous tonalite to granodiorite, and post-tectonic, peraluminous and strongly peraluminous, two-mica±cordierite±Al silicate granodiorite to leucomonzogranite. Mineral ⁴⁰Ar/³⁹Ar thermochronologic analyses document Variscan emplacement and cooling of the intrusives (293–289 Ma). SiO₂ content in the granitic rocks ranges from 57 to 77 wt%; cumulate gabbro enclaves have SiO₂ as low as 42%. Variations in absolute abundances and ratios involving Hf, Ta, Th, Rb, and the REE, among others, identify genetically linked groups of granitic rocks in the batholith: (1) syn-tectonic biotite±amphibole-bearing tonalites to granodiorites, (2) post-tectonic two-mica±Al-silicate-bearing granodiorites to leucomonzogranites, and (3) post-tectonic biotite±hornblende tonalites to granodiorites. Chondrite-normalized REE patterns display variable values of Ce/Yb (up to 300) and generally small negative Eu anomalies. Degree of REE fractionation depends on whether the intrusives are syn- or post-tectonic, and on their mineralogy. High and variable values of Rb/Y (0.40–4.5), Th/Sm (0.1–3.6), Th/Ta (0–70), Ba/Nb (1–150), and Ba/Ta (50–2100), as well as low values of Nb/U (2–28) and La/Th (1–10) are consistent with a predominant and heterogeneous crustal contribution to the batholith. Whole rock ¹⁸O ranges from +8.2 to +11.7; the mafic cumulate enclaves have the lowest ¹⁸O values and the two-mica granites have the highest values. ¹⁸O values for biotite±honblende tonalitic and granodioritic rocks (9.1 to 10.8) overlap the values of the mafic enclaves and two-mica granodiorites and leucogranites (10.7 to 11.7). The initial Pb isotopic range of the granitic rocks (²⁰⁶Pb/²⁰⁴Pb 18.17–18.45, ²⁰⁷Pb/²⁰⁴Pb 15.58–15.77, ²⁰⁸Pb/²⁰⁴Pb 38.20–38.76) also indicates the predominance of a crustal source. Although the granitic groups cannot be uniquely distinguished on the basis of their Pb isotope compositions most of the post-tectonic tonalites to granodiorites as well as two-mica granites are somewhat less radiogenic than the syn-tetonic tonalites and granodiorites. Only a few of the mafic enclaves overlap the Pb isotope field of the granitic rocks and are consistent with a cogenetic origin. The Sila batholith was generated by mixing of material derived from at least two sources, mantle-derived and crustal, during the closing stages of plate collision and post-collision. The batholith ultimately owes its origin to the evolution of earlier, more mafic parental magmas, and to complex intractions of the fractionating mafic magmas with the crust. Hybrid rocks produced by mixing evolved primarily by crystal fractionation although a simple fractionation model cannot link all the granitic rocks, or explain the entire spectrum of compositions within each group of granites. Petrographic and geochemical features characterizing the Sila batholith have direct counterparts in all other granitic massifs in the Calabrian-Peloritan Arc. This implies that magmatic events in the Calabrian-Peloritan Arc produced a similar spectrum of granitic compositions and resulted in a distinctive type of granite magmatism consisting of coeval, mixed, strongly peraluminous and metaluminous granitic magmas.  相似文献   

Hydraulic modeling of the 2011 New Madrid Floodway activation: a case study on floodway activation controls   总被引：2，自引：2，他引：0  

Adam Luke  Brad Kaplan  Jeff Neal  Jeremiah Lant  Brett Sanders  Paul Bates  Doug Alsdorf 《Natural Hazards》2015,77(3):1863-1887

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Late-stage volcano geomorphic evolution of the Pleistocene San Francisco Mountain, Arizona (USA), based on high-resolution DEM analysis and 40Ar/39Ar chronology     

Dávid Karátson  Tamás Telbisz  Brad S. Singer 《Bulletin of Volcanology》2010,72(7):833-846

The cone-building volcanic activity and subsequent erosion of San Francisco Mountain, AZ, USA, were studied by using high-resolution digital elevation model (DEM) analysis and new ⁴⁰Ar/³⁹Ar dating. By defining remnants or planèzes of the volcano flanks in DEM-derived images, the original edifice can be reconstructed. We propose a two-cone model with adjacent summit vents which were active in different times. The reconstructed cones were 4,460 and 4,350 m high a.s.l., corresponding to ∼2,160 and 2,050 m relative height, respectively. New ⁴⁰Ar/³⁹Ar data allow us to decipher the chronological details of the cone-building activity. We dated the Older and Younger Andesites of the volcano that, according to previous mapping, built the stage 2 and stage 3 stratocones, respectively. The new ⁴⁰Ar/³⁹Ar plateau ages yielded 589–556 ka for the Older and 514–505 ka for the Younger Andesites, supporting their distinct nature with a possible dormant period between. The obtained ages imply an intense final (≤100 ka long) cone-building activity, terminating ∼100 ka earlier than indicated by previous K-Ar ages. Moreover, ⁴⁰Ar/³⁹Ar dating constrains the formation of the Inner Basin, an elliptical depression in the center of the volcano initially created by flank collapse. A 530 ka age (with a ±58.4 ka 2σ error) for a post-depression dacite suggests that the collapse event is geochronologically indistinguishable from the termination of the andesitic cone-building activity. According to our DEM analysis, the original cone of San Francisco Mountain had a volume of about 80 km³. Of this volume, ∼7.5 km³ was removed by the flank collapse and subsequent glacial erosion, creating the present-day enlarged Inner Basin, and ∼2 km³ was removed from the outer valleys by erosion. Based on volumetric analysis and previous and new radiometric ages, the average long-term eruption rate of San Francisco Mountain was ∼0.2 km³/ka, which is a medium rate for long-lived stratovolcanoes. However, according to the new ⁴⁰Ar/³⁹Ar dates for the last ≤100 ka period, the final stratovolcanic activity was characterized by a greater ∼0.3 km³/ka rate.  相似文献   

Source location using time‐reverse imaging     

Brad Artman  Igor Podladtchikov  Ben Witten 《Geophysical Prospecting》2010,58(5):861-873

We present the chain of time‐reverse modeling, image space wavefield decomposition and several imaging conditions as a migration‐like algorithm called time‐reverse imaging. The algorithm locates subsurface sources in passive seismic data and diffractors in active data. We use elastic propagators to capitalize on the full waveforms available in multicomponent data, although an acoustic example is presented as well. For the elastic case, we perform wavefield decomposition in the image domain with spatial derivatives to calculate P and S potentials. To locate sources, the time axis is collapsed by extracting the zero‐lag of auto and cross‐correlations to return images in physical space. The impulse response of the algorithm is very dependent on acquisition geometry and needs to be evaluated with point sources before processing field data. Band‐limited data processed with these techniques image the radiation pattern of the source rather than just the location. We present several imaging conditions but we imagine others could be designed to investigate specific hypotheses concerning the nature of the source mechanism. We illustrate the flexible technique with synthetic 2D passive data examples and surface acquisition geometry specifically designed to investigate tremor type signals that are not easily identified or interpreted in the time domain.  相似文献