Is the Linné impact crater morphology influenced by the rheological layering on the Moon's surface? Insights from numerical modeling          下载免费PDF全文

Elena Martellato  Valerio Vivaldi  Matteo Massironi  Gabriele Cremonese  Francesco Marzari  Andrea Ninfo  Junichi Haruyama 《Meteoritics & planetary science》2017,52(7):1388-1411

Linné is a simple crater, with a diameter of 2.23 km and a depth of 0.52 km, located in northwestern Mare Serenitatis. Recent high‐resolution data acquired by the Lunar Reconnaissance Orbiter Camera revealed that the shape of this impact structure is best described by an inverted truncated‐cone. We perform morphometric measurements, including slope and profile curvature, on the Digital Terrain Model of Linné, finding the possible presence of three subtle topographic steps, at the elevation of +20, ?100, and ?200 m relative to the target surface. The kink at ?100 m might be related to the interface between two different rheological layers. Using the iSALE shock physics code, we numerically model the formation of Linné crater to derive hints on the possible impact conditions and target physical properties. In the initial setup, we adopt a basaltic projectile impacting the Moon with a speed of 18 km s^?1. For the local surface, we consider either one or two layers, in order to test the influence of material properties or composite rheologies on the final crater morphology. The one‐layer model shows that the largest variations in the crater shape take place when either the cohesion or the friction coefficient is varied. In particular, a cohesion of 10 kPa marks the threshold between conical‐ and parabolic‐shaped craters. The two‐layer model shows that the interface between the two layers would be exposed at the observed depth of 100 m when an intermediate value (~200 m) for the upper fractured layer is set. We have also found that the truncated‐cone morphology of Linné might originate from an incomplete collapse of the crater wall, as the breccia lens remains clustered along the crater walls, while the high‐albedo deposit on the crater floor can be interpreted as a very shallow lens of fallout breccia. The modeling analysis allows us to derive important clues on the impactor size (under the assumption of a vertical impact and collision velocity equal to the mean value), and on the approximate, large‐scale preimpact target properties. Observations suggest that these large‐scale material properties likely include some important smaller scale variations, disclosed as subtle morphological steps in the crater walls. Furthermore, the modeling results allow advancing some hypotheses on the geological evolution of the Mare Serenitatis region where Linné crater is located (unit S14). We suggest that unit S14 has a thickness of at least a few hundreds of meters up to about 400 m.  相似文献   

Spatial modeling of pyroclastic cover deposit thickness (depth to bedrock) in peri‐volcanic areas of Campania (southern Italy)          下载免费PDF全文

Matteo Del Soldato  Veronica Pazzi  Samuele Segoni  Pantaleone De Vita  Veronica Tofani  Sandro Moretti 《地球表面变化过程与地形》2018,43(9):1757-1767

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Using the size and position of drumlins to understand how they grow,interact and evolve          下载免费PDF全文

Jeremy C. Ely  Chris D. Clark  Matteo Spagnolo  Anna L.C. Hughes  Chris R. Stokes 《地球表面变化过程与地形》2018,43(5):1073-1087

Drumlins are subglacial bedforms streamlined in the direction of ice flow. Common in deglaciated landscapes, they have been widely studied providing rich information on their internal geology, size, shape, and spacing. In contrast with bedform investigations elsewhere in geomorphology (aeolian and fluvial dunes and ripples for example) most drumlin studies derive observations from relict, and thus static features. This has made it difficult to gain information and insights about their evolution over time, which likely hampers our understanding of the process(es) of drumlin formation. Here we take a morphological approach, studying drumlin size and spacing metrics. Unlike previous studies which have focussed on databases derived from entire ice sheet beds, we adopt a space‐for‐time substitution approach using individual drumlin flow‐sets distributed in space as proxies for different development times/periods. Framed and assisted by insights from aeolian and fluvial geomorphology, we use our metric data to explore possible scenarios of drumlin growth, evolution and interaction. We study the metrics of the size and spacing of 36 222 drumlins, distributed amongst 71 flow‐sets, left behind by the former British‐Irish Ice Sheet, and ask whether behaviour common to other bedform phenomena can be derived through statistical analysis. Through characterizing and analysing the shape of the probability distribution functions of size and spacing metrics for each flow‐set we argue that drumlins grow, and potentially migrate, as they evolve leading to pattern coarsening. Furthermore, our findings add support to the notion that no upper limit to drumlin size exists, and to the idea that perpetual coarsening could occur if given sufficient time. We propose that the framework of process and patterning commonly applied to non‐glacial bedforms is potentially powerful for understanding drumlin formation and for deciphering glacial landscapes. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Using UAV acquired photography and structure from motion techniques for studying glacier landforms: application to the glacial flutes at Isfallsglaciären          下载免费PDF全文

Jeremy C. Ely  Conor Graham  Iestyn D. Barr  Brice R. Rea  Matteo Spagnolo  Jeff Evans 《地球表面变化过程与地形》2017,42(6):877-888

Glacier and ice sheet retreat exposes freshly deglaciated terrain which often contains small‐scale fragile geomorphological features which could provide insight into subglacial or submarginal processes. Subaerial exposure results in potentially rapid landscape modification or even disappearance of the minor‐relief landforms as wind, weather, water and vegetation impact on the newly exposed surface. Ongoing retreat of many ice masses means there is a growing opportunity to obtain high resolution geospatial data from glacier forelands to aid in the understanding of recent subglacial and submarginal processes. Here we used an unmanned aerial vehicle to capture close‐range aerial photography of the foreland of Isfallsglaciären, a small polythermal glacier situated in Swedish Lapland. An orthophoto and a digital elevation model with ~2 cm horizontal resolution were created from this photography using structure from motion software. These geospatial data was used to create a geomorphological map of the foreland, documenting moraines, fans, channels and flutes. The unprecedented resolution of the data enabled us to derive morphological metrics (length, width and relief) of the smallest flutes, which is not possible with other data products normally used for glacial landform metrics mapping. The map and flute metrics compare well with previous studies, highlighting the potential of this technique for rapidly documenting glacier foreland geomorphology at an unprecedented scale and resolution. The vast majority of flutes were found to have an associated stoss‐side boulder, with the remainder having a likely explanation for boulder absence (burial or erosion). Furthermore, the size of this boulder was found to strongly correlate with the width and relief of the lee‐side flute. This is consistent with the lee‐side cavity infill model of flute formation. Whether this model is applicable to all flutes, or multiple mechanisms are required, awaits further study. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Biogeomorphology of the Mediterranean Posidonia oceanica seagrass meadows          下载免费PDF全文

Matteo Vacchi  Giovanni De Falco  Simone Simeone  Monica Montefalcone  Carla Morri  Marco Ferrari  Carlo Nike Bianchi 《地球表面变化过程与地形》2017,42(1):42-54

Here we review the multiple interactions between the endemic Mediterranean seagrass, Posidonia oceanica, and coastal geomorphologic processes as an outstanding example of biogeomorphology, taking into account recent advances in the field. Seagrass meadows are among the most important elements for the functioning of marine coastal ecosystems, and represent a major focus for research and conservation. Being considered a priority habitat, P. oceanica meadows are protected by several European Union directives and national laws. In this paper we examine: the role of sedimentary features in controlling the development of the meadows; the interplay between P. oceanica leaf litter (i.e. beached necromass) cast ashore and erosional‐depositional processes on the beaches; the interactions between meadows and nearshore hydrodynamics, and; possible linkages between geomorphological features of the seafloor and the architecture of meadows. Finally, we provide perspectives for future research on P. oceanica and other Mediterranean seagrass meadows in a biogeomorphological context with specific reference to climate change. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

The dynamics of mountain erosion: Cirque growth slows as landscapes age     

Iestyn D. Barr  Jeremy C. Ely  Matteo Spagnolo  Ian S. Evans  Matt D. Tomkins 《地球表面变化过程与地形》2019,44(13):2628-2637

Glacial cirques are widely used palaeoenvironmental indicators, and are key to understanding the role of glaciers in shaping mountain topography. However, notable uncertainty persists regarding the rate and timing of cirque erosion. In order to address this uncertainty, we analyse the dimensions of 2208 cirques in Britain and Ireland and model ice accumulation to investigate the degree of coupling between glacier occupation times and cirque growth. Results indicate that during the last ~120 ka, cirques were glacier-free for an average of 52.0 ± 21.2 ka (43 ± 18%); occupied by small (largely cirque-confined) glaciers for 16.2 ± 9.9 ka (14 ± 8%); and occupied by large glaciers, including ice sheets, for 51.8 ± 18.6 ka (43 ± 16%). Over the entire Quaternary (i.e. 2.6 Ma), we estimate that cirques were glacier-free for 1.1 ± 0.5 Ma; occupied by small glaciers for 0.3 ± 0.2 Ma; and occupied by large glaciers for 1.1 ± 0.4 Ma. Comparing occupation times to cirque depths, and calculating required erosion rates, reveals that continuous cirque growth during glacier occupation is unlikely. Instead, we propose that cirques attained much of their size during the first occupation of a non-glacially sculpted landscape (perhaps during the timeframe of a single glacial cycle). During subsequent glacier occupations, cirque growth may have slowed considerably, with the highest rates of subglacial erosion focused during periods of marginal (small glacier) glaciation. We propose comparatively slow rates of growth following initial cirque development because a ‘least resistance’ shape is formed, and as cirques deepen, sediment becomes trapped subglacially, partly protecting the bedrock from subsequent erosion. In support of the idea of rapid cirque growth, we present evidence from northern British Columbia, where cirques of comparable size to those in Britain and Ireland developed in less than 140 ka. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd.  相似文献   

KAGRA引力波探测器中蓝宝石测试镜光学性质研究          下载免费PDF全文

李鹏博  ZEIDLER Simon  LEONARDI Matteo  王浩宇  朱宗宏 《天文学报》2021,62(6):62

低温制冷技术是下一代激光干涉仪引力波探测器的核心技术之一. 日本引力波探测器KAGRA (Kamioka Gravitational Wave Detector)作为该技术的前沿开拓者, 将运行在20K的超低温环境中, 并使用在低温下热噪声较低的单晶蓝宝石晶体作为测试镜. 然而, 高质量大尺寸低吸收率的蓝宝石晶体极难制备. 此外, 由于蓝宝石晶体存在晶格结构不均匀, 很容易导致不必要的双折射效应, 从而影响探测器的目标灵敏度. 基于上述问题, 开发了两套大尺寸光学测量系统, 首次系统研究了KAGRA低温蓝宝石测试镜的光学特性. 首先, 根据探测器对测试镜热噪声的要求, 开发了一套基于光热共光路干涉技术的光学测量系统, 该系统可对测试镜以及测试镜表面涂层的光学吸收进行有效的表征. 其次, 基于光学吸收测量系统, 开发了一套双折射效应测量系统, 该系统可以有效表征测试镜中双折射的均匀性. 目前两套测量系统的搭建与调试已完成, 对蓝宝石测试镜光学吸收的测量灵敏度达到了1.5ppm/cm, 双折射测量系统的空间分辨率小于0.3mm times 0.3mm. 该工作对降低大尺寸低温测试镜双折射效应及提高探测器灵敏度具有重要意义.  相似文献   

Combining genetic and linearized algorithms for a two-step joint inversion of Rayleigh wave dispersion and H/V spectral ratio curves     

Matteo Picozzi  Dario Albarello 《Geophysical Journal International》2007,169(1):189-200

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Hard X-ray emission from elliptical galaxies     

S. W. Allen  T. Di Matteo  A. C. Fabian 《Monthly notices of the Royal Astronomical Society》2000,311(3):493-506

We report the detection of hard X-ray emission components in the spectra of six nearby, giant elliptical galaxies observed with the ASCA satellite. The systems studied, which exhibit strong dynamical evidence for supermassive black holes in their nuclei, are M87, NGC 1399 and NGC 4696 (the dominant galaxies of the Virgo, Fornax and Centaurus clusters, respectively) and NGC 4472, 4636 and 4649 (three further giant ellipticals in the Virgo cluster). The ASCA data for all six sources provide clear evidence for hard emission components, which can be parametrized by power-law models with photon indices in the range Γ=0.6–1.5 (mean value 1.2) and intrinsic 1–10 keV luminosities of 2×10⁴⁰–2×10⁴² erg s⁻¹. Our results imply the identification of a new class of accreting X-ray source, with X-ray spectra significantly harder than those of binary X-ray sources, Seyfert nuclei or low-luminosity active galactic nuclei, and bolometric luminosities relatively dominated by their X-ray emission. We discuss various possible origins for the hard X-ray emission and argue that it is most likely to be due to accretion on to the central supermassive black holes, via low radiative efficiency accretion flows coupled with strong outflows. In the case of M87, our detected power-law flux is in good agreement with a previously reported measurement from ROSAT High Resolution Imager observations, which were able to resolve the jet from the nuclear X-ray emission components. We confirm previous results showing that the use of multiphase models in the analysis of the ASCA data leads to determinations of approximately solar emission-weighted metallicities for the X-ray gas in the galaxies. We also present results on the individual element abundances in NGC 4636.  相似文献   

Measuring the fractal dimensions of ideal and actual objects: implications for application in geology and geophysics   总被引：1，自引：0，他引：1  

Guido Gonzato  Francesco Mulargia  & Matteo Ciccotti 《Geophysical Journal International》2000,142(1):108-116

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