Interrogation of the Megathrust Zone in the Tohoku-Oki Seismic Region by Waveform Complexity: Intraslab Earthquake Rupture and Reactivation of Subducted Normal Faults     

Semechah K. Y. Lui  Don Helmberger  Shengji Wei  Yihe Huang  Robert W. Graves 《Pure and Applied Geophysics》2015,172(12):3425-3437

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Seismic fragility curves of as-built single-span masonry arch bridges     

Giovanni Tecchio  Marco Donà  Francesca da Porto 《Bulletin of Earthquake Engineering》2016,14(11):3099-3124

Masonry arch bridges are crucial elements in the railway transportation network throughout Europe. Although significant advances in seismic risk assessment of various bridge types have been made by developing fragility curves of generalized classes of structures, there are no comparable tools for masonry arch structures. In this context, this paper presents the construction of seismic fragility curves of single-span masonry bridges according to the limit analysis method. An iterative procedure is implemented to define the capacity curve of the equivalent single degree of freedom system through non-linear kinematic analysis. The process involves determination of the collapse mechanism, calculation of the limit load multiplier, and definition of the thrust line. The intrinsic variability of the seismic action is incorporated with the use of different sets of elastic spectra compatible with EC 8 Type-1 spectrum for various types of soil, with peak ground acceleration varying over the range 0.05–1.5 g. The fragility curves of the generalized classes of single-span masonry bridges are finally obtained from the effective ranges of the main geometric and material parameters affecting arch bridge capacity.  相似文献   

Shallow degassing events as a trigger for very-long-period seismicity at Kīlauea Volcano,Hawai‘i     

Matthew Patrick  David Wilson  David Fee  Tim Orr  Don Swanson 《Bulletin of Volcanology》2011,73(9):1179-1186

The first eruptive activity at Kīlauea Volcano’s summit in 25 years began in March 2008 with the opening of a 35-m-wide vent in Halema‘uma‘u crater. The new activity has produced prominent very-long-period (VLP) signals corresponding with two new behaviors: episodic tremor bursts and small explosive events, both of which represent degassing events from the top of the lava column. Previous work has shown that VLP seismicity has long been present at Kīlauea’s summit, and is sourced approximately 1 km below Halema‘uma‘u. By integrating video observations, infrasound and seismic data, we show that the onset of the large VLP signals occurs within several seconds of the onset of the degassing events. This timing indicates that the VLP is caused by forces—sourced at or very near the lava free surface due to degassing—transmitted down the magma column and coupling to the surrounding rock at 1 km depth.  相似文献   

Large-scale silicic alkalic magmatism associated with the Buckhorn Caldera, Trans-Pecos Texas, USA: comparison with Pantelleria, Italy     

Don F. Parker  John C. White 《Bulletin of Volcanology》2008,70(3):403-415

Three major rhyolite systems in the northeastern Davis and adjacent Barrilla Mountains include lava units that bracketed a large pantelleritic ignimbrite (Gomez Tuff) in rapid eruptions spanning 300,000 years. Extensive silicic lavas formed the shields of the Star Mountain Formation (37.2 Ma-K/Ar; 36.84 Ma ³⁹Ar/⁴⁰Ar), and the Adobe Canyon Formation (37.1 Ma-K/Ar; 36.51-³⁹Ar/⁴⁰Ar). The Gomez Tuff (36.6 Ma-K/Ar; 36.74-³⁹Ar/⁴⁰Ar) blanketed a large region around the 18×24 km diameter Buckhorn caldera, within which it ponded, forming sections up to 500 m thick. Gomez eruption was preceded by pantelleritic rhyolite domes (36.87, 36.91 Ma-³⁹Ar/⁴⁰Ar), some of which blocked movement of Star Mountain lava flows. Following collapse, the Buckhorn caldera was filled by trachyte lava. Adobe Canyon rhyolite lavas then covered much of the region. Star Mountain Formation (~220 km³) is composed of multiple flows ranging from quartz trachyte to mildly peralkalic rhyolite; three major types form a total of at least six major flows in the northeastern Davis Mountains. Adobe Canyon Formation (~125 km³) contains fewer flows, some up to 180 m thick, of chemically homogenous, mildly peralkalic comendite, extending up to 40 km. Gomez Tuff (~220 km³) may represent the largest known pantellerite. It is typically less than 100 m thick in extra-caldera sections, where it shows a pyroclastic base and top, although interiors are commonly rheomorphic, containing flow banding and ramp structures. Most sections contain one cooling unit; two sections contain a smaller, upper cooling unit. Chemically, the tuff is fairly homogeneous, but is more evolved than early pantelleritic domes. Overall, although Davis Mountains silicic units were generated through open system processes, the pantellerites appear to have evolved by processes dominated by extensive fractional crystallization from parental trachytes similar to that erupted in pre- and post-caldera lavas. Comparison with the Pantelleria volcano suggests that the most likely parental magma for the Buckhorn series is transitional basalt, similar to that erupted in minor, younger Basin and Range volcanism after about 24 Ma. Roughly contemporaneous mafic lavas associated with the Buckhorn caldera appear to have assimilated or mixed with crustal melts, and, generally, may not be regarded as mafic precursors of the Buckhorn silicic rocks, They thus form a false Daly Gap as opposed to the true basalt/trachyte Daly gap of Pantelleria. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic rhyolites.  相似文献   

Large vesicles record pathways of degassing at basaltic volcanoes   总被引：2，自引：2，他引：0  

Margherita Polacci  Don R. Baker  Liping Bai  Lucia Mancini 《Bulletin of Volcanology》2008,70(9):1023-1029

Volcanic degassing is directly linked to magma dynamics and controls the style of eruptive activity. To better understand how gas is transported within basaltic magma we perform a 3D investigation of vesicles preserved in scoria from the 2005 activity at Stromboli volcano (Italy). We find that clasts are characterized by the ubiquitous occurrence of one to a few large vesicles, exhibiting mostly irregular, tortuous, channel-like textures, orders of magnitude greater in volume than all the other vesicles in the sample. We compare observations on natural samples with results from numerical simulations and experimental investigations of vesicle size distributions and demonstrate that this type of vesicle invariably forms in magmas with vesicularities > 0.30 (and possibly > 0.10). We suggest that large vesicles represent pathways used by gas to flow non-explosively to the surface and that they indicate the development of an efficient system that sustains persistent degassing in basaltic systems.  相似文献   

农村土地调查水域中界址点的准确定位     

宋宏伟  林宏伟  顾栋材 《现代测绘》2010,33(4)

农村土地调查调查底图上水域中界址点点位不准随处可见。界址点定位不准影响界址线位置和宗地面积和土地权属和附属资料的制作。因此,水域中界址点如何准确定位是一个急待解决的带有普遍性的问题。  相似文献   

American beginnings: The prehistory and palaeoecology of Beringia     

Don E. Dumond 《Geoarchaeology》1997,12(7):811-815

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Application of petrographic and geochemical methods to sourcing felsitic archaeological materials in Southeastern New England     

O. Don Hermes  D. Ritchie 《Geoarchaeology》1997,12(1):1-30

At least four volcanic complexes of different age and petrologic character occur in southeastern New England. Each complex contains a variety of fine-grained felsitic rocks, and three of these are known to have been quarried by prehistoric people for material used in the production of stone tools. These volcanics include a Late Proterozoic calcalkaline suite (Lynn-Mattapan) and several alkaline suites of Ordovician to Carboniferous age (Blue Hill, Spencer Hill, and Wamsutta suites). Each suite exhibits unique petrographic and geochemical features that help to constrain sources of felsitic archaeological materials. Distinctive petrographic features are: (1) Lynn/Mattapan: mostly pyroclastic rocks that typically contain broken crystals, volcanic clasts, and relict pumice and glass shards; phenocrysts of plagioclase, quartz, and perthite, commonly in glomeroporphyritic clusters; accessory sphene and prominent late-stage epidote; some varieties exhibit distinct flow-banding. (2) Blue Hill and Spencer Hill rocks: mainly lava flows; abundant perthite and quartz phenocrysts, with minor or no plagioclase; accessory minerals may include fluorite, aegerine, riebeckite, zircon, and allanite. (3) Wamsutta rhyolite: phenocrysts solely of anorthoclase; quartz restricted to late-stage filling of vesicles, and to planar, subparallel fractures in-filled as lithophysae; lava flows with devitrified glass matrix. Major element geochemistry is of limited use in distinguishing the volcanic groups, but trace element signatures are distinct and provide excellent criteria to discriminate rocks from each suite. Compared to the Lynn/Mattapan suite, the Blue Hill and Spencer Hill rocks exhibit higher concentrations of Rb, Y, Zr, Nb, La, Ce and Zn, and lower concentrations of Sr and Ba. Wamsutta rhyolite is intermediate in composition, but distinct. Examination of material from six prehistoric quarries, and debitage collected at seven archaeological sites, demonstrates that most samples can be assigned to one of the above volcanic suites based on combined petrographic and geochemical attributes. These geologic attributes add a significant element of quantification to archaeological sourcing problems that lead to improved identification of materials compared to hand sample characterization alone. The volcanics from source areas proximal to the Boston basin were important to Early and Middle Archaic period populations across most of southeastern Massachusetts. During the Late/Terminal Archaic period, these materials were being transported extensively throughout eastern and southeastern Massachusetts, the Narragansett Bay area, and parts of Rhode Island. Thus, routinely applied geological methods can provide useful approaches to constrain the sources of felsites from southeastern New England found in archaeological contexts. © 1997 John Wiley & Sons, Inc.  相似文献   

Determining chondrule size distributions from thin-section measurements     

Don D. Eisenhour 《Meteoritics & planetary science》1996,31(2):243-248

Abstract— A method is described for correcting thin-section-derived chondrule sizes for three common sources of bias: (1) the non-equatorial sectioning of chondrules, (2) the non-zero thickness of thin sections, and (3) the unequal probability of sectioning different size chondrules. Application of the correction procedure to chondrule data from CO chondrites results in a reduction of mean and median chondrule diameters, an increase in minimum diameters, and transforms nearly log-normal distributions to distributions that conform to a Weibull probability function. The Weibull-function form of CO chondrule size distributions is similar to the form of chondrule distributions in ordinary chondrites obtained by disaggregation analyses.  相似文献   

Biogeographical drivers of ragweed pollen concentrations in Europe     

Matyasovszky  István  Makra  László  Tusnády  Gábor  Csépe  Zoltán  Nyúl  László G.  Chapman  Daniel S.  Sümeghy  Zoltán  Szűcs  Gábor  Páldy  Anna  Magyar  Donát  Mányoki  Gergely  Erostyák  János  Bodnár  Károly  Bergmann  Karl-Christian  Deák  Áron József  Thibaudon  Michel  Albertini  Roberto  Bonini  Maira  Šikoparija  Branko  Radišić  Predrag  Gehrig  Regula  Rybníček  Ondřej  Severova  Elena  Rodinkova  Victoria  Prikhodko  Alexander  Maleeva  Anna  Stjepanović  Barbara  Ianovici  Nicoleta  Berger  Uwe  Seliger  Andreja Kofol  Weryszko-Chmielewska  Elżbieta  Šaulienė  Ingrida  Shalaboda  Valentina  Yankova  Raina  Peternel  Renata  Ščevková  Jana  Bullock  James M. 《Theoretical and Applied Climatology》2018,133(1-2):277-295

Theoretical and Applied Climatology - The drivers of spatial variation in ragweed pollen concentrations, contributing to severe allergic rhinitis and asthma, are poorly quantified. We analysed the...  相似文献