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This paper presents an efficient methodology for computing constant‐ductility inelastic response spectra. The computation of constant‐ductility spectra involves numerical root‐finding algorithms to find the strongest structure providing a desired ductility response. Smooth inelastic structural behavior is modeled using a first‐order nonlinear differential equation and the transient structural response is solved using an implicit algorithm requiring Newton iterations at each time step. For structural models with smooth hysteretic behavior (not piece‐wise linear), a simple root‐finding method involving a combination of hyperbolic fits, linear interpolation, and Newton's method converges upon the highest strength (conservative) solution with a small number of iterations. The effect of the hysteretic smoothness on the occurrence of multiple roots is examined for two near‐fault and two far‐fault earthquake records, and for two measures of ductility and for normalized hysteretic energy. The results indicate how the smoothness of the hysteretic behavior affects ductility demand and constant‐ductility response spectra. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Annemarie Christophersen Nicola Litchfield Kelvin Berryman Richard Thomas Roberto Basili Laura Wallace William Ries Gavin P. Hayes Kathleen M. Haller Toshikazu Yoshioka Richard D. Koehler Dan Clark Monica Wolfson-Schwehr Margaret S. Boettcher Pilar Villamor Nick Horspool Teraphan Ornthammarath Ramon Zuñiga Robert M. Langridge Mark W. Stirling Tatiana Goded Carlos Costa Robert Yeats 《Natural Hazards》2015,79(1):111-135
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We examined mammal occurrence and variability through the Late Pleistocene vertebrate fossil deposit of Grant Hall in Victoria Fossil Cave, Naracoorte, South Australia. To determine long‐term patterns of change, we compared the composition and relative abundance trends of the assemblage with a nearby Middle Pleistocene deposit in Cathedral Cave. Total species richness did not change through the Grant Hall sequence, dated from 93 ± 8 to 70 ± 5 ka. However, species relative abundances varied between ecologically divergent species, and in some cases between species that demonstrate similar environmental preferences. For some species this variation is comparable to that recorded in Cathedral Cave. Of those showing similar trends between the two deposits, the forest inhabitant, Pseudomys fumeus, recorded an 8.6% decline through Grant Hall, coincident with a 9.7% increase in the dry heath/mallee dweller Pseudomys apodemoides. These patterns indicate that climatic transition from relatively warm, moist to cooler, drier conditions impacted some species in similar ways through climatic cycles of the past. However, the majority of the fauna demonstrated complex responses that are individual and variable through time. Statistical tests of species trends from the Grant Hall assemblage caution that large fossil samples are required to validate patterns observed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Donald L. Forbes George S. Parkes Gavin K. Manson Lorne A. Ketch 《Marine Geology》2004,210(1-4):169-204
Storms play a major role in shoreline recession on transgressive coasts. In the southern Gulf of St. Lawrence (GSL), southeastern Canada, long-term relative sea-level rise off the North Shore of Prince Edward Island has averaged 0.3 m/century over the past 6000 years (>0.2 m/century over 2000 years). This has driven long-term coastal retreat at mean rates >0.5 m/a but the variance and details of coastal profile response remain poorly understood. Despite extensive sandy shores, sediment supply is limited and sand is transferred landward into multidecadal to century-scale storage in coastal dunes, barrier washover deposits, and flood-tidal delta sinks. Charlottetown tide-gauge records show mean relative sea-level rise of 3.2 mm/a (0.32 m/century) since 1911. A further rise of 0.7±0.4 m is projected over the next 100 years. When differenced from tidal predictions, the water-level data provide a 90-year record of storm-surge occurrence. Combined with wind, wave hindcast, and sea-ice data, this provides a catalogue of potentially significant coastal storms. We also document coastal impacts from three recent storms of great severity in January and October 2000 and November 2001. Digital photogrammetry (1935–1990) and shore-zone surveys (1989–2001) show large spatial and temporal variance in coastal recession rates, weakly correlated with the storm record, in part because of wave suppression or coastal protection by sea ice. Large storms cause rapid erosion from which recovery depends in part on local sand supply, but barrier volume may be conserved by washover deposition. Barrier shores with dunes show high longshore and interdecadal variance, with extensive multidecadal healing of former inlet and overwash gaps. This reflects recovery from an episode of widespread overwash prior to 1935, possibly initiated by intense storms or groups of storms in the latter half of the 19th century. With evidence from the storms of 2000–2001, this points to the importance of storm clustering on scales of weeks to years in determining erosion vulnerability, as well as the need for a long-term, large-scale perspective in assessing coastal stability. The expected acceleration in relative sea-level rise, together with projections of increasing storm intensity and greatly diminished winter ice cover in the southern GSL, implies a significant increase in coastal erosion hazards in future. 相似文献
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The anthropogenic contribution of trace metals to settling particulate matter (SPM) and surficial sediments was determined on the high-energy continental shelf adjacent to Sydney, Australia. Settling particulate matter and surficial sediment was collected in the vicinity of a major sewage outfall and at five control sites on the middle shelf (80-100 m water depth). Sediment traps were deployed on 10 occasions for up to 2 weeks during the summer and winter of 1995 and SPM was analyzed for Ag, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Cobalt, Fe, Mn and Ni act conservatively in SPM and in sediments regionally and are used as normalizing elements to determine anthropogenic enrichment. Surficial sediments and SPM are enriched in Ag, Cr, Cu, Pb and Zn near a major ocean outfall and at four of the five control sites, although sewage particles contribute < 5% of trace metals in the total sample. Silver is the most sensitive trace metal tracer for establishing the presence of sewage particulate matter. Sewage particulate matter flux near the outfall was estimated using a two end-member mixing model and is below 0.5 g m(-2) day(-1) during all deployment periods. The mean sewage particulate matter flux at sampling locations 30 km and 60 km north of the outfall are <0.13 g m(-2) day(-1) and <0.01 g m(-2) day(-1), respectively, indicating an efficient dispersal of anthropogenic material on this high energy continental shelf. 相似文献
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Christopher A.‐L. Jackson Gavin M. Elliott Elisabeth Royce‐Rogers Robert L. Gawthorpe Tor E. Aas 《Basin Research》2019,31(3):514-538
“Salt” giants are typically halite‐dominated, although they invariably contain other evaporite (e.g. anhydrite, bittern salts) and non‐evaporite (e.g. carbonate, clastic) rocks. Rheological differences between these rocks mean they impact or respond to rift‐related, upper crustal deformation in different ways. Our understanding of basin‐scale lithology variations in ancient salt giants, what controls this and how this impacts later rift‐related deformation, is poor, principally due to a lack of subsurface datasets of sufficiently regional extent. Here we use 2D seismic reflection and borehole data from offshore Norway to map compositional variations within the Zechstein Supergroup (ZSG) (Lopingian), relating this to the structural styles developed during Middle Jurassic‐to‐Early Cretaceous rifting. Based on the proportion of halite, we identify and map four intrasalt depositional zones (sensu Clark et al., Journal of the Geological Society, 1998, 155, 663) offshore Norway. We show that, at the basin margins, the ZSG is carbonate‐dominated, whereas towards the basin centre, it becomes increasingly halite‐dominated, a trend observed in the UK sector of the North Sea Basin and in other ancient salt giants. However, we also document abrupt, large magnitude compositional and thickness variations adjacent to large, intra‐basin normal faults; for example, thin, carbonate‐dominated successions occur on fault‐bounded footwall highs, whereas thick, halite‐dominated successions occur only a few kilometres away in adjacent depocentres. It is presently unclear if this variability reflects variations in syn‐depositional relief related to flooding of an underfilled presalt (Early Permian) rift or syn‐depositional (Lopingian) rift‐related faulting. Irrespective of the underlying controls, variations in salt composition and thickness influenced the Middle Jurassic‐to‐Early Cretaceous rift structural style, with diapirism characterising hangingwall basins where autochthonous salt was thick and halite‐rich and salt‐detached normal faulting occurring on the basin margins and on intra‐basin structural highs where the salt was too thin and/or halite‐poor to undergo diapirism. This variability is currently not captured by existing tectono‐stratigraphic models largely based on observations from salt‐free rifts and, we argue, mapping of suprasalt structural styles may provide insights into salt composition and thickness in areas where boreholes are lacking or seismic imaging is poor. 相似文献
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Traditional ecological knowledge (TEK) guides resource management across the globe, but is at risk amid social and ecological change. This has prompted numerous calls for TEK maintenance efforts, but these remain largely unexamined in the literature. Here, we discuss three examples of in situ TEK maintenance from Malekula Island in Vanuatu, locally known as kastom schools. Based on qualitative data, we find that the kastom schools may create several opportunities to maintain TEK (e.g., establishing local control over education), and argue that they represent the creative and adaptive management of tradition in dynamic social–ecological contexts. However, a number of challenges, both practical (e.g., lack of funding) and epistemological (e.g., changing modes of cultural transmission), threaten the efficacy of the kastom schools. We argue that in situ modes of TEK maintenance have promise, but that issues of power and heterogeneity require serious consideration if such measures are to succeed. 相似文献