On the generation of oceanic surface waves by underwater volcanic explosions     

Dean G. Duffy   《Journal of Volcanology and Geothermal Research》1992,50(3)

The oceanic surface waves generated by submarine volcanism are modeled as the response of a compressible ocean to an underwater point explosion at an arbitrary depth over an elastic half-space. We generalize the work of Kajiura and Miyoshi by allowing the elastic sea floor to influence both the sound and surface gravity waves. The classic work of Press and Ewing is extended to allow for the movement of the oceanic free surface. From numerical inversion techniques, we find that most of the energy is radiated away as surface gravity waves. A mixture of direct and reflected P- (compressional) and S-type (distortional) head waves may produce high-frequency, large-amplitude oscillations in the sea surface.  相似文献   

Fault‐controlled fluid flow inferred from hydrothermal vents imaged in 3D seismic reflection data,offshore NW Australia          下载免费PDF全文

Craig Magee  Oliver B. Duffy  Kirsty Purnell  Rebecca E. Bell  Christopher A.‐L. Jackson  Matthew T. Reeve 《Basin Research》2016,28(3):299-318

Fluid migration pathways in the subsurface are heavily influenced by pre‐existing faults. Although studies of active fluid‐escape structures can provide insights into the relationships between faults and fluid flow, they cannot fully constrain the geometry of and controls on the contemporaneous subsurface fluid flow pathways. We use 3D seismic reflection data from offshore NW Australia to map 121 ancient hydrothermal vents, likely related to magmatic activity, and a normal fault array considered to form fluid pathways. The buried vents consist of craters up to 264 m deep, which host a mound of disaggregated sedimentary material up to 518 m thick. There is a correlation between vent alignment and underlying fault traces. Seismic‐stratigraphic observations and fault kinematic analyses reveal that the vents were emplaced on an intra‐Tithonian seabed in response to the explosive release of fluids hosted within the fault array. We speculate that during the Late Jurassic the convex‐upwards morphology of the upper tip‐lines of individual faults acted to channelize ascending fluids and control where fluid expulsion and vent formation occurred. This contribution highlights the usefulness of 3D seismic reflection data to constraining normal fault‐controlled subsurface fluid flow.  相似文献   

Data-moderate assessments of Cape monkfish Lophius vomerinus and west coast sole Austroglossus microlepis in Namibian waters     

JN Kathena  A Kokkalis  MW Pedersen  JE Beyer  UH Thygesen 《African Journal of Marine Science》2018,40(3):293-302

There is global interest in providing scientific advice on optimal harvesting of all commercially exploited fish stocks. Nevertheless, many commercially important stocks lack analytical assessments. Therefore, we evaluate a data-moderate stock assessment method: the stochastic surplus production model in continuous time (SPiCT). The method was applied to two Namibian stocks: (i) the data-rich Cape monkfish Lophius vomerinus, where results are compared to a new data-rich assessment using a state–space assessment model (SAM); and (ii) the data-moderate west coast sole Austroglossus microlepis, which is an important bycatch species in the Cape monkfish fishery, but currently unassessed. The information available to the data-moderate assessment is total commercial catch, commercial catch per unit effort (CPUE), and survey CPUE. SPiCT and SAM gave largely consistent estimates of relative fishing mortality (F/F_MSY) and relative exploitable biomass (B/B_MSY) for the Cape monkfish stock, although with some discrepancies. Differences in the biomass estimates between the two assessments suggest that further investigation is required to understand the cause, and that some caution is necessary when considering the biomass of the stock. SPiCT shows that the west coast sole may be overexploited, although the confidence bounds were too wide for a firm conclusion. Similarity in the estimates of F/F_MSY for Cape monkfish in recent years, using SPiCT relative to SAM, likewise indicates the suitability of SPiCT for managing west coast sole.  相似文献   

Rural settlement change in the Republic of Ireland — a preliminary discussion   总被引：1，自引：0，他引：1  

Patrick J. Duffy 《Geoforum》1983,14(2):185-191

One of the notable repercussions of the population stability and growth in Ireland in the past two decades has been the impact on settlement in rural areas. Rural areas in the vicinity of towns and cities especially have experienced this urban-generated settlement expansion. This preliminary examination looks at the changes which have taken place in rural settlement patterns and briefly discusses their implications.  相似文献   

Shock compression and isentropic release of granite     

Toshimori Sekine  Thomas S. Duffy  Allan M. Rubin  William W. Anderson  Thomas J. Ahrens 《Geophysical Journal International》1995,120(2):247-261

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Historical variation in guano production from the Peruvian and Benguela upwelling ecosystems     

David Schneider  David Cameron Duffy 《Climatic change》1988,13(3):309-316

Analysis of the historical record shows that reductions in guano production in the eastern tropical Atlantic Ocean were not related to El Niño events in the Pacific. Guano production in the Atlantic was negatively correlated with guano production in the Pacific. Significant reductions in guano production in the Atlantic occurred 1 to 4 years after increases in guano production in the Pacific. Negative association is consistent with the hypothesis that global shifts in weather associated with the Southern Oscillation affect guano production.  相似文献   

Modeling the Impact of Black Spruce on the Fire Regime of Alaskan Boreal Forest   总被引：1，自引：0，他引：1  

T. S. Rupp  A. M. Starfield  F. S. Chapin III  P. Duffy 《Climatic change》2002,55(1-2):213-233

In the boreal biome, fire is the major disturbance agent affecting ecosystem change, and fire dynamics will likely change in response to climatic warming. We modified a spatially explicit model of Alaskan subarctic treeline dynamics (ALFRESCO) to simulate boreal vegetation dynamics in interior Alaska. The model is used to investigate the role of black spruce ecosystems in the fire regime of interior Alaska boreal forest. Model simulations revealed that vegetation shifts caused substantial changes to the fire regime. The number of fires and the total area burned increased as black spruce forest became an increasingly dominant component of the landscape. The most significant impact of adding black spruce to the model was an increase in the frequency and magnitude of large-scale burning events (i.e., time steps in which total area burned far exceeded the normal distribution of area burned). Early successional deciduous forest vegetation burned more frequently when black spruce was added to the model, considerably decreasing the fire return interval of deciduous vegetation. Ecosystem flammability accounted for the majority of the differences in the distribution of the average area burned. These simulated vegetation effects and fire regime dynamics have important implications for global models of vegetation dynamics and potential biotic feedbacks to regional climate.  相似文献   

Fermi acceleration in astrophysical jets     

Frank M. Rieger  Valentí Bosch-Ramon  Peter Duffy 《Astrophysics and Space Science》2007,309(1-4):119-125

We consider the acceleration of energetic particles by Fermi processes (i.e., diffusive shock acceleration, second order Fermi acceleration, and gradual shear acceleration) in relativistic astrophysical jets, with particular attention given to recent progress in the field of viscous shear acceleration. We analyze the associated acceleration timescales and the resulting particle distributions, and discuss the relevance of these processes for the acceleration of charged particles in the jets of AGN, GRBs and microquasars, showing that multi-component powerlaw-type particle distributions are likely to occur.  相似文献   

Epifaunal communities thrive in an estuary with hypoxic episodes     

Alessandra Sagasti  Linda C. Schaffner  J. Emmett Duffy 《Estuaries and Coasts》2000,23(4):474-487

We characterized the abundance and species composition of sessile and mobile epifaunal assemblages in the York River, a tributary of the Chesapeake Bay, U.S., during the summer hypoxia seasons in 1996 and 1997. We collected communities on artificial substrates in two areas of the river that have historically experienced different exposure to hypoxia. Despite frequent hypoxic stress, epifauna formed dense communities in both areas. Dominant species comprised a range of phyla and included the polychaetesPolydora cornuta andSabellaria vulgaris, the bryozoansMembranipora tenuis andConopeum tenuissimum, the tunicateMolgula manhattensis, the barnacleBalanus improvisus, the anemoneDiadumene leucolena, and the hydroidsEctopleura dumortieri andObelia bicuspidata. Common mobile species included the nudibranchsCratena kaoruae andDoridella obscura, the amphipodsMelita nitida andParacaprella tenuis, the polychaeteNereis succinea, and the flatwormStylochus ellipticus. We found few differences in species composition between the two areas, even though one area usually experienced lower oxygen concentrations during hypoxic events, suggesting that hypoxia does not exclude any epifaunal species, in the York River. We did find differences between the two study areas in percent cover and abundance of some species. While tunicates, hydroids, and anemones were equally abundant in both areas during both study years, bryozoans and the polychaeteS. vulgaris were more abundant in the area with gereally higher oxygen, suggesting that they may be less tolerant of hypoxic stress. The polychaeteP. cornuta was more abundant in the area that usually had lower oxygen. These results suggest that many epifaunal species have high hypoxia tolerance, and most epifaunal species found in the lowr York River are able to survive in hypoxic areas. Epifaunal species are not necessarily more susceptible to hypoxia than infaunal species in the York River. Epifaunal communities in areas with brief hypoxic episodes and moderate hypoxia (0.5–2 mg O₂ I⁻¹) can persist with little change in species composition, and with few changes in abundance, as oxygen concentrations fall.  相似文献   

Early Carboniferous blueschist facies metamorphism in metapelites of the West Sudetes (Northern Saxothuringian Domain,Bohemian Massif)     

E. ŽÁČKOVÁ  J. KONOPÁSEK  P. JEŘÁBEK  F. FINGER  J. KOŠLER 《Journal of Metamorphic Geology》2010,28(4):361-379

The metamorphic evolution of micaschists in the north‐eastern part of the Saxothuringian Domain in the Central European Variscides is characterized by the early high‐pressure M1 assemblage with chloritoid in cores of large garnet porphyroblasts and a Grt–Chl–Phe–Qtz ± Pg M2 assemblage in the matrix. Minerals of the M1–M2 stage were overprinted by the low‐pressure M3 assemblage Ab–Chl–Ms–Qtz ± Ep. Samples with the best‐preserved M1–M2 mineralogy mostly appear in domains dominated by the earlier D1 deformation phase and are only weakly affected by subsequent D2 overprint. Thermodynamic modelling suggests that mineral assemblages record peak‐pressure conditions of ≥18–19 kbar at 460–520 °C (M1) followed by isothermal decompression 10.5–13.5 kbar (M2) and final decompression to <8.5 kbar and <480 °C (M3). The calculated peak P–T conditions indicate a high‐pressure/low‐temperature apparent thermal gradient of ～7–7.5 °C km^?1. Laser ablation inductively coupled plasma mass spectrometry isotopic dating and electron microprobe chemical dating of monazite from the M1–M2 mineral assemblages give ages of 330 ± 10 and 328 ± 6 Ma, respectively, which are interpreted as the timing of a peak pressure to early decompression stage. The observed metamorphic record and timing of metamorphism in the studied metapelites show striking similarities with the evolution of the central and south‐western parts of the Saxothuringian Domain and suggest a common tectonic evolution along the entire eastern flank of the Saxothuringian Domain during the Devonian–Carboniferous periods.  相似文献