3D crustal structure and long-period ground motions from a M9.0 megathrust earthquake in the Pacific Northwest region     

Kim B. Olsen  William J. Stephenson  Andreas Geisselmeyer 《Journal of Seismology》2008,12(2):145-159

We have developed a community velocity model for the Pacific Northwest region from northern California to southern Canada and carried out the first 3D simulation of a M_w 9.0 megathrust earthquake rupturing along the Cascadia subduction zone using a parallel supercomputer. A long-period (<0.5 Hz) source model was designed by mapping the inversion results for the December 26, 2004 Sumatra–Andaman earthquake (Han et al., Science 313(5787):658–662, 2006) onto the Cascadia subduction zone. Representative peak ground velocities for the metropolitan centers of the region include 42 cm/s in the Seattle area and 8–20 cm/s in the Tacoma, Olympia, Vancouver, and Portland areas. Combined with an extended duration of the shaking up to 5 min, these long-period ground motions may inflict significant damage on the built environment, in particular on the highrises in downtown Seattle.  相似文献   

Mercury Dynamics in a San Francisco Estuary Tidal Wetland: Assessing Dynamics Using In Situ Measurements     

Brian A. Bergamaschi  Jacob A. Fleck  Bryan D. Downing  Emmanuel Boss  Brian A. Pellerin  Neil K. Ganju  David H. Schoellhamer  Amy A. Byington  Wesley A. Heim  Mark Stephenson  Roger Fujii 《Estuaries and Coasts》2012,35(4):1036-1048

We used high-resolution in situ measurements of turbidity and fluorescent dissolved organic matter (FDOM) to quantitatively estimate the tidally driven exchange of mercury (Hg) between the waters of the San Francisco estuary and Browns Island, a tidal wetland. Turbidity and FDOM??representative of particle-associated and filter-passing Hg, respectively??together predicted 94?% of the observed variability in measured total mercury concentration in unfiltered water samples (UTHg) collected during a single tidal cycle in spring, fall, and winter, 2005?C2006. Continuous in situ turbidity and FDOM data spanning at least a full spring-neap period were used to generate UTHg concentration time series using this relationship, and then combined with water discharge measurements to calculate Hg fluxes in each season. Wetlands are generally considered to be sinks for sediment and associated mercury. However, during the three periods of monitoring, Browns Island wetland did not appreciably accumulate Hg. Instead, gradual tidally driven export of UTHg from the wetland offset the large episodic on-island fluxes associated with high wind events. Exports were highest during large spring tides, when ebbing waters relatively enriched in FDOM, dissolved organic carbon (DOC), and filter-passing mercury drained from the marsh into the open waters of the estuary. On-island flux of UTHg, which was largely particle-associated, was highest during strong winds coincident with flood tides. Our results demonstrate that processes driving UTHg fluxes in tidal wetlands encompass both the dissolved and particulate phases and multiple timescales, necessitating longer term monitoring to adequately quantify fluxes.  相似文献   

Does increasing the spatial resolution of a regional climate model improve the simulated daily precipitation?     

Steven C. Chan  Elizabeth J. Kendon  Hayley J. Fowler  Stephen Blenkinsop  Christopher A. T. Ferro  David B. Stephenson 《Climate Dynamics》2013,41(5-6):1475-1495

Three different resolution (50, 12, and 1.5 km) regional climate model simulations are compared in terms of their ability to simulate moderate and high daily precipitation events over the southern United Kingdom. The convection-permitting 1.5-km simulation is carried out without convective parametrisation. As in previous studies, increasing resolution (especially from 50 to 12 km) is found to improve the representation of orographic precipitation. The 50-km simulation underestimates mean precipitation over the mountainous region of Wales, and event intensity tends to be too weak; this bias is reduced in both the 12- and 1.5-km simulations for both summer and winter. In south–east England lowlands where summer extremes are mostly convective, increasing resolution does not necessary lead to an improvement in the simulation. For the 12-km simulation, simulated daily extreme events are overly intense. Even though the average intensity of summer daily extremes is improved in the 1.5-km simulation, this simulation has a poorer mean bias with too many events exceeding high thresholds. Spatial density and clustering of summer extremes in south–east England are poorly simulated in both the 12- and 1.5-km simulations. In general, we have not found any clear evidence to show that the 1.5-km simulation is superior to the 12-km simulation, or vice versa at the daily level.  相似文献   

Earthquake-Induced Deformation Analysis of a Bridge Approach Embankment in Missouri     

W. Liu  R. Luna  R. W. Stephenson  S. Wang 《Geotechnical and Geological Engineering》2011,29(5):845-854

Earthquake-induced deformations for a bridge approach earth embankment are predicted using a calibrated numerical model. The constitutive soil model is a modified hyperbolic model that uses Masing rules and incremental pore pressure relations. The model was calibrated using both laboratory and field data. A shaking table physical model was used to verify the numerical simulation. Additionally, the upper San Fernando dam was modeled to reproduce the deformations in the 1971 earthquake. The subsurface and embankment soil conditions were characterized using field and laboratory methods. The model developed was used to predict the earthquake-induced deformations of an approach embankment to Bridge A1466 in the NMSZ near Hayti, Missouri, where strong earthquakes M > 7.0 are anticipated in the next 50 years.  相似文献   

Probability-based methods for quantifying nonlinearity in the ENSO   总被引：2，自引：2，他引：0  

A. Hannachi  D. Stephenson  K. Sperber 《Climate Dynamics》2003,20(2-3):241-256

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Petrology of the Albany and Torbay Adamellite Plutons,near Albany,Western Australia     

N. C. N. Stephenson 《Australian Journal of Earth Sciences》2013,60(3):219-246

The Albany and Torbay Adamellites are composite plutons emplaced in Pre‐cambrian gneisses of the Albany‐Esperance Block in the vicinity of Albany, Western Australia. The gneissic country rocks have been metamorphosed to the lower granu‐lite facies at Albany and the upper amphibolite facies at Torbay. Granitized aureoles about 1 km wide, metasomatically enriched in SiO₂, K₂O, and various trace elements commonly including Rb, Ba, La, Pb, and Th, are developed in the gneisses around both plutons. Field relations suggest late‐kinematic magmatic emplacement of the Adamellites in the catazone. Both show chemical variation trends comparable with the trends normally associated with fractional crystallization of calc‐alkali magmas, and their normative compositions correspond with the thermal trough in the system An‐Ab‐Or‐Q‐H₂O at 4–7 kb P_H2o, suggesting an origin involving crystal‐liquid equilibria at a water vapour pressure of about this value. The initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7118 for the Albany Adamellite is consistent with derivation of the magma from crustal rocks. The late‐kinematic field characteristics of the plutons and the limited isotopic data available are compatible with emplacement and crystallization during the closing stages of orogeny and regional metamorphism. The magmas are believed to have been generated not at their present sites of emplacement, but in a deeper, higher‐temperature zone of the crust, with magma generated during an earlier phase of the orogeny.  相似文献   

Heterogeneity,cyclicity and diagenesis in a Mississippian brachiopod shell of palaeoequatorial Britain     

Lucia Angiolini  Michael Stephenson  Melanie J. Leng  Flavio Jadoul  Dave Millward  Anthony Aldridge  Julian Andrews  Simon Chenery  Gareth Williams 《地学学报》2012,24(1):16-26

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Quantifying the impacts of climate change and land use/cover change on runoff in the lower Connecticut River Basin          下载免费PDF全文

Hui Wang  Scott R. Stephenson 《水文研究》2018,32(9):1301-1312

Climate change and land use and cover change (LUCC) have had great impacts on watershed hydrological processes. Although previous studies have focused on quantitative assessment of the impacts of climate change and human activities on decreasing run‐off change, few studies have examined regions that have significant increasing run‐off due to both climate variability and land cover change. We show that annual run‐off had a significant increasing trend from 1956 to 2014 in the U.S. lower Connecticut River Basin. Abrupt change point years of annual run‐off for four subbasins are detected by nonparametric Mann–Kendall–Sneyers test and reconfirmed by the double mass curve. We then divide the study period into 2 subperiods at the abrupt change point year in the early 1970s for each subbasin. The Choudhury–Yang equation based on Budyko hypothesis was used to calculate precipitation and potential evapotranspiration, and landscape elasticities of run‐off. The results show that the difference in mean annual run‐off between 2 subperiods for each subbasin ranged from 102 to 165.6 mm. Climate variations were the primary drivers of increasing run‐off in this region. Quantitative contributions of precipitation and potential evapotranspiration in all subbasins are 106.5% and ?3.6% on average, respectively. However, LUCC contributed both positively and negatively to run‐off: ?18.6%, ?13.3%, and 10.1% and 9.9% for 4 subbasins. This may be attributed to historical LUCC occurring after the abrupt change point in each subbasin. Our results provide critical insight on the hydrological dynamics of north‐east tidal river systems to communities and policymakers engaged in water resources management in this region.  相似文献   

Geomorphological control on boulder transport and coastal erosion before,during and after an extreme extra‐tropical cyclone          下载免费PDF全文

Larissa A. Naylor  Wayne J. Stephenson  Helen C. M. Smith  Oliver Way  James Mendelssohn  Andrew Cowley 《地球表面变化过程与地形》2016,41(5):685-700

Extreme wave events in coastal zones are principal drivers of geomorphic change. Evidence of boulder entrainment and erosional impact during storms is increasing. However, there is currently poor time coupling between pre‐ and post‐storm measurements of coastal boulder deposits. Importantly there are no data reporting shore platform erosion, boulder entrainment and/or boulder transport during storm events – rock coast dynamics during storm events are currently unexplored. Here, we use high‐resolution (daily) field data to measure and characterize coastal boulder transport before, during and after the extreme Northeast Atlantic extra‐tropical cyclone Johanna in March 2008. Forty‐eight limestone fine‐medium boulders (n = 46) and coarse cobbles (n = 2) were tracked daily over a 0.1 km² intertidal area during this multi‐day storm. Boulders were repeatedly entrained, transported and deposited, and in some cases broken down (n = 1) or quarried (n = 3), during the most intense days of the storm. Eighty‐one percent (n = 39) of boulders were located at both the start and end of the storm. Of these, 92% were entrained where entrainment patterns were closely aligned to wave parameters. These data firmly demonstrate rock coasts are dynamic and vulnerable under storm conditions. No statistically significant relationship was found between boulder size (mass) and net transport distance. Graphical analyses suggest that boulder size limits the maximum longshore transport distance but that for the majority of boulders lying under this threshold, other factors influence transport distance. Paired analysis of 20 similar sized and shaped boulders in different morphogenic zones demonstrates that geomorphological control affects entrainment and transport distance – where net transport distances were up to 39 times less where geomorphological control was greatest. These results have important implications for understanding and for accurately measuring and modelling boulder entrainment and transport. Coastal managers require these data for assessing erosion risk. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

The geological history of insect-related plant damage     

Jonathan Stephenson  rew C. Scott 《地学学报》1992,4(5):542-552

Biological damage to plants is commonly found from the Devonian but occurs most commonly from the Cretaceous. Damage inflicted on plants whilst they were alive may trigger a pathological response involving the growth of abnormal tissues. Much of the damage is caused by arthropods, particularly insects. Whilst some damage is non-taxon specific, such as simple feeding traces, other damage, such as leaf mines, galls or bark boring, may reveal the co-evolution of host specific taxa and the timing of such interactions. Damaged plants, particularly from the Cretaceous and Tertiary are described and illustrated. The geological history of the evolution of insect-related plant damage is briefly reviewed. Increased variety in the pathological response of plants is seen from the Cretaceous with the evolution of the angiosperms and diversification of numerous insect groups.  相似文献