Use of phytoplankton species indicators to track the origin of phytoplankton blooms in Willapa Bay, Washington     

Jan A. Newton  Rita A. Horner 《Estuaries and Coasts》2003,26(4):1071-1078

We focus on the question of whether high phytoplankton production events observed in a United States Pacific Northwest estuary consist of estuarine species blooms fueled by oceanic nutrient input or reflect offshore oceanic blooms that have advected into the estuary. Our approach is to use certain phytoplankton species as indicators associated with water mass origin, either estuarine or oceanic, to help resolve this question in Willapa Bay, Washington. We used species analysis and primary production data from 10 selected dates in May–September of 1998 and 1999, representing periods of high through low productivity. Out of 108 phytoplankton species identified from Willapa Bay, nine were selected and tested as indicators of oceanic species, six as estuarine, and two as surf zone. Our test results demonstrated the oceanic and estuarine species to be satifactory indicators of source waters. The prevalence of these species indicators in our samples revealed that the highest primary production and the appearance ofPseudo-nitzschia spp. were associated with oceanic intrusions of phytoplankton biomass into Willapa Bay. While the largest blooms were oceanic in origin, numerous medium-sized production events were from either oceanic, surf zone, or estuarine sources, indicating a complex situation.  相似文献   

An estimate of hypocentre location accuracy in a large network: possible implications for tectonic studies in Italy     

Rita Di Giovambattista  Salvatore Barba 《Geophysical Journal International》1997,129(1):124-132

Data recorded by the Italian Telemetered Seismic Network (ITSN) of the Istituto Nazionale di Geofisica (ING) have been widely used in recent years to image slab structures and to find evidence for active processes along the Italian Peninsula. However, the use of seismic data for geostructural purposes may be affected by the well-known trade-off between earthquake location and seismic-velocity parameters. Furthermore, the confidence ellipse predicted by standard procedures may be inadequate for the representation of the probable error of a computed localization. This paper evaluates the probable errors on the hypocentre determinations of the seismic events recorded by the ITSN, using a Monte Carlo method.
We compute synthetic arrival times using a 1-D velocity model appropriate as an average for the Italian area. The hypocentres used are all those recorded by the ITSN during the period January 1992 to March 1994 (1972 events). Station locations are those of the current ITSN configuration. The synthetic arrival times are perturbed with a Gaussian distribution of errors and input to ING's standard hypocentral location procedure, but using crustal velocities differing by 10 per cent from those used to generate them. Each simulation is repeated at least 30 times. Average absolute shifts of hypocentres are assessed in grid cells of linear dimension 33 km covering the whole Italian region.
For regions within the ITSN, shifts are typically 5–10 km in location and up to 20 km in depth. However, for offshore and coastal regions, they are much greater: 50 km or more in both location and depth (far exceeding the equivalent uncertainties quoted by ING bulletins). Possible consequences of this are highlighted by producing a cross-section of subcrustal hypocentres from the Adriatic to the Tyrrhenian Sea, where the large uncertainty in depth precludes any confident interpretation of dipping tectonic features.  相似文献   

Doubtful Events Reported in Current Italian Earthquake Catalogues: The Medieval Earthquakes of Subiaco (Central Italy)     

Di Giovambattista  Rita  Tertulliani  Andrea  Zaccaria  Mari 《Natural Hazards》1997,16(1):39-55

Within the framework of a study of the seismicity of the Aniene Valley (Central Italy), we analysed the medieval earthquakes of Subiaco (1216, 1227, 1299), the largest events reported for the area. Our main goal was to investigate some doubtful events reported in earthquake catalogues and, as such, currently utilised for seismic hazard estimates. A careful screening of the oldest available sources and their filiation pattern up to the present pointed out the uncertainty on the date and nature of these phenomena. A multidisciplinary approach based on the joint analysis of archaeological, geomorphologic and historical evidence allowed us to propose new interpretations concerning these events and their significance for the assessment of seismic hazard in the Aniene Valley. The main conclusion is that the dates of the 1216 and 1227 events are fairly unsupported. In particular, the 1216 earthquake could be dated back to between AD 1159 and 1181.  相似文献   

Occurrence of the Indian genus Hemibos (Bovini, Bovidae, Mammalia) at the Early–Middle Pleistocene transition in Italy     

Bienvenido Martínez-Navarro  Maria Rita Palombo 《Quaternary Research》2004,61(3):314-317

The morphology of the horn-core structure and section shape of the Bos galerianus type specimen, as well as the general anatomy of the frontal and occipital areas of the skull, suggest that the skull is better attributed to the Indian genus Hemibos. This finding contributes to our understanding of faunal dispersal patterns into Europe at the Early–Middle Pleistocene transition.  相似文献   

Thresholds of intrabed flow and other interactions of turbidity currents with soft muddy substrates          下载免费PDF全文

Jaco H. Baas  Rafael Manica  Eduardo Puhl  Ana Luiza de Oliveira Borges 《Sedimentology》2016,63(7):2002-2036

Controlled laboratory experiments reveal that the lower part of turbidity currents has the ability to enter fluid mud substrates, if the bed shear stress is higher than the yield stress of the fluid mud and the density of the turbidity current is higher than the density of the substrate. Upon entering the substrate, the turbidity current either induces mixing between flow‐derived sediment and substrate sediment, or it forms a stable horizontal flow front inside the fluid mud. Such ‘intrabed’ flow is surrounded by plastically deformed mud; otherwise it resembles the front of a ‘bottom‐hugging’ turbidity current. The ‘suprabed’ portion of the turbidity current, i.e. the upper part of the flow that does not enter the substrate, is typically separated from the intrabed flow by a long horizontal layer of mud which originates from the mud that is swept over the top of the intrabed flow and then incorporated into the flow. The intrabed flow and the mixing mechanism are specific types of interaction between turbidity currents and muddy substrates that are part of a larger group of interactions, which also include bypass, deposition, erosion and soft sediment deformation. A classification scheme for these types of interactions is proposed, based on an excess bed shear stress parameter, which includes the difference in the bed shear stress imposed by the flow and the yield stress of the substrate and an excess density parameter, which relies on the density difference between the flow and the substrate. Based on this classification scheme, as well as on the sedimentological properties of the laboratory deposits, an existing facies model for intrabed turbidites is extended to the other types of interaction involving soft muddy substrates. The physical threshold of flow‐substrate mixing versus stable intrabed flow is defined using the gradient Richardson number, and this method is validated successfully with the laboratory data. The gradient Richardson number is also used to verify that stable intrabed flow is possible in natural turbidity currents, and to determine under which conditions intrabed flow is likely to be unstable. It appears that intrabed flow is likely only in natural turbidity currents with flow velocities well below ca 3·5 m s^?1, although a wider range of flows is capable of entering fluid muds. Below this threshold velocity, intrabed flow is stable only at high‐density gradients and low‐velocity gradients across the upper boundary of the turbidity current. Finally, the gradient Richardson number is used as a scaling parameter to set the flow velocity limits of a natural turbidity current that formed an inferred intrabed turbidite in the deep‐marine Aberystwyth Grits Group, West Wales, United Kingdom.  相似文献   

Some Open Issues on Rockfall Hazard Analysis in Fractured Rock Mass: Problems and Prospects     

Anna Maria Ferrero  Maria Rita Migliazza  Marina Pirulli  Gessica Umili 《Rock Mechanics and Rock Engineering》2016,49(9):3615-3629

  相似文献   

A thermo-plastic constitutive law for brittle-plastic behavior of rocks at high temperatures     

Tomasz Hueckel  Alberto Peano  Rita Pellegrini 《Pure and Applied Geophysics》1994,143(1-3):483-510

Mechanical properties of rocks change under the influence of, temperature. Stress at the onset of yielding, ultimate strength, dilatancy, strain hardening and softening, and the confining pressure at brittle-ductile transition are all reduced by the increasing temperature. This study presents a framework of constitutive modeling of thermo-brittle-plastic behavior of rocks which encompasses these changes. The constitutive law is based on a thermo-plasticity theory first proposed for metals byPrager (1958). Two phenomenological mechanisms have been identified as central for the modeling: temperature dependence of the yield locus (thermal softening), and temperature dependence of the strain-hardening function (thermally enhanced ductility). Material parameters for two rocks, Carrara marble and Westerly granite, were determined on the basis of additional hypotheses. These parameters are used in numerical simulations of triaxial tests at different temperatures. The obtained stress-strain curves compare well to the experimental results. The changes with temperature in the stress at the onset of yielding are more accurately reproduced that the evolution of hardening or softening. Suggestions for possible improvements and future research directions are indicated.  相似文献   

Direct and Indirect pCO2 Measurements in a Wide Range of pCO2 and Salinity Values (The Scheldt Estuary)     

Michel Frankignoulle  Alberto Vieira Borges 《Aquatic Geochemistry》2001,7(4):267-273

Recent improvements in both Infra-red spectroscopy and equilibrator techniqueshave allowed to determine, for the first time, pCO₂using simultaneously and continuously both the direct and indirect methods in an estuary where pCO₂ values range from 500 to 8500 atm and salinity from 0 to 30. Our results show that both methods are in excellent agreement in the wholeestuary (r² = 0.999, n = 1075, p < 0.0001). Thus, the NBS (US National Bureau of Standards) scale, although inadequate for seawater samples, is appropriate for estuarine waters and can be applied with confidence to calculate pCO₂.  相似文献   

Simulations of strong ground motion in SW Iberia for the 1969 February 28 (M_s= 8.0) and the 1755 November 1 (M∼ 8.5) earthquakes – II. Strong ground motion simulations     

Raphaël Grandin  José Fernando Borges  Mourad Bezzeghoud  Bento Caldeira  Fernando Carrilho 《Geophysical Journal International》2007,171(2):807-822

This is the second paper of a series of two concerning strong ground motion in SW Iberia due to earthquakes originating from the adjacent Atlantic area. The aim of this paper is to use the velocity model that was proposed and validated in the companion paper for seismic intensity modelling of the 1969 ( M _s= 8.0) and 1755 ( M = 8.5–8.7) earthquakes.
First, we propose a regression to convert simulated values of Peak Ground Velocity (PGV) into Modified Mercalli Intensity (MMI) in SW Iberia, and using this regression, we build synthetic isoseismal maps for a large ( M _s= 8.0) earthquake that occurred in 1969. Based on information on the seismic source provided by various authors, we show that the velocity model effectively reproduces macroseismic observations in the whole region. We also confirm that seismic intensity distribution is very sensitive to a small number of source parameters: rupture directivity, fault strike and fault dimensions. Then, we extrapolate the method to the case of the great ( M = 8.5–8.7) 1755 earthquake, for a series of hypotheses recently proposed by three authors about the location of the epicentral region. The model involving a subduction-related rupture in the Gulf of Cádiz results in excessive ground motion in northern Morocco, suggesting that the source of the 1755 earthquake should be located further west. A rupture along the western coast of Portugal, compatible with an activation of the passive western Iberian margin, would imply a relatively low average slip, which, alone, would could not account for the large tsunami observed in the whole northern Atlantic ocean. A seismic source located below the Gorringe Bank seems the most likely since it is more efficient in reproducing the distribution of high intensities in SW Iberia due to the 1755 earthquake.  相似文献   

Brazilian health regions and scales: A geographical perspective     

Raul Borges Guimarães 《New Zealand geographer》2007,63(2):97-105

Abstract:  This paper offers a geographical perspective on the way in which health regions have been defined and established in São Paulo as part of overall Brazilian health policy. To accomplish this, I first situate the Brazilian case in the international debate over the regionalization of health services. Second, I examine health regionalization in the case of São Paulo and show how the process is dynamic and complex, involving geographical scales that go well beyond the administrative boundaries of Brazilian municipalities.  相似文献