Analyse fréquentielle régionale des précipitations journalières maximales annuelles au Québec,Canada / Regional frequency analysis of annual maximum daily precipitation in Quebec,Canada

Abstract

Abstract A complete regional analysis of daily precipitations is carried out in the southern half of the province of Quebec, Canada. The first step of the regional estimation procedure consists of delineating the homogeneous regions within the area of study and testing for homogeneity within each region. The delineation of homogeneous regions is based on using L-moment ratios. A simulation-based testing of statistical homogeneity allows one to verify the inter-site variability. The second step of the procedure deals with the identification of the regional distribution and the estimation of its parameters. The General Extreme Value (GEV) distribution was identified as an appropriate parent distribution. This distribution has already been recommended by several previous research studies for regional frequency analysis of precipitation extremes. The parameters of the GEV distribution are estimated based on the computation of the regional L-CV, L-C_S and the mean of annual maximal daily precipitations. The third step consists of the estimation of precipitation quantiles corresponding to various return periods. The final procedure allows for the estimation of these quantiles at sites where no precipitation information is available. The use of a jack-knife resampling procedure with data from the province of Quebec allows one to demonstrate the robustness and efficiency of the regional estimation procedure. Values of the root mean square error were below 10% for a return period of 20 years, and 20% for a return period of 100 years.     

阿德朗达克-西魁北克地震带地壳三维速度结构成像

根据在阿德朗达克-西魁北克地震带及其邻近地区的59台短周期数字地震仪记录的直达P波走时观测值,用地震层析成像方法反演了该地区地壳三维速度结构.结果表明,地壳上层（0-5km）在阿德朗达克穹隆山的中南部地区出现正速度异常;第二层（5-10km）及第三层（10-15km）的速度横向变化较小,介质相对比较均匀;第四层（15-25km）出现显著的速度异常,一个是位于地震带中部的正速度异常（+4％）,它与布格重力正异常一致;另一个是位于阿德朗达克穹隆山下的负速度异常（-4％）.结合已有的地质及地球物理资料进行对比,可以认为阿德朗达克是一个正在发展的穹隆上升山,但其热源前锋尚未到达地面的大陆热点.     

Diagenetic and low-grade metamorphic terranes of Gaspé Peninsula related to the geological structure of the Taconian and Acadian orogenic belts, Quebec Appalachians

Abstract Illite crystallinity (IC) measurements, determination of the proportion of 2M mica-polytypes and organic-matter reflectance measurements establish regional diagenetic/low-grade metamorphic trends for the Taconian and Acadian belts of Gaspé Peninsula. IC varies as a function of many factors besides maximum burial temperature and heating time. Correlation between IC and %2M illite polytypes for the Fortin Group and Temiscouata Formation suggests (i) that the amount of high-grade detrital mica in the samples is low, and (ii) that IC can be used with some confidence as an estimator of regional thermal maturation levels. Correlation of these parameters with available organic reflectance values further supports this assumption. The illites of the Temiscouata and western Fortin groups are mostly phengitic in composition, whereas in the eastern outcrop belt they are more Mg- and Fe-rich (celadonitic), but generally also of lower grade and lower 2M content. The d(060) values for illites measured on the unorientated <2-μm fraction of samples fall between 1.502 and 1.503 Å (range: 1.500–1.504 Å), indicating relatively low octahedral occupancy by Mg and Fe (between one-fifth and one-third of the available spaces). Pyrophyllite and paragonite were not detected. Chlorites are Fe-rich and ripidolitic. The IC map for the Acadian belt of the peninsula displays general congruence between IC contours (2200 sample points) and structural trends for the 27,000-km² area. The highest grades (anchimetamorphic) are associated with the oldest rocks (Honorat and Matapedia groups) exposed in the cores of major anticlines. Anchimetamorphic grades associated with the western outcrop belt of the Lower Devonian Fortin Group require 7–8 km of subsidence to accommodate sufficient thickness of overlying younger rocks (on top of 4–5 km of Fortin Group deep-water clastics) to explain the grades in terms of burial metamorphism assuming a geothermal gradient of 30° C km^?1. The lowest-grade diagenetic rocks occupy a large area in the northeastern part of the peninsula, smaller areas in the northwestern part of the Acadian belt, in the centre of Chaleurs Bay synclinorium, and in the Ordovician Mictaw Group. The contact between the Taconian and Acadian belt is marked by a distinct maturation discontinuity. The Grand Pabos fault juxtaposes rocks of contrasting maturation levels (Matapedia Group against Fortin Group) in the west, but shows no maturation offset further east in the Honorat Group. The fault zone limiting the Fortin Group in the north is also associated with a major IC jump.     

INTERNATIONAL HYDROLOGICAL DECADE / WORKING GROUP ON “THE INFLUENCE OF MAN ON THE HYDROLOGICAL CYCLE”

Abstract

Floods, as extreme hydrological phenomena, can be described by more than one correlated characteristic, such as peak, volume and duration. These characteristics should be jointly considered since they are generally not independent. For an ungauged site, univariate regional flood frequency analysis (FA) provides a limited assessment of flood events. A recent study proposed a procedure for regional FA in a multivariate framework. This procedure represents a multivariate version of the index-flood model and is based on copulas and multivariate quantiles. The performance of the proposed procedure was evaluated by simulation. However, the model was not tested on a real-world case study data. In the present paper, practical aspects are investigated jointly for flood peak (Q) and volume (V) of a dataset from the Côte-Nord region in the province of Quebec, Canada. The application of the proposed procedure requires the identification of the appropriate marginal distribution, the estimation of the index flood and the selection of an appropriate copula. The results of the case study show that the regional bivariate FA procedure performed well. This performance depends strongly on the performance of the two univariate models and, more specifically, the univariate model of Q. The results show also the impact of the homogeneity of the region on the performance of the univariate and bivariate models.

Editor D. Koutsoyiannis     

Globalized conflicts of discourse: the type of conflict of proxies*

The article describes a new form of transnational environmental conflict that developed in the wake of globalisation. Activist in this new type of conflict still act as proxies of groups under pressure but in contrast to transnational environmental conflicts hitherto the target of their protests is rather their own society at home than the location of the pressured group. Despite these conditions it is claimed that this type of metaphorical conflict is going to become more frequent as alliances are built along the oppostion to a dominant discourse. According to the model, conflicts of values are easier to transfer on stages abroad or across the Atlantic than conflicts of interests and motivation for activists is higher as the return is affecting their home society. Dynamic and features of this type of conflict are explained with help of discourse theory.     

Chemographic relationships of biotite and cordierite in the McGerrigle thermal aureole, Gaspé, Quebec

Abstract Biotite and cordierite occur in a 1-km wide zone of pelitic hornfelses around the McGerrigle pluton. These phases display systematic changes in X _Fe that can be attributed to continuous reactions involving chlorite or andalusite in the system KFMASH. Through much of the zone biotite and cordierite were products of the 'breakdown'of chlorite. Close to the pluton this continuous reaction was terminated by a discontinuous reaction that introduced andalusite. Pelites which interdigitate with apophyses of the intrusive at the pluton margin contain assemblages that record a continuous reaction between biotite, cordierite, andalusite, muscovite, and quartz or, alternatively, the discontinuous breakdown of muscovite and quartz to K-feldspar and andalusite.
The mole fraction of Fe in biotite and cordierite increased significantly with the progress of the first continuous reaction and apparently decreased during the second continuous reaction. The K _D of Fe-Mg between the minerals decreased and apparently increased, respectively, during the two reactions.
Biotite-cordierite-chlorite assemblages are interpreted to have been stable at temperatures between 525° C and 615° C and biotite-cordierite-andalusite assemblages stable at temperatures between 615° C and 635° C. The confining pressure was estimated to have been < 2 kbar.
The results of this study suggest that the K _D of Fe-Mg between biotite and cordierite is a function of temperature, the Fe-Mg exchange characteristics of the controlling continuous reaction and non-ideal mixing of Fe and Mg.     

Modern Sphagnumδ13C signatures follow a surface moisture gradient in two boreal peat bogs,James Bay lowlands,Québec

Carbon isotopic composition of Sphagnum macrofossils can potentially be used as a palaeohydrological tool for peat‐based climatic studies since a relationship between Sphagnum δ¹³C values and peatland surface moisture has been presented in previous studies. In order to verify this hypothesis, modern Sphagnum δ¹³C values were measured along a moisture (microtopographic) gradient in two boreal peat bogs. Isotopic measurements were performed on bulk material of S. fuscum, S. magellanicum, S. capillifolium and S. pulchrum. Isotopic variations found within and between Sphagnum species along the microtopographic gradient were compared using analysis of variance. A significant positive correlation (P < 0.0001) was found between Sphagnum δ¹³C values and their position along the surface moisture gradient. Results show that ¹³C‐depleted values are related to low water table depths (WTD), while ¹³C‐enriched values correspond to a water table that is close to the peat surface. Although the mechanisms underlying carbon fractionation processes in mosses are not well understood, we demonstrate that water resistance to CO₂ diffusion is an important fractionation process that is observed in bulk Sphagnum δ¹³C measurements, since drier and wetter samples exhibit consistent and very different isotopic signatures. Copyright © 2008 John Wiley & Sons, Ltd.     

Dynamics of a headwater system and peatland under current conditions and with climate change

Interactions between headwater aquifers and peatlands have received limited scientific attention. Hydrological stresses, including those related to climate change, may adversely impact these interactions. In this study, the dynamics of a southern Québec headwater system where a peatland is present is simulated under current conditions and with climate change. The model is calibrated in steady state on field‐measured data and provides satisfactory results for transient‐state conditions. Under current conditions, simulations confirm that the peatland is fed by the fractured bedrock aquifer year‐round and provides continuous baseflow to its outlets. Climate change is simulated through its impact on groundwater recharge. Predicted precipitation and temperature data from a suite of regional climate model scenarios provide a net precipitation variation range from +10% to ?30% for the 2041–2070 horizon. Calibrated recharge is modified within this range to perform a sensitivity analysis of the headwater model to recharge variations (+10%, ?15% and ?30%). Total contribution from the aquifer to rivers and streams varies from +14% to ?44% of the baseline for +10% to ?30% recharge changes from spring 2010 data, for example. With higher recharge, the peatland receives more groundwater, which could significantly change its vegetation pattern and eventually ecosystem functions. For a ?30% recharge, the peatland becomes perched above the aquifer during the summer, fall and winter. Recharge reductions also induce sharp declines in groundwater levels and drying streams. Copyright © 2013 John Wiley & Sons, Ltd.     

High‐resolution seismic reflection profiling of neotectonic faults in Lake Timiskaming,Timiskaming Graben,Ontario‐Quebec,Canada

The Timiskaming Graben is a 400 km long, 50 km wide north‐west trending morphotectonic depression within the Canadian Shield of eastern North America and experiences frequent intraplate earthquakes. The graben extends along the border of Ontario and Quebec, connecting southward with the Nipissing and Ottawa‐Bonnechere grabens and the St. Lawrence Rift System which includes a similar structure underlying the Hudson Valley of the eastern USA. Together they form a complex failed rift system related to regional extension of North American crust during the breakup of Rodinia and, later, Pangea. The Timiskaming Graben lies within a belt of heightened seismic activity (Western Quebec Seismic Zone) with frequent moderate magnitude (greater than magnitude 5) earthquakes including a magnitude 6.2 in 1935. These events threaten aging urban infrastructure built on soft glacial sediments; post‐glacial landslides along the Ottawa Valley suggest earthquakes as large as magnitude 7. The inner part of the Timiskaming Graben is filled by Lake Timiskaming, a large 110 km long post‐glacial successor to glacial Lake Barlow that was ponded by the Laurentide Ice Sheet 9500 years ago. The effects of frequent ground shaking on lake floor sediments was assessed by collecting more than 1000 line kilometres of high‐resolution ‘chirp’ seismic profiles. Late glacial Lake Barlow glaciolacustrine and overlying post‐glacial sediments are extensively deformed by extensional faults that define prominent horsts and grabens; multibeam bathymetry data suggest that faults influence the morphology of the modern lake floor, despite high sedimentation rates, and indicate recent neotectonic deformation. The Lake Timiskaming area provides evidence of post‐glacial intracratonic faulting related to recurring earthquake activity along a weak spot within the North American plate.     

Determining the number of manual measurements required to improve peat thickness estimations by ground penetrating radar

Ground penetrating radar (GPR) is often used for investigating peat thickness. The quality of GPR measurements depends on electromagnetic wave (EMW) velocity estimates. The objective of this study is to determine the number of manual measurements required to minimize EMW velocity error in peatlands. A total of 175 manually measured peat thicknesses are used with a depth‐to‐target method to assess EMW velocity in two southern Quebec peatlands. Mean measured EMW velocities are 0·040 and 0·039 m ns^–1 with standard deviations of 0·013 and 0·008 m ns^–1. Statistical analyses show that at least 30 calibration points are required to minimize the EMW velocity error, regardless of the geological setting. Copyright © 2008 John Wiley & Sons, Ltd.