The Spatial and Temporal Characteristics of Pc3 Geomagnetic Activity over Canada in 2000, as a Guide to Planning the Times of Aeromagnetic Surveys     

Marc A. Vallée  Larry Newitt  Ian R. Mann  Mouhamed Moussaoui  Régis Dumont  Pierre Keating 《Pure and Applied Geophysics》2007,164(1):161-176

Geomagnetic activity affects aeromagnetic surveys. Geomagnetic variations are quite complex and can be quantified in different ways. A measure of geomagnetic activity that is useful for planning aeromagnetic surveys is the Pc3 pulsation index developed by the Australian Space Weather Agency. Purposeful to developing guidelines for planning aeromagnetic surveys in Canada, we study the variations in Pc3 index amplitude over Canada in 2000. This study shows distinct patterns associated with the sub-auroral zone, the auroral zone, and the polar cap. Average Pc3 index activity is higher during the months of February, July, September, and November in the auroral and sub-auroral zones. The station in the polar cap exhibits maximum activity near midday during the summer months. Detailed analysis of a magnetic storm shows that Pc3 index amplitude during the beginning of the solar storm is least important at the polar cap. The mean Pc3 index also relates to solar wind parameters such as the solar wind velocity and the vertical polarity of the interplanetary magnetic field. Analysis of the morning maximum of the Pc3 index observed in the auroral zone can be used to develop guidelines for planning aeromagnetic surveys in Canada and other areas of the world affected by auroral zones.  相似文献   

Simulating coseismic deformation of quartz in the middle crust and fabric evolution during postseismic stress relaxation — An experimental study   总被引：3，自引：0，他引：3  

Claudia A. Trepmann  Bernhard Stckhert  Dorothe Dorner  Rasoul Hamidzadeh Moghadam  Martina Küster  Klaus Rller 《Tectonophysics》2007,442(1-4):83-104

Non-steady state deformation and annealing experiments on vein quartz are designed to simulate earthquake-driven episodic deformation in the middle crust. Three types of experiments were carried out using a modified Griggs-type solid medium deformation apparatus. All three start with high stress deformation at a temperature of 400 °C and a constant strain rate of 10^− 4 s^− 1 (type A), some are followed by annealing in the stability field of α-quartz for 14–15 h at zero nominal differential stress and temperatures of 800–1000 °C (type A + B), or by annealing for 15 h at 900 °C and at a residual stress (type A + C).The quartz samples reveal a very high strength > 2 GPa at a few percent of permanent strain. The microstructures after short-term high stress deformation (type A) record localized brittle and plastic deformation. Statisc annealing (type A + B) results in recrystallisation restricted to the highly damaged zones. The new grains aligned in strings and without crystallographic preferred orientation, indicate nucleation and growth. Annealing at non-hydrostatic conditions (type A + C) results in shear zones that also develop from deformation bands or cracks that formed during the preceding high stress deformation. In this case, however, the recrystallised zone is several grain diameters wide, the grains are elongate, and a marked crystallographic preferred orientation indicates flow by dislocation creep with dynamic recrystallisation. Quartz microstructures identical to those produced in type A + B experiments are observed in cores recovered from Long Valley Exploratory Well in the Quaternary Long Valley Caldera, California, with considerable seismic activity.The experiments demonstrate the behaviour of quartz at coseismic loading (type A) and subsequent static annealing (type A + B) or creep at decaying stress (type A + C) in the middle crust. The experimentally produced microfabrics allow to identify similar processes and conditions in exhumed rocks.  相似文献   

Southern Quebec (Canada) summer-season heat spells over the 1941–2000 period: an assessment of observed changes     

M. N. Khaliq  P. Gachon  A. St-Hilaire  T. B. M. J. Ouarda  B. Bobée 《Theoretical and Applied Climatology》2007,88(1-2):83-101

Summary Summer-season (May–September) daily maximum temperature (T _max) and daily minimum temperature (T _min) observations and three types of heat spells obtained from these temperature observations at seven weather stations located in southern Quebec (Canada) for the 60-year period from 1941 to 2000 are studied to assess temporal changes in their characteristics (i.e. frequency of occurrence, seasonal hot days and extremal durations of heat spells). Type-A and Type-B heat spells are obtained respectively from T _max and T _min observations and Type-C heat spells from simultaneous joint observations of T _max and T _min using suitable thresholds and spells of duration ≥1-day and ≥3-day. The results of this investigation show that the majority of the selected percentiles (i.e. 5P, 10P, 25P, 50P, 75P, 80P, 90P, 92P, 95P, and 98P) of T _max observations show a negative time-trend with statistically significant decreases (at 10% level) in some of the higher percentiles and in the maximal values at four out of seven stations. Almost all of the selected percentiles (same as for the T _max) and the maximal and minimal values of T _min observations show a positive trend, with statistically significant increases for all seven stations. Examination of frequencies of occurrence of heat spells, seasonal hot days and annual extremes of heat spell durations indicate that many of these characteristics of heat spells have undergone statistically significant changes over time at some of the stations for Type-A and Type-B heat spells as compared to Type-C heat spells. The Type-C heat spells are generally small in number and are found to be relatively temporally stable. More severe Type-C heat spells, i.e. the ones having T _max and T _min values simultaneously above very high thresholds and with duration ≥3-day have been rarely observed in southern Quebec.  相似文献   

Silica fume stabilization of an expansive clay subgrade and the effect of silica fume-stabilised soil cushion on its CBR     

B. R. Phanikumar  Jagapathi Raju m  Ramanjaneya Raju e 《Geomechanics and Geoengineering》2020,15(1):64-77

ABSTRACT

Expansive soil subgrades, which are subjected to dual swell-shrink problem consequent upon absorption and evaporation of water, need to be improved by chemical stabilization or compacted cushion or geosynthetic reinforcement in order that pavements constructed over them are even, stable and safe. This paper presents extensive experimental data on plasticity, free swell index (FSI) and compaction characteristics of a highly swelling expansive clay stabilized with varying silica fume contents. In another series of tests on a laterite soil to be used as a cushion over the expansive clay subgrade, plasticity properties, compaction characteristics and strength characteristics were determined at varied silica fume contents. Further, CBR of the expansive clay subgrade was determined in the laboratory stabilizing it with varied silica fume contents and providing a cushion of 50 mm thickness of silica fume-stabilized lateritic soil. Liquid limit (LL), plasticity index (PI) and free swell index (FSI) of the expansive clay decreased with increasing silica fume contents. The compaction and strength characteristics of both the soils improved with silica fume stabilization. The CBR of the expansive clay provided with silica fume-stabilized cushion improved significantly.  相似文献   

Lithostratigraphic analysis of sedimentary basins | C.E.B. Conybeare, 1979. Academic Press,New York,N.Y., U.S. $39.50.     

Joa˜e Jose´ Bigarella 《Earth》1981,17(3):287-288

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Spectral analysis of oscillations with a time-variable frequency     

Jaroslav Střeštík  Reviewer M. Hvoždara 《Studia Geophysica et Geodaetica》1979,23(4):333-348

Summary The paper presents a method of evaluating oscillations with a time-variable frequency using a computer. The given function is first interpolated at points which are not distributed equidistantly in time, but the digitizing step varies with time according to a known optional regularity. The spectrum of the obtained function is computed for various of these interpolations and tests are run to determine when the interpolation best compensates the time variation of the frequency. The initial and terminal frequency in the given sample is then determined. The usability of this method with respect to various types of oscillations with a variable frequency and its accuracy in comparison to sonagrams are discussed.  相似文献   

The PT phase relations of a primary oceanite from the Reykjanes peninsula,Iceland     

Sven Maaløe  Sveinn P Jakobsson 《Lithos》1980,13(3):237-246

The field relationships and petrographic features of the oceanites of the Reykjanes peninsula suggest that they might have originated as primary magmas. The principal phase relationships of primary liquids formed by the partial melting of lherzolites are defined. The phase relations obtained for oceanite RE78 between 0 and 30 kbar at dry conditions suggest that the oceanite originated as a primary magma at 25 kbar and 1580°C, and erupted at a temperature near 1300°C.  相似文献   

一次弓状降雹回波区流场的反演     

胡明宝  刘俄  汤达章 《热带气象学报》1998,14(3):282-288

通过对一次典型弓状降雹回波区的流场进行反及特点分析,发现用矩不变量法反演出的回波区流场结构,与藤田关于弓状回波的概念模式非常吻合,利用该方法估测出的流场,散度场、涡度场所表现出的信息,与降雹实况是一致的,该研究可为中小尺度强天气的监测,提供高时空分辨率的流场资料。  相似文献   

Le volcanisme aux Nouvelles Hébrides (Mélanésie)     

E. Aubert de la Rüe 《Bulletin of Volcanology》1937,2(1):79-142

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Solar Spectral Irradiance at 782 nm as Measured by the SES Sensor Onboard Picard     

M. Meftah  A. Hauchecorne  A. Irbah  G. Cessateur  S. Bekki  L. Damé  D. Bolsée  N. Pereira 《Solar physics》2016,291(4):1043-1057

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