Seismic expression of active extensional faults in northern Umbria (Central Italy)     

Cristiano Collettini  Massimiliano Barchi  Cristina Pauselli  Costanzo Federico  Giampaolo Pialli 《Journal of Geodynamics》2000,29(3-5)

This paper deals with the geometry and kinematics of the active normal faults in northern Umbria, and their relationship with the seismicity observed in the area. In particular, we illustrate the contribution of seismic reflection data (a network of seismic profiles, NNW–SSE and WSW–ENE trending) in constraining at depth the geometry of the different active fault systems and their reciprocal spatial relationships. The main normal fault in the area is the Alto Tiberina fault, NNW trending and ENE dipping, producing a displacement of about 5 km, and generating a continental basin (Val Tiberina basin), infilled by up to 1500 m with Upper Pliocene–Quaternary deposits. The fault has a staircase trajectory, and can be traced on the seismic profiles to a depth of about 13 km. A set of WSW-dipping, antithetic faults can be recognised on the profiles, the most important of which is the Gubbio fault, bordering an extensional Quaternary basin and interpreted as an active fault based on geological, geomorphologic and seismological evidence. The epicentral distribution of the main historical earthquakes is strictly parallel to the general trend of the normal faults. The focal mechanisms of the major earthquakes show a strong similarity with the attitude of the extensional faults, mapped at the surface and recognised on the seismic profiles. These observations demonstrate the connection between seismicity in the area and the activity of the normal faults. Moreover, the distribution of the instrumental seismicity suggests the activity of the Alto Tiberina fault as the basal detachment for the extensional tectonics of the area. Finally, the action of the Alto Tiberina fault was simulated using two dimensional finite element modelling: a close correspondence between the concentration of shear stresses in the model and the distribution of the present earthquakes was obtained.  相似文献   

δ18O and chemical composition of Libyan Desert Glass,country rocks,and sands: New considerations on target material     

Antonio LONGINELLI  Giampaolo SIGHINOLFI  Vincenzo De MICHELE  Enricomaria SELMO 《Meteoritics & planetary science》2011,46(2):218-227

Oxygen isotope and chemical measurements were carried out on 25 samples of Libyan Desert Glass (LDG), 21 samples of sandstone, and 3 of sand from the same area. The δ¹⁸O of LDG samples range from 9.0‰ to 11.9‰ (Vienna Standard Mean Ocean Water [VSMOW]); some correlations between isotope data and typological features of the LDG samples are pointed out. The initial δ¹⁸O of a bulk parent material may be slightly increased by fusion due to the loss of isotopically light pore water with no isotope exchange with oxygen containing minerals. Accordingly, the δ¹⁸O of the bulk parent material of LDG may have been about 9.0 ± 1‰ (VSMOW). The measured bulk sandstone and sand samples have δ¹⁸O values ranging from 12.6‰ to 19.5‰ and are consequently ruled out as parent materials, matching the results of previous studies. However, separated quartz fractions have δ¹⁸O values compatible with the LDG values suggesting that the modern surface sand inherited quartz from the target material. This hypothesis fits previous findings of lechatelierite and baddeleyite in these materials. As the age of the parent material reported in previous studies is Pan‐African, we measured the δ¹⁸O values of bulk rock and quartz from intrusives of Pan‐African age and the results obtained were compatible with the LDG values. The main element abundances (Fe, Mg, Ca, K, Na) in our LDG samples conform to previous estimates; Fe, Mg, and K tend to be higher in heterogeneous samples with dark layers. The hypothesis of a low‐altitude airburst involving silica‐rich surface materials deriving from weathered intrusives of Pan‐African age, partially melted and blown over a huge surface by supersonic winds matches the results obtained.  相似文献   

Magnetotelluric response of a uniformly stratified earth containing a magnetized layer     

D. Kao  D. Orr 《Geophysical Journal International》1982,70(2):339-347

Summary The magnetotelluric (MT) response is studied of a uniformly stratified earth which contains a magnetized layer. The impedance as a function of the layer parameters (resistivity, ρ permeability, μ and thickness h ) is discussed. The MT response from a layer (μ, ρ, h ) is equivalent to that from a layer (μ/μ_r=μ₀, μ_rρ, μ_r h ) where μ_r is the relative permeability of the layer. Thus the effect of a magnetized layer is to make it apppear μ_r times more resistive and μ_r times thicker than an unmagnetized equivalent layer. Master curves of apparent resistivity and phase are computed for three-layer models with varying permeability associated with varying resistivity in each layer. An example of MT field data is presented in which the most reasonable interpretation is that a magnetized layer exists beneath the observatory site.  相似文献   

Correlations between ground observations of Pi 2 geomagnetic pulsations and satellite plasma density observations     

M. Lester  D. Orr 《Planetary and Space Science》1983,31(2):143-160

Ground observations of Pi 2 geomagnetic pulsations are correlated with satellite measurements of plasma density for three time intervals. The pulsations were recorded using the IGS network of magnetometer stations and the plasma density measurements were made on board GEOS-1 and ISEE-1. Using the technique of complex demodulation, the amplitude, phase and polarisation characteristics of the Pi 2 pulsations are observed along two meridional profiles; one from Eidar, Iceland (L = 6.7) to Cambridge, U.K. (L = 2.5) and the other from Tromso, Norway (tL = 6.2) to Nurmijarvi, Finland (L = 3.3). The observed characteristics of the Pi 2 pulsations are then compared with the plasma density measurements. Close relationships between the plasmapause position and the position of an ellipticity reversal and a variation in H component phase are observed. A small, secondary amplitude maximum is observed on the U.K./Iceland meridian well inside the position of the projection of the equatorial plasmapause. The primary maxima on the two meridians, in general occur close to the estimated position of the equatorward edge of a westward electrojet. Using the plasma density measurements, the periods of surface waves at the plasmapause for two intervals are estimated and found to be in good agreement with the dominant spectral peaks observed at the ground stations near the plasmapause latitude and within the plasmasphere. The polarisation reversal, together with phase characteristics, spectral evidence and the agreement between the theoretical and observed periods leads to the suggestion that on occasions a surface wave is excited on the plasmapause as an intermediate stage in the propagation of Pi 2 pulsations from the auroral zone to lower latitudes.  相似文献   

Harmonics in spectra of PI 2 pulsations     

Bruce Roth  David Orr 《Planetary and Space Science》1973,21(8):1273-1286

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Thermal maturity of the axial zone of the southern Apennines fold-and-thrust belt (Italy) from multiple organic and inorganic indicators     

S. Corrado  L. Aldega  P. Di Leo  C. Giampaolo  C. Invernizzi  S. Mazzoli  M. Zattin 《地学学报》2005,17(1):56-65

The reconstruction of the thermal history of folded and thrust units is crucial to define the pattern of tectonic loading and the time-space evolution of an orogen where tectonic exhumation processes occurred at shallow crustal levels. In the present study, a well-constrained reconstruction of the thermal maturity in the axial zone of the southern Apennines has been achieved by the combined use of different thermal indicators in diagenesis. The major results are: (i) documentation of a jump in thermal maturity from the Apenninic Platform derived tectonic unit (from immature to early mature stages of hydrocarbon maturation) to the Lagonegro Basin derived tectonic units (late diagenetic zone); (ii) documentation of along-strike slighter variations in the Lagonegro units, concerning thermal maturity (thus maximum burial temperatures). This can be related to changes in amounts of tectonic burial and erosion/exhumation because of the lack of cylindricity of contractional structures; (iii) recognition of an independent thermal evolution of the allochthonous chain compared with the Apulian Platform tectonic unit with Mt Alpi area (in the late mature stage of hydrocarbon generation) interpreted as a sector of localized, intense exhumation within the External Zone of the orogen.  相似文献   

Characteristics of Stable Flows over Southern Greenland     

Andrew Orr  Edward Hanna  Julian C.R. Hunt  John Cappelen  Konrad Steffen  AG Stephens 《Pure and Applied Geophysics》2005,162(10):1747-1778

The main characteristic features of stable atmospheric flows over a large mountain plateau are summarised and then compared with mesoscale and synoptic scale numerical simulation, meteorological analysis, satellite imagery, and surface observations for the cases of flows over Southern Greenland for four wind directions. The detailed features are identified using the concepts and scaling of stably stratified flow over large mountains with variations in surface roughness, elevation, and heating. For westerly and easterly winds detached jets form at the southern tip, where coastal jets converge, which propagate large distances across the ocean. Near coasts katabatic winds can combine with barrier jets and wake flows generated by synoptic winds. Note how the approach flow rises/falls over southern Greenland for easterly/westerly winds, leading in both cases to more cloud on the western side. Some conclusions are drawn about the large-scale influences of these flows; detached jets in the atmosphere; air-sea interaction; formation of low pressure systems. For accurate simulations of these flows, mesoscale models are necessary with resolutions of order of 20 km or less.  相似文献   

Recent radar measurements of turbulence and microphysical parameters in marine boundary layer clouds     

A. B. White  C. W. Fairall  A. S. Frisch  B. W. Orr  J. B. Snider 《Atmospheric Research》1996,40(2-4)

We present a collection of research related to radar measurements of turbulence and microphysical properties in clouds. The radars used in these studies operate at frequencies ranging from 404 MHz to 34.6 GHz. We discuss the relative contributions made by the two primary radar scattering mechanisms to the measured values of radar reflectivity at the different frequencies. The desired turbulence and microphysical information is obtained from the radar reflectivity and other elements of the Doppler velocity spectra. Methods and examples are given with emphasis on liquid water clouds associated with the marine boundary layer.  相似文献   

Uptake and elimination of lindane and a phthalate ester in tropical corals and mussels     

J.E Solbakken  A.H Knap  P.L Orr 《Marine environmental research》1985,16(2):103-113

Phthalate esters and γ-hexachlorocyclohexane are among the organic xenobiotics which are most abundant in the atmospheric fallout over Bermuda. It was therefore of interest to study the uptake and elimination of these synthetic components in the most important reef building coral. Diploria strigosa and the mussel Arca zebra, from Bermudian waters. Radioactive labelled components (¹⁴C-γ-hexachlorocyclohexane, diisononyl [carboxyl-¹⁴C] phthalate) were used in the study and the samples were analyzed by liquid scintillation counting.The highest concentrations of radioactivity were found in hepatopancreas and more phthalate ester than lindane was taken up. In gill, muscle and coral tissues the uptake of lindane was higher than that of the phthalate ester. In all tissues analyzed the elimination rate of lindane was higher than that of the phthalate ester.The acute effects of phthalate esters on corals are probably less than those of lindane, due to the low uptake and low toxicity. However, the poor elimination of phthalate esters may lead to long-term effects.  相似文献   

Rock mechanics applied to shaft pillar mining     

J. C. Johnson  S. A. Orr 《Geotechnical and Geological Engineering》1990,8(4):385-392

Summary The Bureau of Mines is investigating methods for evaluating and optimizing shaft designs for deep metal mines. This paper describes one such project at the Homestake Mine in Lead, SD. To determine a safe approach for the extraction of ore from the Ross Shaft pillar at Homestake, a basic rock mechanics approach has been taken that involves laboratory testing, field measurements, and computer modelling. The results of the study show that ore bodies in the Ross pillar can be mined safely and that the shaft will remain in elastic rock. On the basis of this work, other mines can develop finite-element modelling to evaluate the stability of mine openings and increase resource recovery.  相似文献