Dispersion of waves in a continuously stratified elastic medium

Summary It is shown that the waves travelling at normal incidence in a continuously stratified elastic medium in which the longitudinal and the transverse wave velocities increase linearly are appreciably dispersed. Dispersion curves are given showing the variation of phase and group velocities, with frequency and different laws of increase in density. The results are relevant to seismology and underwater acoustics.A part of this paper was presented at the meetings of the Canadian Association of Physicists held in Toronto in June 1967     

Usual assumptions in the treatment of wave propagation in heterogeneous elastic media

Summary Several assumptions are usually made in seismology in the treatment of wave propagational problems in heterogeneous elastic media. These assumptions are pointed out and some of them are critically examined.This paper was presented in a modified form at the meetings of the Canadian Association of Physicists in Toronto in June, 1967.The author was formerly known asRavindra N. Gupta     

Model tank experiments for resistivity measurements on sloping and vertical non conducting dykes

Summary Model resistivity experiments over sloping and vertical, non-conducting dykes have been carried out and reported in this paper. The results of vertical dykes as compared to the sloping dykes are very interesting and not so far reported in the available literature. Of particular interest is distinct resistivity high in the centre of the two vertical dykes, followed by lows over the dykes and again by highs on either side. As expected the curves are symmetrical. As against this, in the cases of sloping dykes, there is a distinct low, in between the dykes, followed by highs over the dykes, the curves being asymmetrical.     

Deformation of the rocks of Simla Hills

Simla Hills form a part of Lesser Himalaya. Metamorphic rocks of this area (Pre-Cambrian), forming Chail-Jutogh nappe, are thrust over a series of mostly unfossiliferous rock formations ranging in age from Palaeozoic to Eocene. The rocks of the area are characterised by meso-structures belonging to three phases of deformation. The second phase structures, both in the allochthon as well as in the para-autochthon units are synchronous with the nappe formation. The third structure in the para-autochthon unit has been related with the movement of nappe. A model explaining the probable kinematics of thrusting in the Simla Hills has been suggested.

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Zusammenfassung Die Simla-Berge sind ein Teil des Lesser Himalaya. Metamorphe Gesteine dieses Gebietes (Präkambrium), die die Chail-Jutogh-Decke bilden, sind über einer Serie vorwiegend fossilfreier Formationen (Paläozoikum bis Eozän) überschoben. Die Gesteine dieses Gebietes sind durch Meso-Strukturen, die zu drei Phasen der Deformation gehören, gekennzeichnet. Die Strukturen der zweiten Phase, zu der allochthone sowie para-autochthone Einheiten gehören, sind gleichaltrig mit der Anlage der Deckenbildung. Die Strukturen der dritten Phase in der para-autochthonen Einheit hängen mit der weiteren Bewegung der Decke zusammen. Ein Modell, das die wahrscheinliche Kinematik der Überschiebung in den Simla-Bergen erklärt, wird vorgeschlagen.

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Résumé Les monts Simla représentent une partie du « Lesser Himalaya ». Les roches métamorphiques de cette région (Précambrien), formant la nappe du « Chail-Jutogh », ont glissé par-dessus une série de formations (du Paléozoique à l'Eocène) en majorité dépourvues de fossiles. Les roches de cette région sont caractérisées par des interstructures appartenant à trois phases de la déformation. Les structures de la 2^e phase, auxquelles appartiennent les unités allochtones et para-autochtones se sont formées en même temps que la nappe. Les structures de la 3^e phase, dans l'unité para-autochtone, sont en rapport étroit avec le déplacement postérieur de la nappe. Une possibilité d'explication de la cinématique probable du glissement dans les monts Simla est proposée.

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Simla Lesser Himalaya. — —, Chail-Jutogh, , - . -, . - , - , . - . , , , .

     

Theoretical Love wave dispersion in a single layer model

Summary From a study of the Love wave dispersion in a single layer model it is shown that the shape of the dispersion curves is very insensitive to the changes in the density ratio. The bilogarithmic grids giving dispersion curves for different shear velocity ratios and a mean density ratio of 1.20 should be sufficient for interpretation by the method of curve matching. Such grids and the numerical data are given both for the phase velocity and the group velocity. An example is given illustrating the use of these grids.     

Trigger of Successive Filament Eruptions Observed by SDO and STEREO

Using multiwavelength observations from the Solar Dynamics Observatory (SDO) and the Solar Terrestrial Relations Observatory (STEREO), we investigate the mechanism of two successive eruptions (F1 and F2) of a filament in active region NOAA 11444 on 27 March 2012. The filament was inverse J-shaped and lay along a quasi-circular polarity inversion line (PIL). The first part of the filament erupted at \(\sim2{:}30\) UT on 27 March 2012 (F1), the second part at around 4:20 UT on the same day (F2). A precursor or preflare brightening was observed below the filament main axis about 30 min before F1. The brightening was followed by a jet-like ejection below the filament, which triggered its eruption. Before the eruption of F2, the filament seemed to be trapped within the overlying arcade loops for almost 1.5 h before it successfully erupted. Interestingly, we observe simultaneously contraction (\(\sim12~\mbox{km}\,\mbox{s}^{-1}\)) and expansion (\(\sim20~\mbox{km}\,\mbox{s}^{-1}\)) of arcade loops in the active region before F2. Magnetograms obtained with the Helioseismic and Magnetic Imager (HMI) show converging motion of the opposite polarities, which result in flux cancellation near the PIL. We suggest that flux cancellation at the PIL resulted in a jet-like ejection below the filament main axis, which triggered F1, similar to the tether-cutting process. F2 was triggered by removal of the overlying arcade loops via reconnection. Both filament eruptions produced high-speed (\(\sim1000~\mbox{km}\,\mbox{s}^{-1}\)) coronal mass ejections.     

The petrology and geochemistry of massif anorthosites and gabbros of the Bavali fault zone,North Kerala

The massif anorthosites and gabbros occurring in the north Kerala region are localised along the Bavali fault. Several other bodies of granophyres and syeites also occupy this fault. All these bodies are considered to be a continuous graduating igneous series. This paper aims at delineating the field relations, petrochemistry and origin of massif anorthosites and gabbros occurring in the vicinity of the fault. Anorthosites (An 70-55) are nonlayered and highly deformed with no igneous structure present. Gabbros show relict poikilitic texture with a mineralogy of plagioclase, clinopyroxene, hornblende and biotite. Geochemical study suggests dominantly calc-alkaline characteristics for both anorthosites and gabbros. However, their chemical variation is not transitional to indicate evolution by continuous differentiation from a single parent magma. The rock types seem to be chemically unrelated and appear to have evolved independently from discreet magma sources and the magma migration might have only been promoted by the Bavali lineament.     

Petrology and geochemistry of the Grubergebirge anorthosite and marginal rocks,central Dronning Maud Land: Further characterization of the Late Neoproterozoic magmatic event in East Antarctica

The Grubergebirge anorthosite, a Late Neoproterozoic massif-type anorthosite, was emplaced into Late Mesoproterozoic-aged metamorphosed orthogneisses and supracrustal rocks in the Wohlthat Mountains. Mineralogically and chemically, the marginal rocks to the anorthosite massif classify as ferromonzodiorite and ferromonzonite. Variations in trace and rare earth element abundances and normalized patterns between the anorthosite and associated marginal ferromonzodiorite (and minor ferromonzonite) and distinct differences between the ferromonzodiorite and ferromonzonite have been observed. Whereas the magmas from which the anorthosite crystallized have been slightly contaminated by incorporating crustal material (now occurring as enclaves), the marginal ferromonzodiorite represent rocks that originated due to mixing (hybridization) of injected primitive ferrodiorite magma(s) with preexisting crustal material, resulting in the hybrid ferromonzodiorite.     

Modeling and Measuring the Flux Reconnected and Ejected by the Two-Ribbon Flare/CME Event on 7 November 2004

Observations of the large two-ribbon flare on 7 November 2004 made using SOHO and TRACE data are interpreted in terms of a three-dimensional magnetic field model. Photospheric flux evolution indicates that ?1.4×10⁴³ Mx² of magnetic helicity was injected into the active region during the 40-hour buildup prior to the flare. The magnetic model places a lower bound of 8×10³¹ ergs on the energy stored by this motion. It predicts that 5×10²¹ Mx of flux would need to be reconnected during the flare to release the stored energy. This total reconnection compares favorably with the flux swept up by the flare ribbons, which we measure using high-time-cadence TRACE images in 1?600 Å. Reconnection in the model must occur in a specific sequence that would produce a twisted flux rope containing significantly less flux and helicity (10²¹ Mx and ?3×10⁴² Mx², respectively) than the active region as a whole. The predicted flux compares favorably with values inferred from the magnetic cloud observed by Wind. This combined analysis yields the first quantitative picture of the flux processed through a two-ribbon flare and coronal mass ejection.