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J. Edwards 《Geophysical Journal International》1982,68(3):609-624
Summary. Rotational remanent magnetizations and partial rotational remanent magnetizations have been induced in four specimens using alternating magnetic fields of 55 mT maximum peak strength and 128 Hz, and speeds of rotation between 0.0016 and 0.4 rev s−1 . Each partial rotational remanent magnetization ( PRRM ), was produced by rotating the specimen only at the maximum setting of the alternating field. The variation of PRRM with (a) speed of rotation, ω, and (b) total angle of rotation, θ, was investigated. In (a), PRRM fell slowly but steadily as ω increased; for (b) it rose sharply as θ increased up to 60° and reached a maximum for θ between 90° and 120°. Alternating field demagnetizations of PRRMs were performed with the specimen (a) at rest, and (b) rotating about an axis perpendicular to the field. Rotation significantly enhanced the demagnetization process. Variation of the time T , taken to remove the inducing alternating field produced no detectable effect in the case of PRRM , but affected the value of ω at which a given feature of the RRM —ω curve appeared, and the product θF (=ω T ) appears to be more important than either ω or T separately. Current theories on RRM can be used to explain some of the new experimental data on PRRM . 相似文献
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Summary. Rotational remanent magnetization, RRM, is the magnetization acquired when a sample is rotated during alternating field demagnetization. Although the existence of RRM has been well documented in different laboratories, until now no physical mechanism explaining its origin has been given. We propose that the RRM originates from thermal fluctuations biased by a precessional torque associated with the alternating field. Our theory is consistent with the observation that no directional preference exists in the experimental situation until the sample is rotated relative to the alternating field. Moreover, our theory predicts that the combined sample rotation and precession will produce a RRM that switches direction when the frequency of sample rotation increases from any value below the frequency of the alternating field to any value above that frequency as observed in experiments. Although no precise theory is given for the intensity of RRM, the model presented here can qualitatively explain previous intensity observations. 相似文献
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The rotational stability of an ice-age earth 总被引：2，自引：0，他引：2
Jerry X. Mitrovica John Wahr Isamu Matsuyama Archie Paulson 《Geophysical Journal International》2005,161(2):491-506
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F. Bocchio 《Geophysical Journal International》1985,81(2):463-467
Summary. In view of present attempts to build orbiting gravity gradiometers with an accuracy of about 10−4 E, perturbing gravitational gradients arising from tide-generating bodies and from rotational deformations induced by polar motion are evaluated. 相似文献
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J. Edwards 《Geophysical Journal International》1986,85(1):209-215
Summary. These experiments support Stephenson's predictions that partial anhysteretic remanent magnetizations produced in rotating samples deviate from the steady field direction, which is collinear with the rotation axis, by amounts depending on the angle, between the alternating magnetic field axis and the rotation axis. A similar effect was observed for partial rotational remanent magnetizations. Possible differences between the two remanence types were noted. 相似文献
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Giorgio Ranalli 《Geophysical Journal International》2000,141(2):535-537
It is shown that any non-zero torque resulting from differences in angular velocity between individual shells in the Earth would be an extremely short transient phenomenon as a consequence of the viscosity of the asthenosphere. Consequently, it cannot be a factor in the origin of the toroidal velocity field of degree one ('westward drift') of the lithosphere. 相似文献
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J. Edwards 《Geophysical Journal International》1980,60(2):283-288
Summary. Several tests have been carried out to investigate how the generation of rotational remanent magnetization depended on the frequency of the applied demagnetizing field. The equipment used is described. The investigation was carried out using two specimens, one being a synthetic specimen of magnetite, and the other a cylindrical rock sample. These specimens gave virtually identical behaviour with varying frequency, unlike the differing behaviours reported previously by Wilson & Lomax. For each of the separate alternating field frequencies used (ranging from 50 to 1210 Hz), as the rotational speed of each specimen was reduced from 0.1 cycle s−1 , the corresponding rotational remanent magnetization increased to a maximum value when the rotational speed was in each case just a little greater than 0.01 cycle s−1 , after which the rotational remanence decreases as the rotational speed decreases. 相似文献
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One answer to the question posed in the title is that we will have more accurate data for arrival times of SH waves, because the rotational component around the vertical axis is sensitive to SH waves although not to P-SV waves. Importantly, there is another answer related to seismic sources, which will be discussed in this paper.
Generally, not only dislocations commonly used in earthquake models but also other kind of defects could contribute to producing seismic waves. In particular, rotational strains at earthquake sources directly generate rotational components in seismic waves. Employing the geometrical theory of defects, we obtain a general expression for the rotational motion of seismic waves as a function of the parameters of source defects.
Using this expression, together with one for translational motion, we can estimate the rotational strain tensor and the spatial variation of slip velocity in the source area of earthquakes. These quantities will be large at the edges of a fault plane due to spatially rapid changes of slip on the fault and/or a formation of tensile fractures. 相似文献
Generally, not only dislocations commonly used in earthquake models but also other kind of defects could contribute to producing seismic waves. In particular, rotational strains at earthquake sources directly generate rotational components in seismic waves. Employing the geometrical theory of defects, we obtain a general expression for the rotational motion of seismic waves as a function of the parameters of source defects.
Using this expression, together with one for translational motion, we can estimate the rotational strain tensor and the spatial variation of slip velocity in the source area of earthquakes. These quantities will be large at the edges of a fault plane due to spatially rapid changes of slip on the fault and/or a formation of tensile fractures. 相似文献
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A. Stephenson 《Geophysical Journal International》1985,83(3):787-796
Summary. Recent experimental work by Edwards has demonstrated that rotational remanent magnetization (RRM) is not a maximum when the alternating field is normal to the rotation axis of the sample (a rock) but is greatest when the angle is about 75°. Experiments involving the production of ARM during sample rotation gave a similar result with a maximum at about 60°. These results are explained here in terms of the response of an isotropic assembly of identical single-domain particles to a strong alternating magnetic field. 相似文献
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