Volume of magma accumulation or withdrawal estimated from surface uplift or subsidence,with application to the 1960 collapse of Kilauea volcano

An elastic point source model proposed by Mogi for magma chamber inflation and deflation has been applied to geodetic data collected at many volcanoes. The volume of ground surface uplift or subsidence estimated from this model is closely related to the volume of magma injection into or withdrawal from the reservoir below. The analytical expressions for these volumes are reviewed for a spherical chamber and it is shown that they differ by the factor 2(1-v), where v is Poisson's ratio of the host rock. For the common estimate v=0.25, as used by Mogi and subsequent workers, the uplift volume is 3/2 the injection volume. For highly fractured rocks, v can be even less and the uplift volume can approach twice the injection volume. Unfortunately, there is no single relation between the inflation of magma reservoirs and the dilation or contraction of host rocks. The inflation of sill-like bodies, for instance, generates no overall change in host rock volume. Inflation of dike-like bodies generates contraction such that, in contrast with Mogi's result, the uplift volume is generally less than the injection volume; for v=0.25, the former is only 3/4 of the latter. Estimates of volumes of magma injection or withdrawal are there-fore greatly dependent on the magma reservoir configuration. Ground surface tilt data collected during the 1960 collapse of Kilauea crater, one of the first events interpreted with Mogi's model and one of the largest collapses measured at Kilauea, is not favored by any one of a variety of deformation models. These models, however, predict substantially different volumes of both magma withdrawal and ground surface subsidence.     

Stress Changes Modelled for the Sequence of Strong Earthquakes in the South Iceland Seismic Zone Since 1706

The South Iceland seismic zone is, roughly speaking, situated between two sections of the mid-Atlantic ridge, i.e., the Reykjanes Ridge southwest of Iceland and the Eastern Volcanic Zone on the island. It is a transform zone, where earthquakes are expected to occur on E-W-trending left-lateral shear faults, equivalent to conjugate, N-S-oriented right-lateral, rupture planes. In fact, earthquakes take place on en-échelon N-S-oriented faults, which is indicated by the distribution of main shock intensities, aftershocks as well as by surface fault traces. The stress field continuously generated in the fault zone by opening of the adjacent ridges is computed and superimposed on the stress field changes induced by a series of 13 earthquakes (M 6) between 1706 and 2000. The level of the pre-seismic stress field is analysed as well as the size of the area under high stress. Finally, the post-seismic stress field of June 2000 is analysed, to see where high stresses might have accumulated. The modelling indicates that the rupture planes located on separated parallel N-S-striking zones are dense enough to lead to an area-wide stress release by the series of events. The obtained pre-seismic stress level for most events is high and stable with the exception of situations when several strong shocks occur over a time span of several days, i.e., display typical main shock-aftershock patterns. The size of areas under high stress aside from of the rupture plane, i.e., where no event occurs at the specific time, is of medium to small size.     

Surface vertical displacements, potential perturbations andgravity changes of a viscoelastic earth model induced by internal point dislocations

Using the viscoelastic correspondence principle, we utilize the surface coseismic spheroidal deformation fields (i.e. vertical displacements, potential perturbations and gravity changes) of SNREI earth models caused by four typical types of point dislocation, derived by Sun & Okubo (1993 ), to deduce the fundamental formulas for spheroidal fields relevant to viscoelastic earth models. In computations, we employ a strike-slip dislocation on a vertical plane buried at the bottom of the lithosphere to estimate the maximal viscous relaxation responses to this kind of source that possibly exist on the surface of the earth. We take the seismic moment as 10²²  N  m, which is characteristic of an average large earthquake. The numerical results demonstrate that, if we take the viscosity as 10¹⁹  Pa  s in the asthenosphere, and 10²¹  Pa  s in the other mantle layers, the rates of surface vertical displacements and gravity changes within about 2.5° for the 10 postseismic years are respectively 1.5–8.1  cm  yr⁻¹ and 4.0–14.9  μgal  yr⁻¹ : the viscous relaxation for this mantle viscosity profile proceeds much faster than for a constant mantle viscosity of 10²¹  Pa  s.     

Deep structure of the Yuzhno-Sakhalinsk mud volcano: Results of multidisciplinary seismic surveys

The paper presents the results of multidisciplinary seismic surveys carried out by refraction and reflection methods for compressional and shear waves on Yuzhno-Sakhalinsk mud volcano. A large extinct (approximately 60–70 years ago) volcano was identified near the active volcano, and its structure was studied. It was found that the recognized intermediate fluid-bearing chambers correlate with the distinguished tectonic dislocations. A supposition was made that the mud volcanism is sequentially developed in the northeastern direction and related to the modern tectonics of the Central Sakhalin Fault.     

Piezomagnetic fields produced by dislocation sources

Tectonomagnetic modeling based on the linear piezomagnetic effect is reviewed with special attention to dislocation models. Stacey's scheme was the prototype for such modeling, as proposed in his first seismomagnetic calculations in 1964. The linear piezomagnetic law is presented, in which the stress-induced magnetization is expressed as a linear combination of stress components. The Gauss law for magnetic field and the Cauchy-Navier equation for static elastic equilibrium are combined through linear piezomagnetism and the Hooke law to yield the basic equation for piezomagnetic potential. A representation theorem for its solution is given by surface integrals of the displacement and its normal derivative over the strained body.A Green's function method is developed to compute the piezomagnetic field produced by a dislocation surface in an elastic half-space. Volterra's formula for piezomagnetic potential is derived by modifying Stacey's scheme for tectonomagnetic modeling. The Green's functions for the problem are called elementary piezomagnetic potentials, which are defined as potentials produced by elementary dislocations. Special consideration is required to construct the elementary piezomagnetic potentials, because the stress field around a point dislocation has a singularity of orderr ^–3. The integral representing elementary piezomagnetic potentials is not uniformly convergent. Owing to inappropriate convergency, the Green's functions obtained in an earlier study led to a puzzling outcome. Revised Green's functions give consistent results with those obtained so far by numerical integrations. Generally the piezomagnetic field produced by dislocation sources is weak in the case of a homogeneous earth model. Two enhancement effects for piezomagnetic signals are suggested: one due to inhomogeneous magnetization and the other via bore-hole observations.     

Dislocation-mediated melting of iron and the temperature of the Earth's core

Summary . Dislocation theories of melting provide a possibility of calculating the melting temperature, from first principles, as the temperature at which the free energy of a crystal saturated with dislocations becomes equal to that of the dislocation-free crystal. After a brief review of the physical bases of the dislocation melting theories, Ninomiya's theory is used to determine the melting temperature as well as the volume and entropy of melting and the slope of the melting curve for iron at atmospheric pressure and under conditions prevailing at the Earth's inner core boundary. The necessary parameters (elastic moduli, Grüneisen parameter) are drawn from seismological earth models. We find a melting temperature of the material of the inner core of about 6150 K, independent of shock-wave experiments but in good agreement with them and with extrapolations using Lindemann's law. With usually accepted values of the melting point depression due to light elements in solution, the temperature at the inner core boundary is found to be T _ICB≅ 5000 K. This temperature is compatible with a temperature of the outer core at the core-mantle boundary T _CMB≅ 3800 K. Dislocation melting theories can thus help constrain the temperature profile in the Earth's core.     

矩形断层向-位错引起的空间重力变化

针对位错理论难以解释断层面之间的旋转转动的问题,该文基于子断层叠加法,利用经典点源位错理论,得出了矩形断层向-位错引起的空间重力变化。利用C++语言编制了弹性半空间中的矩形断层向-位错正演程序,模拟计算并分析了倾角为90°的矩形断层滑动和转动引起的空间重力变化的分布特征。数值模拟结果显示:断层运动引起的空间重力变化与断层的滑动和转动量大小及断层产状有关,断层滑动和转动越大,引起的地表变形范围和量值就越大;断层转动引起的重力变化大小与断层埋深成反关系,即断层埋深越大,相应的重力变化量值就越小;宏观上,矩形断层位错运动引起的重力变化呈近似对称的特征,而断层向错打破了重力变化图像的对称性。     

Learning Wisdom Through Geographical Dislocations

Wisdom is at once one of the most elusive and most valued kinds of knowledge. Empirical research shows that, indeed, across cultures, people hope that life experience will eventually make them wiser. The problem is that, to date, the academic study of wisdom and of the processes by which it can be learned has been dominated by psychologists. The first part of the article reviews the state-of-the-art psychological scholarship on wisdom to show how that conceptualization lacks geographical sensitivity and therefore misses some of the crucial geographical mechanisms by which people become wiser. The second part of the article singles out and focuses on one such mechanism, namely, the learning of wisdom through geographical dislocations. By drawing on insights from the study of international migration, exile, and transculturation in postcolonial contexts, the final part of the article suggests specific learning processes that might strengthen the hypothesis that geographical dislocations and the attendant cross-cultural experiences they generate are often conducive to wisdom.     

腕骨脱位或骨折并脱位的影像分析

目的:分析腕骨脱位及骨折并脱位的影像,探讨外力在腕关节传播的过程。方法:对129例腕骨脱位患者行X线和多层螺旋CT检查,分析腕骨脱位或骨折并脱位的类型。结果:月骨脱位32例,腕中关节脱位2例,月骨周围型脱位95例。95例中经舟状骨月骨周围脱位50例,经桡骨茎突月骨周围脱位23例,经头状骨月骨周围脱位4例,经三角骨月骨周围脱位7例,经尺骨茎突月骨周围性脱11例。在合并其他腕骨骨折的病例中。经桡骨茎突及经舟骨骨折病例X线检查均得到确诊,其余56例中,X线漏诊6例则是通过多层螺旋CT薄层扫描及重建才做出正确诊断,单纯月骨周围型脱位较少见(仅3例),有5例X线检查为单纯月骨周围脱位的病例在CT扫描发现合并腕骨撕脱性小骨折。结论:X线检查对腕关节节损伤的程度有可能低估,多层螺旋CT薄层扫描及重建可作出准确、直观诊断。分析外力损伤腕关节的过程对腕骨脱位或骨折并脱位的影像诊断有重要价值。