Magnetic activity inside the auroral zones and field-aligned currents

Big perturbations of the magnetic field (amplitudes larger than 250 nT) are simply detected by subtracting the values of a model from the measurements of CHAMP satellite. Taking a full year of CHAMP data and organizing them in four subsets of three months length (spring, summer, autumn, winter), it is found that: (a) the two domains where such big perturbations mainly exist are limited, in both hemispheres, by a parallel of high latitude of the corrected geomagnetic coordinates system; (b) a conspicuous seasonal (annual) variation affects the density of the perturbations and is opposite in the two hemispheres. We hold that these perturbations are linked to the midday magnetic activity within the auroral zone, long ago described by one of us (Mayaud, 1956). The source of the perturbations observed at the satellite altitude would be field-aligned currents resulting from the penetration of the solar wind into the magnetospheric cusps. To cite this article: J.-L. Le Mouël et al., C. R. Geoscience 335 (2003).     

Deficit of Large Aftershocks as an Indicator of Afterslip at the Sources of Earthquakes in Subduction Zones

Doklady Earth Sciences - A relative decrease in the fraction of large aftershocks in the first days after earthquakes in subduction zones is demonstrated, and a connection of this phenomenon with...     

Why Are New Approaches to Seismic Hazard Assessment Required?

Doklady Earth Sciences - For the first time, a numerical comparison of the General Seismic Zoning (GSZ) maps with the effect of earthquakes that actually occurred after the publication of the maps...     

Forecasting Aftershock Activity: 4. Estimating the Maximum Magnitude of Future Aftershocks

Izvestiya, Physics of the Solid Earth - In this paper, we consider the problem of forecasting the magnitude of the strongest aftershock starting from a certain instant of time in the future. This...     

A study of seismic noise and calculation of the optimum seismograph constants

Уровень помех на ссйсмических станциях СССР исследовался для периодов от 0,1 до 5–7сек при помощи специальной аппаратуры с увеличением до 20 000. Слектральное распределение помех характеризуется одним или двумя максимумами па периодах от 0,1 до 0,6сек, резким минимумом на периодах от 0,6 до 2,0сек и большим максимумом в области сущестнования штормовых микросейсм (3–8сек). Для сейсмографов высокой чувствительности наиболее выгодной оказывается кривая увеличения с максимумом на периодах около 1сек. В каждом конкретном случае, однако, желателен спецнальный расчет онтималяной кривой увеличения. Исходными данными дли расчета являются зависимость амплитулы помех от периода и требование, чтобы амплитуда записп помех на сейсмограмме не превышала заданной величины. По совокупности этих данных может выть выбрана кривая увеличения, удовлетворяюшая требованиям теории сейсмографа и дающая наибольшсе увеличение при заданном уровне помех иа записи. Необходимые параметры сейсмографа с достаточной точностью расчитываются по нескольким характерным точкам кривой увелнчепия.     

Forecasting Aftershock Activity: 3. Båth’s Dynamic Law

In seismology according to Båth’s well-known law, the magnitude of the strongest aftershock is on average by unity lower than the magnitude of the main shock. At the same time, most of the strongest aftershocks typically occur within a few hours after the main shock. From the practical standpoint, this activity is quite naturally perceived as a direct continuation of the main earthquake. The subsequent strong aftershocks occur against the rarer background shocks, are less expected, and therefore constitute a separate hazard. The average difference in magnitudes between the main shock and the strongest aftershock that occurs a certain time after the main shock gradually increases. In this work, we consider the problem of estimating the magnitudes of the strongest future aftershock at the successive instants of time after the main shock without taking into account the information about the aftershocks that have already occurred before a given time. For these estimates, we construct the theoretical distributions whose shape proves to be independent of time, whereas the time dependence of the shift in the magnitude proves to be known a priori. The predetermination of these dependences at the moment of the strong earthquake gives us grounds to characterize the constructed theoretical model as Båth’s dynamic law.     

Productivity of Mining-Induced Seismicity

Izvestiya, Physics of the Solid Earth - The paper addresses the study of the ability of mining-induced earthquakes to generate successive shocks. Based on the example of the Khibiny...     

The Law of the Repeatability of the Number of Aftershocks

Doklady Earth Sciences - This paper shows that the number of aftershocks with a relative magnitude does not depend on the magnitude of the main shock, and, in global and regional consideration, it...     

Spatial Distribution of Triggered Earthquakes in the Conditions of Mining-Induced Seismicity

Izvestiya, Physics of the Solid Earth - Abstract—The spatial distribution of the triggered seismic events in mining conditions in the tectonically loaded rock masses is studied using the...     

Broken ergodicity,magnetic helicity,and the MHD dynamo

We consider an unforced, incompressible, turbulent magnetofluid constrained by concentric inner and outer spherical surfaces. We define a model system in which normal components of the velocity, magnetic field, vorticity, and electric current are zero on the boundaries. This choice allows us to find a set of Galerkin expansion functions that are common to both velocity and magnetic field, as well as vorticity and current. The model dynamical system represents magnetohydrodynamic (MHD) turbulence in a spherical domain and is analyzed by the methods similar to those applied to homogeneous MHD turbulence. We find a statistical theory of ideal (i.e. no dissipation) MHD turbulence analogous to that found in the homogeneous case, including the prediction of coherent structure in the form of a large-scale quasistationary magnetic field. This MHD dynamo depends on broken ergodicity, an effect that is enhanced when total magnetic helicity is increased relative to total energy. When dissipation is added and large scales are only weakly damped, quasiequilibrium may occur for long periods of time, so that the ideal theory is still pertinent on a global scale. Over longer periods of time, the selective decay of energy over magnetic helicity further enhances the effects of broken ergodicity. Thus, broken ergodicity is an essential mechanism and relative magnetic helicity is a critical parameter in this model MHD dynamo theory.