Mapping of Interplate Coupling in the Kamchatka Subduction Zone from Variations in the Earthquake Size Distribution

Doklady Earth Sciences - The geometry of supposed coupling zones in the Kamchatka subduction zone is determined by the earthquake size distribution based on ealier revealed relationship between its...     

Broken ergodicity in magnetohydrodynamic turbulence

Turbulent magnetofluids appear in various geophysical and astrophysical contexts, in phenomena associated with planets, stars, galaxies and the universe itself. In many cases, large-scale magnetic fields are observed, though a better knowledge of magnetofluid turbulence is needed to more fully understand the dynamo processes that produce them. One approach is to develop the statistical mechanics of ideal (i.e. non-dissipative), incompressible, homogeneous magnetohydrodynamic (MHD) turbulence, known as “absolute equilibrium ensemble” theory, as far as possible by studying model systems with the goal of finding those aspects that survive the introduction of viscosity and resistivity. Here, we review the progress that has been made in this direction. We examine both three-dimensional (3-D) and two-dimensional (2-D) model systems based on discrete Fourier representations. The basic equations are those of incompressible MHD and may include the effects of rotation and/or a mean magnetic field B _o. Statistical predictions are that Fourier coefficients of the velocity and magnetic field are zero-mean random variables. However, this is not the case, in general, for we observe non-ergodic behavior in very long time computer simulations of ideal turbulence: low wavenumber Fourier modes that have relatively large means and small standard deviations, i.e. coherent structure. In particular, ergodicity appears strongly broken when B _o?=?0 and weakly broken when B _o?≠?0. Broken ergodicity in MHD turbulence is explained by an eigenanalysis of modal covariance matrices. This produces a set of modal eigenvalues inversely proportional to the expected energy of their associated eigenvariables. A large disparity in eigenvalues within the same mode (identified by wavevector k ) can occur at low values of wavenumber k?=?| k |, especially when B _o?=?0. This disparity breaks the ergodicity of eigenvariables with smallest eigenvalues (largest energies). This leads to coherent structure in models of ideal homogeneous MHD turbulence, which can occur at lowest values of wavenumber k for 3-D cases, and at either lowest or highest k for ideal 2-D magnetofluids. These ideal results appear relevant for unforced, decaying MHD turbulence, so that broken ergodicity effects in MHD turbulence survive dissipation. In comparison, we will also examine ideal hydrodynamic (HD) turbulence, which, in the 3-D case, will be seen to differ fundamentally from ideal MHD turbulence in that coherent structure due to broken ergodicity can only occur at maximum k in numerical simulations. However, a nonzero viscosity eliminates this ideal 3-D HD structure, so that unforced, decaying 3-D HD turbulence is expected to be ergodic. In summary, broken ergodicity in MHD turbulence leads to energetic, large-scale, quasistationary magnetic fields (coherent structures) in numerical models of bounded, turbulent magnetofluids. Thus, broken ergodicity provides a large-scale dynamo mechanism within computer models of homogeneous MHD turbulence. These results may help us to better understand the origin of global magnetic fields in astrophysical and geophysical objects.     

The Rise of Earthquake Correlation Range and the Chains of Earthquakes before Large Seismic Events

Izvestiya, Physics of the Solid Earth - The paper summarizes the results of the experiment on advance earthquake forecasting using the Reverse Tracing of Precursors (RTP) algorithm based on the...     

Forecasting Aftershock Activity: 5. Estimating the Duration of a Hazardous Period

Izvestiya, Physics of the Solid Earth - Continuing the series of publications on aftershock hazard assessment, we consider the problem of estimating the time interval after a strong earthquake that...     

Large-scale short-term seismicity activation prior to the strongest earthquakes of Japan and the Kurile Islands

The Reverse Tracing of Precursors (RTP) algorithm for the prediction of strong earthquakes has become known owing to the successful predictions of the Tokachi-oki earthquake near Hokkaido Island and the San Simeon earthquake of California in 2003, as well as to other well-documented predictions found on the Internet, some of which also proved to be successful. The RTP predictions with the use of the Japan Meteorological Agency (JMA) data for the zone from Honshu Island to the Middle Kurile Islands deserve special attention. None of the five predictions starting in the middle of 2003, including the last one formulated for the region where the catastrophic earthquake of March 11, 2011, with a magnitude of M = 9 occurred, was a false alarm. One distinctive feature of predictions for this region is the enormous size (about 1000 km) of alarm regions. At the same time, the relatively short alarm interval makes it possible to record a real number of earthquakes with a magnitude of 7.2 and higher during alarm periods, which is about five times larger than on average over the equivalent period, i.e., to reach a probability gain of about five.     

Increased correlation range of seismicity before large events manifested by earthquake chains

“Earthquake chains” are clusters of moderate-size earthquakes which extend over large distances and are formed by statistically rare pairs of events that are close in space and time (“neighbors”). Earthquake chains are supposed to be precursors of large earthquakes with lead times of a few months. Here we substantiate this hypothesis by mass testing it using a random earthquake catalog. Also, we study stability under variation of parameters and some properties of the chains. We found two invariant parameters: they characterize the spatial and energy scales of earthquake correlation. Both parameters of the chains show good correlation with the magnitudes of the earthquakes they precede. Earthquake chains are known as the first stage of the earthquake prediction algorithm reverse tracing of precursors (RTP) now tested in forward prediction. A discussion of the complete RTP algorithm is outside the scope of this paper, but the results presented here are important to substantiate the RTP approach.     

Scaling organization in the dynamics of blocks-and-faults systems

Some elements of the model of scaling organization of fracture tectonics (SOFT) are incorporated into the model of block structure dynamics (BSD). The resulting new model permits to obtain a power law relationship between earthquake energy and fault area with an exponent 3/2, as for observed seismicity. This is an important advantage of the new model in comparison with the BSD model, in which this dependence is generally linear.     

Probabilistic Estimates of Hypocenters from the Data of Kamchatka Seismic Network Stations

Izvestiya, Physics of the Solid Earth - A new approach is proposed for determining earthquake hypocenters aimed at a more comprehensive characterization of its uncertainty and ambiguity....     

统计地震学的两个基本定律对应力的依赖关系

统计地震学长期使用的两个幂律关系式为:描述地震频度-震级关系的古登堡-里克特(Gutenberg-Richter)关系式[1]和描绘主震后余震随时间衰减速率特征的大森-宇津(Omori-Utsu)定律[2]。最近,地震频度-震级关系斜率(b值)与断裂模式的相关性研究确定了应力对b值的影响[3]。在此,我们以类似的方式根据主震的断裂模式对余震序列进行研究。我们发现逆冲型主震的幂律余震衰减速率起始前的延时(c值)一般比正断层型地震的短,走滑型地震的c值则处于二者之间。对断裂模式的这些类似依赖关系表明两个基本幂律都受应力状态控制。只有2%的余震有已知震源机制解。因此,c值和b值是两个独立的估算值,它们可作为推断应力场的新方法来使用,目前应力场依然难以直接测定。