Volume 55, Nº 5 (2019)

The known methods for identifying the clusters of seismic events that are mainly formed by the aftershocks frequently include debatable initial assumptions or a complicated system of successive approximations. One of the most recent and the most logically consistent methods for identifying clusters of aftershocks is the nearest neighbor distance (NND) method, which is however algorithmically most challenging. In this paper, we propose a new declustering method based on a generalized distance (GD) metric, which employs some assumptions of the NDD method but is as simple in practical implementation as the window methods previously proposed for this purpose. In analyzing and substantiating this new method, a procedure of random shuffling of seismic events with respect to time is used for generating a real catalog, which is however free of genetic relationships between different events. The efficiency of the existing window methods, the GD method, and the NND methods is compared by a number of the criteria for 17 regions. It is shown that the GD method is, on average, noticeably more efficient than the standard window methods and compares very favorably with the NND method. In the conclusions, a certain speculativeness of separating the events into the main and dependent shocks is discussed.

Empirical data obtained by studying the Earth’s surface deformations in the fault zones induced by exogenous, endogenous, and manmade processes are presented. It is suggested to analyze induced deformations in the fault zones caused by different factors using a unified approach based on the notions of parametric excitation of processes. Two variants (types) of the formation of induced phenomena are considered. In the first variant, deformational response of faults occurs linearly when an influence directly causes a fault to deform. The second variant is a nonlinear parametric amplifier when the deformational response of a fault zone is anomalously high and induced (excited) by small influences. In accordance with this approach, definitions are given of exogenously induced, endogenously induced, and technology-induced deformations of the fault zones. The examples are presented when both scenarios of process formation, e.g., exogenous and exogenously-induced surface deformations, are simultaneously observed within a single measurement system.

Monte Carlo numerical simulation of the formation of chemical remanent magnetization (CRM) by the mechanism of the growth of volumes from superparamagnetic (SPM) to single-domain (SD) in the ensembles of magnetostatically interacting particles, thermoremanent magnetization (TRM), and experiments on determining paleointensity by the Thellier–Coe and Wilson–Burakov methods are carried out. The obtained results agree with the Smirnov–Tarduno hypothesis (Smirnov and Tarduno, 2005) that the similarity of the spectra of blocking temperatures T_b of CRM and TRM can be due to the narrowness of the interval of the blocking temperatures T_b of CRM and TRM, with the reservation that the similarity can be observed on part of the total interval of the T_b spectrum provided that this interval accommodates a significant fraction of the total CRM intensity. The analytical examination of the case of non-interacting particles (sparse concentration of grains) shows that in this case, the (quasi-)linearity of the Arai–Nagata diagrams is due to the presence of a plateau on the curves of the derivative dCRM/dpTRM (pTRM is partial thermoremanent magnetization) which emerges in a narrow spectrum of blocking temperatures. The results of the numerical experiments suggest that at a particle concentration of above 0.2% magnetostatic interaction leads to the practically full linearity of the Arai–Nagata diagram over a significant interval of the total spectrum of blocking temperatures for CRM. At the same time, on the remaining temperature interval, both the Arai–Nagata diagrams and the CRM(TRM) curves are substantially concave, indicating the lack of similarity between the spectra of blocking temperatures for CRM and TRM. The analysis of the empirical data revealed their resemblance, up to a certain point, to the results of simulation but at the same time clearly demonstrated the noticeable distinction between them, associated with the significant differences in the conditions of the numerical and laboratory experiments.

The results of processing synchronous records from two laser strainmeters, a broadband seismograph, a laser nanobarograph, and a laser meter of hydrospheric pressure variations are discussed. It is established that the sharp change in the atmospheric pressure, which was recorded by a laser nanobarograph, resulted in the generation of solitary waves in the hydrosphere detected by the laser meter of hydrosphere pressure variations. These waves were accompanied by intense deformational perturbations with periods of about 2–2.5 min observed by the laser strainmeters and broadband seismograph. The identification of this phenomenon as a meteotsunami is supported by the subsequent arrival of powerful 1.5-h oscillations in the zone of the location of instrumental complexes, which were recorded by the laser nanobarograph and laser strainmeter.