The authors analyze weak seismic activity at the Korobkovo iron ore deposit in the area of the Kursk Magnetic Anomaly. A sensing system in use enabled recording seismic events with a magnitude from –2.5 to –1.4 induced by a large-scale blast. Localization of hypocenteres was accurate to ∼50 m. The most of origins of the recorded events occurred in the neighborhood of a faulting zone across the zone of mining, and at the interface of bed series. The values of a seismic moment of the events are within of two orders of magnitude 10^5-10^7 N · m at an angular origin frequency of 70–600 Hz. The estimated seismic energy ranges from 0.0006 to 1 J. The reduced seismic energy values from 2·10^-9 to 2·10^-7 J/(N · m) and the low velocities allow categorizing the recorded events as slow earthquakes.

The article presents a new method of classifying acoustic and microseismic emission (KLASI-k), which analyzes waveform parameters (the rise time amplitude RA , average frequency AF , and the waveform index WI ). The method is based on k -means clustering, which makes it possible to separate subsets of events differing in scaled seismic energy (the ratio of emitted seismic energy to released seismic moment) and source duration. In classifying seismic events, there is the fundamental possibility of using the source parameters (seismic energy E s , seismic moment M 0 , and corner frequency f 0 ) as the features of the KLASI-k algorithm. Good correspondence is observed between the classified subsets of events in the transition from waveform parameters { RA , AF , WI } to source parameters { E s , M 0 , f 0 }. The KLASI-k method was applied to the data on mining seismicity induced by two ripple-fired blasts in the Gubkin Mine of the KMAruda Mining Enterprise at the Korobkovskoe iron ore deposit. The analyzed catalogs include 77 microevents recorded after the blast on July 6, 2019 and 259 microevents after the blast on October 24, 2020. Applying the KLASI-k method has made it possible to separate two subsets in the seismic catalogs. The events in the first subset show a scaled seismic energy ( E s / M 0 ) higher than 10 –7 J/(N m), while those in the second subset, lower than 10 –7 J/(N m). The first type of events have a smaller source duration than those of the second type; the released seismic moment is the same.

—A conceptual state of the art review of the research on fault zone resistance to shear is presented. Recent works are analyzed in the context of the approaches formulated in the authors’ presentations made at the Sixth Conference “Triggering Effects in Geosystems.” The analysis of the results obtained in the last two or three decades by different research teams shows that frictional properties of a principal slip zone gouge play a determining role for rupture initiation and propagation. Upgrading the methods for processing weak seismicity data to estimate the “slowness” of microearthquakes confined to a fault zone may provide new approaches in fault zone monitoring to derive indirect information on the material composition of a fault slip zone and, thus, on its seismogenic potential. At present, such methods can be useful in the problems of damage reduction from man-made earthquakes.

—A laboratory setup was constructed in IDG RAS to investigate the process of shearing the contact of rock blocks of one-meter scale. It was used to investigate deformation processes in a fault with a heterogeneous structure of the sliding interface, which contained strong contact patches—analogs of the asperity in the well-known model of Hiroo Kanamori (Kanamori and Stewart, 1978). It is shown that when a large slip occurs, the rupture, which starts in the zone of maximal deficit of interblock displacement, cuts the segments of the fault with lower effective strength, the latter being decreased in previous deformation events. Those previous events may be “slow” slips with low seismic efficiency. In nature the events that “prepare” the fault interface for a large slip may be smaller earthquakes—foreshocks, or they can be either low frequency earthquakes or slow slip events, both can hardly be detected in seismic records. Thereupon a promising diagnostic indication is the shift of the spectrum of ambient seismic noise to lower frequencies caused by the decrease of fault stiffness.

Frictional slip along faults and large fractures is the predominant mechanism behind crustal earthquakes. Laboratory experiments in formulating a slider model are an effective tool for obtaining information about the origination patterns of laboratory earthquakes. This paper presents the results of laboratory acoustic emission (AE) experiments to stud various modes of frictional slip of a model crack and establish a unified evolutionary law for the preparation of fast and slow slip events based on synchronous continuous recording of AE and cumulative displacement of blocks. A new parameter for the state of a crack is introduced, generalized deficit, which makes it possible to monitor the stage of its loading cycle with high accuracy. Generalized deficit takes into account variations in the AE energy flux and displacement of the crack's edges, thereby taking into account the processes occurring at the micro- and macrolevels, respectively. The rate of change in generalized deficit has a single evolutionary pattern for all occurring slip modes and can be used as an indicator for a crack's transition to the limiting state. In the experiments, a functional relationship was established between the frictional strength of a crack, its deformation rate, and the flux of AE energy, which indicates the relatedness of processes occurring at the micro- and macrolevels.

Abstract—The paper introduces a new, unique for Russia, meter-scale laboratory setup created in the Institute of Geosphere Dynamics of the Russian Academy of Sciences (IDG RAS) to study the development of different sliding regimes on rock discontinuities. The experimental procedure is described and the results of the first series of tests aimed at studying the formation of different sliding regimes on rock faults are presented. The laboratory fault was a loaded contact of two 75-cm long blocks made of diabase. The fault was filled with granular material (a fault gouge). Normal stresses on the fault can reach 10 MPa. By varying fault gouge composition and loading rate, we reproduced a wide range of sliding regimes: sliding with constant velocity, regular stick-slip, and aperiodic slow slip episodes. It is shown that a variation in the loading rate can cause a significant change in the sliding regime. Intense frictional crushing of gouge grains is detected in the experiments at relatively low normal pressure of 2 MPa. In the case of high-amplitude stick-slip, besides crushing of the gouge material, also structural phase transformations of quartz grains corresponding to a local temperature increase up to 700°C are revealed. A possible set of the problems related to deformation processes in seismogenic fault zones that can be addressed by modeling on such setups—the pre-seismic stage of inelastic behavior of the main fault zone at critical stress—is outlined.

Abstract—Granular media determine the dynamics of many natural systems including faults in the Earth’s crust. The paper addresses the laboratory study of shear deformation of a model fault simulated by a layer of granular material located between rock blocks. A model fault is a complex dynamic system characterized by the presence of bifurcations and fast and slow slips may take turn aperiodically during deformation. The sliding of the rock blocks is accompanied by the generation of acoustic emission pulses (AEs) which are identified based on the Akaike information criterion. The dynamics of AEs reflects the evolution of mechanical properties of the fault. In the flow of AEs, the subsets with different rise time/amplitude values (RA-values) and different scaling relations are identified. Applying the random forest machine learning algorithm to the analysis of AE catalogue demonstrates the possibility of determining the velocity of fault sliding and the time to both fast and slow slips. The nucleation of a certain slip mode is predetermined by the self-organization processes taking place in the central zone of a fault, and the characteristics of the AE reflect these processes. The proposed approach to the estimation of fault sliding parameters can be promising for the design of new methods for monitoring stressed massifs at mining.

Данная работа посвящена исследованию акустической эмиссии (АЭ), сопровождающей эволюцию модельного разлома, центральная зона которого заполнена гранулированным материалом. Широкий спектр режимов скольжения разлома был реализован благодаря изменению вещественного состава и гранулометрии заполнителя. В работе представлен новый метод количественной категоризация АЭ, основанный на анализе параметра волновой формы. В потоке АЭ, сопровождающем относительное смещение блоков, можно выделить две моды АЭ. Выявлены систематическое снижение b-value моды II при зарождении как быстрых, так и медленных динамических событий, в то же время b-value моды I характеризуется случайными вариациями.

Dynamics of granular media is the key to understanding behavior of many natural systems. In this work we concentrate on studying regularities of deformation of a gouge-filled fault. Confined granular layer – model fault – subjected to an external stress may display sudden slip owing to rearrangement of the granular layer. In nature fast slip along a fault results in an earthquake. To understand fault behavior better, we have conducted a comprehensive analysis of acoustic emission (AE) data that accompany stick-slip in granular media. Here we reveal and trace the emergence of two populations of AE. The first one is characterized by a waveform with a harsh onset, while the second one exhibits a gradual amplitude rise and a tremor-like waveform. During a regular stick-slip the statistical properties of the first population remains intact. The second one is very sensitive to alterations of stress conditions, and its scaling parameters correlate with the change of mechanical characteristics of the fault. Probably, AE populations were identified corresponding to two gouge-filled fault subsystems – a load-bearing granular network and an ensemble of relatively unloaded grains in the granular layer. The detected regularities point to a compound self-organization processes in fault zones and suggest that the final stage of earthquake preparation can be revealed in analyzing the scaling characteristics of seismic-acoustic data.

The new method is proposed for interpreting data of acoustic emission during initiation and growth of dynamic breakaways. The method is based on the analysis of wave form of the emitted acoustic pulses. Clustering of the pulses by the wave form criterion shows that in the localization zone of strains different-scale processes described with various scaling relations take place. All classes of acoustic pulses obey the power-series amplitude-frequency distribution. The sharp-arrival acoustic pulses posses unaltered scaling relations in the period of nucleation and growth of dynamic breakaways whereas the smooth-arrival pulses demonstrate the nonlinear change in the scaling relations. At the final stage of the dynamic breakaway formation, the proportion and amplitude of acoustic pulses with smooth arrival increase.