Tremor Energy Research Articles

Machine Learning-Based Classification of Rock Bursts in an Active Coal Mine Dominated by Non-Destructive Tremors

Rock bursts are dynamic phenomena in underground openings, causing damage to support and infrastructure, and are one of the main natural hazards in underground coal mines. The prediction of rock bursts is important for improving safety in mine openings. The hazard of rock bursts is correlated with seismic activity, but rock bursts are rare compared to non-destructive tremors. The five machine learning classifiers (multilayer perceptron, adaptive boosting, gradient boosting, K-nearest neighbors, and Gaussian naïve Bayes), along with an ensemble hard-voting classifier composed of these classifiers, were used to recognize rock bursts among the dominant non-destructive tremors. Machine learning models were trained and tested on ten sets of randomly selected data obtained from one of the active hard coal mines in the Upper Silesian Coal Basin, Poland. For each of the 627 cases in the database, 15 features representing geological, geomechanical, mining, and technical conditions in the opening as well as tremor energy and correlated peak particle velocity were determined. Geological and geomechanical parameters of the coal seams and surrounding rocks were aggregated into a single GEO index. The share of rock bursts in the database was only about 8.5%; therefore, the ADASYN balancing method, which addresses imbalanced datasets, was used. The ensemble hard-voting classifier most effectively classified rock bursts, with an average recall of 0.74.

Revisiting Seismic Energy of Shallow Tremors: Amplifications Due To Site and Propagation Path Effects Near the Nankai Trough

AbstractWe investigated the effects of the propagation path and site amplification of shallow tremors along the Nankai Trough. Using far‐field S‐wave propagation from intraslab earthquake data, the amplification factors at the DONET stations were 5–40 times against an inland outcrop rock site. Thick (∼5 km) sedimentary layers with VS of 0.6–2 km/s beneath DONET stations have been confirmed by seismological studies. To investigate the effects of thick sedimentary layers, we synthesized seismograms of shallow tremors and intraslab earthquakes at seafloor stations. The ratios of the maximum amplitudes from the synthetic intraslab seismograms between models with and without thick sedimentary layers were 1–2. This means that thin lower‐velocity (<0.6 km/s) sediments just below the stations primarily control the estimated large amplifications. Conversely, at near‐source (≤20 km) distances, 1‐order amplifications of seismic energies for a shallow tremor source can occur due to thick sedimentary layers. Multiple S‐wave reflections between the seafloor and plate interface are contaminated in tremor envelopes; consequently, seismic energy and duration are overestimated. If a shallow tremor occurs within underthrust sediments, the overestimation becomes stronger because of the invalid rigidity assumptions around the source region. After 1‐order corrections of seismic energies of shallow tremors along the Nankai Trough, the scaled energies of seismic slow earthquakes were 10−10–10−9 irrespective of the region and source depth. Hence, the physical mechanisms governing seismic slow earthquakes can be the same, irrespective of the region and source depth.

Detection of Coal Bust Risk in a Kilometer Depth Workface with Hard–Thick Roof Based on Active–Passive Seismic CT

Practice and theory research proved the “square effect” during longwall mining with hard–thick strata lying on the coal seam, which could cause severe underground pressure and even dynamic disasters, such as coal burst; therefore, it became a key area and stage that need special attention. The combined active–passive seismic computed tomography (CT) was introduced to detect the abutment stress concentration in the coal seam. The results of active–passive CT inversion show that the “square effect” appears as early as the workface ahead of the theoretical position of 50 m with a 100 m significant influencing zone, which provides a strong guarantee for accurate risk evaluation of coal burst. Precursor information before the “square effect” can be identified based on the everyday total energy of mining tremors, which had period peaks in this case. The everyday average energy of mining tremors indicates that the seismic type during the “square effect” stage belonged to a foreshock–mainshock pattern. The combination of the seismic events and CT can improve the accuracy of coal burst danger distinguishing notably. The research can provide worthwhile guidance for the monitoring and prevention of coal burst hazards in similar conditions.

The impact of tectonic activity on carbonate density-flow deposition along two sectors of the Apulia Carbonate Platform

ABSTRACTGeneration of thick megabreccias along carbonate platforms apparently relies on the establishment of overpressured zones in the margin and upper slope deposits (particularly during relative sea-level lowstands), but the main triggering mechanism is thought to be seismic tremors. Here, we present a detailed sedimentological analysis of carbonate density-flow deposits south and north of the Mattinata Fault, a major strike-slip fault zone in the Gargano Promontory (Italy). The analysis shows that in the southern sector the deposits of Albian–Cenomanian age (Monte S. Angelo Formation) are made up predominantly of thick and amalgamated debrites (megabreccias), whereas some 25 km to the north they are composed predominantly of prograding high-density turbidites. Moreover, detailed analysis of Maastrichtian slope deposits (Monte Acuto Limestones) from the southern sector shows that they make up a N–S-prograding system of coalesced lobes composed of high-density turbidites and subordinate debrites. We infer that preconditional factors (e.g., platform progradation, tectonic oversteepening, and high pore pressures in the margin and upper-slope deposits) for triggering the density flows varied along strike of the platform, but the main controlling factors were the activity of the prominent strike-slip Mattinata Fault and the propagation of tremor energy to its near- and far-field regions: large earthquakes triggered thick (up to 40 m) and amalgamated Albian–Cenomanian debrites in proximity (south of) to the fault, whereas the subdued effect of the tremors triggered thinner debrites (5–10 m) and rock falls in the far-field region north of the fault. Moreover, predominantly high-density turbidite deposits were emplaced in the far-field region during lower-magnitude earthquakes. During the Maastrichtian the thick succession of high-density turbidites and scattered thick debrites south of and adjacent to the Mattinata Fault may record an overall quiescent period of the fault. The results are of relevance for understanding the spatiotemporal distribution of density-flow deposition along carbonate platforms in tectonically active regions—in particular with respect to the activity of large strike-slip faults.

Cataloging Tectonic Tremor Energy Radiation in the Cascadia Subduction Zone

AbstractFor the past ∼12 years the Pacific Northwest Seismic Network has been automatically detecting and locating tectonic tremor across the Cascadia subduction zone, resulting in a catalog of more than 500,000 tremor epicenters to date, which has served as a valuable resource for tremor and slip research. This manuscript presents an updated methodology for routine tremor detection in Cascadia and a new catalog of over 180,000 tremor epicenters including amplitudes detected along the subduction zone margin from 2017 to 2021. The events are detected via cross‐correlation of continuous vertical envelope data of 128 stations from northern California to northern Vancouver Island. The modified approach results in less scatter and a 55% increase in detected epicenters than previously observed, as well as a newly identified tremor source offset updip from the main tremor and slip region at the southern edge of the subduction zone. Radiated seismic energy in the 1.5–5 Hz band is used to assign epicenters an energy magnitude (MeL), which is calibrated to the ML of local earthquakes. Southern Cascadia is most active, but the highest tremor energy rates occur in northern Cascadia. Tremor in central Cascadia is systematically weaker and less frequent. Individual epicenter magnitudes range from ∼0.5–2 and spatiotemporally cluster into 1,060 swarms with cumulative MeL ranging from ∼0.8 to 3.7. The swarms reflect underlying slow slip events and occur with an earthquake‐like energy distribution with a b value ∼1. Tremor epicenters, however, follow a tapered Gutenberg‐Richter distribution with high b values, suggesting individual tremor bursts and their constituent low‐frequency earthquakes are fault‐dimension limited.

Geomechanical analysis of location and conditions for mining-induced tremors in LGOM copper mines

This paper presents the results of the statistical analyses of rock mass seismicity associated with O/ZG Rudna exploitation and geomechanical analyses concerning the location and conditions of tremor occurrences in LGOM conditions, illustrated by the example of O/ZG Rudna. As part of the statistical analyses, the assessment of rock mass seismicity formation in O/ZG Rudna throughout the whole mine area in the years 2006–2015 is presented, the results of which were the basis for subsequent geo-mechanical analyses. Within the parameters of seismic activity, the analysis covered the number of recorded events, the total value of energy emission and the index of individual energy expenditure. The presented analyses also refer to the locations of tremor source epicentres in relation to the exploitation front, distinguished into low energy and high energy tremors located ahead of the exploitation front, in the area of opening-up works and gobs. These recent results were the starting point for research and calculations on geo-mechanical analyses. These numerical calculations using the finite element method (FEM) carried out the energy density distribution of elastic deformation in the vicinity of the exploitation front. FEM calculations were designed to establish the factors and conditions that determine the location of tremor sources and the mechanism of rock destruction. Both of these factors are directly related to the magnitude of the energy emitted during the tremor. Appropriate energy measurements of elastic deformation have been adopted to determine rock mass areas which are potentially threatened by tremor occurrences of varying energy. Measures of the energy density of shear and volumetric strain enable the determination of the nature of rock mass destruction in the vicinity of mine workings, which in turn gives the basis for linking these measurements with tremor energy and location relative to the exploitation front. The results of numerical computations were compared with the results of statistical analyses on the locations of tremor sources with different energies in relation to the exploitation front in O/ZG Rudna.

Wristbands Containing Accelerometers for Objective Arm Swing Analysis in Patients with Parkinson's Disease.

In patients with Parkinson’s disease (PD), arm swing changes are common, even in the early stages, and these changes are usually evaluated subjectively by an expert. In this article, hypothesize that arm swing changes can be detected using a low-cost, cloud-based, wearable, sensor system that incorporates triaxial accelerometers. The aim of this work is to develop a low-cost, assistive diagnostic tool for use in quantifying the arm swing kinematics of patients with PD. Ten patients with PD and 11 age-matched, healthy subjects are included in the study. Four feature extraction techniques were applied: (i) Asymmetry estimation based on root mean square (RMS) differences between arm movements; (ii) posterior–anterior phase and cycle regularity through autocorrelation; (iii) tremor energy, established using Fourier transform analysis; and (iv) signal complexity through the fractal dimension by wavelet analysis. The PD group showed significant (p < 0.05) reductions in arm swing RMS values, higher arm swing asymmetry, higher anterior–posterior phase regularities, greater “high energy frequency” signals, and higher complexity in their XZ plane signals. Therefore, the novel, portable system provides a reliable means to support clinical practice in PD assessment.

К оценке протяженности по латерали участков наличия углеводородов по данным сейсмической локации нефти и газа (СЛОНГ)

In the method of seismic location of oil and gas (SLONG), intended for predicting the oil and gas prospects of objects based on the data of seismic exploration method CDP-2D, the length of the laterally allocated sections of the presence of hydrocarbons is determined by statistical processing of all graphs of the energy distribution by depth of micro tremors. However, in this case, the results of processing depend on the repetition factor of impulse accumulations of fluctuations used. Therefore it is proposed to use a different approach to determine the length of the lateral sections of the presence of HC based on the processing of micro tremors recorded during CDP-2D, according to the method proposed by G.V. Vedernikov, E.A. Khagoev and T.I. Chichinina. As a result of applying this technique, it was found that all oil and gas fields are accompanied by anomalies in the micro tremors field in terms of energy and spectral characteristics of vibrations. Not stopping on the possibility of solving the inverse problem, we only note that according to this provision, the presence of a deposit should lead to anomalies in the micro tremors field and, in particular, to an increase in the energy oscillation. Therefore, if the presence of a deposit is established in any way, then we should expect the appearance of a section with an increased energy oscillation, which can be used to estimate the length of the deposit laterally. The fact of the presence of a deposit can be established by the results of processing the same CDP-2D profile using SLONG technology. If a positive SLONG result is obtained, a section with an increased energy of micro tremors should appear on the corresponding section of the profile, which will lead to the solution of the problem. Key words: Location, microtremors, length, anomaly.

Factors Influencing Rock Burst Hazard in Deep Copper Ore Mine, SW Poland

In underground mines of copper ores, which are situated in Lower Silesia in SW Poland, the most common and dangerous threats pose seismic tremors and rock bursts. Copper ore exploitation is carried out in three mines, which are owned by KGHM Polish Copper JSC, i.e. Lubin mine, Rudna mine and Polkowice-Sieroszowice mine. Despite many rock burst preventive operations carried out over several decades of mining activity and aimed at counteracting seismic dynamic events, these phenomena have not been eliminated. The applied rock burst prevention measures only limit or mitigate the effects of seismic events. In mining, a concept of seismicity is used, which is defined as the tendency of an intact rock mass to seismic tremors induced by mining work in an area that was previously aseismic. Tremors and their results i.e. rock bursts affect not only excavations and underground infrastructure, but also the terrain surface. In the KGHM’s mines, seismic activity is monitored by the Mining Geophysics Stations. The number, coordinates and energy of tremors and rock bursts are registered, which helps determine the rock mass reaction to the adopted system and operation technology. The main purpose of the paper is to analyse seismic dynamic phenomena damaging mining excavations, i.e. rock bursts, in the Lubin mine, which took place from the beginning of the mine’s operation in 1975 to 2016 (over 41 years) and to identify and investigate geological and mining factors (parameters) facilitating the growth of seismic and rock burst hazards. The following factors (parameters) favourable for the occurrence of dynamic phenomena with damaging effects in excavations were taken into consideration: the seismic activity of the rock mass (spontaneous and provoked tremors), the deposit depth and thickness, geomechanical properties of rocks, exploitation systems, the method of elimination of mined-out space, the occurrence of gobs, tectonic disturbances and the life time of excavations. The results of the observation of selected parameters made it possible to determine the causes of rock bursts as well as to evaluate the impact of the exploitation system including the technology and rock burst prevention on seismic and rock burst hazard. Moreover, seismic activity of the mining division with the highest number and energy of rock bursts was analysed. The effectiveness of rock burst prevention measures used in this division was assessed too. The results of the analyses indicated some interdependencies between factors that may affect the phenomena discussed.

Passive Seismic Tomography as a Tool of Rock Burst Hazard Prognosis in Copper Ore Mine in Poland

In Poland, underground mines of copper ores, which belong to KGHM Polish Copper JSC, have been struggling with seismic dynamic events such as tremors and rock bursts since almost the first years of exploitation i.e. the 70s of the twentieth century. Mining activities infringe the original stress balance and make the rock mass accumulate energy and then release it, which triggers seismic hazard even far away from a tremor epicentre. Therefore, prediction of the position, time and energy of tremors plays a significant role in mining operation especially in work safety. For this purpose, many observation methods including seismology, seismic, geotechnical-geological monitoring, are used; unfortunately, most of them help describe the state of the rock mass after but not prior to the occurrence of the seismic phenomena. Only passive seismic tomography is promising since it can be used to forecast, to some extent, the location of places of seismic energy excessive accumulation. In this method, on the basis of seismic events recorded in a given period, zones of high and low seismic wave velocity are determined (calculated), which in the near future may pose areas of increased seismic activity. The phenomenon of the increase of seismic longitudinal wave velocity with the increase of stress in rocks makes the ground of tomography calculations. The prime purpose of the paper is to assess passive seismic tomography as a means for forecasting and evaluation of seismic and rock burst hazard. To accomplish this, the analysis of seismic activity and archival seismic tomography results (seismic wave velocity zones and seismic anomaly zones) with reference to seismic phenomena, their energy, number and location were carried out. On the basis of obtained the results, the effectiveness of seismic hazard forecast with the use of passive seismic tomography was assessed. The research was carried out for one mining division of the Polkowice-Sieroszowice mine and covered ten years. This division was selected due to its high seismic activity and the permanent use of the passive seismic tomography to assess the seismic risk. Linear correlation and determination coefficients between seismic activity characteristics and seismic anomaly as well as longitudinal wave velocity were calculated. It was found that in the study area the effectiveness of passive seismic tomography in forecasting the seismic hazard is relatively satisfying since about half of the tremors were located within zones of high seismic activity (substantial velocity of P-waves and seismic positive anomalies)..

The ratio of response spectra from seismic-type free-field and building foundation vibrations: the influence of rockburst parameters and simple models of kinematic soil-structure interaction

Mining-related seismicity is a significant problem in regions with the exploitation in underground mines. Despite the fact that mining tremors result from human activity and are classified as so-called paraseismic shocks, as with earthquakes, they are random events. Moreover, these rockbursts could cause significant damage to surface structures, including buildings. This paper deals with the analysis of experimentally obtained results in terms of the differences between the mine-induced vibrations described by the response spectra from the free-field near a given building and the simultaneously recorded vibrations in the building foundations. The influences of epicentral distance, mining tremor energy and the value of peak ground acceleration on the curves of free-field—foundation response spectra ratio were studied. The impact of the type of building on the transmission of response spectra from the free-field vibrations to the building foundations was also analysed for three types of apartment buildings (low-rise, medium-rise, high-rise). The usefulness of the approximate models of the phenomenon of soil-structure interaction during earthquakes proposed in the literature is also estimated in this paper in specific instances of mining tremors. Furthermore, the study presents original, simple, empirical models for the evaluation of the differences in the response spectra originating from free-field and building foundation vibrations in the mining region.

Detection of small crustal deformation caused by slow slip events in southwest Japan using GNSS and tremor data

We stacked daily Global Navigation Satellite System (GNSS) displacement increments in southwest Japan to detect the cumulative crustal deformation accompanying non-volcanic low-frequency tremors from April 1, 2004 to December 31, 2009, which are difficult to identify for individual slow slip events (SSEs). We successfully detected the crustal deformation associated with the tectonic stress releases coincident with tremor activity, which was larger than that caused by short-term SSEs detected in previous studies. To investigate the characteristics of the detected crustal deformation, we estimated the parameters of a rectangular fault model in segments along the Nankai Trough using a non-linear inversion method. Consequently, we obtained results that were concordant with those of previous studies and positive linear correlations between the moment and tremor energy in some segments. The linear regression slopes differed, reflecting the fact that the excitation efficiency of the tremors resulting from slow slip was different for each segment. Our results suggest that tremor activity serves as a proxy for SSEs, reflecting the different characteristics of SSEs in segments.

Temporal Changes of Seismic Velocity Caused by Volcanic Activity at Mt. Etna Revealed by the Autocorrelation of Ambient Seismic Noise

On active volcanoes, ambient noise-based seismic interferometry, able to detect very slight variations in seismic velocity associated with magma transport towards the surface, can be a very useful monitoring tool. In this work, we performed the autocorrelation of ambient seismic noise recorded at Mt. Etna volcano, by three stations located close to the active summit craters, during April 2013 - October 2014. Such an interval was chosen because of the number and variety of eruptions. The method implemented to perform autocorrelation was the phase cross-correlation, which does not require normalization of the signals. The detected seismic velocity variations were very consistent for all three stations throughout the study period, mainly ranging between 0.3 and -0.2%, and were time-related to both sequences of paroxysmal eruptions and more effusive activities. In particular, we observed seismic velocity decreases accompanying paroxysmal eruptions, suggesting an intense pressurization within the plumbing system, which created an area of extensional strain with crack openings. It is worth noting that classical cross-station approach failed to detect seismic velocity changes related to volcano activity. In addition, seismic velocity variations over time were integrated with ground deformation data recorded by GPS stations and volcanic tremor centroid locations. Finally, we showed that, although the investigated frequency band (1-2 Hz) contains most of the volcanic tremor energy, our results did not indicate a particular contamination of seismic velocity variation measurements by variations of tremor sources.

Nature and Energy of Earthquakes or Seismology for Dummies

The question of the origin of earthquakes is still not amenable to solution, and geophysicists, having guilty glances, only shrug their shoulders. Time goes by, the Earth flies along its orbit in the milk of the Milky Way, but people still suffer from seismic disasters. The problems of seismologists are particularly acute in simulating the occurrence of earthquake foci and forecasting these terrible phenomena. Finally, the secret of the dungeon made seismologists stop in their hopeless race for success, look around and wonder: what have they studied over the past 100 years if there is still no clear and consistent theory of the origin of earthquakes? Doubts about the results of their work penetrated the world of ordinary people, and it became clear that explaining the process of earthquakes, the scientists wandered into such a jungle that they got lost. As a result, it turned out that the fruit of the era of the classical interpretation of earthquakes, developed by the patriarch of seismology Mr. Reid, turned out to be a deaf dead end. Moreover, it turned out that the theory of elastic deformation of Raid tectonic plates contradicts the fundamental laws of physics [4] and cannot explain the most important thing - where the energy of tremors is taken in the earth's crust and how the battery of earthquakes works. The purpose of this paper is to describe the theory of earthquakes not for seismologists; we no longer have hope for them, but for ordinary people. Moreover, we want to do it in an ordinary language, so that all people far from geophysics would understand what an earthquake is and where nature takes energy for such disasters. We want people to say when mentioning the mysteries of seismology - a piece of cake!

Regional seismic activity in relation to tectonic structure in the PGG S.A. coal mines

The article presents seismological analysis in the mines of Polska Grupa Górnicza S.A. (PGG S.A.) in relation with the geological and tectonic structure of the exploited rock mass. There are grounds for seismic activity, to be associated with the structural features of the rock mass in which underground exploitation is carried out. The analysis included high-energy tremors (with energy E &gt; 105 J), which occurred in 2018. High energy tremors can cause mining damage on the surface. In 2018, three structural units out of five covering the Upper Silesian Coal Basin formed a rock formation coal mine of PGG S.A. The parameter analyzed was unit energy expenditure (JWE). It reflects the participation of two important pieces of information: total energy of tremors and mining of coal in a given period. The analysis shows that in 2018 JWE fell in total at PGG. However, it grew in the main trough, which translates into an increase in the risk of induced seismicity. Due to geological features, the area of exploitation covering the main trough, induces high-energy tremors that can cause effects on the surface. In other structural units, in 2018, JWE drops.

Spatiotemporal Variation of Tectonic Tremor Activity Before the Tohoku‐Oki Earthquake

AbstractA slow slip event (SSE) and tectonic tremors occurred approximately 1.5 month prior to the occurrence of the 2011 Tohoku‐Oki earthquake near the Japan Trench. Although we cannot completely rule out other sources of noise near the observation site, slow earthquakes would demonstrate the nucleation of a fast slip event from prior slow earthquake activity. Here we report on tectonic tremor activity detected from short‐period ocean‐bottom seismometer (OBS) data with a modified frequency scanning method that allows robust tectonic tremor detection by incorporating information from multiple frequency passbands in order to suppress false detections. We have identified at least five tectonic tremor sequences on the OBS records from the end of January 2011 to just before the occurrence of the Tohoku‐Oki earthquake in March 2011. To reveal the spatial distributions of tectonic tremors before the Tohoku‐Oki earthquake, we then calculated tremor energy, with corrected site amplification, from the identified tectonic tremor time window at each OBS that detected tremors. Possible sources of tremors were distributed in trenchward side of the SSE fault prior to the main shock. These tremors could be modulated by SSE to take into account consistent timing between tremor and SSE term, and consistency of spatial locations between estimated tremor sources and SSE faults. This spatiotemporal pattern in tectonic tremor activity demonstrates a significant separation of occurrence sources between tectonic tremors and regular earthquakes.

Ground-motion prediction equation and site effect characterization for the central area of the Main Syncline, Upper Silesia Coal Basin, Poland

Abstract The aim of the study was to find the best model of ground-motion prediction equation (GMPE) forecasting peak ground acceleration (PGA) caused by induced seismicity. The maximum values of PGA on the surface are a major seismic threat for the infrastructure, especially in the highly urbanized areas, such is the Upper Silesian Metropolitan Area. The forecasting equations were estimated based on the values of PGA, epicenter distances and mining tremor energy registered by 14 surface seismometer stations located in the central area of the Main Syncline of the Upper Silesia Coal Basin. Data were collected within the period from January 2010 to December 2016, and the total number of seismic events used in the calculations was 15 541. The final model predicted the PGA values and amplification coefficients representing the characteristics of the site effects under seismometer stations.

Insights into lava fountain eruptions at Mt. Etna by improved source location of the volcanic tremor

We analysed volcanic tremor recorded during ten lava fountain eruptions at Mount Etna volcano over the second half of 2011. The seis- mic signal, recorded by a network of 19 broadband stations, was corrected for site effects. The site amplification factors obtained for all the seismic stations were calculated using 18 regional earthquakes. To quantitatively estimate the goodness of the site correction, the vol- canic tremor source locations obtained by using site corrections were compared with those performed without such corrections. The seismic signal was filtered in two different frequency bands before applying correction: (i) the band 1-2 Hz, which contains most of the tremor energy, and (ii) the band 5-10 Hz, in which, likely due to scattering phenomena, the assumption of isotropic radiation behind the volcanic tremor source location method is valid. The results revealed that the seismic signal correction for site effects improved the tremor location results. Such improved tremor locations, together with volcanological and geodetic data, allowed us to identify two dis- tinct periods characterised by different tremor locations during lava fountains (July - August 20 and August 20 - November 15). Such differences were probably due to magma recharge phenomena, taking place during the former period.

Spatiotemporal Variations in Slow Earthquakes Along the Mexican Subduction Zone

AbstractSlow earthquakes in Mexico have been investigated independently in different areas. Here we review differences in tremor behavior and slow slip events along the entire subduction zone to improve our understanding of its segmentation. Some similarities are observed between the Guerrero and Oaxaca areas. By combining our improved tremor detection capabilities with previous results, we suggest that there is no gap in tremor between Guerrero and Oaxaca. However, some differences between Michoacan and Guerrero are seen (e.g., SSE magnitude, tremor zone width, and tremor rate), suggesting that these two areas behave differently. Tremor initiation shows clear tidal sensitivity along the entire subduction zone. Tremor in Guerrero is sensitive to small tidal normal stress as well as shear stress, suggesting that the subduction plane may include local variations in dip. Estimation of the energy rate shows similar values along the subduction zone interface. The scaled tremor energy estimates are similar to those calculated in Nankai and Cascadia, suggesting a common mechanism. Along‐strike differences in slow deformation may be related to variations in the subduction interface that yield different geometrical and temperature profiles.

Geomechanical analysis of location and conditions for mining-induced tremors in LGOM copper mines

Abstract This paper presents the results of the statistical analyses of rock mass seismicity associated with O/ZG Rudna exploitation and geomechanical analyses concerning the location and conditions of tremor occurrences in LGOM conditions, illustrated by the example of O/ZG Rudna. As part of the statistical analyses, the assessment of rock mass seismicity formation in O/ZG Rudna throughout the whole mine area in the years 2006–2015 is presented, the results of which were the basis for subsequent geo-mechanical analyses. Within the parameters of seismic activity, the analysis covered the number of recorded events, the total value of energy emission and the index of individual energy expenditure. The presented analyses also refer to the locations of tremor source epicentres in relation to the exploitation front, distinguished into low energy and high energy tremors located ahead of the exploitation front, in the area of opening-up works and gobs. These recent results were the starting point for research and calculations on geo-mechanical analyses. These numerical calculations using the finite element method (FEM) carried out the energy density distribution of elastic deformation in the vicinity of the exploitation front. FEM calculations were designed to establish the factors and conditions that determine the location of tremor sources and the mechanism of rock destruction. Both of these factors are directly related to the magnitude of the energy emitted during the tremor. Appropriate energy measurements of elastic deformation have been adopted to determine rock mass areas which are potentially threatened by tremor occurrences of varying energy. Measures of the energy density of shear and volumetric strain enable the determination of the nature of rock mass destruction in the vicinity of mine workings, which in turn gives the basis for linking these measurements with tremor energy and location relative to the exploitation front. The results of numerical computations were compared with the results of statistical analyses on the locations of tremor sources with different energies in relation to the exploitation front in O/ZG Rudna.