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Gas extraction from the Groningen gas field resulted in significant induced seismicity. We analyze the magnitude‐frequency distribution of these earthquakes in space, time and in view of stress changes calculated based on gas production and reservoir properties. Previous studies suggested variations related to reservoir geometry and stress. While we confirm the spatial variations, we do not detect a clear sensitivity of b‐value to Coulomb stress changes. However, we find that b‐value correlates positively with the rate of Coulomb stress changes. This correlation is statistically significant and robust to uncertainties related to stress change calculation. This study thus points to a possible influence of stress change rate on the probability of the magnitude of induced earthquakes. Plain Language Summary: Gas extraction from an underground reservoir in the Netherlands has induced significant seismicity. We analyze how stress changes and the rate of stress changes influence the magnitude of these earthquakes. We find that more smaller earthquakes tend to occur at higher stress change rates. Earthquakes triggered at a lower stress change rate may thus grow to larger magnitudes than those triggered at high stress change rate. This observation is statistically significant and independent of the method used to calculate stress change. Key Points: We report a positive correlation between the b‐value and the rate of Coulomb stress change of induced earthquakes in GroningenThis trend is statistically significant and robust to changes in the mechanical model used to calculate the stress changesWe interpret earthquake growth inhibition through a decrease of nucleation lengths at high stress change rates [ABSTRACT FROM AUTHOR]

Seismic activity in Aswan is influenced by the complex interactions of tectonic plates, the accumulation of stress, and the presence of geological fault systems. It revealed that epicenters are well distributed along four fault segments in a conjugate pattern, indicating a prominent E-W compressional stress. This research aims to explore the characteristics of seismicity and seismotectonics, with a focus on assessing their implications for risk reduction and disaster management in this densely populated region. A data review from the Egyptian National Seismological Network (ENSN) identified 464 earthquakes occurred between 2000 and 2021, with local magnitudes ranging from 0.3 to 4.4, and depths up to 25 km. The calculated Gutenberg-Richter b-value is approximately 0.87 ± 0.05, indicating a gradual stress accumulation. The current analysis shows a more consistent level of moderate seismic activity, unlike previous studies in Aswan region that reported a wide range of b-values from 0.554 to 1.07. This suggests that while earlier research captured a wider range of seismic behaviors, recent data indicates a stabilization in earthquake frequency and intensity. Additionally, the fractal dimension (Dc) calculated at 1.57 ± 0.04 shows an intermediate level of complexity and reflecting a clustering pattern of earthquakes. The variations in the b-value with different magnitudes and depths signify the involvement of active smaller faults, responsible for earthquakes up to magnitude 2.2, which then transition to fractured zones inducing earthquakes up to magnitude 2.5. This transition is followed by a decline in seismic activity, indicating regions that are potentially more likely to experience larger earthquakes. Moreover, stress disparities at various depths contribute to smaller earthquakes within the 5-10 km depth range. Return period analysis suggests that the earthquakes of magnitude 3.7 or higher are expected to occur approximately once every decade in Aswan. These findings are of utmost importance for earthquake risk reduction, hazard assessment, and the sustainable development of Aswan area. [ABSTRACT FROM AUTHOR]

Rock-burst prediction is an important issue faced by deep coal mining operations and holds significant significance for ensuring the safety of workers and the sustainable development of mines. This study investigates the crack-propagation behavior of coal and magnetite under uniaxial compression, introduces the characteristic parameter γ within the framework of the flicker noise spectrum (FNS), analyzes the trends in the variation of acoustic emission (AE) b-value and γ-value, and explores the relationship between these two parameters. Experimental results reveal that the proportion of tensile cracks is significantly higher than shear cracks during the loading process, shear failure becomes the main factor as the specimen approaches failure. Both the b-value and γ-value are proven to effectively reflect the damage evolution process of coal and magnetite and exhibit noticeable changes prior to collapse. Specifically, the peak γ-value serves as a precursor indicator for coal and magnetite collapse. Furthermore, this study uncovers a negative linear relationship between the b-value and γ-value. By delving into the feature parameter γ of AE signals, this research offers a new perspective and approach for predicting the instability of coal and magnetite formations and monitoring dynamic hazards. It contributes to a better understanding of the damage evolution process of coal and magnetite formations and provides valuable guidance and reference for preventing and mitigating dynamic hazards associated with coal and magnetite. Highlights: A novel monitoring indicator for coal and magnetite dynamic hazards, known as the γ-value, was introduced within the framework of the Flicker Noise Spectroscopy method. The study revealed a notable negative linear correlation between the b-value and the γ-value derived from acoustic emission signals. Experimental and on-site data have demonstrated that b-value and γ-value can effectively prevent rock burst. [ABSTRACT FROM AUTHOR]

The Red Sea region, situated between the Arabian and African Plates, experiences significant seismic activity due to its tectonic dynamics, with earthquakes ranging from minor to potentially destructive events. This study aims to develop smoothed seismicity models for the region by using an enhanced seismic catalog specific to the Red Sea. This facilitates a detailed spatial and temporal analysis of seismic events, focusing on seismic source characterization essential for probabilistic seismic hazard assessments. A rigorous declustering method excludes foreshocks and aftershocks, focusing on independent seismic events. The analysis uses a spatial grid (0.1 ∘ cells in latitude and longitude) to determine seismic event rates, which are then refined using various smoothing techniques. Special attention is given to seismic activity within 0–35 kms of depth, leading to distinct rate models that inform urban development and seismic hazard mitigation strategies in the Red Sea area. These models are crucial for improving resilience, safety, and informed decision-making for urban planning and disaster preparedness, addressing the challenges posed by the region's tectonic and seismic complexities. [ABSTRACT FROM AUTHOR]

This study explores the b-value variations prior to M ≥ 6.0 earthquakes in Taiwan, examining their potential as earthquake precursors. Focusing on the 2018 Hualien earthquake and others between 1999 and 2021, we found that many large earthquakes occurred in areas with low b-values a year prior, although there were no significant temporal changes near the epicenters. However, for more accurate earthquake precursors, incorporating additional factors is recommended to minimize uncertainty. [ABSTRACT FROM AUTHOR]

Purpose: Demonstrate the feasibility and evaluate the performance of single‐shot diffusion trace‐weighted radial echo planar spectroscopic imaging (Trace DW‐REPSI) for quantifying the trace ADC in phantom and in vivo using a 3T clinical scanner. Theory and Methods: Trace DW‐REPSI datasets were acquired in 10 phantom and 10 healthy volunteers, with a maximum b‐value of 1601 s/mm2 and diffusion time of 10.75 ms. The self‐navigation properties of radial acquisitions were used for corrections of shot‐to‐shot phase and frequency shift fluctuations of the raw data. In vivo trace ADCs of total NAA (tNAA), total creatine (tCr), and total choline (tCho) extrapolated to pure gray and white matter fractions were compared, as well as trace ADCs estimated in voxels within white or gray matter‐dominant regions. Results: Trace ADCs in phantom show excellent agreement with reported values, and in vivo ADCs agree well with the expected differences between gray and white matter. For tNAA, tCr, and tCho, the trace ADCs extrapolated to pure gray and white matter ranged from 0.18–0.27 and 0.26–0.38 μm2/ms, respectively. In sets of gray and white matter‐dominant voxels, the values ranged from 0.21 to 0.27 and 0.24 to 0.31 μm2/ms, respectively. The overestimated trace ADCs from this sequence can be attributed to the short diffusion time. Conclusion: This study presents the first demonstration of the single‐shot diffusion trace‐weighted spectroscopic imaging sequence using radial echo planar trajectories. The Trace DW‐REPSI sequence could provide an estimate of the trace ADC in a much shorter scan time compared to conventional approaches that require three separate measurements. [ABSTRACT FROM AUTHOR]

The Gutenberg-Richter (GR) and Gumbel methodologies were applied to analyze seismic activity parameters (specifically, b-values) in the central Himalaya region, covering latitudes between 26° and 31° E and longitudes between 80° and 88° N during the time frame from 1964 to 2021. Additionally, Gumbel's techniques were utilized to gauge the frequency of occurrence for moderate-tolargemagnitude earthquakes. Within a circular area with a diameter of 250 kilometers, we determined the b-values for the primary source regions of the ten past major earthquakes. The estimated b-value based on GR relation varies from 0.82±0.06 to 1.02±0.10, whereas the b-value based on Gumbel's method ranges from 0.86±0.30 to 1.88±0.32. The results indicate that Gumbel's distribution approach is effective for regions where large earthquake data is available, and the b-values, estimated from the GR method, are found to be more appropriate for the tectonics of the source regions. The Lo-Mustang earthquake region and Bajhang earthquake regions are identified as probable regions for the occurrence of a large earthquake in less than 100 years, which also supports the existence of a western Nepal seismic gap between Uttarakhand, India, and central Nepal. The findings describe the seismic risk in the epicenters of previous earthquakes in terms of b-value, recurrence intervals, and earthquake probability for each magnitude. [ABSTRACT FROM AUTHOR]

For earthquakes (M ≥ 4.0) occurring along and around the East Anatolian fault zone and the Dead Sea fault zone within ten years immediately before the MW7.8 Gaziantep earthquake, Türkiye, of February 6, 2023, we explored the correlation between seismicity and the earth's rotation. We statistically evaluated the correlation using the Schuster's test. The results are quantitatively assessed by a p-value. We found a clear downward trend in the p-values from early 2020 to late 2022 in the studied region. We also obtained a spatial distribution of the p-values showing a low p-value area near the northeastern end of the aftershock zone. Although the stress induced by the rotation of the earth is very weak, it could control the earthquake occurrence when the focal medium is loaded to the critical state to release a large earthquake. The decrease in the b-value in the Gutenberg–Richter (G-R) relation is considered in the form of the tectonic stress increase in the crust. We investigated the b-value as a function of time in the study region. We found that the b-value had decreased for about eleven years before the p-value started to decrease, with a relative reduction of 57%. Therefore, the result of the lower p-values obtained in the present study infers that the earthquakes were dominated by the earth's rotation prior to the MW7.8 Türkiye earthquake due to a critical state of the focal region.

Abstract This study explores the b-value variations prior to M ≥ 6.0 earthquakes in Taiwan, examining their potential as earthquake precursors. Focusing on the 2018 Hualien earthquake and others between 1999 and 2021, we found that many large earthquakes occurred in areas with low b-values a year prior, although there were no significant temporal changes near the epicenters. However, for more accurate earthquake precursors, incorporating additional factors is recommended to minimize uncertainty. Graphical Abstract

b-value analysis obtained using earthquake catalogues has been associated with stress accumulation for a very long time. In this study, the spatial and temporal distribution of the b-value, also known as the frequency magnitude distribution factor, was calculated and examined before and after the February 6, 2023, Kahramanmaraş earthquakes (Mw 7.7 and Mw 7.6). For this, all earthquakes that occurred between 1900 and the earthquakes of February 6, 2023, and all aftershocks that occurred until September 1, 2023, were used. A circular area with a radius of 300 km, including nearby active faults from the center of the first earthquake to the center of the second earthquake, was divided into grids of equal size. The b-value was calculated for each grid using the maximum likelihood method. Very low b values were detected in the area where the first earthquake occurred, and it was observed that the b-value decreased relatively in the area where the second earthquake occurred. From the change in b-value over time, it was determined that the b-value has decreased significantly in recent years. This situation is associated with stress accumulation in the area where both earthquakes occurred, especially the low b values of the region where the first earthquake occurred. The fact that b values obtained using aftershocks are still low suggests that stress in the region is not completely released, has not been completely relieved and aftershocks will continue for a long time. [ABSTRACT FROM AUTHOR]

Using the earthquake catalog provided by the Sichuan Earthquake Network Center, spatial and temporal b-value variations were calculated for in regional and local scales based on assessing the completeness of the earthquake catalog and declustering. The results show that (1) b-value temporal variations in regional scale ranged from 0.689 to 1.169, with a mean value of 0.928; while, the local-scale temporal variations ranged from 0.694 to 1.223, with a mean value of 0.925. The b-values in the study area were below the mean value before the moderate and large earthquakes occurrence, and all b-values exhibited the anomalous feature of a sudden decrease before the earthquake low peak rise after the earthquake. (2) The seismotectonic characteristic of the area is the higher value of slip rate of the NW section of Xianshui River Fault Zone; therefore, a large amount of stress was accumulated in the Moxi section of the SE section, leading to a M = 6.8 earthquake in Luding. Before the earthquake, the study area has a low b-value area. The b-value decreased within a short period after the earthquake, dividing the area into asperity. This area still has a future risk of moderate to strong earthquakes. (3) The error in the b-values for most of the earthquakes in the regional and local scales regions is between 0.05 and 0.15, and only individual grid points have larger b-value errors (> 0.2), indicating high confidence in the information. In addition, when conducting a b-value study, choosing a suitable study area is important to avoid missing the b-value anomaly area. [ABSTRACT FROM AUTHOR]

Dengan menggunakan data gempa bumi dari katalog USGS dan BMKG dari tahun 2009 hingga 2021, penelitian dilakukan untuk mengestimasi nilai Mc, nilai-b, dan nilai-a. Gempa bumi terjadi pada 6° LS - 2° LU dan 100° BT - 103° BT, dengan magnitudo 3 SR hingga 7 SR, dan kedalaman tertinggi adalah 300 km, yang mencakup wilayah provinsi Bengkulu. Penelitian ini dilakukan dengan menggunakan metode EMR dan software ZMAP 6.0 di Matlab digunakan. Menurut analisis di atas, USGS memperoleh Mc sekitar 4,7 SR hingga 5, nilai-b berkisar 0,9 hingga 1,5, dan variasi nilai-a sekitar 6 hingga 9,5. Sebaliknya, BMKG memperoleh Mc sekitar 3,8 hingga 5,2, nilai-b berkisar 0,55 hingga 0,85, dan variasi nilai-a sekitar 5,2 hingga 5,8. Pemetaan nilai Mc menunjukkan bahwa semua kabupaten di Provinsi Bengkulu memiliki nilai Mc yang rendah, yang menunjukkan bahwa data gempa untuk daerah-daerah ini cukup lengkap dibandingkan dengan daerah lain. Menurut pemetaan nilai-b dan nilai-a, wilayah yang memiliki tingkat kegempaan yang relatif tinggi dan memiliki potensi gempa besar berada di sekitar wilayah timur laut dan tenggara Provinsi Bengkulu.

Abstract This work presents particle-based numerical simulations on coal pillars in a coal mine based underground water reservoir (CMUWR). We aim to replicate the stress–strain characteristics and present the acoustic emission behavior of the coal under complex dynamic stress paths. The study reveals failure characteristics of coal exposed to monotonic/cyclic shear load under constant/cyclic normal loads. Based on the evolution of stress-time-dependent bond diameter implemented in particle model, different damage paths are established for dry and water-immersed samples under two loading frequencies. Furthermore, the numerical Gutenberg–Richter’s b-value was calculated from the released energy emanating from bond failure, and this work presents the evolution of numerical Gutenberg–Richter’s b-value. The numerical simulation contributes to a micromechanical understanding of the failure mechanisms of coal under water-immersion and cyclic stress, providing valuable insights for strength prediction of CMUWR.

Anisotropic behaviors of layered rocks, characterized by the distinct mechanical responses to varying loading directions, have been widely studied in laboratory tests. However, understanding the microscale failure mechanisms of beddings and rock matrices is still challenging in laboratory scale. In this study, we present a numerical modeling based on PFC3D to investigate the mechanical responses of slates with five bedding angles (0°, 30°, 45°, 60°, 90°) under differential cyclic loading (DCL). The beddings and matrices are modeled using the same contact model to ensure the comparability of parameters, with the weakened parameters of beddings reasonably determined through X-ray diffraction (XRD). The damage evolution paths are characterized by the degradation of the bond diameter. The simulation results replicate realistic stress–strain curves documented in laboratory tests. We develop an acoustic emission (AE) algorithm for respectively monitoring the AE events occurring in beddings and matrices. Additionally, the release of the bond energy is captured to determine the b-values in simulation, and experimental data are used to validate its rationality. Finally, the macroscopic failure patterns obtained from numerical simulations are compared to the failed samples in laboratory test and the nuclear magnetic resonance (NMR) results, demonstrating a consistent correlation and verifying the validity of the proposed model. Highlights: The force chain evolution for different bedding angles was analyzed under differential cyclic loading. A dual system for monitoring AE events in beddings and rock matrices was created based on the 3D particle model. The method of calculating numerical b-value was given based on the released energy at bond failure. [ABSTRACT FROM AUTHOR]

The distinction between the shear behavior of tensile- and shear-induced fractures is critical to understanding the deformation and failure of geologic discontinuities at different scales. To investigate these differences, a series of direct shear tests were performed on sandstone specimens with a continuous fracture created by either splitting or shearing. The acoustic emission (AE) technique was used to examine variations in grain-size cracking behavior between specimens with tensile- and shear-induced fractures. An increase in normal stress for both fracture types correlates with increased microcrack density and energy release. However, there are notable differences: during the shear process, tensile-induced fractures produce AE sequences similar to the seismic patterns observed along natural tectonic faults, with foreshocks, mainshocks, and aftershocks. In contrast, the AE sequence for shear-induced fractures during the shear process lacks prominent mainshocks and deviates progressively from the power-law function with time as normal stress increases. In addition, the AE b-value for tension-induced fractures initially shows a gradual decrease as the mainshock approaches and then slowly increases during the aftershock period. In contrast, the b-value remains nearly constant for shear-induced fractures due to the low roughness and heterogeneity of the fracture surface. These differences highlight the strong correlation between AE responses and fault heterogeneity, paving the way for fault characterization and risk assessment in subsurface energy extraction. Highlights: The cracking behavior of both tensile- and shear-induced fractures in direct shear tests is investigated using the AE technique. In direct shear tests, the AE sequences of tensile fractures follow a power law, while a significant deviation from the power law is observed in the AE sequence of shear fractures. The power-law evolution of the AE sequence before and after the mainshock, together with anomalous b-values, can be used as indicators to distinguish young faults from mature faults. [ABSTRACT FROM AUTHOR]

The Tonga-Kermadec subduction zone lies between the Pacific and Australian plates. The location shows the highest rate of subduction for the Pacific plate and a dominant tension. Two great earthquakes occurred in the region in 2006 and 2009 whose magnitudes were Mw = 8.0 and 8.1. There are about 170 islands around the Tonga subduction zone; these islands are volcanic centers that have been regularly in eruption during the last several decades. The present study presents the results from the determination of time-dependent variations in the slope of the recurrence curve (the b-value) at the Tonga subduction zone during 2005–2022, and depth-dependent variations in b. The time-dependent variations in b reflect the general tendency of great earthquakes occurring upon the background of lower b-values in the surface layer only, at depths of 0–100 km. The comparison between the depth-dependent variations in b and the tectonic model for the Toga subduction zone implies the hypothesis that lower b-values may reflect greater stresses in the upper part of the plunging plate due to its bending. Higher b-values seem to be connected to tensional mechanisms. A region of higher b-values at depths of 90–100 km has been identified for the Tonga subduction zone, as well as for other subduction zones, which can be related to the presence of a magmatic front at these depths, which is related to active volcanism. [ABSTRACT FROM AUTHOR]

In the present study, the spatio-temporal variation of the seismic b-value in the vicinity of the Kopili fault and its surrounding area has been analysed using the unified and homogenous earthquake catalog of historical and instrumental (1950–2021) earthquake events. The study region is subdivided into 16 equisized square grids of 1° × 1° dimension, and the b-value is computed for each grid using the maximum likelihood method. The spatial distribution of the b-value varies from 0.58 to 1.14. The Kolmogorov–Smirnov (K-S) test has been conducted to check the significance of the spatial-temporal and depth-wise distributions of the b-value. The epicentral location of April 28th, 2021, lies in the low-b-value square grid. Likewise, the temporal b-value curve shows a decreasing trend before the occurrence of the April 28th, 2021 earthquake. The mean return period of the April 28th, 2021earthquake and the most probable maximum annual magnitude earthquake are also computed for this region. Meanwhile, the spatial associations and anomalous patterns between the b-value and factors like seismic moment or energy release and focal depth are assessed, as they contribute to a more comprehensive understanding of the seismicity in this area. The antithetical relationship between the b-value and seismic moment or energy release is established. While variation in b-value with depth provides new insights, low b-values are linked to the top of the crust, which could mean that the crust is uniform and that a lot of stress is building up. [ABSTRACT FROM AUTHOR]

This study explores the feasibility of using fluctuations in the recurrence magnitude dispersion factor (b-value) as a seismic precursor for the Mizoram earthquake that occurred on November 26, 2021, in the Indo-Burma region of northeast India. Employing a comprehensive and homogeneous earthquake catalog spanning from 1900 to 2020, the seismic analysis involved delustering and completeness testing. The research implements a sub-sectional b-value calculation method, dividing the study area into uniformly sized grid cells (2° × 2°) and performing temporal b-value mapping for each grid. The epicenter of the Mizoram earthquake was located within a grid cell characterized by an intermediate b-value. Time-series analysis of the b-value indicated a notable decline preceding the main event, suggesting its potential as a seismic precursor. The study also examines depth-dependent variations in the b-value, revealing an inverse relationship between the b-value and crustal stress. To evaluate the significance of b-value anomalies, the Kolmogorov–Smirnov (K-S) statistic was employed instead of visual inspection. Additionally, the research provides probabilistic estimates of seismic hazard parameters, including the most probable maximum yearly earthquake, mean return period, and probabilities of earthquakes of varying magnitudes. These findings contribute to a deeper understanding of the complex seismotectonic framework and high lithospheric variability in the investigated region. [ABSTRACT FROM AUTHOR]

This work presents particle-based numerical simulations on coal pillars in a coal mine based underground water reservoir (CMUWR). We aim to replicate the stress–strain characteristics and present the acoustic emission behavior of the coal under complex dynamic stress paths. The study reveals failure characteristics of coal exposed to monotonic/cyclic shear load under constant/cyclic normal loads. Based on the evolution of stress-time-dependent bond diameter implemented in particle model, different damage paths are established for dry and water-immersed samples under two loading frequencies. Furthermore, the numerical Gutenberg–Richter's b-value was calculated from the released energy emanating from bond failure, and this work presents the evolution of numerical Gutenberg–Richter's b-value. The numerical simulation contributes to a micromechanical understanding of the failure mechanisms of coal under water-immersion and cyclic stress, providing valuable insights for strength prediction of CMUWR. [ABSTRACT FROM AUTHOR]

We use the Godano et al. (2022, https://doi.org/10.1029/2021ea002205) method for evaluating the b maps of the faults associated with the largest earthquakes M ≥ 7.0 that occurred in California. The method allows an independent evaluation of the b parameter, avoiding the overlap of the cells and the omission of some earthquakes, while keeping all the available information in the catalog. We analyzed four large earthquakes: Landers, Hector Mine, Baja California, and Searles Valley. The maps obtained confirm that the b value can be considered as a strain meter and allow us to elucidate the presence of barriers, such as obstacles to the propagation of the fracture, on the fault of the analyzed earthquakes. A further estimated parameter is the time window during which aftershocks occur in the cell, Δt. This quantity is very useful for a better definition of the aftershock generation mechanism. It reveals where the stress is released in a short time interval and how the complexity of the faulting process controls the occurrence of aftershocks on the fault, and also the duration of the entire sequence. Plain Language Summary: The use of the Godano et al. (2022, https://doi.org/10.1029/2021ea002205) method for evaluating the b maps for the on‐fault seismicity during the occurrence of aftershocks allows us to put some constraints on the faulting process during the aftershock sequences. Key Points: Independent cells b value spatial maps evaluationNew operator‐independent griding method for spatial discretization [ABSTRACT FROM AUTHOR]

The Alborz Mountains are among the areas exhibiting high tectonic and seismic activity in northern Iran. Studying key parameters of tectonic structures, including quantitative analysis and observational studies, in such active regions is essential to identify potential active faults and assess the consequent seismic hazards. This study focuses on seismicity and seismotectonics by analyzing seismic parameters, including b-value, mean seismic activity rate, earthquake recurrence time, seismic moment, and fractal dimension derived from micro and teleseismic data. The b-values vary between 0.6 and 1.1 in the tectonically active parts of the study area, corresponding with the reverse/thrust and strike-slip active faults. Large earthquakes might be prone to occur at 10–25 km depth because both catalogues show low b-values (b < 1.0) concentrations at this depth range. The high fractal dimension (> 1.5), high seismic activity rate, large seismic moment parameters, and its continuously increasing trend. Short recurrence periods (20–50 years) of M 6.5 events also emphasize the high seismic activity and high seismic hazard. On the other hand, the prevalence of low b-values is notably observed in areas encompassing densely populated cities such as Rasht, Lahijan, Amol, Babol, Sari, Behshahr, Gorgan, and the megacity of Tehran. Furthermore, we have identified asperities where the Gorgan Plain, the Khazar, and the Alamutrud Fault Zones are located. These findings emphasize the seismic hazard potential in the identified areas and urban centers within the study area. Therefore, particular attention should be directed towards areas exhibiting low b-values when assessing and mitigating seismic hazards. It underscores the necessity for additional focus on seismic hazard assessment and implementation of mitigation strategies in the Alborz region. [ABSTRACT FROM AUTHOR]

This paper introduces a software tool developed within the MATLAB environment, called Tremors, aimed at streamlining the pre-processing and analysis of seismic catalogues, with a particular emphasis on determining the Magnitude of Completeness. It will outline the criteria for event selection, as well as various techniques to derive the Magnitude of Completeness values, including the recent and widely used Lilliefors statistical method. The study also addresses the important issue of short-term aftershock incompleteness and proposes solutions for managing it. Moreover, the software generates high-quality, customizable figures, and georeferenced raster images in.tif format as output. A standalone version of the App is also available (i.e., the users do not need a MATLAB license on their PC/laptop). [ABSTRACT FROM AUTHOR]

Abstract Gas extraction from the Groningen gas field resulted in significant induced seismicity. We analyze the magnitude‐frequency distribution of these earthquakes in space, time and in view of stress changes calculated based on gas production and reservoir properties. Previous studies suggested variations related to reservoir geometry and stress. While we confirm the spatial variations, we do not detect a clear sensitivity of b‐value to Coulomb stress changes. However, we find that b‐value correlates positively with the rate of Coulomb stress changes. This correlation is statistically significant and robust to uncertainties related to stress change calculation. This study thus points to a possible influence of stress change rate on the probability of the magnitude of induced earthquakes.

Seismic activity in Aswan is influenced by the complex interactions of tectonic plates, the accumulation of stress, and the presence of geological fault systems. It revealed that epicenters are well distributed along four fault segments in a conjugate pattern, indicating a prominent E-W compressional stress. This research aims to explore the characteristics of seismicity and seismotectonics, with a focus on assessing their implications for risk reduction and disaster management in this densely populated region. A data review from the Egyptian National Seismological Network (ENSN) identified 464 earthquakes occurred between 2000 and 2021, with local magnitudes ranging from 0.3 to 4.4, and depths up to 25 km. The calculated Gutenberg-Richter b-value is approximately 0.87 ± 0.05, indicating a gradual stress accumulation. The current analysis shows a more consistent level of moderate seismic activity, unlike previous studies in Aswan region that reported a wide range of b-values from 0.554 to 1.07. This suggests that while earlier research captured a wider range of seismic behaviors, recent data indicates a stabilization in earthquake frequency and intensity. Additionally, the fractal dimension (Dc) calculated at 1.57 ± 0.04 shows an intermediate level of complexity and reflecting a clustering pattern of earthquakes. The variations in the b-value with different magnitudes and depths signify the involvement of active smaller faults, responsible for earthquakes up to magnitude 2.2, which then transition to fractured zones inducing earthquakes up to magnitude 2.5. This transition is followed by a decline in seismic activity, indicating regions that are potentially more likely to experience larger earthquakes. Moreover, stress disparities at various depths contribute to smaller earthquakes within the 5–10 km depth range. Return period analysis suggests that the earthquakes of magnitude 3.7 or higher are expected to occur approximately once every decade in Aswan. These findings are of utmost importance for earthquake risk reduction, hazard assessment, and the sustainable development of Aswan area.

Abstract To assess the damage and fracture behavior of wood under load, a wood damage assessment method was proposed based on acoustic emission (AE) b-values and seismic magnitude difference entropy. First, AE signals from Pinus sylvestris var. mongolica (softwood) and Zelkova schneideriana (hardwood) specimens were collected separately at a sampling frequency of 500 kHz in a three-point bending test. Then, 52 dB was taken as the threshold of the AE event, and the b-value and seismic magnitude difference entropy were calculated at 4-s intervals. Finally, by comparing with the load‒time curve, the b-value and seismic magnitude difference entropy were used to evaluate the damage fracture degree. The results showed that an increase in the b-value indicates the accumulation of strain energy, and vice versa, corresponding to the concentrated release of strain energy. At the same time, the test process can be divided into three stages—elastic, elastic‒plastic and plastic—based on the level of the seismic magnitude difference entropy.

The debonding between fabric and matrix/substrate hampers the strength and durability of fiber-reinforced cementitious matrix (FRCM) strengthened elements. One of the ways to improve the performance is to use mechanical anchorages. However, damage mechanisms associated with such systems are complex, and structural health monitoring of such systems is quite challenging. While earlier studies have concentrated on monitoring the health of FRCM coupons using acoustic emission techniques, they did not account for the effect of impregnation or use of mechanical anchorages. Also, very few studies are available on the health monitoring of full-scale FRCM-strengthened specimens. The current investigation employs AE-based health monitoring to classify the damage characteristics of reinforced concrete (RC) beams strengthened with FRCM. Two strengthening strategies, with and without mechanical anchorages, are employed. The non-anchored system involves conventional strengthening using two layers of pre-impregnated fabric, while the mechanically anchored method utilizes pre-impregnated fabric and a distributed anchorage system. The AE data is then analyzed using several parameters correlated with the digital image correlation (DIC) technique. Trends of sentry function, historical index, and cumulative signal strength (CSS) provide insights into major event occurrences and changes in the underlying damage modes. Three different b-values indicate a transition from micro to macro cracks during different loading stages. On the other hand, frequency content and RA-AF analysis are employed as qualitative tools to identify the source and type of damage. The strengthened RC beams with mechanical anchorages exhibited a 20.9 % increase in flexural capacity compared to those without, as evidenced by the AE parameters and DIC techniques. Overall, the study revealed that acoustic emission health monitoring could effectively evaluate the overall condition of the strengthened system, even with the complexity of a multi-part composite system.

Objective: To compare image quality and diagnostic performance using different b-values for the zooming technique with diffusion-weighted imaging (ZOOMit-DWI) in thyroid nodules Materials and Methods: A total of 51 benign thyroid nodules and 50 thyroid papillary carcinomas were included. ZOOMit-DWI was performed with b-values of 0, 500, 1000, 1500 and 2000 s/mm². The sharpness was evaluated as subjective index. The signal intensity ratio (SIR), signal-to-noise ratio (SNR) and apparent diffusion coefficient (ADC) were measured as objective indices. Pairwise comparisons were performed among the different b-value groups using the Friedman test. A receiver operating characteristic curve of the ADC value was used to evaluate diagnostic performance. The DeLong test was used to compare diagnostic effectiveness among the different b-value groups Results: In both the papillary carcinoma group (P = 0.670) and the benign nodule group (P = 0.185), the sharpness of nodules was similar between b-values of 1000 s/mm2and 1500 s/mm². In the papillary carcinoma group, the SIRnodule was statistically higher in DWI images with a b-value of 1500 s/mm²than in DWI images with b-values of 500 s/mm²(P = 0.004), 1000 s/mm²(P = 0.002), and 2000 s/mm²(P = 0.003). When the b-values were 1500 s/mm²(P = 0.008) and 2000 s/mm²(P = 0.009), the SIRnodule significantly differed between the papillary carcinoma group and the benign nodule group. When b = 500 s/mm², the ADC had an AUC of 0.888. When b = 1000 s/mm², the ADC had an AUC of 0.881. When b = 1500 s/mm², the ADC had an AUC of 0.896. When b = 2000 s/mm², the ADC had an AUC of 0.871. The DeLong test showed comparable diagnostic effectiveness among the different b-value groups except for between b-values of 2000 s/mm2and 1500 s/mm², with a b-value of 2000 s/mm²showing lower effectiveness Conclusion: This study suggests that 1500 s/mm²may be a suitable b-value to differentiate benign and malignant thyroid nodules in ZOOMit-DWI images, which yielded better image quality. [ABSTRACT FROM AUTHOR]

On 6 February 2023, Türkiye experienced a pair of consecutive earthquakes with magnitudes of Mw 7.8 and 7.5, and accompanied by an intense aftershock sequence. These seismic events were particularly impactful on the segments of the East Anatolian Fault Zone (EAFZ), causing extensive damage to both human life and urban centers in Türkiye and Syria. This study explores the analysis of a dataset spanning almost one year following the Turkiye mainshocks, including 471 events with a magnitude of completeness (Mc) ≥ 4.4. We employed the maximum likelihood approach to estimate the b-value and Omori-Utsu parameters (K, c, and p-values). The estimated b-value is 1.21 ± 0.1, indicating that the mainshocks occurred in a region characterized by elevated stress levels, leading to a sequence of aftershocks of larger magnitudes due to notable irregularities in the rupture zone. The aftershock decay rate (p-value = 1.1 ± 0.04) indicates a rapid decrease in stress levels following the main shocks. However, the c-value of 0.204 ± 0.058 would indicate a relatively moderate or low initial productivity of aftershocks. Furthermore, the k-value of 76.75 ± 8.84 suggests that the decay of aftershock activity commenced within a range of approximately 68 to 86 days following the mainshocks. The fractal dimension (Dc) was assessed using the correlation integral method, yielding a value of 0.99 ± 0.03. This implies a tendency toward clustering in the aftershock seismicity and a linear configuration of the epicenters. The slip ratio during the aftershock activity was determined to be 0.75, signifying that 75% of the total slip occurred in the primary rupture, with the remaining fraction distributed among secondary faults. The methodologies and insights acquired in this research can be extended to assist in forecasting aftershock occurrences for future earthquakes, thus offering crucial data for future risk assessment. [ABSTRACT FROM AUTHOR]

To study the effect of high-strength filling materials on the mechanical bearing characteristics of rectangular open ore pillars during the replacement process of ore pillar protection, the mechanical load-bearing characteristic experiments were carried out under uniaxial load on ore pillar specimens with different widths of openings by using the Zhongji electronic universal testing machine and DS5 acoustic emission signal acquisition system. The whole failure process was monitored and recorded by a fast camera, and the mechanical load-bearing characteristics and failure mechanism of rectangular openings filled with high-strength filling materials were summarized. The experimental results showed that: The deformation and failure of the OPB and OPFB model specimens can be divided into four stages: compaction stage, elastic deformation stage, yielding stage, and post-peak failure stage,? showed synchronous response with the evolution of AE ringing counts. The b-value curve of the OPB model specimen gradually decreased, while the b-value curve of the OPFB model specimen showed a gentle trend. The enhanced backfill material effectively reduced the occurrence of sudden failure and had the greatest impact on improving the residual strength after failure. The compressive strength and elastic modulus of the OPB and OPFB model specimens decreased with the increase of excavation and backfilling width. The failure mode of the OPB specimens transformed from splitting failure plane deviation to shear failure plane, showing a transition from ductile to brittle failure, while the combined system after backfill exhibited ductile failure. This research provides scientific basis for the extraction and stability of ore pillars. [ABSTRACT FROM AUTHOR]

Until now, numerous efforts have been made to find earthquake precursors. One of the factors that can predict the occurrence of future earthquakes is a decrease in the b-value parameter. In this study, for the metropolis of Tehran, with a population of over 8 million, located on or near many active faults, it is estimated that if the maximum seismic potential of these faults happened again, the greatest disaster in human history would occur. In this case, the analyses indicate a minimum of several hundred thousand casualties and sometimes more than a million. In the current study, various faults around Tehran were investigated, and given that the faults on Tehran have not had serious seismic activity for over a thousand years, this article focused exclusively on adjacent faults, particularly the Eshtehard faults. Therefore, in the current study, the seismicity and tectonics of western Tehran were investigated by analyzing seismic parameters using earthquake data collected from 2003 to 2023. In general, the investigation of the temporal changes in the study area showed that the b-value decreased before the December 20, 2017, earthquake and an increasing trend afterward. Observing anomalies in the b-value before and after the main movement in the area shows that changes in this parameter can be considered a precursor for estimating the time and location of earthquakes. Therefore, a useful step can be taken toward knowing the local seismic hazards by using earthquake data recorded by seismic networks and continuously monitoring the changes in the b-value. [ABSTRACT FROM AUTHOR]

Seismic swarms in a volcanic field can be indicators of the movements of volcanic activity and stagnant magma in the Earth's crust. In the Tancítaro-Parícutin volcanic region, to the west of the Michoacán-Guanajuato volcanic field in Mexico, at least six seismic swarms have occurred in the last 25 years. However, greater precision is still required due to the distance between and non-permanence of the seismic stations. We used data from a broadband station of the Earth Sciences Research Institute (INICIT-UMSNH) and records from Mexican National Seismological Service (SSN), Center for Geosciences (UNAM) and Mexican National Center for Prevention of Disasters (CENAPRED) to relocate and obtain focal mechanisms for four selected seismic events. We applied the fractal methodology to analyze the inter-event times of the seismic swarm sequences. Two well-defined swarm sequences were identified, and, subsequently, the fractal behavior of the logarithm of inter-event times was analyzed by means of the Hurst and Holder exponent. Our goal was the identification of the different dynamical stages acting during the seismic swarm generation processes, that seem to be related to the stress transfer in different seismogenic faults. By means of the b-values and the temporal evolution of the Hurst exponent, at least five different stages can be distinguished during the Tancítaro-Parícutin seismic swarms. These stages appear to be determined by dynamic changes in the seismic sequence, also indicated by the focal mechanisms whose fits with faults that were apparently activated during the seismic swarm. The Tancítaro-Parícutin seismic swarm processes indeed show multi-fractal behavior, which may be related to different stages in the diffusion process. [ABSTRACT FROM AUTHOR]

East Java is one of the seismically active regions in part of the Sunda Arc whose seismicity pattern must be studied. Therefore, a spatio-temporal analysis of seismicity between 2002 - 2022 in East Java has been conducted. This analysis aims to investigate the seismotectonic conditions in the East Java region over the last twenty years, especially the seismicity patterns associated with significant earthquakes in East Java. The analysis was carried out by quantifying the spatial and temporal variations of seismicity parameters using b-value and z-value. The used data used are earthquake data from the USGS earthquake catalog during 2002 - 2022 in the East Java region. The analysis was performed using the ZMAP 6.0 program code using the maximum likelihood method. The results of the temporal analysis of b-values show that almost all significant earthquakes in East Java were characterized by a decrease in b-values of up to 0.2. Spatially, the significant earthquake on 10 April 2021 was associated with a low b-value (0.9). Temporal z-value analysis shows that the significant East Java earthquake was preceded by a quiet period (positive z-value) between 4 - 5 years (2003 - 2008 and 2012 - 2016). Spatial analysis of the z-value in the last 7 shows an increase in the z-value before the significant earthquakes occurred on 16 July 2019, 18 March 2020, and 10 April 2021. Therefore, the results of this study indicate that the b-value and z-value potentially can be used as precursors of the significant East Java earthquake. [ABSTRACT FROM AUTHOR]

This study demonstrates the feasibility and performance of the point‐resolved spectroscopy (PRESS)‐based, single‐shot diffusion trace‐weighted sequence in quantifying the trace apparent diffusion coefficient (ADC) in phantom and in vivo using a 3‐T MRI/MRS scanner. The single‐shot diffusion trace‐weighted PRESS sequence was implemented and compared with conventional diffusion‐weighted (DW)‐PRESS variants using bipolar and unipolar diffusion‐sensitizing gradients. Nine phantom datasets were acquired using each sequence, and seven volunteers were scanned in three different brain regions to determine the range and variability of trace ADC values, and to allow a comparison of trace ADCs among the sequences. This sequence results in a comparatively stable range of trace ADC values that are statistically significantly higher than those produced from unipolar and bipolar DW‐PRESS sequences. Only total n‐acetylaspartate, total creatine, and total choline were reliably estimated in all sequences with Cramér–Rao lower bounds of, at most, 20%. The larger trace ADCs from the single‐shot sequences are probably attributable to the shorter diffusion time relative to the other sequences. Overall, this study presents the first demonstration of the single‐shot diffusion trace‐weighted sequence in a clinical scanner at 3 T. The results show excellent agreement of phantom trace ADCs computed with all sequences, and in vivo ADCs agree well with the expected differences between gray and white matter. The diffusion trace‐weighted sequence could provide an estimate of the trace ADC in a shorter scan time (by nearly a factor of 3) compared with conventional DW‐PRESS approaches that require three separate orthogonal directions. [ABSTRACT FROM AUTHOR]

Rock crack is one of the main factors responsible for rock failure. Uniaxial compression creep tests are performed using acoustic emission techniques, a high-sensitivity, non-radiative, non-destructive testing method to understand the influence of crack number on the precursor characteristics of short-term creep damage in the fractured rock mass. Based on the Grassberger-Procaccia (G-P) algorithm, the calculation step size for the correlation dimension value (D 2) of the acoustic emission ringing count rate is consistent with that for the acoustic emission b-value. The influence of the number of pre-cracks on the Acoustic emission precursor characteristics of red sandstone creep is analyzed. The results show that near the destabilization of the specimen, the Acoustic emission accumulative ringing count surges in a stepwise manner, the Acoustic emission b-value decreases, the D 2-value increases, the Acoustic emission amplitude shows high intensity and high frequency, and the ringing count increases sharply, all with the characteristics of failure precursors. During the accelerated creep stage of the specimens, with the increase of pre-cracks number, the precursory time points of acoustic emission b-value and D 2-value advance, and their acoustic emission ringing counts increase sharply. [ABSTRACT FROM AUTHOR]

Foreshocks and aftershocks occurred before and after the ML6.8 (Mw7.0) earthquake in eastern Taiwan on 18 September 2022. We explore the epicentral distribution and temporal variations for the mainshock, foreshocks, and aftershocks. Most of the events were located in the area around the Longitudinal Valley. Most foreshocks occurred around the mainshock, while the aftershocks happened outwards from the foreshock area. The temporal variations in seismic-wave energy show that the largest foreshock and the mainshock were responsible for releasing most of the energy during the earthquake sequence. In addition, the b values of the Gutenberg-Richter frequency-magnitude law were 0.62 for foreshocks, 0.87 for aftershocks, and 0.71 for the whole seismic activity by using the least squares method and 0.52 for foreshocks, 0.84 for aftershocks, and 0.65 for the whole seismic activity by using the maximum likelihood method. The b values increase from foreshocks to aftershocks, suggesting the possibility that the fluid pressure of faults during foreshocks is higher than that of the faults during aftershocks due to the outward migration of water. The p-value of the Omori-Utsu law for the aftershock sequence was estimated to be 0.92 for all aftershocks in the study, 1.39 for the aftershocks occurred in the first 6 days, and 1.30 for the aftershocks occurred in the first 12 days. The foreshock sequence could not be described by the inverse Omori law. [ABSTRACT FROM AUTHOR]

This study aims to explore the possibility of detecting indices that could potentially provide warning about the proximity of internal damage to critical levels, beyond which catastrophic fracture is impending. In this direction, advantage was taken of the Cumulative Counts that were recorded during the mechanical loading of specimens made of either plain or fiber-reinforced concrete. The parameter adopted for the analysis was the average rate of change in the Cumulative Counts. Τhe evolution of the specific parameter was considered in the Natural Time Domain, rather than in the conventional time domain. Experimental data from already published three-point bending protocols were used. It was revealed that the specific parameter attains, systematically, a limiting value equal to unity exactly at the instant at which the load reaches its maximum value, which is not identical to the load recorded at the instant of fracture. Similar observations were made for a complementary protocol with uniaxially compressed mortar specimens. The conclusions drawn were supported by the b-values analysis of the respective acoustic data, again in terms of Natural Time. It is, thus, indicated that the evolution of the average rate of change in the Cumulative Counts in the Natural Time Domain provides an index about the proximity of the applied load to a value beyond which the specimen enters into the critical state of impending fracture. [ABSTRACT FROM AUTHOR]

Assessment of study success using conditional power (CP), the predictive power of success (PPoS) and probability of success (PoS) is becoming increasingly common for resource optimization and adaption of trials in clinical investigation. Determination of these measures is often a non-trivial mathematical task. Further, the terminologies used across the literature are not consistent, and there is no consolidated presentation on this. We have made a structured presentation on these measures for both trial success and clinical success: first, we have summarized the expressions of CP, PPoS and PoS in a general setting and subsequently, expressions for these measures are obtained for continuous, binary, and time-to-event endpoints in single-arm and two-arm trial settings. Many of these expressions are previously published; however, some of the expressions are very new including the expressions for testing median of time-to-event endpoint in a single-arm trial. We have also shown that 1 / (no. of events) consistently underestimates the variance of log(median) and alternative expression for variance was derived. Examples are given along with the comparison of CP and PPoS. Expressions presented in this paper are implemented in LongCART package in R and in R shiny app https://ppos.shinyapps.io/public/. [ABSTRACT FROM AUTHOR]

Abstract We use the Godano et al. (2022, https://doi.org/10.1029/2021ea002205) method for evaluating the b maps of the faults associated with the largest earthquakes M ≥ 7.0 that occurred in California. The method allows an independent evaluation of the b parameter, avoiding the overlap of the cells and the omission of some earthquakes, while keeping all the available information in the catalog. We analyzed four large earthquakes: Landers, Hector Mine, Baja California, and Searles Valley. The maps obtained confirm that the b value can be considered as a strain meter and allow us to elucidate the presence of barriers, such as obstacles to the propagation of the fracture, on the fault of the analyzed earthquakes. A further estimated parameter is the time window during which aftershocks occur in the cell, Δt. This quantity is very useful for a better definition of the aftershock generation mechanism. It reveals where the stress is released in a short time interval and how the complexity of the faulting process controls the occurrence of aftershocks on the fault, and also the duration of the entire sequence.

Predicting rock bursts is essential for maintaining worker safety and the long-term growth of subsurface infrastructure. The purpose of this study is to investigate the precursor reactions and processes of rock instability. To determine the degree of rock damage, the research examines the time-varying acoustic emission (AE) features that occur when rocks are compressed uniaxially and introduces AE parameters such as the b-value, γ-value, and βt-value. The findings suggest that the evolution of rock damage during loading is adequately reflected by the b-value, γ-value, and βt-value. The relationships between b-value, γ-value, and βt-value are studied, as well as the possibility of using these three metrics as early-warning systems for rock failure.

ABSTRACTThe potential earthquake and tsunami hazard along the Sumatra subduction margin, especially around the coast of West Sumatra-Bengkulu, was investigated based on the availability of pre-seismic surface displacement data and shallow crustal earthquake catalogue data from 1907 to 2016. The pre-seismic surface displacement data is based on the displacement data prior to and corrected displacement data after major earthquakes. Using the results of our previous study on the local covariance function and the relationship of Correlation Dimension (DC) with the b-value of Gutenberg-Richter (GR) Law, we estimated the maximum horizontal crustal strain rate (SHmax) and DC around the study area. Least squares prediction based on horizontal displacement data using the local covariance function is used to estimate the displacement model in the entire gridding study area with a 10 km × 10 km size. Furthermore, DC is calculated based on the b-value using the maximum likelihood method based on the input of a constant number of earthquake samples, assuming the regional b-value of GR Law equals 1. Furthermore, the spatial correlation of SHmax and DC can define the area of possible earthquake hazard potential. The identification results are then linked with previous stress reconstruction results for seismic hazard study and analysis. Based on the finding, we then estimate the Seismic Hazard Function (SHF) and Tsunami Height simulation to estimate the possible hazard risk at several observation points. We suggest that the result of this study could be beneficial to understand better the potential seismic and tsunami hazard in the future, mainly to support mitigation purposes.

ABSTRACTThe North-Eastern region of India has the distinction of being one of the most seismically active and tectonically complex regions in the world. The region has periodically jolted by a number of large earthquakes. The temporal and spatial frequency-magnitude distribution (FMD) of earthquakes in three major selected regions of North-East India, namely Shillong–Mikir Hills, Arunachal Himalaya, and Assam Foredeep region, are examined in this study. Temporal variation of ‘b’ shows a significant declination prior to a large earthquake, which strongly advocates for a medium-term (months-year) earthquake precursor. Similarly, spatial distribution map is prepared by estimating b-value at every [Formula: see text] grid using the nearest 150 events, which is vital in understanding the stress regime of a specific region. The present study critically demonstrates the higher b-value regions associated with minimum seismicity and vice-versa, especially focusing on large earthquake scenario. High anomalies of ‘b’ were found in the regions of Shillong–Mikir hills and Arunachal Himalaya, whereas the Assam-Foredeep region, free from seismic activity for a long period, shows a low. It may be due to the accumulation of stress energy within the region for a long time and could be an alarming sign for future large events.

Seismic b-value is one of the most important parameters for seismological research and seismic hazards assessment, while the accuracy of the b-value largely depended on the completeness of seismic catalog. This article compares eight methods for estimating the minimum magnitude of completeness (Mc). The results indicate that the modified maximum curvature method (MMAXC), exhibits greater stability and accuracy, closely approximating the standard M[sub c] obtained from the synthetic seismic catalogs. We then calculate the b-value using the instrumental seismic catalog from 2000-2023 in the eastern Tibetan Plateau. The results indicate that the five major earthquakes occur in regions with lower b-value. In addition, the temporal evolution of b-value before and after major earthquakes exhibits a common trend of decreasing before earthquakes, and increasing after earthquakes, which may reflect the stress accumulation and release during earthquakes. Combining the results of maximum shear strain rate and b-value, we identify five regions characterized by low b-value and high shear strain rate, indicating a higher potential seismic hazard in the future. [ABSTRACT FROM AUTHOR]

The b‐value in earthquake magnitude‐frequency distribution quantifies the relative frequency of large versus small earthquakes. Monitoring its evolution could provide fundamental insights into temporal variations of stress on different fault patches. However, genuine b‐value changes are often difficult to distinguish from artificial ones induced by temporal variations of the detection threshold. A highly innovative and effective solution to this issue has recently been proposed by van der Elst (2021, https://doi.org/10.1029/2020jb021027) by means of the b‐positive estimator, which is based on analyzing only the positive differences in magnitude between successive earthquakes. Here, we demonstrate the robustness of the estimator, which remains largely unaffected by detection issues due to the properties of conditional probability. We illustrate that this robustness can be further improved by considering positive differences in magnitude, not only between successive earthquakes but also between different pairs of earthquakes. This generalized approach, defined as the "b‐more‐positive estimator," enhances efficiency by providing a precise estimate of the b‐value while including a larger number of earthquakes from an incomplete catalog. However, our analysis reveals that the accuracy of the b estimators diminishes when earthquakes below the completeness threshold are included in the catalog. This leads to the paradoxical observation that greater efficiency is achieved when the catalog is more incomplete. To address this, we introduce the "b‐more‐incomplete estimator," where the b‐more‐positive estimator is applied only after artificially filtering the instrumental catalog to make it more incomplete. Our findings show the superior efficiency of the b‐more‐incomplete method. Plain Language Summary: Earthquake magnitudes can vary widely, and the b‐value is a common metric used to measure the frequency of earthquakes with large versus small magnitudes. In addition, the b‐value could serve as an indicator of the stress state of different fault patches, making it a valuable tool in earthquake research. However, since small earthquakes are often obscured by previous larger ones, determining whether changes in the b‐value are genuine or simply caused by detection problems can be challenging. To address this issue, a new approach called the b‐positive estimator has been recently developed. The method only considers positive changes in magnitude between successive earthquakes. In this study, we confirm that the b‐positive estimator is a powerful and effective technique to estimate the b‐value and is largely unaffected by issues related to detecting earthquakes. We extend the method by considering positive differences in magnitude, encompassing not only successive earthquakes but also different pairs of earthquakes. In particular we show that the b‐positive estimator is more efficient when the catalog is more incomplete. This allows us to develop modifications to the b‐positive method providing a more efficient tool to monitor the b‐value in ongoing seismic sequences. Key Points: Conditional probability detecting consecutive earthquakes makes positive magnitude difference distribution weakly affected by incompletenessThe b‐positive estimator can be enhanced by including more earthquake pairs, not only consecutive onesThe b‐positive estimator can be enhanced by making the catalog more incomplete [ABSTRACT FROM AUTHOR]