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Mine blasting produces excavation geometry changes which induce stress change that can be observed in the seismic source parameter apparent stress calculated for local seismic events. Using high apparent stress as a proxy for increasing stress within a rock mass, areas experiencing increases in the local stress conditions can be determined. This paper presents the use of apparent stress of seismic events to identify areas within a rock mass experiencing local stress change. Examples from a deep Canadian mine, operating in excess of 2900 m below surface, are provided. [ABSTRACT FROM AUTHOR]

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Investigating spatiotemporal changes in crustal stress associated with major earthquakes has implications for understanding seismogenic processes. However, in individual earthquake cases, the characteristics of the stress after it reaches its maximum value are rarely discussed. In this study, we use the 2021 MS6.4 Yangbi earthquake in Yunnan, China and events of magnitudes ML ≥ 3.0 occurred in the surrounding area in the previous 11 years to investigate the spatiotemporal evolution of apparent stress. The results indicate that apparent stress began to increase in January 2015 and reached a maximum in January 2020. Apparent stress then remained at a high level until October 2020, after which it declined considerable. We suggest that the stress was in the accumulation stage from January 2015 to January 2020, and entered the meta-instability stage after October 2020. During the meta-instability stage, the zone of decreasing stress expanded continuously and the apparent stress increased around the Yangbi earthquake source region. These features are generally consistent with the results of laboratory rock stress experiments. We propose that apparent stress can be a good indicator for determining whether the stress at a specific location has entered the meta-instability stage and may become the epicenter of an impending strong earthquake. [ABSTRACT FROM AUTHOR]

Experimental research of bone strength remains costly and limited for ethical and technical reasons. Therefore, to predict the mechanical state of bone tissue, as well as similar materials, it is desirable to use computer technology and mathematical modeling. Yet, bone tissue as a bio-mechanical object with a hierarchical structure is difficult to analyze for strength and rigidity; therefore, empirical models are often used, the disadvantage of which is their limited application scope. The use of new analytical solutions overcomes the limitations of empirical models and significantly improves the way engineering problems are solved. Aim of the paper: the development of analytical solutions for computer models of the mechanical state of bone and similar materials. Object of research: a model of trabecular bone tissue as a quasi-brittle material under uniaxial compression (or tension). The new ideas of the fracture mechanics, as well as the methods of mathematical modeling and the biomechanics of bone tissues were used in the work. Compression and tension are considered as asymmetric mechanical states of the material. Results: a new nonlinear function that simulates both tension and compression is justified, analytical solutions for determining the effective and apparent elastic modulus are developed, the residual resource function and the damage function are justified, and the dependences of the initial and effective stresses on strain are obtained. Using the energy criterion, it is proven that the effective stress continuously increases both before and after the extremum point on the load-displacement plot. It is noted that the destruction of bone material is more likely at the inflection point of the load-displacement curve. The model adequacy is explained by the use of the energy criterion of material degradation. The results are consistent with the experimental data available in the literature. [ABSTRACT FROM AUTHOR]

We calculated apparent stresses for 70 earthquakes (MW ≥ 5.0) occurring in the aftershock region of the 2010 MW8.8 Bio-Bío earthquake from January 1990 to September 2019. We identified that the average apparent stress was approximately 0.487 MPa between January 1990 and December 2005 and approximately 1.063 MPa within the period from January 2006 to January 2010. The latter one is 2.2-fold greater than the former, representing a significant difference as determined by a z test, with a 99% confidence level. Moreover, we analyzed the temporal evolution of the apparent stress and found that apparent stress rapidly increased from 0.43 to 1.2 MPa during the pre-event period from March 2006 to the occurrence of the Bio-Bío MW8.8 mainshock, and this increased apparent stress was found to be significant at the 98% confidence level. Furthermore, we calculated the spatial distribution of the apparent stress in the study region and observed two higher-apparent-stress regions, within one of which the epicenter of the MW8.8 event was located. On the basis of the inverse correlation between b value and stress, the temporal evolution and spatial distribution of b values were calculated and compared with those of the apparent stress. The comparison showed that the b values decreased approximately 4 years before the occurrence of the mainshock, while the apparent stress increased substantially; for the region of lower b, the apparent stress is higher, and vice versa. Therefore, the inverse correlation between b value and stress is supported by the results obtained in the present study and can be probably considered as one of the precursors to great earthquakes. [ABSTRACT FROM AUTHOR]

The access tunnel in the main powerhouse of the Shuangjiangkou hydropower station is located in an area with high in-situ stress and complex geological conditions in Southwest China. Strain-structure rockbursts occurred frequently and posed serious threats to the safety of personnel and equipment during the tunnel excavation. The maximum depth of the rockburst failure reached 1.8 m at the left sidewall of the tunnel. A three-dimensional microseismic (MS) monitoring technology was introduced to monitor microcracks within the tunnel surrounding rock in real time. Using Matlab software to write a program, the main frequency values of MS signals were extracted. Based on MS monitoring, some source parameters were obtained. Three parameters, including apparent stress, apparent volume and main frequency value, were used to analyze the activity state within the surrounding rock. This method had a high time resolution and can guide the on-site construction in real time. The combination of the three parameters can better characterize different damage characteristics of the surrounding rock in real time. When the apparent stress of some events was relatively high, the apparent volume of some events was relatively large and the main frequency values of some events were relatively low, the risk of rockbursts was relatively high. Finally, a 3D numerical simulation software (RFPA3D) was used for a numerical calculation to explore strain-structure rockburst mechanisms. An area where the rockburst risk was relatively high and rockburst prediction was relatively difficult was delineated, and this paper provided a new idea for predicting the stronger strain-structure rockbursts. Understanding of activity state within surrounding rock is very important for controlling rockburst occurrence or weakening rockburst strength. The research results have significant value for safe and efficient construction on site. [ABSTRACT FROM AUTHOR]

Access tunnel in the main powerhouse of Shuangjiangkou hydropower station was deep buried with high in situ stress and complex geological conditions. Microseismic monitoring technology was established to monitor microcrack evolution process inside the surrounding rock in early excavation stage. Serious falling blocks in the left spandrel of the tunnel were predicted in a timely manner by delimiting major damage areas in the tunnel. Based on comparative analysis on microseismic activity law and field failure characteristics of the access tunnel, a quantitative index was supposed between slight rockburst like falling blocks and microseismic events. Moreover, the change law of daily average apparent stress difference and b value were analyzed based on microseismic event data. In addition, a three-dimensional numerical simulation software (RFPA3D) was used to simulate the damage distribution around the tunnel, and a relationship between spatial position of tunnel damage and direction of the maximum principal stress was qualitatively analyzed. The study results showed that advance speed of the tunnel working face was an important factor affecting the state of stress redistribution in surrounding rock mass, and the change law of b values of microseismic events could be used to predict activity state inside the surrounding rock effectively, which reflected mechanical properties and stress state of surrounding rock. In particular, field falling blocks became more serious with increasing b value, and field surrounding rock was relatively stable with minor b value. A risk of surrounding rock instability was relatively high with small b values. It provided an efficient method of predicting and assessing slight rockburst like falling blocks. The study results can provide significant guidance for field construction and later construction planning. [ABSTRACT FROM AUTHOR]

We investigate the variability of Brune stress drop (∆σ) and apparent stress (τa) of 23 earthquakes occurred in a small crustal volume adjacent to the hypocenter of the destructive Mw 6.1 L'Aquila earthquake. Their magnitude range is 2.7 ≤ Mw ≤ 4.1. Interevent variability of stress drop and apparent stress results in a factor of 10, well beyond the individual‐event uncertainty. Radiation efficiency ηsw = τa/∆σ varies mostly between 0.1 and 0.2, but in the days immediately before and after the main shock, ηsw tends to be smaller decreasing to values as low as 0.06. This may be the consequence of ruptures migrating in those days into a focal volume with higher dynamic strength. The temporal change of ηsw is tentatively interpreted as a spatial variation due to the earthquake migration into the locked portion of the fault that originated the main shock. Consistently, no variation in stress drop and apparent stress is observed between foreshocks and aftershocks but the smallest and largest ∆σ result in a good correlation with the largest and smallest b‐values, respectively, imaged by other authors in the rupture nucleation volume. Key Points: Variations of stress parameters are significant beyond estimate uncertaintiesStress release of aftershocks does not differ from the one of foreshocksA finer spatial resolution is reached compared to previous studies [ABSTRACT FROM AUTHOR]

This article addresses the question of how moment magnitude, Mw, local magnitude, ML, and energy magnitude, ME, of small to moderate earthquakes would scale with each other in an ideal elastic medium and why they scale differently in reality. It turns out that ML, in the way it is commonly determined, is a poor and inconsistent measure of earthquake size. For moderate to large events, the situation could be improved with a new magnitude, MA, that is not biased by the Wood-Anderson response. Mw is robust and can in principle be determined in a consistent way over the entire imaginable magnitude range, but it accounts only for the static component of the earthquake source. Could ME be an alternative? A simple conceptual analysis reveals the relation between radiated seismic energy, seismic moment, static stress drop, apparent stress, radiation efficiency and rupture velocity. Numerical simulations based on an extended-source model show that, to estimate the radiated seismic energy (and thus also ME), one needs to take into account the effects of rupture directivity and radiation pattern. Anelastic attenuation and the bandwidth of the recording instrument determine the magnitude limit below which pulse widths and corner frequencies remain nearly constant. Below this limit, all information about the dynamics of the source is lost and attempts to correct for this in the presence of noise and aleatory signal variability, even with well-calibrated attenuation models, are probably futile. We thus have to accept the fact that ME (just as ML) is a different measure of earthquake size for small earthquakes than for moderate to large earthquakes. [ABSTRACT FROM AUTHOR]

Scaled energy, apparent stress, seismic moments, stress drops and corner frequencies are measured through the Levenberg-Marquardt nonlinear inversion modeling of S-wave displacement spectra for 489 selected earthquakes ( M 2.05-5.52) from the 2001 M 7.7 Bhuj earthquake sequence. The iterative inversion scheme is formulated based on the ω-square source spectral model, which enabled us to estimate stable source parameters. The estimated seismic moment ( M) and source radius ( r) vary from 1.5 × 10 to 2.4 × 10 to N m and 139.1-933.9 m, respectively, while estimated stress drops (Δ σ) and the multiplicative factor ( E) values range from 0.1 to 14.4 MPa and 1.0-4.1, respectively. The corner frequencies ( f) are found to be ranging from 1.4 to 9.3 Hz. The mean standard deviation for f, r and Δ σ are estimated to be 0.7 Hz, 91.4 m and 2.9 MPa, respectively. The radiated seismic energy and apparent stresses range from 2.1 × 10 to 4.1 × 10 Joule and 0.005-8.0 MPa, respectively. Our estimated corner frequencies and seismic moments satisfy the relation M ∞ f, where ε (measure for a deviation from self-similarity) is found to be 1.33 for the larger earthquakes ( M ≥ 2 × 10 N m), while the parameter ε is estimated to be 6.74 for smaller earthquakes ( M < 2 × 10 N m). We feel that the larger value of ε may require to satisfy the increasing trend of scaled energy with moment for smaller earthquakes. We also notice that stress drops increase with seismic moment, approximately as Mo (Δ σ∝ M) for smaller events ( M < 10 N m), while for larger earthquakes ( M ≥ 2 × 10 N m) stress drop increases approximately with M (Δ σ∝ M). Adding credence to this non-self-similar theory, our estimated seismic moments and source radii ( r) also reveal a break in the linear self-similar source scaling at M = 2 × 10 N m and r = 300 m, which is attributed to constant source radius for smaller earthquakes. Further, a comparative study between apparent stresses and static stress drops suggests a probable frictional overshoot mechanism for larger earthquakes, while smaller shocks are showing both partial stress drop and frictional overshoot mechanisms. We hypothesize that larger events are probably subject to the regional state-of-stress and fluid flow in the fault zone, whereas smaller earthquakes are sensitive to the local state-of-stress associated with material heterogeneities and fluid flows within the fault zone. We also propose that the relations developed in this study could be useful for accessing proper seismic hazard in the region. [ABSTRACT FROM AUTHOR]