Search

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]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

With co-seismic surface rupture slip displacements provided by the field observation for the 2001 M S8.1 West Kunlun Mountain Pass earthquake, this paper estimates the rupture speed on the main faulting segment with a long straight fault trace on the surface based on a simple slip-weakening rupture model, in which the frictional overshoot or undershoot are involved in consideration of energy partition during the earthquake faulting. In contrast to the study of Bouchon and Vallée, in which the rupture propagation along the main fault could exceed the local shear-wave speed, perhaps reach the P-wave speed on a certain section of fault, our results show that, under a slip-weakening assumption combined with a frictional undershoot (partial stress drop model), average rupture speed should be equal to or less than the Rayleigh wave speed with a high seismic radiation efficiency, which is consistent with the result derived by waveform inversion and the result estimated from source stress field. Associated with the surface rupture mechanism, such as partial stress drop (frictional undershoot) associated with the apparent stress, an alternative rupture mechanism based on the slip-weakening model has also been discussed. [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]

A method of estimation of the stress level in the focal region of an earthquake is proposed in this paper. The stress level in the focal region before and after the December 26, 2004 M9.0 Sumatra earthquake is estimated. The result shows that the stress value before this major earthquake occurred was about 2.79 MPa and dropped to 1.51 MPa after its occurrence with a decrease of about 46%. Therefore, this large earthquake occurred under a relatively lower stress level. [ABSTRACT FROM AUTHOR]

On the basis of the assumption that ω2 model accords with source displacement spectra, we have obtained the mathematical expressions for calculating apparent stresses of moderate-small shocks from low-frequency flat level and corner frequency. By using digital seismic records, apparent stress values are calculated for 823 moderate-small shocks of 4 earthquake series in Yunnan area following corrections for instrument response, propagation influence and site effect. The results show that for the 4 earthquake series in Yunnan area, apparent stress hints precursory information, which means that if a moderate-small shock occurs with apparent stress larger than 1 MPa in an earthquake series, a moderate-strong earthquake will occur afterwards; and if there is not moderate-small shock with apparent stress larger than 1 MPa after a moderate-strong event in an earthquake series, strong aftershock will not occur. The research also indicates that the average apparent stress value is 0.8 MPa in Yunnan area, therefore, apparent stress is not obviously related to seismic magnitude. [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]

Based on the representation theorem of seismic energy radiation, in this study, we have quantitatively investigated the effect of free surface on the radiation energy distribution due to a coupling interaction between free surface and near surface finite fault for the reverse earthquake faulting. Corresponding to the finite faulting, a 2-D pseudostatic-reverse-fault-dislocation solution has been used in the calculation of the work done by the seismic response against tree surface. The results indicate that, due to a strong coupling interaction between the free surface and near surface fault, the total radiated seismic energy ER is much larger than that radiated only from the fault itself (EF), especially for the shallow reverse faulting. In convention, EF is commonly used in the estimation of earthquake energy radiation. However, when the fault depth H, the distance between the free surface and top of fault location, in- creases, the effect of the coupling interaction between the fault and free surface decreases gradually. Therefore, the total radiated energy ER approaches to the EF when the depth H is about 2 times the fault length I. The current study could provide us a partial explanation of the apparent stress discrepancy observed at the far field and near field in the recent large earthquake. Moreover, the current study also has a significant implication of how to quantitatively describe the near fault strong ground motion and associated seismic hazard from the earthquake source energy point of view. [ABSTRACT FROM AUTHOR]

We develop a data set of aftershock recordings of the 1999, M = 7.4 Izmit and M = 7.2 Duzce (Turkey) earthquakes to study their source parameters. We combined seismograms from 44 stations maintained by several sources (organizations) to obtain a unified data set of events (2.1 ≤ Mw ≤ 5.5). We calculate source parameters of these small earthquakes by two methods that use different techniques to address the difficulty in obtaining source spectra for small earthquakes subject to interference from site response. One method (program NetMoment (NM), H utchings, 2004) uses spectra of direct S waves in a simultaneous inversion of local high-frequency network data to estimate seismic moment, source corner frequency ( f c), site attenuation ( k) and whole-path Q. This approach takes advantage of the source commonality in all recordings for a particular earthquake by fitting a common Brune source spectrum to the data with a and individual k. The second approach (M ayeda et al., 2003) uses the coda method (CM) to obtain “nonmodel-based” source spectra and moment estimates from selected broadband recording sites. We found that both methods do well for events that allow the comparison with seismic moment estimates derived from waveform modeling. Also, source spectra obtained from the two methods are very closely matched for most of the events they have in common. We use an F test to examine the trade-off between k and f c picks identified by the direct S-wave method. About half of the events could be constrained to have less than a 50% average uncertainty in f c and k. We used these source spectra solutions to calculate energy and apparent stress and compare these to estimates from the selected “good quality” source spectra from CM. Both studies have values mutually consistent and show a similar increase in apparent stress with increasing moment. This result has added merit due to the independent approaches to calculate apparent stress. We conclude that both methods are at least partially validated by our study, and they both have usefulness for different circumstances of recording local small earthquakes. CM would work well in studies for which there is a broad magnitude range of events and NM works well for local events recorded by band-limited recorders. [ABSTRACT FROM AUTHOR]

According to energy partition principle, we have derived a generalized formula used to calculate the radiation efficiency. It overcomes the numerical errors involved in the estimation of radiation efficiency caused by the uncertainties owe to the different frictional mechanisms which is used to describe the earthquake faulting. Using real seismic data published in the previous studies, we have recalculated the radiation efficiency with associated to the different frictional mechanisms, and compared with previous results lack of consideration of frictional mechanism. The results indicate that, based on the new formula, the radiation efficiency we have estimated is always less than 1, and the unphysical conclusion of radiation efficiency greater than 1 is avoided completely. [ABSTRACT FROM AUTHOR]

On the basis of the assumption that ω 2 model accords with source displacement spectra of moderate-small shocks, we calculate the apparent stress values of 1 020 moderate-small shocks recorded by the Digital Seismic Network of Yunnan Province by using the low-frequency flat level and corner frequencies. The results show that the apparent stress is of good significance in earthquake prediction. The moderate-small shock with apparent stress larger than 0.9 MPa can be used as a referential index to predict moderate-strong earthquakes in Yunnan area. And its relevant predictability evaluation ( R value) has a high confidence level. [ABSTRACT FROM AUTHOR]

The method of radiation energy ( E R) of the earthquake wave measured by the peak velocity ( r·v) of the ground motion is applied to a detailed study on the temporal and spatial distribution of the seismic apparent stresses ( σ a) for the moderate and small earthquakes and two aftershock sequences in Yunnan area. The results show that there exists an obvious non-homogeneity for the seismic apparent stresses in the spatial distribution. The concentrated regions of the high apparent stresses are related to the active places of the moderate and small earthquakes. Before the Dayao M=6.2 earthquake, there was a period in which the apparent stresses were high and the value was 5 times of the average value, 0.25 MPa. The relatively high values of apparent stresses distribute around the epicentral area of the major shock and nearby. It indicates that the variation characteristics of the apparent stresses can be taken as a new kind of criterion for the earthquake-risk forecast. Usually the ratio of the apparent stresses of the aftershock sequence σ aA to the ones σ aM of main shock is less than 1.0. [ABSTRACT FROM AUTHOR]

According to the rupture dynamics of earthquakes, variations of the apparent stress and the difference between the static stress drop and the dynamic stress drop during the rupture of earthquakes are analyzed for the July 20, 1995 M L=4.1 Shacheng, Hebei, China, earthquake sequence. Results obtained show that the apparent stress for main-shock is about 5 MPa, and the average apparent stress for aftershocks 0.047 MPa. During the rupture of the main-shock, the dynamic stress drop is approximately 1.6 times greater than the static stress drop with the difference of nearly 2.7 MPa. The dynamic stress drop is less than the static stress drop for all aftershocks with the average difference of −0.75 MPa. Therefore, when the mainshock occurs the final stress on the focal fault is higher than the dynamic frictional stress, corresponding to that the fault is abruptly locked. When the aftershocks occur the final stress on the focal fault is lower than the dynamic frictional stress, corresponding to that the fault overshoots. It can be seen from the above results that there could be some differences in the physic processes between the mainshock and the aftershocks. [ABSTRACT FROM AUTHOR]

The behavior of apparent stress for normal-fault earthquakes at subduction zones is derived by examining the apparent stress (, whereis radiated energy andM0 is seismic moment) of all globally distributed shallow (depth,) earthquakes with normal-fault mechanisms that occurred in or near subduction zones between 1987 and 2001 for whichandM0 are available. Accurately determined hypocentres from the Engdahl–Hilst–Buland (EHB) catalogue establish the fine detail of the Wadati–Benioff zone. In many cases, we can relate trends in apparent stress to specific features within the subduction zone and compare these with trends for interplate-thrust earthquakes in the same subduction zones. There are two depth ranges over whichτa for normal-fault earthquakes shows maxima. The highest and most anomalous values ofτa are found in the deeper depth range from 35 to 70 km. The high-τa events (up to 5 MPa) are characteristically intraslab and in proximity to zones of intense deformation such as a sharp slab bend or where opposing slabs collide. High-τa events in the region of the shallower maximum (hypocentres between 10–35 km and) are also generally intraslab, but occur where the lithosphere has just begun subduction beneath the overriding plate. They usually occur in cold slabs near trenches where the direction of plate motion across the trench is oblique to the trench axis, or where there are local contortions or geometrical complexities of the plate boundary. Loweris associated with events occurring at the outer rise (OR) complex (between the OR and the trench axis), as well as with intracrustal events occurring just landward of the trench. The average apparent stress of intraslab-normal-fault earthquakes is considerably higher than the average apparent stress of interplate-thrust-fault earthquakes. In turn, the averageτa of strike-slip earthquakes in intraoceanic environments is considerably higher than that of intraslab-normal-fault earthquakes. The variation of averageτa with focal mechanism and tectonic regime suggests that the level ofτa is related to fault maturity. Lower stress drops are needed to rupture mature faults such as those found at plate interfaces that have been smoothed by large cumulative displacements (from hundreds to thousands of kilometres). In contrast, immature faults, such as those on which intraslab-normal-fault earthquakes generally occur, are found in cold and intact lithosphere in which total fault displacement has been much less (from hundreds of metres to a few kilometres). Also, faults on which highτa oceanic strike-slip earthquakes occur are predominantly intraplate or at evolving ends of transforms. At subduction zones, earthquakes occurring on immature faults are likely to be more hazardous as they tend to generate higher amounts of radiated energy per unit of moment than earthquakes occurring on mature faults. We have identified earthquake pairs in which an interplate-thrust and an intraslab-normal earthquake occurred remarkably close in space and time. The intraslab-normal member of each pair radiated anomalously high amounts of energy compared to its thrust-fault counterpart. These intraslab earthquakes probably ruptured intact slab mantle and are dramatic examples in whichMe (an energy magnitude) is shown to be a far better estimate of the potential for earthquake damage than. This discovery may help explain why loss of life as a result of intraslab earthquakes was greater in the 20th century in Latin America than the fatalities associated with interplate-thrust events that represented much higher total moment release. [ABSTRACT FROM AUTHOR]

Statistical properties of reported earthquake precursors show apparent focal mechanism dependence. Intensity of anomaly is described by the ‘anomaly ratio’ as defined by the number of stations/items reporting anomalies before the target earthquake over the number of stations/items in operation around the target earthquake. Variation of the ‘anomaly ratio’ with the magnitude of the target earthquake was studied for dip-slip earthquakes all over China, strike-slip earthquakes in eastern China, and strike-slip earthquakes in western China, respectively. It is observed that for strike-slip earthquakes, the ‘anomaly ratio’ increases linearly with the magnitude of the target earthquake, while earthquakes in eastern China and western China have different slopes. For dip-slip earthquakes, however, the ‘anomaly ratio’ has no statistically significant change with the magnitude of the target earthquake. Limited data imply that the ‘anomaly ratio’ seems proportional to the apparent stress of the target earthquake. The result might be heuristic for the analysis of candidate earthquake precursors. [ABSTRACT FROM AUTHOR]