Non-shear Components Research Articles

Shear behavior of gypsum boards sheathed CFS framed shear walls with enlarged edge members

This study investigates the influence of nonshear components on the shear performance of cold-formed steel (CFS) framed shear walls. Regarding the connection fields between nonshear components and shear walls as reinforced edge members (REMs), full-scale model tests of six gypsum board sheathed CFS framed shear walls were conducted with a focus on investigating the shear behavior of CFS framed shear walls with enlarged edge members. A numerical simulation method for predicting the shear performance of CFS framed shear walls with enlarged edge members was established and verified. The results show that, (1) After the “diaphragm effect” was weakened or even eliminated, the REMs still had the ability to resist the bending moment and shear force, preventing CFS structures from collapse. (2) The REMs (containing wing walls) changed the mechanical feature of CFS framed shear walls that depended only on the “diaphragm effect” to resist the shear force and transformed the wall’s plastic development mechanism, improving the energy dissipation capacity of the walls over four times. Such a “wing wall effect” should be considered when estimating the influence of nonshear components. (3) The recommended response modification factor should be increased by at least 1.3 times due to the REMs. (4) The relative errors between the simulated and test results were within 8%.

Effect of 3.5 wt% NaCl and Cathodic Charging on the Atomic Strain Distribution of a Plastically Deformed AA 7004

The effects of environments in altering the atomic strain distribution in AA 7004 while subjected to slow strain rate testing to environmentally assisted cracking are investigated. Two different temper conditions—one where predominantly G.P. zones are present and the other with predominantly η′/η precipitates were chosen for the present study. Three different test environments—glycerol (Gly), 3.5 wt% NaCl (OCP), and 3.5 wt% NaCl with 100 mV cathodic charging vs. open-circuit potential (CP) were used. Under the above environmental conditions, the alloy aged at 140°C for 24 h, containing predominantly G.P. zones, showed the existence of the tensile nonshear components of the strain. On the other hand, the alloy aged at 140°C for 48 h, containing predominantly η′/η precipitates, showed only one of the two nonshear strain components that were tensile in nature, with a simultaneous reduction in the shear component of strain. The work highlights that the effects of the environment on the deformation behavior of the alloy are evident by way of alterations in strain distribution at the atomic level, which could possibly explain the increase in dynamic recovery for the microstructure containing primarily the G.P. zones, and the decrease in dynamic recovery for microstructures consisting predominantly of η′/η precipitates.

The Mechanism of Microearthquakes Related to a Gas Storage Using Differently Constrained Source Models: A Case Study of the Háje Location, Czech Republic

The resolution of a source mechanism is investigated in terms of three differently constrained source models: the moment tensor, the shear-tensile crack source model, and the double couple source model. The moment tensor (MT) is an unconstrained description of a general dipole source; the shear-tensile crack (STC) represents a slip along a fault with an off-plane component and the double couple (DC) corresponds to a simple shear slip along a fault. The inversion of body wave amplitudes is applied on microseismic events located in the vicinity of underground gas storage Haje (Czech Republic) where volume changes in the source can be expected. The orientation of the simple shear fracture component is resolved almost always well, independently of the source model used. On the other hand, the non-shear components differ largely among the source models considered, from both the model definition and robustness of the inversion. A comparison of the inversion results for the three alternative source models permits an assessment of the reliability of the non-shear components retrieved. Application of the STC model to all events appears to be the most appropriate. The analysis confirms a shear slip for three events and a tensile fracturing for other three events.

Microearthquake mechanism from wave amplitudes recorded by a close-to-surface seismic array at Ocnele Mari, Romania

The resolution of event mechanism is investigated in terms of the unconstrained moment tensor source model and the sheartensile crack source model representing a slip along the fault with an off-plane component. Data is simulated as recorded by the actual seismic array installed at Ocnele Mari (Romania), where sensors are placed in shallow boreholes. Noise is included as superimposed on synthetic data, and the analysis explores how the results are influenced (i) by data recorded by the complete seismic array compared to that provided by the sub-array of surface sensors, (ii) by using threeor one-component sensors, and (iii) by inverting Pand S-wave amplitudes vs. P-wave amplitudes only. The orientation of the pure shear fracture component is resolved almost always well. On the other hand, the noise increase distorts the non-double-couple components (non-DC) of the moment tensor unless a high quality dataset is available. The shear-tensile crack source model yields considerably less spurious non-shear fracture components. Incorporating recordings at deeper sensors in addition to those obtained from the surface ones allows for the processing of noisier data. Performance of the network equipped with threecomponent sensors is only slightly better than that with uniaxial sensors. Inverting both Pand Swave amplitudes compared to the inversion of P-wave amplitudes only markedly improves the resolution of the orientation of the source mechanism. Comparison of the inversion results for the two alternative source models permits the assessment of the reliability of non-shear components retrieved. As example, the approach is investigated on three microseismic events occurred at Ocnele Mari, where both large and small non-DC components were found. The analysis confirms a tensile fracturing for two of these events, and a shear slip for the third.

Small Scale Earthquake Mechanisms Induced by Fluid Injection at the Enhanced Geothermal System Reservoir Soultz (Alsace) in 2003 using Alternative Source Models

The geothermal reservoir at Soultz-sous-Forets is a valuable natural laboratory for understanding the mechanisms of microearthquakes generated during stimulations and circulation tests. An ongoing effort currently exists regarding the retrieval of mechanisms aimed to indicate the type of fracturing of the rock massif. As a default, a moment tensor description has been applied. Nevertheless, the retrieval of the mode of fracturing still remains ambiguous. Recent studies indicate a prevailing shear slip but, rarely, a non-shear pattern has also been observed. The moment tensor, used today as a universal tool for descriptions of the mechanism, captures general balanced dipole sources. However, in the case of small-scale earthquakes, the moment tensor need not always be reliably determined. In an effort to fit the data, there may be notable non-shear components caused by the low quality of input data. Constraining the source model to directly determine a simpler one is convenient for describing the physical phenomena expected for a particular focus. An opening of new fractures can be described, to a first approximation, by a tensile crack, optionally combined with a shear slip. Such an alternative model is called a shear-tensile crack (STC) source model. The combination is practical, and can be used to both identify events that reflect purely mode-I (tensile) failure and to determine the dilation angle of the fracture undergoing shear. The latter is particularly important in enhanced geothermal system reservoirs such as Soultz, where shear-related dilation is believed to be the primary mechanism underpinning permeability creation during stimulation injections. We performed a synthetic case study by simulating seismic data as recorded by the actual seismic array installed at Soultz-sous-Forets. Synthetic P and S amplitudes for several shear-tensile source models were inverted for several types of station coverage. The analysis explored how results were influenced by mislocation, mismodeling, and noise contamination of data. In most cases, the orientation of the mechanism was well resolved. Determination of shear vs. non-shear content within the mechanism was more difficult. From all of the factors influencing resolution that we explored, the quality of the monitoring system (the number of stations and their distribution with respect to the focus) and noise contamination were of the highest impact. The STC source model yielded considerably less spurious non-shear fracture components than the moment tensor. From the bulk of the seismicity recorded during the stimulation in 2003, we concentrated on the first phase of the injection when only a single borehole at the site was stimulated. We processed thirteen small earthquakes with magnitudes larger than 1.4 that were not treated in previous studies. We determined that their source mechanisms were dominantly pure shear slips on pre-existing faults, just as the earthquakes investigated earlier were. The results were also in agreement with the stress pattern from in situ measurements.

Disputable Non-Double-Couple Mechanisms of Several Strong Earthquakes: Second-Degree Moment Approach

The earthquake source mechanism (description of the geometry of the source and its strength in terms of forces equivalent to rupturing of the rock mass) is routinely modeled as a moment tensor (MT) describing the earthquake focus as a point. However, sometimes this approximation is not satisfied, and seismic radiation keeps the directivity due to the finite extent of the source. Inversion into the MT then may yield a biased mechanism. Synthetic study in the Adamova and Silený (2010) demonstrated the appearance of spurious non‐double‐couple components in the mechanism even for a pure double‐couple (DC) source. Their method was designed to reduce the spurious source components by using the second‐degree moments to evaluate their contribution into the records and subtract it from the data. Here we applied the procedure to five moderate to large regional events with large nonshear components. They are mostly located on large tectonic faults where predominantly pure shear slip is expected. We studied one event on the prominent North Anatolian fault, three events in the Pacific area, and one event in Bolivia. In most cases, the non‐DC components essentially were reduced, and the geometry of the mechanism remained largely unchanged. This confirms the hypothesis that part of the non‐DC components in regional MT solutions may be spurious due to the neglect of the source finiteness in the routine procedure of the MT retrieval. In addition, the geometrical and kinematical characteristics of the foci provided by the second‐degree moments (the source ellipsoid and rupture velocity vector) are mostly consistent with the fault geometry, aftershock distribution, and estimates of rupture speed from available previous studies.

Comparison of picture frame and Bias-Extension tests for the characterization of shear behaviour in natural fibre woven fabrics

The investigation of the shear behaviour of technical natural fibres is vital for the insurance of aesthetics and performance of light weight, high strength, and eco-friendly composites. In this study, Egyptian jute fibre plain weave fabrics of various areal densities were investigated to describe their shear behaviour in terms of shear forces, shear angles and shear lock angles, using the Bias-Extension and the Picture Frame test methods. Results show that both methods are valid for natural fibres and produce comparable results. Whereas the Bias-Extension test presents a fast and simple test procedure, the analysis of the results is more complex due to the interaction of non-shear components. On the other hand, the Picture Frame test proves to be time consuming and in need of a more complex test rig, but results in pure shear deformations throughout the sample.

Shear and tensile earthquakes caused by fluid injection

[1] We apply rock mechanics concepts to the seismological observations in order to explain why during hydraulic injection some events display tensile and some shear deformation. The presence of non-shear components depends on the differential stress and the fracture orientation with respect to the σ1 direction. Provided the slip vector is parallel to the traction we define four types of earthquakes according to the ratio of the shear and tensile components. Assuming a Griffith failure envelope, hybrid events containing both shear and tensile components can occur for fractures striking within 22.5° of σ1. We argue that pure tensile fractures striking parallel to σ1 are unlikely in the presence of natural fractures. The low shear traction of tensile events also implies their small stress drops. By applying the analysis to two different data sets, Soultz-sous-Forets and Cotton Valley, we show that different orientations of natural fractures and differential stress in the targeted formations made each region favorable for different non-DC components in the injection-induced seismicity.

Intraplate earthquake swarms in West Bohemia/Vogtland (Central Europe)

West Bohemia (Czech Republic) and Vogtland (Germany) are among the most active intraplate earthquake-swarm areas in Europe with the largest events mostly of magnitudes $M_L$ \< 4.0. The principal char-acteristics of the West Bohemia/Vogtland earthquake swarms are derived on the basis of local observations from the network WEBNET during the period between 1991 and 2009. Swarm microearthquakes clustered in number of small focal areas; however, about 90\% of the total seismic moment was released in the Nový Kostel (NK) focal zone, which was formed by an NNW striking and steeply dipping fault plane. The focal depths ranged between 5 and 22 km in the whole region and between 4.5 and 11 km in the NK zone, while most of the swarm events clustered at depths from 8.5 to 9.5 km. All larger earthquake swarms took place in the NK zone; though they were located close, they differed significantly in their evolution. Two swarms, the 2000 ($M_L$ ≤ 3.3) and 2008 ($M_L$ ≤ 3.8) swarms were located on the same portion of the NK focal zone which implies reactivation of the same fault segment. Attention was paid to source mechanisms of the 1997 and 2000 swarms, particularly to the non-shear components in the 1997-swarm earthquakes. All the 1997 sources were of dipole character: the slightly compressive dipoles dominating in the first swarm phase were replaced by tensile dipoles in the second phase. On the contrary, the 2000 swarm events possessed pure double-couple sources which resulted in pure shears along the NK fault. We infer that the pure-shear rupturing in the 2000 swarm was on account of the favourably oriented NK fault plane with respect to the local tectonic stress field whereas the additional tensile forces were needed for rupturing due to the unfavourably oriented 1997-swarm fault segments. Further, we analyzed statistic characteristics and we show that the magnitude-frequency distribution with the b-value ≈ 1.0 is typical for the West Bohemia/Vogtland earthquake swarms and that scalar moments $M_0$ and the WEBNET magnitudes $M_L$ are related according to power-law $M_0$ ∝ 10$^{M_L}$, which is inconsistent with the definition of the moment magnitude $M_0$ ∝ 10$^{1.5 M_w}$ given by Kanamori (1977). We also show that this inconsistency results in a discrepancy in b-value of the magnitude-frequency distribution. Taking into account total seismic moment of the 2000 and 2008 swarms we infer that $M_{L_{MAX}}$ ∼ 5.0 to 5.3 is the maximum expected magnitude in the main NK focal zone and thus in the whole region. There is still an open question concerning the internal and external triggering of the West Bohemia/Vogtland earthquake swarms. We refer to the results of our recent study and infer that the earthquake swarm probably represents gradually propagating rupture along the fault and that both static and dynamic Coulomb stress changes along the fault plane due to co-seismic slip contribute significantly to triggering of the swarm events. Repeatedly observed almost simultaneous occurrence of seismic activity in different focal zones suggests that common triggering forces act in a broader area of West Bohemia/Vogtland.

Role of crustal fluids in triggering the West Bohemia/Vogtland earthquake swarms: Just what we know (a review)

We summarise the results of seismological studies related to triggering mechanisms, driving forces and source processes of the West Bohemia/Vogtland earthquake swarms with the aim to disclose the role of crustal fluids in the preparation, triggering and governing of the swarms. We present basic characteristics distinguishing earthquake swarms from tectonic mainshock-aftershock sequences and introduce existing earthquakes swarm models. From the statistical characteristics and time-space distribution of the foci we infer that self-organization is a peculiarity of West Bohemia/Vogtland swarms. We discuss possible causes of the foci migration in these swarms from the viewpoint of co-seismic and/or post-seismic stress changes and diffusion of the pressurized fluids, and we summarize hitherto published models of triggering the 2000-swarm. Attention is paid to the source mechanisms, particularly to their non-shear components. We consider possible causes of different source mechanisms of the 1997-and 2000-swarms and infer that pure shear processes controlled solely by the regional tectonic stress prevail in them, and that additional tensile forces may appear only at unfavourably oriented faults. On data from the fluid injection experiment at the HDR site Soultz (Alsace), we also show that earthquakes triggered by fluids can represent purely shear processes. Thus we conclude that increased pore pressure of crustal fluids in the region plays a key role in bringing the faults from the subcritical to critical state. The swarm activities are mainly driven by stress changes due to co-seismic and post-seismic slips, which considerably depend on the frictional conditions at the fault; crustal fluids keep the fault in a critical state. An open question still remains the cause of the repeatedly observed almost simultaneous occurrence of seismic activity in different focal zones in a wider area of West Bohemia/Vogtland. The analysis of the space-time relations of seismicity in the area between 1991 and 2007 revealed that during a significant part of this time span the seismicity was switching among distant focal zones. This indicates a common triggering force which might be the effect of an increase of crustal-fluid pore-pressure affecting a wider epicentral region.

The effect of biaxial texture on the effective electromechanical constants of polycrystalline barium titanate and lead titanate thin films

Effective electromechanical constants as a function of biaxial crystallographic texture in polycrystalline films are modeled using a self-consistent approach. The film is modeled by assuming Gaussian distributions of two Euler angle textures about perfect orientation with varying spread, or full width at half maximum. We see that independent in-plane texturing has little effect on the piezoelectric displacement tensor. Increased out-of-plane texturing gives rise to an enhanced piezoelectric effect for barium titanate films, but not for lead titanate. Twist texturing about these out-of-plane angles shows a further enhancement in the non-shear components of the piezoelectric displacement tensor for both materials. Finally, we use the effective piezoelectric coupling factor as the primary figure of merit for the effective piezoelectric properties of polycrystal devices, thus utilizing all electromechanical constants of this simulation. This quantity shows a primary dependence on the out-of-plane texture.

Mining-induced microseismicity: Monitoring and applications of imaging and source mechanism techniques

The study of microseismicity in mines provides an ideal method for remote volumetric sampling of rock masses. The nature and uniqueness of microseismic monitoring is outlined in the context of acquisition hardware and software requirements. Several topics are used to highlight the potential for novel applications of microseismicity and to outline areas where further study is required. These topics reflect some of the current interest areas in seismology, namelyb values and source parameters, fault-plane solutions, modes of failure and moment tensor inversion, imaging and seismicityvelocity correlations. These studies suggest potential correlations between zones of high seismic velocity, high microseismic activity and maximal stress drops, which can be interpreted spatially to be the locations of highly stressed ground with a potential for rock bursting. Fault-plane solutions are shown to be useful in determining the slip potential of various joint sets in a rock mass. Source parameter studies and moment tensor analysis clearly show the importance of non-shear components of failure, andb values for microseismicity appear to be magnitude-limited and related to spatial rather than temporal variations in effective stress levels.

Computer simulation of the screw dislocation motion in b. c. c. metals under the effect of the external shear and uniaxial stresses

An atomistic study of the motion of the 1/2 [111] screw dislocation was carried out for a shear stress applied on {112} planes and for uniaxial stresses along [012], [001] and [111]. Central force interactions described by the three different empirical potentials used in the previous work (Duesbery, Vitek & Bowen 1973) were assumed. The distortions of the core and the subsequent dislocation motion always reflected the twinning-antitwinning asymmetry of shear on {112} planes. The non-shear components of the stress tensor introduced further asymmetries which vary with interatomic forces. The application of the results of this study to the theory of slip and twinning in b. c. c. metals, is discussed.