Local Stress Changes Research Articles

The effect of static Coulomb stress changes on the earthquake interaction in South-Central Apennines (Italy)

We have computed static stress changes associated to several earthquakes occurred in the Apennine chain, in Italy. Stress associated with fault slip has been computed by the Okada (1992) formulation. Static Coulomb stress changes associated to three subevents forming the Irpinia, 1980, Ms=6.9 main shock indicate that such subevents have been consecutively triggered, each one by stress changes produced by previous ones. Furthermore, aftershocks of this complex faulting event are well correlated with zones of maximum increase of Coulomb stress. The interplay of regional stress and of local stress changes due to the mainshock produces an aftershock distribution considerably wide and a large variability of focal mechanisms. Variability of focal mechanism is consistent with a low level of background regional stress (less than 2 Mpa). The analysis of two further seismic sequence in the central Apennine, occurred on 1979 close to Norcia town (ML=5.9) and on 1984 in National Park of Abruzzo (ML=5.5), also show a clear correlation of aftershock occurrence with positive Coulomb stress changes generated by mainshocks. The static stress change due to the mainshock of 1984, in Abruzzo region, is likely to have triggered, 4 days after, a further mainshock (ML=5.1) on the northern edge prolongation of the main fault, where the Coulomb stress change is maximum.Such evidences indicate a strong correlation among earthquakes in the Apennine chain, trough static stress changes, at several time and space scales. Modelling of such effects is useful both for improving our knowledge of the earthquake dynamics and for a better evaluation of seismic hazard in Italy.

Evidence for static stress interaction among earthquakes in the south-central Apennines (Italy)

We have computed static stress changes caused by several earthquakes that occurred in the Apenninic chain (Italy). Static stress associated with fault slip has been computed using the Okada (1992) formulation. Static Coulomb stress changes associated with the three subevents forming the 1980 Irpinia MS = 6.9 main shock indicate that each subevent was consecutively triggered by stress changes produced by the previous ones. Furthermore, aftershocks of this complex faulting event are well correlated with zones of Coulomb stress increase. The interplay of regional stress and local stress changes due to the main shock produces an aftershock distribution wider than expected and a large variation in focal mechanism. The variation in focal mechanisms is consistent with a low level of background regional stress (less than 2 MPa). Moreover, static stress changes due to the Irpinia earthquake appear to have triggered a moderate‐magnitude (ML ≈ 5) seismic sequence in an adjacent tectonic area (close to the town of Potenza), with a delay of some years. The analysis of a further two seismic sequences in the central Apennines, which occurred in 1979 close to the town of Norcia (ML = 5.9) and in 1984 in the Abruzzo National Park (ML = 5.5), also show a clear correlation between aftershocks and the positive Coulomb stress changes generated by the main shocks. Aftershocks of the 1979 Norcia earthquake cluster at two lateral edges of the main fault, as expected for a moderate‐magnitude main shock in which the local stress change is considerably lower than the regional stress field. The static stress changes due to the 1984 main shock in Abruzzo are likely to have triggered a further main shock four days later (ML = 5.1) at the northern edge of the main fault, where the Coulomb stress change is maximum. This evidence indicates a strong correlation between the earthquakes in the Apenninic chain, through static stress changes, at several time‐ and space‐scales. Modelling of such effects is useful both for improving our knowledge of the earthquake dynamics, and for a better evaluation of seismic hazard.

Determination of the Effects of Strain on Electrical Resistivity in Patterned Interconnects

AbstractSensitive measurements of electromigration-induced resistance changes in metallization interconnects have been previously interpreted as due to precipitation effects, vacancy concentration changes and local stress changes (due to the piezoresistance effect). The latter have the potential for characterizing the early stages of electromigration-induced diffusive phenomena prior to larger scale effects such as voiding and subsequent localized joule heating which seriously complicate the interpretation of small resistance changes. However the utility of such “early" measurements is also hindered by lack of an accurate knowledge of the stress coefficient of resistivity as a proper characterization of the change in strain state of the Al. We present measurements of the effects of volumetric strain on the resistivity of Al interconnects where the strain is induced by thermal expansion mismatch between the Al and surrounding passivations. The piezoresistance effect is characterized by properly accounting for the degree of interconnect constraint (and volumetric strain) induced by thermal expansion mismatch as a function of temperature for both passivated and unpassivated lines. Sensitive interconnect resistance versus temperature measurements for differently constrained interconnects (with different volumetric strains) thus allows for the measurement of the piezoresistance effect. Other effects such as solute or vacancy concentration changes with temperature are minimized since the measurements are performed by cooling the passivated and unpassivated lines from room temperature to approximately 70K, rather than by significant heating above room temperature. We determine the piezoresistance coefficient, defined as dρ/dɛv, where ρ = resistivity and ɛv = volumetric strain, to be approximately 1.5−5 Ω-cm, in rough agreement with previous work. The interpretation of sensitive resistance measurements as volumetric strains in isolated sections of interconnects undergoing electromigration-induced diffusion processes is described for specialized test structures.

Detailed Mapping of Focal Mechanisms in/around the 1995 Hyogo-ken Nanbu Earthquake Rupture Zone.

Earthquake focal mechanisms before and after the 1995 Hyogo-ken Nanbu earthquake have been investigated using seismic records from regional seismic networks. Before the mainshock, seismicity was very active at the Tamba Plateau, a neighboring area of the Hyogo-ken Nanbu earthquake rupture zone. In contrast, the seismicity along the Hyogo-ken Nanbu earthquake rupture zone was not so active. Most earthquakes in these regions had source mechanisms of E-W compression and were of the strike-slip or reverse-fault type. Most aftershocks along the Hyogo-ken Nanbu earthquake rupture zone have strike-slip solutions with P-axis in the E-W or ESE-WNW direction, which is compatible with the trend of aftershock distribution and the strike of active faults the same as the mainshock mechanism. Simultaneously, many other aftershocks were of the reverse-fault type with E-W compression. This area is still controlled by the regional stress field of E-W compression observed before the mainshock. Although, we could find various types of mechanisms in the aftershock sequence, some normal fault-type events were also observed in the mainshock rupture zone. We could find events of SE-NW compression, and this direction is nearly perpendicular to the trend of the mainshock rupture zone. Some aftershocks that occurred near the epicenter of the mainshock had solutions of N-S compression. The geometry of the active fault systems and/or local stress change induced by the mainshock may cause these complex features of focal mechanisms. After the mainshock, the focal mechanisms of earthquakes in the Tamba Plateau were approximately E-W compressional; the same as that before the mainshock.

Stress analysis in the intraplate area of Gazli, Uzbekistan, from different sets of earthquake focal mechanisms

Occurrence of intraplate earthquakes have been related either to reactivation of preexisting zones of weakness in a uniformly oriented regional stress field or to local stress changes. More recently, buildup of pore pressure anomalies has been proposed to explain both the low recurrence rate and some misorientation of rupture planes in the prevailing regional stress field. In this study, we analyze local stress field orientation in the area of the three Ms = 7.0 Gazli (western Uzbekistan) earthquakes by using different sets of earthquakes focal mechanisms. We show that stress tensor inversions from both seven 4.2 ≤ Ms ≤ 7.0, forty‐five 0.1 ≤ ML ≤ 3.2 and twenty‐five 1.0 ≤ ML ≤ 3.2 earthquake focal mechanisms give constant maximum horizontal stress direction in agreement with the one deduced from the India‐Asia collision. The best model for the local stress tensor exhibits a significant (25°) discrepancy from vertical for one of the principal stresses. We note, moreover, that the common assumption that one principal stress axis is oriented vertically is not strictly supported by stress states derived from earthquake focal mechanisms available in the world stress database. By evaluating each hypothesis of stress inversion methods from earthquake focal mechanisms, it is shown that, especially in intraplate settings, the first motion focal solution should be the most appropriate one for a formal inversion and that the magnitude of the considered event may not be the only criterion to assess the quality of a stress inversion. This is particularly timely because more and more focal mechanisms are moment tensor solutions instead of first motion solutions. Concerning the Gazli sequence, the slip conditions (pore pressure and frictional coefficient) are evaluated for each of the three mainshocks in terms of an independently determined local stress field. Because variations in orientations between local and regional stress field are not detected, and because the three mainshock fault planes seem to be relatively well oriented for a frictional activation in the local stress field, it is concluded that this seismic sequence is localized on preexisting weakness zones and is not due to local stress orientation anomalies.

A Molecular Dynamics Study of Cu Segregation to the Σ11 Grain Boundary In Al

AbstractWe present results of molecular dynamics (MD) simulation studies of Cu segregation to the Σ11 grain boundary (GB) in Al. The simulations were performed with Embedded Atom Method (EAM) potentials for Al and Al-Cu. The results predict that copper atoms tend to order along either side of the interface even at the pure symmetrical GB, forming alternating chains along the direction. The nucleation of the chains is driven by a change in the local atomic level stress induced by the pre-existing Cu atoms at the GB.

Life prediction of pressure vessel nozzles

When the material yields local stress and strain behaviour changes, especially if there is a notch, determination of the local strain value can be difficult. Therefore it is not easy to predict the life of mechanical components in the low-cycle region. In the present work pressure vessels are considered and fatigue tests carried out. The most stressed zones, which are at the connections between the nozzles and the vessel, are subjected to cyclic loads with subsequent repeated plastic strains that cause nucleation and propagation of fatigue cracks. The life of such a mechanical component under low cycle fatigue can be predicted by utilizing the life strain curves ε− N f or the energy approach (plastic strain and total strain energy density). In the present work, life prediction is performed by considering several different approaches. The results are compared with the experimental results obtained by fatigue testing pressure vessel nozzles. The material considered is Fe 510 B UNI 7070-72 steel.

対称的に組成傾斜したアルミナ系高次機能セラミックスの製造と性質

Hyperfunctional Al2O3 ceramics with symmetrically graded structures of the A12O3/TiC/ Ni/TiC/Al2O3 and Al2O3/Cr3C2/Ni/Cr3C2/Al2O3 were fabricated by SHS/HIP. The SHS/HIP is both a new sintering process of such heterogeneous materials with different sintering tempreratures and a recycling process using a chemical oven of Si waste in zinc smelting. Strong residual compressive stress of 200-800 MPa were produced in the outer Al2O3 layers mainly due to the thermal expansion mismatch between the outer Al2O3 and inner cermet layers. The compressive stress acted to enhance intrinsic toughness and hardness of Al2O3. Moreover, the local stress change produced by the surface damage reached to the opposite side through disturbance of the internal stress balance of compression/tension/ compression designed in these materials. This effect is potentially available to give a damage detectable function.

The origin of sedimentary basins: a status report from the task force of the International Lithosphere Program

Better insights into the mechanisms of basin formation have a direct bearing on the predictive power of forward models for basin fill. Models that link flexure, normal faulting and thrusting on a subbasin scale provide important constraints on the tectonic control of the sedimentary record, enabling a quantitative comparsion with eustatic contributions to the basin architecture. Thus of special importance is the need to link processes with different spatial and temporal scales involved in the evolution of extensional and compressional basins by numerical modelling. A new generation of basin modelling concepts and techniques is one of the main objectives of the Task Force Origin of Sedimentary Basins of the International Lithosphere Program. The focus of this work is on the quantification of the effects of the thermomechanical structure of the lithosphere and its interplay with regional and local stress changes. Other important developments include the step towards three-dimensional modelling and the full integration of rapidly expanding fission track and other data sets to constrain vertical motions in basins. As natural laboratories for the interactive testing and development of new basin modelling techniques, a number of basins with high quality data from industry, government and academia have been selected on the basis of specific testable problems.

Arterial permeability dynamics and vascular disease

There is a growing consensus that regional susceptibility to atherosclerosis correlates topographically with an increased endothelial permeability to macromolecules such as low-density lipoprotein. Earlier research suggested that increases in arterial macromolecular permeability accompany the adaptation of the endothelial lining to changes in fluid dynamic shear stress, and that permeability might therefore be chronically increased where the endothelium is exposed to a shear stress environment that changes throughout the day. Thus the temporal variability of hemodynamic stresses at the vessel wall, with time constants of many minutes or a few hours, may affect local susceptibility to disease. Changes in the hemodynamic stresses on the endothelial surface (‘local’ stress) result from the normal variations in more ‘global’ hemodynamic variables such as blood flow rate, heart rate, and flow partition at branches, that occur throughout the day in response to changes in peripheral metabolic demand. Thus, at any given time, the permeability at a site is determined by: (1) the steady-state relationship between the local permeability and local shear stress; (2) the dynamics of the permeability change induced by changes in local shear; and (3) the extent to which the shear stress at the site is affected by changes in the global variables. Regional variations in any or all of these three factors can lead to corresponding variations in endothelial permeability, macromolecular uptake and, apparently, atherosclerotic risk. Among the three factors, the first may be relatively unimportant if most transport takes place while the endothelium is responding to hemodynamic changes. The last two factors suggest two ways in which hemodynamic variability can contribute to regional variations in uptake and disease: those sites that become more permeable in response to a given change in local hemodynamic stress, or are subject to larger changes, may be more susceptible to disease than sites that respond less strongly to a change in shear stress or are exposed to more stable hemodynamic environments. Since little is known about the dynamics of such changes in permeability, this is an important area for experimental exploration. To support such investigations, an initial phenomenological model is proposed relating the time course of vascular permeability changes to the associated response of the endothelium to changes in local wall shear.

Magnetomechanical damping in iron

We have carried out a complete, detailed study of magnetomechanical damping on a set of annealed and deformed iron specimens. The results for macroeddy-current and microeddy-current damping are consistent with previous data on iron. The macroeddy peak gives a good indicator of achieving saturation. The microeddy damping offers a usable method for estimating domain size. The slope of damping versus amplitude in the hysteretic Rayleigh region is inversely proportional to the square of a measure of internal stress, as predicted by Smith and Birchak (SB). At higher amplitudes, in annealed and slightly deformed specimens, the damping increases more rapidly than in the Rayleigh region, a phenomenon not previously recognized, and contrary to existing models. The very long straight line in the Rayleigh region, implying a lack of any linear scale for the hysteresis, suggests that there is a fractal nature to the process. This suggestion is consistent with the SB theory. A possible model for the elementary hysteretic event is the reorientation of a quadrupole as the local stress changes sign; if this process involves a random sampling of the internal stress field, the lack of scale can be accounted for.

Study of the stress state in boron-aluminium under active loading

Methods of X-ray structure analysis are used for studying kinetics of the stress state of the boron-fiber-aluminium-matrix composite. It is shown that the composite behavior under load depends on the degree of plastic deformation development in the matrix. Plastic deformation in the matrix in the first stage contributes to local stress changes and then results in its increasing.

Effects of posture on flow-volume curve configuration in normal humans.

Tien et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 46: 565-570, 1979) found reproducible details in the configuration of averaged maximal expiratory flow-volume curves and suggested that these details may correspond to sudden relocations of airway choke points. The occurrence of choke points depends on factors affecting local airway pressure-diameter behavior. We postulated that changes in posture as they affect the distribution of lung recoil on airways might change the locations of choke points and thereby alter flow-volume configuration. Twenty normal adults performed five flow-volume curves in each of four postures (standing, supine, right, and left lateral recumbent). Volume was measured with a Krogh spirometer and airflow with a Fleisch No. 4 pneumotachometer. Curves were digitally filtered and plotted relative to upright total lung capacity. Five curves in each posture were averaged at increments of 0.1 l/s of flow and average volumes at given flows were compared using the Student's t test. Significant differences (P less than 0.01) in mean volumes at given flows occurred in all subjects from standing to supine and/or right to left lateral postures. Large changes in configuration were apparent in one of the two postural pairs in eight subjects. We conclude that changes in posture result in significant changes in flow-volume configuration in most normal adults. These findings are consistent with the wave-speed theory of flow limitation and suggest that small changes in local airway stresses can significantly alter the location and motion of airway choke points during forced expiration.

Local magnetic field variations and stress changes near a slip discontinuity on the San Andreas fault.

Data from an array of proton magnetometers in central California indicate that a systematic decrease in magnetic field of about 2 γ in 5 years has occurred in a localized region near Anzar, California, just north of the creeping section of the San Andreas fault. This field change has most likely resulted from changes in crustal stress in this region, although an unknown second-order effect of secular variation cannot be excluded as a alternate explanation. Tectonomagnetic models have been developed using dislocation modeling of slip on a finite section of fault. Assuming a fault geometry and rock magnetization, these models relate changes in stress, fault slip, and fault geometry to surface magnetic field anomalies. A large-scale anomaly, opposite in sense to that observed but of similar amplitude, would be expected to have accumulated in this area during the past 70 years. A localized 5-bar decrease in shear strain on the fault resulting from about 2 cm of slip on a 0.25-km square patch at a depth of 1 km beneath the surface trace of the fault opposite the magnetometer could explain the observed data and still be compatible with the geodetic strain measurements in the area. Other models of limited local slip are equally possible. The occurrence of a moderate magnitude earthquake in this region will allow comparison of stress changes estimated by different techniques.

An analysis of local changes in gravity due to deformation

Deformation causes changes in gravity even though the measuring station is fixed relative to the center of the earth and the total mass in the vicinity of the station does not change. Deformation has two effects: the density at a point changes in response to changes in local stresses and the point itself moves relative to the station. The general expression derived here shows that the gravity change depends on the uplift immediately beneath the station and the deformation of cavities at depth — cracks, pores, magma reservoirs, etc. The approximation is made that density is uniform except for cavities, but no assumptions about the constitutive behavior of the medium are necessary.