Static Stress Changes Research Articles

Usefulness of Coulomb Static Stress Changes in Earthquake Hazard Studies: An Example from the Lake Van Area, Eastern Turkey

It has been globally documented over different tectonic environments that Coulomb static stress changes caused by a mainshock can promote or demote stresses along the neighboring faults and thus triggers or delays following seismicity. In the present study Coulomb stress changes of the earthquakes in the Lake Van area are calculated using available data and the likely source faults. The calculated stress change maps demonstrate that the large earthquakes in the Lake Area are mostly stressed by the preceding earthquakes, suggesting earthquake rupture interactions. It is further suggested that Coulomb stress maps could be used for constraining the likely locations of the future large earthquakes and in the earthquake hazard mitigation studies.

Determination of the stability of residual pillars in a room-and-pillar mining goaf under eccentric load

In room-and-pillar mining (RPM), the roof of a coal seam is supported by coal pillars; however, the roof is non-uniformly deformed with time. Moreover, coal pillars at different positions are subjected to different stresses and some coal pillars are prone to the effects of eccentric load, thus influencing their stability. Therefore, by taking Bandingliang Coal Mine, Shaanxi Province, China, as the engineering background, the non-uniform deformation characteristics of the roof of a room-and-pillar mining goaf (RPMG) were first analysed by using numerical simulation and theoretical analysis. The residual pillars in the RPMG were partitioned into a uniform deformation zone, a transition zone, and a sub-uniform deformation zone; thereafter, the stress distribution in coal pillars under non-uniform deformation was revealed to show that coal pillars were subjected to non-uniform stresses; subsequently, the distributed force under the eccentric load was concentrated to attain the changes in stress state of coal pillars under eccentric load, including behaviour such as a non-uniformly compressed state, critical state, and a tensile stress state; finally, the pillar stability under the eccentric load was judged by taking the No. 19 coal pillar as an example. The result showed that the shear stress generated by the coal pillar was 0.58 MPa, which was lower than the allowable shear stress (1.51 MPa). As a result, the pillar did not collapse, consistent with actual conditions on site. The result is expected to provide a theoretical basis for controlling pillar stability in the RPMG. The theory of the stability of the residual pillars in the RPMG provided in this paper provides a new direction for determining the stability of pillars, and the study findings have been applied in specific mines and verified.

Spatiotemporal Evolution of Pore Pressure Changes and Coulomb Failure Stress in a Poroelastic Medium for Different Faulting Regimes

AbstractSpatial distribution of aftershocks has been explained by the co‐seismic static Coulomb Failure Stress changes (ΔCFS) to some extent. In practice, the earth's crust is porous medium saturated with fluid filling pores, cavities, cracks, and faults. The pore fluid flow plays an important role in the evolution of the stress field in porous medium of the earth. The ΔCFS can be influenced by the co‐seismic pore pressure changes and the post‐seismic pore fluid flow. In order to understand such impacts, we built 3D fault‐slip finite element models to study the evolution of the pore pressure changes and the ΔCFS based on the fully coupled poroelastic theory. The strike‐slip, reverse, and normal faulting models were investigated separately. The patterns of co‐seismic ΔCFS were similar to the elastic stress changes on a homogeneous half‐space, but there were considerable differences in details especially in the near‐fault area when considering co‐seismic pore pressure change. Due to post‐seismic pore fluid flow, the near‐field stress shadow narrowed gradually in the strike‐slip model. In the reverse faulting model, both the near‐field stress shadow and enhanced areas expanded. In the normal faulting model, the stress shadow near the epicenter reduced. The pore pressure changes decayed sharply at the beginning and then gradually approached to zero because the system evolves to drained conditions. These results can help us to understand the effect of pore fluid flow on Coulomb Failure Stress evolution and might improve the understanding of earthquake triggering and aftershock forecasting.

Multi point monitoring method of prestressed tendon based on distributed sensors

This paper presents a multi-point strain monitoring method based on distributed sensors, which can monitor the multi-point stress of prestressed tendons in concrete. Firstly, the special sensor protection device is installed in the designated position of the component. Then, the sensor is placed in the device and attached to the monitored prestressing tendon. After concrete pouring, the device can form a closed space around the sensor to ensure that the sensor can freely expand and move in a small range when the prestressed tendon is tensioned. The proposed method is applied to the monitoring of the construction period and initial operation period of a large-span spatial structure, and the research results show that the method proposed in this paper can well realize the multi-point monitoring of the prestressed tendon strain in the concrete, and effectively solve the engineering problems; through the analysis of the long-term monitoring data, we can accurately grasp the influence of each construction condition on the structure stress, and clarify the actual stress state and long-term change trend of the structure. The obtained monitoring data play a positive role in guiding the construction of prestressed structure, and the construction safety can be objectively evaluated by analyzing the monitoring data.

Thermomechanical method in application to measurement of changes in stress states in substrate-PVD coating systems

Thermomechanical test methods with temperature modulation (MT TMA) are increasingly used to measure a number of useful properties of materials, e.g. rheological properties of polymers. This is due to the possibility of measuring thermal effects with very high resolution. The article describes and verifies a new possibility of implementing, using this method, diagnostic task, consisting in the measurement of changes in mechanical stress states in PVD thin-film systems under the influence of thermal energy. The present paper provides a description of the measurement method and a set of results of diagnostic test, performed with its use, for the thermal stability of stresses in the substrate-coating system samples. The obtained results were also compared with the results of tests carried out using other “traditional” methods and with the results of operational tests of tools with modified, involving the same coatings, working surfaces. The results document a complete applicability of the method developed.

The 30 October 2020, MW = 7.0, Samos earthquake: aftershock relocation, slip model, Coulomb stress evolution and estimation of shaking

We study the major MW = 7.0, 30 October 2020, Samos earthquake and its aftershocks, by calculating improved locations using differential travel times and waveform cross-correlations. We image the rupture of the mainshock using local strong motion data, and we examine the Coulomb stress evolution prior to the mainshock, as well as the coseismic stress changes. Lastly, we estimate the produced shaking using all the available information from strong motion data and testimonies. Earthquake relocations reveal the activation of the E-W oriented Kaystrios fault, in the North basin of Samos with a possible extension to the West. The kinematic rupture inversion suggests non-uniform bilateral rupture on a ∼60 km × ∼20 km fault area, with the main rupture propagating towards the West and maximum slip up to approximately 2.5 m. Improved locations of the aftershock sequence are anti-correlated with areas of maximum slip on the fault surface. Similarly, the Coulomb stress change calculations show that only off-fault earthquake clusters are located within lobes of increasing positive static stress changes. This observation is consistent with assuming a fault area of either uniform slip, or variable slip according to the obtained slip model. Both scenarios indicate typical stress patterns for a normal fault with E-W orientation, with stress lobes of positive ∆CFF increments expanding in E-W orientation. In the case of the variable slip model, both negative and positive stress changes show slightly larger values compared to the uniform slip model. Finally, Modified Mercalli Intensities based on the fault model obtained in this study indicate maximum intensity (VII +) along the northern coast of Samos Ιsland. Spectral acceleration values at 0.3 s period also demonstrate the damaging situation at Izmir.

The northern Thessaly strong earthquakes of March 3 and 4, 2021, and their neotectonic setting

A sequence of earthquakes occurred on March 3rd and 4th in Northern Thessaly, northern Greece, associated with previously unknown, blind normal faults within the crystalline Palaeozoic basement of the Pelagonian geotectonic zone. Surficial ground deformation, such as liquefaction phenomena in fluvial plains, as well as soil fissures and rock falls, have been mapped. Geological indications of the unmapped seismic fault, i.e., reactivated shear zones, open cracks, etc., have been identified within the bedrock. Based on geological indications, the main fault projection to the surface could be considered a 15 km NW-SE trending structure and average dip of 45o to the NE. The seismic source of the main shock was modelled, and the Coulomb static stress changes calculated for receiver faults similar to the source. The determination of the active tectonic regime of the region by geodetic data and the well-known faults of NE Thessaly plain are also presented, as well as the revised historical and instrumental seismicity. This earthquake raises new concerns and challenges, revising some established views, such as the status of main stress orientations, the orientation of active tectonic structures, the occurrence of a seismogenic fault in a mountainous massif of crystalline rocks without typical geomorphological expression and the role of blind faults in Seismic Hazard Assessment.

Diverse rupture processes of the 2014 Kangding, China, earthquake doublet (MW 6.0 and 5.7) and driving mechanisms of aftershocks

An unusual earthquake doublet ruptured the high-risk middle segment of the Xianshuihe fault in November 2014, exhibiting significant variations in the rupture and aftershock characteristics. By conducting rupture kinematic inversions jointly with local broadband seismic data, strong-motion data, and coseismic InSAR data, we find diverse rupture processes of this earthquake doublet. The first event ruptured upward along the dip and bilaterally along the strike with the duration of 8.0 s, whereas the second event ruptured mainly around the hypocenter with the duration of 3.5 s. The estimated moment magnitudes of the first and second events of this earthquake doublet were MW 6.0 and MW 5.7, respectively. The further analysis of rupture model-based static and dynamic stress change suggests that the first event is likely responsible for triggering the second event. Based on the comprehensive analysis of aftershock migration features, we find complex and diverse driving mechanisms of aftershocks. Aftershocks of the first event of the earthquake doublet were likely driven by afterslip. Early aftershocks of the second event were also likely driven by afterslip; however, later aftershocks were likely driven by fluid diffusion. The revealed diverse rupture characteristics of the 2014 Kanding earthquake doublet sequence suggest the inherent strength and/or stress heterogeneities on the seismogenic faults.

Experimental investigation of mechanical characteristics for linings of twins tunnels with asymmetric cross-section

A large-scale 3D combined geomechanical model test is conducted in this study to investigate the mechanical characteristics for linings of asymmetrically closely-spaced twin-tunnels constructed in sandy ground. A series of experimental results (i.e., excavation and overloading) effectively reveal the mechanical features of the linings and the stress release and displacement characteristics of the sandy ground for asymmetrical twin-tunnels during the excavation and overloading under the condition of great buried depth (vertical stress) and high stress coefficient (the ratio of lateral to vertical stress). Afterward, numerical analyses are conducted by a finite difference program FLAC3D to verify experimental results. The influences of construction sequence, stress coefficient, clear distance and lining stiffness on mechanical behaviors of linings and stratum are discussed in some details. The experimental results show that during the excavation of the asymmetrically closely-spaced twin-tunnels, the linings are in a state of compression. The lining of the smaller diameter tunnel which excavated later is susceptible to bias pressure. The bending moment located on the lateral side of the larger diameter tunnel close to the smaller diameter tunnel decrease when the smaller diameter tunnel is excavated. The change of stress release direction in the middle soil pillar is the main reason that results in the change of stress state in linings. The overloading process only causes the bending moments increasing continuously, but not affect the basic distribution patterns in linings. Numerical results indicate that if the smaller diameter tunnel is excavated first, the continuous tunneling of the larger diameter tunnel will cause sharp changes in lining moment of smaller diameter tunnel, but it will not cause serious adverse effects on the existing tunnel lining (larger diameter tunnel) if the larger diameter tunnel is excavated first.

Preliminary study of stress changes evolution on central part of Sumatran Fault influenced by large interplate earthquakes and tectonic stress rates

The inland seismic activity in Great Sumatran Fault (GSF) has significantly increased over the past several decades after the occurrence of historical large interplate earthquakes along the plate boundary. This condition led to some occurrences of historical intraplate earthquakes along Sumatran fault. To quantitatively examine the physical mechanisms between intraplate earthquakes and interplate earthquakes, we estimated the static coseismic stress changes of Coulomb failure function (ΔCFF) using receiver fault approach from large historical-recorded interplate earthquakes and the increase in tectonic stress rates. We examined this research in the central part of GSF since this zone is assumed to have the most heterogeneous stress field and thus became our focus study area. The cumulative ΔCFF models showed almost all segments in the central part of GSF suffered negative changes (<-0.1 MPa) which assumed to be unlikely to rupture in short time. However, the preliminary analysis of the increase in tectonic stress rate indicated that large intraplate earthquakes occurred on Angkola and Siulak segments were dominantly influenced by the increase in interseismic stress rate just after the series of large subduction earthquake occurrences, apart from the decreased stress changes from those major interplate earthquakes.

Application of the concept of criterion of a complex stress state to a simple tension for appraisal of resistance of fatigue of structural materials. Part 2. Drawing up criterion and its checking on compliance to experimental data

The criterion for appraisal of resistance of fatigue of structural material at action on it of repeatedly variables loads and static loads in the form of a bend or tensioncompression together with torsion, and also at action of loads, which create two-axis regular change of stress state in a dangerous point of material is constructed. The received criterion will acceptable be coordinated with the known experimental data. Keywords: dangerous point of material, regular cycle of loading, equivalent amplitude, equivalent average stress, chart of extreme amplitudes of stresses. bdsho@nkmz.donetsk.ua

Temporal variations in coda attenuation associated with the 2008 Wenchuan (MW7.9) Earthquake in SW, China

In this study, waveform data obtained from Western Sichuan Seismic Array (WSSA) in China was utilized to reveal the temporal variations in coda attenuation around the eastern Tibet Plateau and Western Sichuan. Based on the single-scattering model, coda attenuation factor Qc−1 is calculated in narrower overlapping frequency bands at 1.0–24 Hz by measuring the coda decay rates for local earthquakes before and after the Wenchuan mainshock. The temporal variations in coda attenuation are investigated within three periods. The period I lasted from January 2007 to the end of 2007. The period II lasted from January 2008 till Wenchuan earthquake. The period III lasted from the mainshock to the end of 2008. The resulted temporal variations demonstrate an increase in average Qc−1 by approximately 35%–45% in the vicinity of Longmenshan and 30%–35% in Sichuan Basin after the Wenchuan earthquake in lower frequency bands within 1.25–8 Hz. On the contrary, the average Qc−1 is shown to decrease by approximately 10%–18% in southern segment of Longmenshan, 15%–38% in the Chuan-Dian block, and 10–12% in the South China block. These results are confirmed by a statistical t-test at 99.9% confidence level. No statistically significant change in Qc−1 (<10%) is found in the Songpan-Ganzi block after the mainshock. Temporal variations of coda attenuation differ significantly in individual blocks after the mainshock. The coda attenuation is proposed to be a beacon to tectonic static stress changes associated with the Wenchuan earthquake.

Mechanism and Stability Analysis of Deformation Failure of a Slope

Force distribution during progressive slope failure is an important element in slope stability analysis. In this study, five mechanical failure modes are proposed for thrust- and pull-type slopes, respectively, and five field forms of thrust-type slopes are described. The properties of progressive failure are evaluated quantitatively: the failure mode of slope obeys the geo-material rule under the peak stress state, and the instability range is gradually developed. The critical stress state zone is in the process of dynamic change with the development of deformation. It appears that the driving sliding force is greater than the frictional resistance along the sliding surface. When rock or soil stabilizing stresses are at maximum, the vector sum of the driving sliding stress and stabilizing stress is equal to zero at the critical state. The frictional resistance is equal to the driving sliding force in the stable and less-stable regions, and the normal pressure is wherever equal to the counterpressure. Rigid, flexible, and rigid-flexible design theories are proposed for slope control. New terms are defined and used to evaluate the stability. The conventional local and surplus stability factors of slopes and their calculation are explained. The force distribution rule is analyzed during progressive failure, and the conventional stability factor definition is discussed. The geological settings and monitoring data of landslides are used to analyse changes in the critical stress state. An example is given to illustrate the failure process analysis. The results show that progressive failure can be well represented and the safety factor can be well described by the main thrust method (MTM), comprehensive displacement method (CDM), and surplus displacement method (SDM), which can be used to feasibly evaluate slope stability.

Monitoring of rock stress change using instrumented rebar rock bolts

Rock stress is causing unwanted deformations of deep underground spaces. Large deformations increase the risk of failure. The underground excavation causes rock stress changes in the surrounding rock mass, and the resulting deformations can be measured. In this paper, we present a method to monitor stress changes in the rock mass using rebar rock bolts instrumented with strain gauges to track the stress within the bolt. Next to that, we describe in-situ testing of this method using heating-induced stress in a natural underground environment. The heating experiment aims to create stress changes using rope heaters inserted into the rock mass and located symmetrically around a single instrumented rock bolt. The heat flux induced to the rock mass leads to volume expansion. The restricted thermal expansion causes an increase in the internal rock stress conditions. These conditions create a strain that can be measured and back-calculated as the rock stress change. The instrumented rock bolt and testing setup were installed in the Underground Research Laboratory located in a granitic rock below the Aalto University campus. The single bolt experiment demonstrates how instrumented rock bolts could monitor the changes in the rock mass stress state. The system can be used as a part of a real-time rock stress monitoring system in mining and rock engineering projects. The final part of the paper describes how this monitoring system can positively affect geotechnical risk management and increase the overall safety of underground construction.

Rupture Process of the 2020 Mw7.0 Samos Earthquake and its Effect on Surrounding Active Faults

AbstractOn October 30, 2020, a Mw7.0 normal faulting earthquake struck the eastern Aegean Sea, causing casualties, and substantial damage at Samos island and Izmir province. We constrained the rupture history of the main shock by jointly inverting GPS static offsets, high‐rate GPS recordings, strong motion waveforms, and teleseismic broadband data. The results revealed that the slip distribution was dominated by a slip patch which spans a depth range of 3–13 km and occupies ∼30 km along strike. The rupture propagated toward SW and updip and the maximum slip amplitude reached 4.6 m at 7 km depth. The remarkably low aftershock productivity within the main asperity suggests a near complete stress release. Coseismic Coulomb stress changes effectively explain the entire aftershock sequence implying absence of short‐term postseismic stress transfer mechanisms. The static stress change calculations also suggest that active faults around Sıgacık and Kusadasi Bays have been brought closer to rupture.

Study on the Correlation between Soil Consolidation and Pile Set-Up Considering Pile Installation Effect

In saturated fine-grained soil, the development and dissipation of excess pore water pressure (EPWP) during and after pile jacking change the effective stress of the surrounding soil, and thereby affect the pile set-up. In this paper, the entire process of steel-pipe pile jacking (the installation process and the subsequent consolidation phase) is simulated with three-dimensional (3D) finite element models, considering the pore water effect. After the model verification, a comprehensive numerical analysis was performed to investigate the development and dissipation of EPWP, changes in soil stress state, and the side shear resistance of pile with time after installation. On this basis, not only the influence of ks, cu, E, and OCR on EPWP generation during pile jacking and subsequent soil consolidation effect after pile installation but also the correlation between pile set-up and EPWP dissipation is investigated.

Influence of Turn-Rolling on the Residual Stresses and Microstructure of C45E and the Effects on Fatigue Life under Cyclic Loading

Abstract The microstructure and the residual stress state have a significant influence on the service life of the component. The deep rolling process already enables a significant increase in the strength and service life of highly stressed components. By using the hybrid manufacturing process of turn rolling, the edge zone properties can be influenced to such an extent that the service life is further increased compared to conventional deep rolling. In addition to a change in the residual stress state, the use of the turning process temperature also leads to a significant grain refinement in the edge zone area, which has a positive effect on the component service life. This modification of the edge zone can be significantly influenced by the machining speed.

Decades of Ground Deformation in the Weihe Graben, Shaanxi Province, China, in Response to Various Land Processes, Observed by Radar Interferometry and Levelling

Ground deformation is usually used as direct evidence for early warning of geological hazards. The Weihe Graben, located in the southern margin of the Ordos Plateau, is surrounded by many active faults. Earthquakes (e.g., the 1556 Huaxian M 8 earthquake), mine accidents and ground fissures are the major hazards that pose great threats to this densely populated region. In order to characterise both tectonic and anthropogenic activities in the Weihe Graben, we use Envisat data from 2003 to 2010 and Sentinel-1 data from 2014 to 2021, combined with levelling data from 1970 to 2014, to investigate the long-term ground deformation. We generate four InSAR rate maps using the small-baseline subset (SBAS) algorithm. The uncertainties of the InSAR rates are 1–2 mm/year by calculating the differences between the InSAR and levelling measurements. From the deformation time series, we found that most of the faults surrounding the Weihe Graben move at a relatively slow rate (&lt;3 mm/year). Elastic dislocation modelling based on the InSAR and levelling data yields a slip rate of 2.3 ± 0.3 mm/year for the Huashan Fault, the seismogenic fault for the 1556 Huaxian earthquake. Anthropogenic deformation is much stronger than the tectonic deformation. We identified localised subsidence of 12 mines with a deformation rate ranging from 5 to 17 mm/year. The cities of Xi’an and Xianyang also show evident subsidence, which is likely to be caused by groundwater extraction. Land subsidence in Xi’an has slowed down from an average rate of 10–20 mm/year between 2003 and 2010 to about 5–10 mm/year between 2017 and 2020, but in Xianyang, subsidence has increased dramatically in the past five years from 1 mm/year to 7 mm/year. This is because new industrial and urban development centres have gradually moved from Xi’an to Xianyang. We identified a region bounded by the Kouzhen-Guanshan and Fufeng-Liquan Faults with strong subsidence, as a result of excessive extraction of groundwater. To quantify the effects of crustal groundwater unloading on faults, we calculated the static Coulomb stress changes on the two faults and found that Coulomb stress changes are localised in the upper 5 km with a magnitude of 0.01–0.02 bar/year. The Coulomb stress changes might be large enough (0.1 bar) to affect local seismicity if such excessive extraction of groundwater continued for 10 years.

Evolution of Seismicity During a Stalled Episode of Reawakening at Cayambe Volcano, Ecuador

Cayambe Volcano is an ice-capped, 5,790 m high, andesitic-dacitic volcanic complex, located on the equator in the Eastern Cordillera of the Ecuadorian Andes. An eruption at Cayambe would pose considerable hazards to surrounding communities and a nationally significant agricultural industry. Although the only historically documented eruption was in 1785, it remains persistently restless and long-period (LP) seismicity has been consistently observed at the volcano for over 10 years. However, the sparse monitoring network, and complex interactions between the magmatic, hydrothermal, glacial, and tectonic systems, make unrest at Cayambe challenging to interpret. In June 2016 a seismic “crisis” began at Cayambe, as rates of high frequency volcano-tectonic (VT) earthquakes increased to hundreds of events per day, leading to speculation about the possibility of a forthcoming eruption. The crisis began 2 months after the Mw7.8 Pedernales earthquake, which occurred on the coast, 200 km from Cayambe. Here we show that the 2016 seismicity at Cayambe resulted from four distinct source processes. Cross correlation, template matching, and spectral analysis isolate two source regions for VT earthquakes–tectonic events from a regional fault system and more varied VTs from beneath the volcanic cone. The temporal evolution of the LP seismicity, and mean Q value of 9.9, indicate that these events are most likely generated by flow of hydrothermal fluids. These observations are consistent with a model where a new pulse of magma ascent initially stresses regional tectonic faults, and subsequently drives elevated VT seismicity in the edifice. We draw comparisons from models of volcano-tectonic interactions, and speculate that static stress changes from the Pedernales earthquake put Cayambe volcano in an area of dilation, providing a mechanism for magma ascent. Our findings provide a better understanding of “background” seismicity at Cayambe allowing faster characterization of future crises, and a benchmark to measure changes driven by rapid glacial retreat.

Correction to: Seismotectonic implications of the 2020 Samos, Greece, Mw 7.0 mainshock based on high‐resolution aftershock relocation and source slip model

The 30 October 2020, Mw 7.0 Samos mainshock took place in the offshore north of Samos Island in eastern Aegean area, previously struck in 1904 with a comparable magnitude earthquake offshore the southern coastline. The investigation of the aftershock seismicity evolution and the properties of the activated fault network was accomplished with aftershock relocation performed with the double-difference and cross-correlation techniques. The highly accurate relocated seismicity illustrates a well-defined E–W activated structure located deeper than 5 km with an average depth of ~ 12 km. Moment tensor solutions indicate mostly normal faulting with an average T-axis ~ 185ο. Strong-motion waveform modeling revealed a N-dipping fault plane with a coseismic slip patch of 36 km $$\times$$ 22 km and a maximum slip equal to 1 m at 12 km depth. The slip is mainly concentrated in a single asperity implying a rupture mode of asperities breaking in isolated earthquakes rather than to cooperate to produce a larger rupture. Coulomb stress calculations unveil increased positive static stress changes values at the locations of the majority of the aftershocks and activation of minor fault segments by stress transfer.