Seismic Deformation Research Articles

Focal Mechanisms of Intraslab Earthquakes: Insights From Pseudotachylytes in Mantle Units

AbstractDevastating seismic events occur mainly in subduction zones, and a significant percentage of them are intraslab earthquakes. The geologic record of these events holds valuable information that needs to be investigated for a comprehensive seismic risk assessment. Here we investigate pseudotachylytes formed in oceanic peridotites and that are interpreted to result from intraslab seismic rupture. Each vein has recorded the seismic slip direction and slip sense of a single coseismic shear‐heating event. The well‐preserved exposures, showing individual veins up to 7 m in length and about 3 cm in width, of Cima di Gratera, in the Schistes Lustrés ophiolitic units of Corsica, offer unparalleled opportunities to investigate intraslab rupture kinematics in mantle rocks. The principal ferromagnetic phase in these rocks is a Ti‐poor magnetite. We use the anisotropy of magnetic susceptibility (AMS) recorded in pseudotachylyte generation veins (bulk susceptibilities range from 600 to 20,000 × 10−6 [SI] volume, with P′ ranging from 1.05 to 2.5) to reconstruct the co‐seismic deformation parameters, that is, fault plane attitude, direction and sense of slip. These new results, internally consistent at the vein level, span across oblate and prolate symmetries and reveal that seismic deformation recorded in these veins was kinematically diverse and included mostly normal mechanisms acting along the same subduction zone. In addition, our investigations show that the magnetic fabric of peridotite‐hosted pseudotachylytes provides key information bearing on the complex dynamics of frictional melts at a unprecedently high spatial resolution.

Crystal‐Plastic Deformation in Seismically Active Carbonate Fault Rocks

AbstractThe spatial separation of macroscopic rheological behaviors has led to independent conceptual treatments of frictional failure, often referred to as brittle, and viscous deformation. Detailed microstructural investigations of naturally deformed carbonate rocks indicate that both frictional failure and viscous mechanisms might operate during seismic deformation of carbonates. Here, we investigate the deformation mechanisms that were active in two carbonate fault zones in Greece by performing detailed slip‐system analyses on data from automated crystal‐orientation mapping transmission electron microscopy and electron‐backscatter diffraction. We combine the slip‐system analyses with interpretations of nanostructures and predictions from deformation mechanism maps for calcite. The nanometric grains at the principal slip surface should deform by diffusion creep but the activation of the (0001)<20> slip system is evidence for a contribution of crystal plasticity. A similar crystallographic preferred orientation appears in the cataclastic parts of the fault rocks despite exhibiting a larger grain size and a different fractal dimension, compared to the principal slip surface. The cataclastic region exhibits microstructures consistent with activation of the (0001)<20> and {104}<021> slip systems. Postdeformational, static recrystallization, and annealing produce an equilibrium microstructure with triple junctions and equant grain size. We propose that repeated introduction of plastic strain and recrystallization reduces the grain size and offers a mechanism to form a cohesive nanogranular material. This formation mechanism leads to a grain‐boundary strengthening effect resulting in slip delocalization which is observed over 6 orders of magnitude (μm‐m) and is expressed by multiple faults planes, suggesting cyclic repetition of deformation and annealing.

Constant Volume Ring Shear Specimen Trimming and Testing

The constant volume ring shear (CVRS) apparatus can use intact/undisturbed specimens to measure the peak and residual undrained shear strengths to estimate the post-peak strength reduction for seismic stability and permanent deformation analyses. A trimming apparatus and specimen container were fabricated to allow the trimming of an intact annular specimen directly into a container that is used for the shearing phase of the test. This article describes the specimen trimming, recommendations for handling and converting the trimming apparatus to the shearing container, which can be done either by hand or with a specially prepared trimmer holder, and suggestions for maintaining an undrained or constant volume shear condition. CVRS undrained peak and residual shear strengths for soils with different plasticity and clay size fractions are presented, and they are in agreement with peak undrained strength ratios from direct simple shear tests. This article also introduces correlations for peak and residual undrained shear strength ratios as a function of plasticity index for verification of future test results and planning level design.

Seismic Test and Simulation of Spring Vibration Isolated Foundation for Turbo-Generator

The 1 : 8 model of turbo-generator vibration isolated foundation of common islands in nuclear plants was established for vibration characteristic tests and pseudodynamic experiments. The finite element model was established by SeismoStruct for time-history analysis. Frequencies, modal shapes and seismic responses, deformation curves, and spring deformations were compared and analyzed. Results from tests and experiments show that the natural frequencies of spring vibration isolation foundation are lower than those of common frame foundations and the vertical frequencies are far from the working disturbance frequency of the turbo-generator units. The spring vibration isolation device can reduce the acceleration response of the TG (turbo-generator) deck and redistribute the horizontal earthquake action of the foundation according to the stiffness to give full play to the seismic capacity of the columns. The errors of natural vibration frequencies and maximum seismic response are approximately 15% and 10%, respectively, and the simulation results are in good agreement with the test and experiment data. The proportion and distribution of spring deformation are close, and the test study shows the convenient and precise realization of the simulation. Results of seismic experiments and numerical simulations show that the foundation design meets the standard of the “Code for Seismic Design of Buildings” in China, which realizes the goal of spring vibration isolation and seismic resistance. The foundation design is also reasonable, safe, and reliable.

On the Detection Capabilities of Underwater Distributed Acoustic Sensing

AbstractThe novel technique of distributed acoustic sensing (DAS) holds great potential for underwater seismology by transforming standard telecommunication cables, such as those currently traversing various regions of the world’s oceans, into dense arrays of seismo‐acoustic sensors. To harness these measurements for seismic monitoring, the ability to record transient ground deformations is investigated by analyzing ambient noise, earthquakes, and their associated phase velocities, on DAS records from three dark fibers in the Mediterranean Sea. Recording quality varies dramatically along the fibers and is strongly correlated with the bathymetry and the apparent phase velocities of recorded waves. Apparent velocities are determined for several well‐recorded earthquakes and used to convert DAS S‐wave strain spectra to ground motion spectra. Excellent agreement is found between the spectra of nearby underwater and on‐land seismometers and DAS converted spectra, when the latter are corrected for site effects. Apparent velocities greatly affect the ability to detect seismic deformations: for the same ground motions, slower waves induce higher strains and thus are more favorably detected than fast waves. The effect of apparent velocity on the ability to detect seismic phases, quantified by expected signal‐to‐noise ratios, is investigated by comparing signal amplitudes predicted by an earthquake model to recorded noise levels. DAS detection capabilities on underwater fibers are found to be similar to those of nearby broadband sensors, and superior to those of on‐land fiber segments, owing to lower velocities at the ocean‐bottom. The results demonstrate the great potential of underwater DAS for seismic monitoring and earthquake early warning.

Modelling and slenderness design of high-capacity hybrid beam–columns under lateral cyclic loading

The ‘dual-steel’ concept involves combining High-Strength Steel (HSS) and mild steel to control the energy dissipation and overall failure of structures under seismic loads. In this study, the performance and design of a hybrid hollow beam–column were investigated with a focus on the seismic resistance. The hollow section was fabricated with mild steel plates (grade 250) and HSS tubes (grade 750) and can be used as a lightweight replacement for conventional composite members. A finite-element (FE) model was developed and validated against available experimental data. To consider the cyclic softening of HSS tubes, a combined kinematic and isotropic plasticity model was incorporated into the FE model. The cyclic performance of the hybrid hollow sections was compared with that of equivalent concrete-filled square composite members, and the strength and weight reduction benefits were assessed. Furthermore, considering the current and modified slenderness limits, a sensitivity study was performed on the section geometry. An optimum design for the section geometry was proposed, in which the HSS tube elements significantly increase the axial and lateral capacities of the hybrid section and the mild steel plates provide the required ductility to mitigate seismic deformations. The overall failure mechanism of this design is governed by mild steel plate elements, rather than a sudden failure initiated in the HSS tubes.

Shaking Table Tests on a New Antislide Pile under Earthquakes

A retaining form of a shock-absorbing antislide pile is proposed for slope engineering. A flexible material (shock-absorption layer) is filled in front of an ordinary antislide pile, which is used to absorb a large amount of seismic energy, thereby decreasing the transmission of seismic energy to the antislide pile. The flexible material thus reduces the seismic response, hence improving the aseismic capacity of the antislide pile. To verify the seismic performance of the shock-absorbing antislide pile, a shaking table contrast test was conducted and the results were compared with those from an ordinary antislide pile. The test results show that the flexible material absorbs a portion of the seismic deformation of the slip mass, decreasing the final displacement of the shock-absorbing antislide pile compared to that of the ordinary antislide pile, thereby reducing the sensitivity of the pile body to the displacement. Under the same conditions, the acceleration response of the slope body at the same height is lower for the shock-absorbing antislide pile than that for the ordinary pile, with the seismic performance of the former being superior to that of the latter. Furthermore, the shock-absorbing antislide pile is similar to the ordinary pile in terms of the dynamic earth pressure distribution form of the pile shaft; however, its value is relatively smaller, and the former exhibits better dynamic stress performance than the latter. The test results should prove useful for aseismic design of slopes.

A Study on the Correction Factors of Soil Non-linearity Considering Korean Regional Conditions for Seismic Deformation Method Applied to Multi-Utility Tunnels

A Study on the Correction Factors of Soil Non-linearity Considering Korean Regional Conditions for Seismic Deformation Method Applied to Multi-Utility Tunnels

Study on Seismic Coefficient Calculation Method of Slope Seismic Stability Analysis

In this paper, a pseudostatic seismic coefficient evaluation method for slope dynamic stability analysis was explored with Yushu Airport Road 3# landslide as a typical engineering case, and the shaking table test and numerical calculation were performed during the exploration. The loading waveform was selected as Yushu wave, and the acceleration time‐history of seismic waves was measured and analyzed, revealing the failure mode of slopes. Based on the rigid‐body limit equilibrium theory, the instantaneous additional seismic forces of each block and the time‐history landslide stability coefficient were calculated. According to the time‐history of the landslide, dynamic stability coefficients were calculated. Subsequently, we proposed a pseudostatic seismic coefficient evaluation method and discussed the seismic coefficient slope dynamic stability analysis. The results showed that as the vibration frequency rose, the average acceleration and the residual displacement of the slope decreased, but the slope grew more dynamically stable. With the proposed method, we calculated the period of slope seismic action to be 0.126 s and the average maximum acceleration to be 0.156 g, which was close to the designed ground motion acceleration of 0.15 g. Besides, we calculated the safety factor of landslides under earthquake to be 0.93∼0.97, which was close to that obtained from the building code method and in accordance with the present seismic deformation and failure mode of landslides. Moreover, the results obtained from the method of nuclear power plant specification were relatively small compared to other specification methods. The research is significant because it provides a new idea for the evaluation of seismic landslide stability in practical engineering.

Deformations in the Episcopal Basilica in Varna: Evidences of Strong Historical Earthquakes in Northwestern Bulgaria

Our archeoseismological investigations in the Episcopal basilica in Varna have revealed signs of seismic deformations in its walls: numerous shifts, tilts, and rotations of the wall parts around the vertical axis, as well as subvertical through-going joints cutting several stone blocks. A cluster of (at least) three seismic events occurred for a hundred years (from the early 5th to the early 6th centuries AD). Judging by kinematic indicators in the basilica structures built of high-quality stone blocks, the source of seismic motions was located north-northeast of the basilica. Strong seismic oscillations propagated apparently from the southwest. The seismic sources were along seismically active faults localized north and south of Varna. The local seismic intensity of seismic oscillations could reach Il ≤ 9 on MSK-64 scale. The intensity of the seismic oscillations increased due to unfavorable ground conditions at the location of the basilica. These data should be taken into account when assessing the seismic hazard assessment of Varna to build a new map of seismic zoning of northeastern Bulgaria.

Aseismic Deformation During the 2014 Mw 5.2 Karonga Earthquake, Malawi, From Satellite Interferometry and Earthquake Source Mechanisms

AbstractAseismic deformation has been suggested as a mechanism to release the accumulated strain in rifts. However, the fraction and the spatial distribution of the aseismic strain are poorly constrained during amagmatic episodes. Using Sentinel‐1 interferograms, we identify the surface deformation associated with the 2014 Mw5.2 Karonga earthquake, Malawi, and perform inversions for fault geometry. We also analyze aftershocks and find a variety of source mechanisms within short timescales. A significant discrepancy in the earthquake depth determined by geodesy (3–6 km) and seismology (11–13 km) exists, although both methods indicate Mw5.2. We propose that the surface deformation is caused by aseismic slip from a shallow depth. This vertical partitioning from seismic to aseismic strain is accommodated by intersecting dilatational faults in the shallow upper crust and sedimentary basin, highlighting the importance of considering aseismic deformation in active tectonics and time‐averaged strain patterns, even in rifts with little volcanism.

Global sensitivity analysis of probabilistic tunnel seismic deformations using sparse polynomial chaos expansions

There is an increasing interest in utilizing surrogate models to perform the global sensitivity analysis (GSA) for the uncertainty quantification since they allow to quantify efficiently the relative importance of each input parameter with relatively small computational costs. This paper aims at investigating the feasibility of applying this method to a stochastic soil-tunnel system in seismic conditions. An advanced technique named sparse polynomial chaos expansions (SPCE) is introduced to build a surrogate model that allows performing a GSA combined with the Sobol’ indices. The accuracy and efficiency of the SPCE-GSA method are validated by comparison with the true numerical predictions and Monte Carlo simulations. Parametric sensitivity analyses are performed for a wide range of the soil shear wave velocities, ground motion intensities, probability distribution types, and coefficients of variation, assuming a nonlinear soil behavior. The influences of the sampling size, polynomial degree, and ground motion characteristics on the variability in the sensitivity indices are evaluated. The results show that the soil shear wave velocity and modulus reduction factor are the two variables that significantly affect the seismic deformations of tunnels.

Optimum position of outrigger-belt system in a high-rise RCC building through pushover analysis

This study aims to investigate the behaviour of high-rise RCC buildings with core and outrigger-belt system, and to find the optimum position for the outrigger-belt system in that building. For this purpose, Pushover Analysis is used to capture the seismic response for the buildings of 10, 15, 20, 25, and 30 storeys with varying positions outrigger-belt system. Pushover analysis is a static procedure which uses a simplified nonlinear technique to calculate seismic structural deformations. The position of outrigger-belt arrangement changes from the first storey to top storey of the 3D building models, which gives the data regarding the behaviour of the building models with the change in position of that arrangement throughout its height. The analysis of these building models is performed in two different directions using two different load patterns in each direction. The results depict the optimum positions of the outrigger-belt system depending on lateral load patterns, the direction of loading, and the height of a building. It also shows how the optimum position of an outrigger-belt system can affect the performance of the buildings, which is measured in terms of roof displacement, storey shear, the fundamental period of vibration, base shear, and performance point of the buildings.

Seismic Deformations in the Archeological Monuments of Mugkala and Mugtepa (Fergana Depression, Uzbekistan)

The article provides data on the geological, tectonic, and seismological situation of the region. Results of archeoseismological field studies of the ancient fortress and castle of Mugkala and Mugtepa in the Fergana Valley (Namangan region, Uzbekistan) are considered. At the archeological sites, we revealed such characteristic destruction and damage as wedges, inclinations, shaking, sagging, and extend through cracks and interbrick cracks in city walls, confirming their seismogenic origin. Similar seismic deformations can be considered as evidence of the high local seismic oscillation intensity. It was noted that seismic shocks propagated along the sublatitudinal axis. Both the Mugtepa and Mugkala archeological sites are located between the North Fergana Fault and North Fergana flexural-fracture zone. The seismicity of the research area is associated with the development of the Kasansay group of young Quaternary anticlinal folds. A new residence on Mugtepa could have been built by new kings of the Fergana Valley at the end 1st century BCE, which was destroyed in the 1st century CE by a strong earthquake with a local seismic intensity of IL = VIII–IX (MSK-64 scale). The residence of the Turkic Khaganate could have been built by new kings of Fergana Valley in a new location. Mugkala could also have been destroyed by a strong earthquake with a seismic intensity of IL = VIII–IX (MSK-64 scale) at the end of the 8th century CE. This earthquake caused the various deformations described in the paper.

Precast concrete spreader‐walls to improve the reparability of RC frame buildings

AbstractRecent earthquakes have demonstrated that reinforced concrete (RC) frames, which form a beam‐sway mechanism, sustain damage to beams and floors that can be particularly difficult and costly to repair. This paper proposes a new structural system, which combines RC frames with precast concrete spreader‐walls. The spreader‐walls are fixed to frames with connections that allow them to pivot and are carefully arranged so that they distribute seismic deformation demands over the building height. This in turn allows the designer to force plastic hinges to occur at column ends without the risk of a soft‐story mechanism forming and without costly damage to beams and floors. Nonlinear time history analyses of two sets of 4‐, 8‐, and 12‐story buildings are conducted with and without the spreader‐walls. The analyses show that the system behaves as intended and has the potential to enhance the reparability of RC frame structures. To this end, experimental research is recommended to ensure that the proposed connection details behave as desired prior to their implementation in practice.

Study on seismic failure probability of high earth-rock dam considering dam body deformation and slope stability

The reliability analysis is one of the main methods for the quantitative analysis of the safety in the geotechnical engineering. This method can provide the failure probability with a clear physical meaning. Due to the complex structure of high earth-rock dams and the non-linear characteristics of the material properties, it is very difficult to perform the reliability analysis on such large nonlinear structures. Currently, there are few studies on the reliability analysis of high earth-rock dams that consider the earthquakes, the dam body deformation and the dam slope stability at the same time. In this paper, the dam cracks generated by the earthquakes are used as the criteria for the dam body seismic deformation evaluation, and the inclination method is adopted for the dam body seismic deformation analysis. The simplified Bishop method combined with the ratio of the safety margin method is used to analyze the dam slope stability. In order to consider the soil material properties, the thickness of the compressible soil layer and the uncertainty of the earthquakes, a seismic failure probability analysis method for evaluating the seismic danger of high earth-rock dams considering the dam body deformation and the dam slope stability is established based on the reliability theory. Taking a concrete face rockfill dam as an example, the method is used to analyze the seismic failure probability of the dam during the design reference period. It provides the reference for the seismic design and the risk analysis, and establishes the risk level of high earth-rock dams.

Performance of GRACE Mascon Solutions in Studying Seismic Deformations

AbstractGRACE (Gravity Recovery and Climate Experiment) mascon (mass concentration) solutions are widely used in cryosphere science and hydrology research. Mascon solutions have been demonstrated to perform analogous to or better than spherical harmonic (SH) solutions at the basin scale. Although the mascon solutions are expected to facilitate an improved local recovery of seismic gravity signals of large earthquakes, the application of mascon solutions to earthquake analysis remains to be investigated. In this study, we examine the performance of the mascon solutions for seismic gravity signals induced by three M9 class (2011 Tohoku‐Oki, 2004 Sumatra, and 2010 Chile) and three smaller earthquakes and compare them with SH solutions and theoretical gravity changes modeled according to the dislocation theory. We analyze the coseismic and postseismic gravity changes and conclude that the mascon solutions contain information almost identical to the SH solutions and retrieve coseismic gravity change signals with resolutions equivalent to Gaussian filter radii of 210–270 km. The mascon solutions have strengthened gravity change signals of approximately twice the strength of the SH solutions. However, mascon solution cannot fully recover the complete seismic deformation since it is still a spatially “band‐limited” data set that uses the spatial smoothing in the aggressive regularization. We found that the mascon solutions contain “seismic‐like” gravity change signals several months before the Tohoku‐Oki and Chile earthquakes occurred.

Rate of seismic deformation in the Gulf of Aqaba inferred from moment-tensor summation

This study aims to quantify the rate of coseismic deformation in the Gulf of Aqaba. Earthquake catalogue, Gutenberg-Richter relationship and fault plane solutions were integrated to measure the size and shape of deformation using the moment-tensor summation technique. First, the Gutenberg-Richter relationship was established using seismicity data from the period of 1964–2019. Then, the moment-tensor summation based on 44 focal mechanism solutions was used to calculate the shape of deformation. The eigenvalues of moment-tensor reflect the diversity of focal mechanism solutions that alternate from normal to strike-slip fault styles in the deformation zone. The analysis reveals a dominant shear deformation in the Gulf of Aqaba that extends in a direction of N42.2°E at a rate of 2.6 ± 0.04 mm yr−1and shortens in the direction of N305.2°E at a rate of 2.0 ± 0.02 mm yr−1. These results suggest that the active deformation occurring in the Gulf of Aqaba is due to the relative tectonic movements between the Arabian and African plates, as well as Sinai subplate.

Investigating the vulnerability of Bridge by comparing the results of instrumentation and wavelet function

Many structural damages occurs due to breakdown of constituents. The onset of these fractures is usually accompanied by cracks, the spread of which poses a serious threat to their structures and behavior. Accordingly, the methods of diagnosis and detection of cracks have been the subject of much research to date. The existence of cracks changes the natural and mode frequency of seismic deformations, which analyzes these changes by identifying cracks. These methods are known as Structural Health Monitoring (SHM) techniques, which manage and evaluate the expected behavior and performance of structures over the life of the structure. There are various ways to evaluate and identify these changes, each of which has its strengths and weaknesses. These systems should be able to answer questions such as the location of damage and failure to structures. The modern methods of structural health monitoring are based on the dynamic properties of structures, most of which use modal analysis or Fourier series conversion. In the Fourier transform, information is given about the frequencies in a signal, while no information is recorded since a particular frequency occurs. To determine the location of a crack or any other damage of this kind, it is important to know when a particular frequency occurs that Fourier transform in this field is weak. A novel and efficient method of signal analysis, which has been welcomed by researchers in recent years, is called Wavelet Transform (WT) and has great ability to detect all kinds of discontinuities or inconsistencies, such as sudden loss of hardness, loss of performance, and failure. Bridges are one of the most important structural members, so this research will investigate an example of them, because of its historical importance, by the wavelet transform method.

Integration of coseismic deformation into WebGIS for near real-time disaster evaluation and emergency response

Earthquakes are one of the destructive natural disasters. Immediate emergency response in the first few hours is important for life rescue. The near real-time ground deformation maps generated after earthquakes are crucial for hazard assessments, which normally take a couple of hours or longer to be generated using conventional ways. In this study, we propose a near real-time coseismic ground deformation map generation system with the aim of assisting rapid seismic hazard evaluations and emergency responses. This framework adopts the source parameters published by seismological agencies and uses the empirical equations to generate the near real-time coseismic ground deformation maps. The source parameters of an earthquake, such as the focal mechanism, are programmatically accessed from the United States Geological Survey National Earthquake Information Center (USGS-NEIC) in a nearly real-time manner. The ground deformation estimated using empirical equations is integrated as self-adapting spatial data fusion and visualized on an interactive WebGIS platform. We develop the WebGIS platform, namely QuickDeform at https://www.insar.com.cn , and successfully applied the system to several recent large magnitude earthquakes. We find that the proposed framework functions robustly and proficiently to automatically generate the seismic deformation map within several minutes after the occurrence of an earthquake. The generated deformation map shows good agreement when compared to the data from real earthquakes. QuickDeform can be used as a volunteered geographic information platform for crowdsourcing disaster data for rescue and model validation.