Fault Displacement Research Articles

Fluid migration in faulted shale rocks: channeling below active faulting threshold

During fluid injection tests performed inside the clay-rich Tournemire fault zone, the monitored fault displacement exhibited limited amplitudes whereas a sharp increase of the permeability occurred as the fluid pressure reached a threshold value. The injected fluid channeled through the fractured zone or at the interface between the host rock and the fault core over decameter distances without triggering large irreversible deformation of the fault zone. To assess the underlying hydro-mechanical mechanisms of this sudden increase of permeability, a numerical model was set up to simulate an injection test inside a fracture. When the fluid pressure outweighs the mechanical contribution of the heterogeneities along the fracture planes, the sudden increase of permeability appears. The existence of the channeling process, occurring below a critical fluid pressure at the fracture scale, could explain why it is possible to generate fault leakage inside a non-active fault zone crossing shale rocks. Based on the in-situ and laboratory monitoring, an analytical expression based on TPHM (Two-Part Hooke’s Model) can reproduce the stress-dependent permeability evolution. For low values of the effective stress, a simple cubic law formulation does not reproduce correctly the sharp increase of permeability identified once the Fracture Opening Pressure (FOP) is reached.

Structural performance of buried pipeline undergoing strike-slip fault rupture in 3D using a non-linear sand model

Nonlinear structural response of buried continuous pipeline undergoing strike-slip fault rupture, i.e., where soil masses get displaced in the horizontal plane along a fault line, is studied in a detailed manner. A detailed analysis technique employing ABAQUS/Standard with implicit formulation to study the behavior of buried continuous pipelines crossing fault movements is proposed and established with suitable validations. A three-dimensional nonlinear finite element (FE) model including both material and geometric nonlinearities is used for this study. Firstly, a non-linear sand constitutive model is adopted and implemented in commercial FE package ABAQUS. The adopted material model is validated with available experimental tri-axial test results. This material model is thereafter suitably calibrated to develop a FE model of buried pipeline undergoing fault rupture for a specific large-scale experimental test. The study identified important soil strength parameters from direct shear soil tests conducted for the large-scale test program and converted them suitably with respect to the adopted sand constitutive model. The FE model is then validated against full-scale experimental results. It is observed that the developed FE model yields highly accurate results in comparison to available numerical results for this experiment. Analysis results indicated that, consideration of sand non-linear mobilized shear strength appropriately in numerical modelling may result in significantly improved prediction of generated pipeline strains with increasing fault displacements.

Best Practices in Physics-based Fault Rupture Models for Seismic Hazard Assessment of Nuclear Installations: Issues and Challenges Towards Full Seismic Risk Analysis

In recent years the International Atomic Energy Agency (IAEA) has been closely following and supporting the use of physics-based rupture models for ground motion prediction (e.g. IAEA Safety Standards Series No. SSG–9 and Safety Report Series No. 85) as well as for fault displacement prediction (IAEA-TECDOC, in preparation), respectively for applications in Seismic Hazard Analysis (SHA) and Fault Displacement Hazard Analysis (FDHA) for nuclear installations. Further strengthening of this effort and dissemination in practices for SHA, FDHA and engineering issues have been done through different international working group activities, being the most outstanding two international workshops on Best Practices in Physics-based Fault Rupture Models for Seismic Hazard Assessment of Nuclear Installations (BestPSHANI) in 2015 and 2018. A PAGEOPH topical volume for the BestPSHANI 2015 was published in Dalguer et al. (Pure Appl Geophys 174:3325–3329, 2017). Now, in this PAGEOPH topical volume we collect several articles from the BestPSHANI 2018 workshop as well as several new contributions. The issue also covers further topics on the assessments of engineering issues that rely on ground motion estimates for the evaluation of structures oriented to full seismic risk analysis. A total of twenty-nine papers have been selected covering topics ranging from the seismological aspects of earthquake source studies, ground motion and fault displacement modeling to the engineering application of simulated ground motion for the analysis of soil structure interaction, structural response and fragility curve analysis for the quantification of seismic vulnerability of structures and their seismic performance. Collectively, the seismological papers discuss several current issues of source characterization and ground motion prediction for SHA, highlighting the usefulness of physics-based models for future applications in practice. The engineering papers describe methodologies to develop integral models from source-to-structures that consider the developments of synthetic seismograms as input for structural response and fragility curves estimation for seismic vulnerability assessment. Therefore, this issue contents advanced seismological and engineering resources that might be useful to scientists, engineers, students and practitioners involved in all aspects of SHA, FDHA and vulnerability analysis of engineering structures for seismic risk.

Normal fault networks and their spatial relationships in Plio-Quaternary sedimentary series: A case study in the Zanjan Depression, NW Iran

Well-exposed normal fault networks in the Plio-Quaternary sedimentary series of the Zanjan Depression, Iran, were studied in order to analyse the spatial relationships and evolution of fault and damage zone structures in low-burial (~200 m) conditions. Despite the poorly-consolidated, geologically young nature of sediment, fault networks show several characteristics more typical of faulting in lithified strata. Key controls on the evolution of fault networks are found to be fault interactions, segment linkage, and the mechanical stratigraphy resulting in dip refraction, fault segmentation, the development of fault bends and steps, vertical fault overlap zone breaching, and bed-parallel slip. The data show a decrease of fracture frequency away from the fault cores. The obtained data show that damage zones width increases with fault displacement in a non-linear manner. Furthermore, damage zones appear more deformed and wider in the hanging-wall than in the footwall. A plot of damage zone width versus total fault throw reveals a positive but non-linear correlation, and the best-fit function corresponds better to a power-law relationship. The relationship between displacement and length shows a sub-vertical growth path with large displacement gradients typical of faulting in partially-lithified strata, due to shale ductility accommodating fault tip-related strains. A model for the evolution of the normal fault system is proposed based on spatial distribution of deformation, particularly fault segmentation, segment linkage, and damage zone development, as influenced by initial fault spacing, mechanical stratigraphy and the low burial conditions.

Stable Rate of Slip Along the Karakax Section of the Altyn Tagh Fault from Observation of Interglacial and Postglacial Offset Morphology and Surface Dating

AbstractDigital elevation maps obtained using TanDEM‐X and Pleiades data combined with newly obtained surface age estimates using cosmogenic radionuclide (CRN) and optically simulated luminescence (OSL) methods are used to quantify the slip rate along the western section of the Altyn Tagh Fault in southern Xinjiang. The reconstruction of the conical shape of massive alluvial fans inferred to be from the Eemian (115±7 ka) from CRN dating shows consistent left‐lateral offsets of 300±20 m, yielding a slip rate of 2.6±0.3 mm/year. Successive episodes of incision have left cut terraces inset in wide canyons, 10–25 m below the fans' surface. The incision was followed by the deposition of a broad terrace of early Holocene age, which is reincised by modern stream channels. Near the village of Shanxili, a 200 m wide valley is partially dammed by a shutter ridge displaced by the fault. A fill terrace deposited upstream from the ridge has an OSL age of 8.8±0.6 ka. The 23±2 m offset of the riser incising the terrace indicates a minimum postdepositional movement on the fault, yielding a Holocene rate of 2.6±0.5 mm/year, consistent with the 115‐ka average slip rate. Scarp degradation analysis using mass diffusion reveals a nonlinear relationship between fault displacement and degradation coefficient along the progressively exposed fault scarp, a pattern suggesting either seismic clustering or variable diffusion rate since the Eemian. Together with the Gozha Co‐Longmu Co fault to the south, the Karakax section of the Altyn Tagh Fault contributes to the eastward movement of the western corner of Tibet.

Thermal Pressurization Weakening in Laboratory Experiments

AbstractThermal pressurization (TP) is expected to be a dominant frictional weakening mechanism during earthquakes. However, most of our understanding of TP relies on theoretical studies. Our experimental setup allows us to test the mechanical response of experimental faults under elevated confining and pore pressures in the laboratory using a rotary‐shear apparatus. We observe dynamic weakening by TP of water‐saturated faults in Frederick diabase sliding at subseismic slip rates of 2.5–5 mm/s under an effective normal stress of 25–50 MPa and effective confining pressure of 20–49 MPa. No other weakening mechanism is activated at these conditions in dry samples. The permeability of the samples is varied by heat treatment before each experiment, and the frictional behavior is tested by velocity‐stepping experiments. Dynamic weakening was investigated after both low and high total fault displacements. For low‐displacement samples: (1) the magnitude and rate of weakening increase as the sample permeability decreases and (2) frictional heating is limited during sliding. These observations are consistent with the expected behavior of TP from theory. Weakening of high‐displacement samples is similar in magnitude to low‐displacement faults, but with slower rates of weakening and less dilation. The difference in weakening of the high‐displacement samples may reflect changes in pore compressibility in the fault zone, which would have a significant effect on the frictional response during TP. The activation of TP at modest slip rates in these experiments supports the hypothesis that TP is an active, and likely dominant, dynamic weakening mechanism during earthquakes in the early stages of slip.

Development of a novel approach for strain demand prediction of pipes at fault crossings on the basis of multi-layer neural network driven by strain data

The active fault is one of the commonest geological disasters in the pipeline construction. Excessive tensile or compressive strain may be induced in pipelines which may lead to the rupture or buckling when the two fault plates generate relative movement on the fault plane so that the pipeline cannot operate normally. In this study, a finite element model of pipelines subjected to fault displacements has been established for obtaining the database of strain demand which contains the prospective engineering conditions by considering the influencing factors, i.e. pipe geometrical parameters, internal pressure, fault parameters, and soil parameters. This process has been conducted by an effective hybrid methodology which can integrate the function of .inp documents generation, automatic calculation, and results extraction based on the technology of Python, Abaqus batch processing, and Matlab. The database can be utilized as training data in the multi-layer neural network for developing the strain demand prediction model which shows accurate results with high efficiency compared with general finite element methods.

Influence factors on the ground surface rupture zone induced by buried normal fault dislocation*

The seismic disaster presents a zonal distribution along the fault strike. In this paper, rupture zone of ground surface soil caused by the uniform dislocation, inclined dislocation and warped dislocation of buried normal fault are studied by constituting a three-dimensional finite element model in Automatic Dynamic Incremental Nonlinear Analysis (ADINA). According to the critical value of surface rupture, the variational features and influencing factors of width and starting position of the “avoiding zone” in engineering construction are analyzed by using 96 model calculations. The main results are as follows: (1) Since the rupture zone of the ground surface soil from the point of mechanics is different from the “avoidance zone” from the point of engineering safety, the equivalent plastic strain and the total displacement ratio should be considered to evaluate the effect of the seismic ground movement on buildings. (2) During fault dislocation, plastic failure firstly occurred on the ground surface soil of the footwall side, and then the larger deformation gradually moved to the side of the hanging wall of the fault with the increase of fault displacement. (3) When the vertical displacement of buried fault reaches 3 m, the width of “avoiding zone” in engineering construction varies within the range of 10–90 m, which is most affected by the thickness of overlying soil and the dip angle of the fault.

Climatically driven displacement on the Eglington fault, Las Vegas, Nevada, USA

Abstract The Eglington fault is one of several intrabasinal faults in the Las Vegas Valley, Nevada, USA, and is the only one recognized as a source for significant earthquakes. Its broad warp displaces Late Pleistocene spring deposits of the Las Vegas Formation, which record hydrologic fluctuations that occurred in response to millennial- and submillennial-scale climate oscillations throughout the late Quaternary. The sediments allow us to constrain the timing of displacement on the Eglington fault and identify hydrologic changes that are temporally coincident with that event. The fault deforms deposits that represent widespread marshes that filled the valley between ca. 31.7 and 27.6 ka. These marshes desiccated abruptly in response to warming and groundwater lowering during Dansgaard-Oeschger (D-O) events 4 and 3, resulting in the formation of a pervasive, hard carbonate cap by 27.0 ka. Vertical offset by as much as 4.2 m occurred after the cap hardened, and most likely after younger marshes desiccated irreversibly due to a sudden depression of the water table during D-O event 2, beginning at 23.3 ka. The timing of displacement is further constrained to before 19.5 ka as evidenced by undeformed spring deposits that are inset into the incised topography of the warp. Coulomb stress calculations validate the hypothesis that the substantial groundwater decline during D-O event 2 unclamped the fault through unloading of vertical stress of the water column. The synchroneity of this abrupt hydrologic change and displacement of the Eglington fault suggests that climatically modulated tectonics operated in the Las Vegas Valley during the late Quaternary.

Analysis of geophysical and meteorological parameters influencing 222Rn activity concentration in Mladeč caves (Czech Republic) and in soils of Phlegrean Fields caldera (Italy)

The present work concerns a detailed analysis of Radon time series to differentiate endogenous from exogenous phenomena which provide anomalous signals. Two-year data from two sites in Czech Republic and in Italy are analyzed in order to contribute to the prevention of natural hazards. A new hybrid forecasting method is implemented and tuned for the identification of Radon anomalies in the time series. It is based on the combination of Multiple Linear Regressions, Empirical Mode Decomposition and Support Vector Regression methods that decompose the signal and analyze the components to distinguish the variations due to Radon originated in depths from those due to environmental parameters. The possible correlations with fumarolic tremors in the Italian site and the faults microdisplacements in the Czech site have been studied, as well as with the earthquakes that have influence on two studied areas. Results show that: (i) the used method is very effective considering the calculated statistical uncertainties; (ii) the outer temperature is the main influencing Radon driving force; (iii) the extracted Radon anomalies due to endogenous phenomena are well correlated with fault displacements, fumarolic tremors, and with earthquakes under a characteristic delay time for each area; (iv) significant correlations among earthquake magnitude and depth with fault displacement and fumarolic tremor are found.

Time to depth conversion: Velocity modelling in the Llanos Basin, Onshore Colombia

Velocity modelling for time to depth conversion or depthing, a routine task in oil and gas exploration, only has been discussed in a few case studies in Colombia. A well derived – velocity modelling was performed in the Llanos basin, east Colombia, using a geologically constrained multilayer – cake. The study area, a foreland basin, presents a simple structural geology with short displacement faults mainly located to the base of the Cenozoic sequence; and horizontal and parallel reflectors, typical of a homocline, that pinch out to the east onto Palaeozoic rocks. The Cenozoic rocks are made up of three formations: late Miocene to Pliocene Guayabo formation, early – middle Miocene Leon formation and middle Eocene – early Oligocene Carbonera formation, unconformably resting upon a regional unconformity of Mesozoic (Cretaceous) rocks to the west and Palaeozoic (undefined) rocks to the east known as the Llanos basin unconformity. The velocity modelling has shown that interval velocities in these Formations vary, from top to bottom, in the Guayabo formation from 1830 to 2438 m/s; from 1676 to 2286 m/s in the Leon formation; and, in the Carbonera formation from 2286 to 3353 m/s. Below the Llanos basin unconformity rocks present a strong increment in the interval velocity values that range from 3962 to 5182 m/s. Although well log data is inconclusive in order to offer an explanation for the velocity reversals in both the low – velocity Leon formation and some Carbonera formation intra – layers, these inversions in velocity are a common feature in both formations. The reliability, based in exploration well prognosis, of this conversion method has demonstrated that the differences between predicted and actual drilling data are not greater than 3%. Finally, by incorporating the well – derived velocities in a geologically controlled multilayer – cake a more accurate geometry of the target zone in depth is provided.

Deformation analysis of a viscoelastic half-space due to a finite and an infinite interacting faults

In seismically active regions the process of stress–strain accumulation near earthquake faults during aseismic period (period in between two major seismic events) has become a subject of research during the last few decades. The occurrence of multiple faults (for example Calaveras, Garlock in the neighbourhood of San Andreas fault) in seismically active region is more likely than that of a single fault (i.e. Sierra Madre fault, Raymond fault). Moreover the earthquake faults involve both the strike-slip and dip-slip faults some of which may be finite and others infinite. The way of interaction of faults with each other controls fault geometries, displacements and strains. Such phenomena encourage us to consider a model of interacting strike-slip and dip-slip faults in which a finite and an infinite interacting faults are taken to study the stress–strain accumulation in the neighbouring fault due to the movement across the other fault. The solutions for displacement, stress and strain are then found before the onset of fault slip and then superpose the effect of fault slip for both the interacting faults using Laplace transform, suitable mathematical technique of modified Green’s function and Correspondence principal. The analytical results and the graphical presentations show that the velocities of both the faults movement and their inclinations have noticeable effects on displacements, stresses and strains.

Ultra-slow throw rates of polygonal fault systems

Abstract Polygonal fault systems (PFSs) are an enigmatic class of small nontectonic extensional faults. PFSs are predominantly hosted in fine-grained sedimentary tiers and are prevalent along many continental margin basins. The genesis of PFSs is widely debated, and little is known about the time frame for polygonal fault growth. We present the first measurements of throw rates for polygonal faults by measuring the vertical offset of seven age-calibrated horizons mapped using three-dimensional seismic reflection data from the Norwegian Sea. Individual polygonal faults exhibit a range of throw rate profiles through time, ranging from near linear to singly or multiply stepped. The stepped profiles have short-term throw rates ranging from 0 to 18 m/m.y. Time-averaged throw rates of 180 polygonal faults over the entire 2.61–0 Ma interval are normally distributed and range between 1.4 and 10.9 m/m.y. We convert our PFS throw rates to displacement rates and compare these to published displacement rates for gravity-driven and tectonic normal faults. We find that the displacement rates of polygonal faults mark the lower limit of a continuous spectrum of extensional fault displacement rates; they are as much as two orders of magnitude slower than those of gravity-driven faults, and as much as three orders of magnitude slower than those of the fastest-growing tectonic faults. We attribute the ultra-slow kinematic behavior to the nontectonic nature of polygonal faults, where throw accumulates primarily through dewatering of the largely fine-grained sediments composing the host layers for the PFSs, and through differential volumetric strain between the fault footwalls and hanging walls.

Centrifugal modeling of continuous shallow tunnels at active normal faults intersection

Both traffic and water conveyance tunnels’ networks are being extended in many earthquake-prone areas as to its faulting sense. Active fault and tunnel intersections lead to an intense coercive displacement of tunnel lining. Here, a series of 1/60 scale centrifuge tests are run on such intersections normal dip-slip fault mechanism. Experimental surface faulting model of 60 degrees is applied on a set of soil and tunnel models through a fault simulator box. The Location and the mechanism of failure together and damage states of the modeled tunnels are assessed, and the fragility curves related to each damage state are plotted. Tunnels are very vulnerable to normal faulting; therefore, a displacement of about 20 to 30 cm could generate the initial cracks in the lining. Any increase in displacement would lead to cracks expansion and enlarging the displacement to 50 cm, causing soil and rockfall into the tunnel, thus blockage. Fault rupture propagation is assessed in soil deposits with and without tunnel. The effects of fault displacement and tunnel collapse on the ground surface, including fault scarp, graben and sinkhole, are observed and assessed. The existence of each one of these surface features can be a potential risk for both surface and buried structures.

Development of fault displacement PRA methodology and its application to a hypothetical NPP

The authors have developed fault displacement (FD) probabilistic risk assessment (PRA) methodology, through application to a hypothetical nuclear power plant (NPP).Core damage frequency (CDF) and its uncertainty of a hypothetical NPP for dip-slip faults and strike-slip faults were evaluated using a probabilistic FD hazard, FD fragilities of building and components, and fault tree and event tree models. Important initiating events, accident sequences, components and structure failures, as well as the range of FD that characterize the core damage risk profile were identified. Through the study, the authors confirmed the feasibility of the methodology, and also identified the important source of uncertainties within the methodology that require further development. Risk insights obtained from the FD PRA can be used to investigate countermeasures to reduce the FD risk.

Performance of geosynthetic-reinforced soil foundations across a normal fault

This paper presents a series of model tests on geosynthetic-reinforced soil (GRS) foundations across a normal fault. The aim was to evaluate the performance of reinforced foundations as a mitigation measure for surface faulting hazards. Experimental tests modeled a 3-m thick foundation in prototype subjected to a fault displacement up to 90 cm. Test variables included the number of reinforcement layers, reinforcement stiffness and location, and foundation height. Digital image analysis techniques were applied to determine the ground settlement profile, angular distortion, shear rupture propagation, and mobilized reinforcement tensile strain at various magnitudes of fault offset. Test results revealed that compared with the unreinforced foundation, reinforcement inclusion could effectively prevent the shear rupture propagating from the bedrock fault to the ground surface. It also spread the differential settlement to a wider influential zone, resulting in an average reduction of 60% in the fault-induced angular distortion at the ground surface. The maximum angular distortion decreased as the foundation height, number of reinforcement layers, and reinforcement stiffness increased. Relationships between the maximum angular distortion and maximum mobilized reinforcement tensile strain with fault displacement were therefore established. Based on the findings from this study, design suggestions and implications are discussed.

Alternative design of buried pipelines at active fault crossings using flexible joints

The use of “flexible joints” in buried high-pressure pipelines is examined herein as an effective design technique for the mitigation of Permanent Ground Displacement (PGD) effects due to fault activation. Pipeline joints that are available in the industry today are considered in connection with the needs of high-pressure pipelines in areas of seismic faults. The efficiency of this novel technique is examined through a series of parametric numerical analyses for both strike-slip and normal faults, while its applicability in common engineering problems is examined through an economic-technical comparison with more conventional techniques. It is concluded that the use of flexible joints provides a cost-efficient design method, that can drastically reduce pipeline strains for medium to large fault displacements.

A Triangulated Irregular Network Constrained Ordinary Kriging Method for Three-Dimensional Modeling of Faulted Geological Surfaces

Three-dimensional (3D) modeling of geological surfaces, such as coal seams and strata horizons, from sparsely sampled data collected in the field, is a crucial task in geological modeling. Interpolation is a common approach for this task to construct continuous geological surface models. However, this problem becomes challenging considering the impact of the faults on geological surfaces. Existing methods tend to solve this problem through three steps, including interpolating stratum and fault surface, applying a fault modeling method to modify the geological surface, and optimizing the modified surface to pass sample points fallen into the fault displacement zone. This paper presents a more concise method to generate a faulted geological surface, in which 1) a constrained Delaunay triangulated irregular network (CD-TIN) is constructed to facilitate the neighborhood search process of the ordinary kriging (OK) interpolation, 2) the CD-TIN is also directly constrained by horizon cut-off lines formed from theoretical fault displacement profiles, and 3) subsequently, neighbors of the location to be estimated are selected effectively in the CD-TIN considering the fault topology. The proposed method significantly improves the time efficiency of the OK interpolation by utilizing the CD-TIN and incorporates fault effects directly into the interpolation process by inserting fault horizontal cut-off lines into CD-TIN. Moreover, by integrating the fault effects directly into the interpolation process, the surface modeling process is accomplished in a single stage instead of two separate stages of interpolation first and then modifying the surface in the fault area. By this strategy, the proposed method significantly improves the time efficiency of the OK interpolation algorithm and achieves more accurate modeling of the faulted geological surface. Experiments were designed to compare the performance of our method with several commonly used approaches, and the results indicate that the proposed TIN-constrained OK method achieves better accuracy and efficiency in modeling faulted geological surfaces than other methods. This method could also be used in geospatial interpolation studies, such as meteorological data interpolation.

Paleoproterozoic Iron Oxide Apatite (IOA) and Iron Oxide-Copper-Gold (IOCG) mineralization in the East Arm Basin, Northwest Territories, Canada

The Paleoproterozoic East Arm Basin of Canada hosts polymetallic vein, iron oxide–apatite (IOA), and potential iron oxide–copper–gold (IOCG) mineral occurrences, mainly associated with a belt of ca. 1.87 Ga intermediate-composition sills termed the Compton intrusions. Advances in our knowledge of the East Arm Basin and of IOA and IOCG deposits within the broader context of iron oxide and alkali-calcic alteration systems enables a new regional analysis of this mineralization and facilitates comparison of these mineral occurrences and host rocks to the nearby Great Bear magmatic zone IOCG districts. The Compton intrusions and co-magmatic Pearson Formation volcanic rocks are comparable in age and composition to intrusive plus volcanic rocks of the Great Bear magmatic zone that host IOA–IOCG mineralization. Taking into account fault displacements, emplacement of Compton intrusions and Pearson Formation volcanic rocks are also consistent with the architecture of modern arcs, supporting a direct relationship with the Great Bear subduction zone. Trace element patterns of uraninite contained in IOA occurrences of the East Arm Basin are also similar to the patterns of uraninite from the Great Bear magmatic zone occurrences, consistent with both regions having experienced similar iron oxide and alkali-calcic alteration and mineralization. Our new results indicate that exploration for IOA, IOCG, and affiliated deposits in the East Arm Basin should focus on delineating increased potassic-iron alteration types and fault/breccia zones associated with these systems through field mapping and application of geochemical, radiometric, magnetic, and gravity surveys.

Loading test on box culvert subjected to fault displacement

Loading test on box culvert subjected to fault displacement