Strike-slip Fault Rupture Research Articles

Rupture process of the 2019 Mw 6.8 Davao Del Sur earthquake, Philippines from geodetic and seismic data

Because of its complex tectonic setting, the Philippines experiences vigorous seismic activity. On December 15, 2019, an Mw 6.8 earthquake struck Davao del Sur, the Philippines, severely damaging infrastructure and adversely affecting the population. In this study, we used Interferometry Synthetic Aperture Radar (InSAR) and teleseismic broadband data to explore the earthquake’s source parameters, rupture process, and tectonic characteristics through a Bayesian modeling approach and Coulomb stress analysis. An analysis of InSAR suggested that the mainshock occurred on an NW–SE oriented single plane within the Cotabato fault system, with the Makilala-Malungon fault being the causative fault. The Joint inversion revealed that the rupture initiated in the middle crust (depth: approximately 16.5 km), exhibiting a blind, left-lateral strike-slip fault rupture propagation with minimal reverse slip and no surface rupture. The slip was concentrated in a distinct asperity spanning a depth of 3–24 km, with the peak slip reaching approximately 1.8 m. The source time function of this event indicated a single pulse with a total source duration of approximately 17 s. The static stress drop value was low, which may be related to the brittle condition of the crust. Coulomb stress changes calculations suggested earthquake risk in the future.

Nonlinear seismic responses of a long-span railway suspension bridge crossing strike-slip fault rupture zones

This study investigates the nonlinear seismic responses of a long-span suspension bridge crossing strike-slip faults and their sensitivity to various parameters and conditions. Four sets of near-fault records containing forward directivity and fling-step effects are selected, corrected, and then incorporated into the analysis. Empirical model is proposed using 54 sets of near-fault records to evaluate the dynamic pulse amplitude in fling-step ground motions. A simplified scaling method considering self-consistency is proposed to obtain the fling-step ground motions with different fault static offset and dynamic pulse amplitude. Multiple parameter method is derived by theoretical analysis to consider the effect of the fault-crossing angle on the wave propagation distance and direction. A nonlinear numerical model of double-pylon suspension bridge is established to study the seismic responses of near-fault and fault-crossing suspension bridges. The results indicate that the girder of the fault-crossing bridge rotates around the midspan, and the most of the bridge responses are slightly smaller than those of the near-fault case, whereas the transverse residual bearing displacement is substantially higher. Moreover, the sensitivity of the bridge responses to the fault-crossing angle, fault-crossing location, permanent displacement, dynamic pulse-type motion, ground motion component, and wave passage effect is comprehensively investigated. The minimum bridge responses, except for the residual bearing displacement, are obtained at a fault-crossing angle of 90° and a fault-crossing location at the middle span. The effects of the permanent displacement, dynamic pulse-type motion, and apparent wave velocity on the bridge responses are highly correlated with the fault-crossing angle. At a fault-crossing angle of 90°, all bridge responses are insensitive to these parameters, except that the peak transverse pylon drift and the bearing displacement increase considerably with the increasing amplitude of dynamic pulse-type motion. When the fault-crossing angle is acute (obtuse), the wave passage has a considerable effect on the bridge responses, and most of the bridge responses increase significantly with an increase in the permanent displacement and dynamic pulse-type motion. However, the permanent displacement has a negligible effect on the peak pylon drift. The wave passage effect is more reasonable to be considered using the apparent wave velocity in the horizontal direction than in the bridge axis direction because the influence of the fault-crossing angle on the propagation distance and direction is taken into account. Furthermore, the vertical component exerts a minimal effect on all bridge responses, whereas the fault-normal component significantly affects most bridge responses.

Study on the multi-criteria seismic mitigation optimization of a single pylon cable-stayed bridge across strike-slip fault rupture zones

Bridge structures across active faults suffer the serious threats from large surface deformation and velocity pulses. This study focuses on developing a multi-criteria optimizing method and investigating the damping effect of the optimized damper system on a cable-stayed bridge across a strike-slip fault. A simplified baseline corrected method is adopted to recover the static offsets in near-fault records and the improved record-decomposition incorporation method is modified to produce artificial across-fault ground motions. A single pylon cable-stayed bridge across a strike-slip fault is taken as the case bridge and the refined nonlinear numerical model is established in OpenSees. The conventional multi-criteria decision making (MCDM) theory is improved by introducing new function forms and a control parameter to assess the best fault-crossing angles of the case bridge. The improved MCDM method is integrated with the beetle antennae search algorithm to optimize the damper system of the case bridge. Finally, the influence of fault-crossing angles and earthquake parameters (permanent displacements and ratios of maximum to permanent displacement) on the damping effect of the optimized damper system are investigated. The results indicate that the cable-stayed bridge reaches optimal seismic performance when the fault-crossing angle is around 90° (75°-105°) as both the biaxial nonlinearity of the pylon and the risk of the girder unseating are reduced. The damper system is efficiently optimized by the proposed method, and the displacement and force demand of the case bridge are balanced. Both the fault-crossing angles and earthquake parameters are observed to have considerable influence on the damping effects. More specifically, the damping effect on most seismic responses is optimized when the fault-crossing angle approaches 90° (60°-120°). As the permanent displacement increases, the damping effect on the pier-girder relative displacement is significantly reduced and the damping effect on the pier moments is moderately decreased. Moreover, the damping effect is improved for all the seismic responses as the ratios of maximum to permanent displacements increase, with the exception of transverse displacement.

Validation of the fault rupture-response spectrum analysis method for ordinary and seismically isolated bridges crossing strike-slip fault rupture zones

The fault rupture-response spectrum analysis (FR-RSA) method approximates the peak response of bridge structures crossing strike-slip faults by superposing the peak quasi-static and dynamic responses in the fault-normal and fault-parallel directions. The first part of this article aims to further validate the accuracy of the FR-RSA method for estimating the peak response of ordinary bridges crossing strike-slip faults. This is achieved by comparing results obtained from the FR-RSA method against nonlinear response history analysis (NLRHA) for two ordinary straight bridges under different fault crossing conditions. The effects of modal combination rule and number of modes on the peak response of the considered ordinary bridges are also examined. The second part of the article investigates the adequacy of the FR-RSA method for estimating the peak response of seismically isolated bridges crossing strike-slip faults. This is achieved by considering two seismically isolated bridges along with different fault crossing angles, fault crossing locations, and input ground motions and by comparing results obtained from the FR-RSA method against NLRHA. This investigation involves examining the effects of modal combination rule, number of modes, damping ratio, and mode type on the peak response of the considered seismically isolated bridges. The analysis results indicate that the peak responses of ordinary and seismically isolated bridges computed from the FR-RSA method are in good agreement with those obtained from NLRHA, thus demonstrating the adequacy of the FR-RSA method for the analysis of bridge structures crossing strike-slip faults.

Evaluating the Response of a Tunnel Subjected to Strike-Slip Fault Rupture in Conjunction with Model Test and Hybrid Discrete–Continuous Numerical Modeling

Evaluating the Response of a Tunnel Subjected to Strike-Slip Fault Rupture in Conjunction with Model Test and Hybrid Discrete–Continuous Numerical Modeling

Fault Source Model and Stress Changes of the 2021 Mw 7.4 Maduo Earthquake, China, Constrained by InSAR and GPS Measurements

ABSTRACTOn 22 May 2021, an Mw 7.4 earthquake struck Maduo, China, within the eastern Bayan Har block of the Tibetan plateau. The eastward-extruding Bayan Har block is marked by active seismicity along its boundary faults, including the 2008 Mw 7.9 Wenchuan earthquake, but large earthquakes within the block are relatively rare. Thus, the Maduo earthquake could provide useful information about crustal deformation of the Tibetan plateau. Early reports, shortly after the earthquake, have suggested a sinistral strike-slip fault rupture, but the fault geometry and slip distribution vary in these models due to the limited observational constraints. Here, we reconstructed a model of fault geometry and coseismic slip using Interferometric Synthetic Aperture Radar and Global Positioning System data. A nonplanar fault model was constructed based on pixel-offset images and the optimized dip angle. The along-strike variation of the dip angle is small, so a single optimized dip is used. Our results suggest that the Maduo earthquake ruptured ∼156 km on a northwest-striking major fault that dips 78°, and ∼24 km on a minor southeast-striking fault that dips 64°. Most fault slip occurred above 15 km depth, and released a moment of ∼1.65×1020 N·m. Using the resolved fault source model, we calculated the change of coulomb failure stress in the region and on the neighboring faults. The Maduo earthquake highlighted intrablock deformation in the Tibetan plateau whereas numerous lithospheric blocks extrude along major strike-slip faults.

Surface foundation subjected to strike-slip faulting on dense sand: centrifuge testing versus numerical analysis

The paper studies strike-slip fault rupture propagation through dense sand and its interaction with surface foundations, combining physical and numerical modelling. A series of centrifuge tests is conducted using a three-section split-box, which allows the modelling of two strike-slip faults per test. A free-field test is initially conducted, followed by four interaction tests. Eight different foundation configurations are studied, varying the foundation location, surcharge load, aspect ratio and rigidity. The experiments are numerically simulated employing three-dimensional finite-element modelling, combining periodic boundaries and a relatively simple yet efficient constitutive model, developed as part of this study. Based on a Mohr–Coulomb yield criterion, the model incorporates post-yield isotropic frictional hardening and softening (MC–HS). Carefully calibrated on the basis of triaxial tests, the model is validated against the centrifuge model tests, and exploited to derive further insights. The MC–HS model covers the entire range from elastic to fully softened response, capturing the deviatoric and volumetric behaviour of dense sand, and especially its pre-softening volumetric response, which is proven to be crucial for the simulation of the complex mechanisms of strike-slip faulting. Both physical and numerical modelling reveal the formation of diagonal shear ruptures at the ground surface (Riedel shears). These are complex helicoidal structures, formed due to the spatial variation of shear stresses. Foundation response is mainly governed by the kinematic constraint offered by its presence. Fault rupture locations close to its sides typically lead to a translational mechanism, whereas locations close to its centreline lead to a rotational one. Foundation rigidity is proven to be a prerequisite for the development of both mechanisms, which rely on the ability of the foundation to resist the developing normal and shear stresses.

Intense foreshock swarm preceding the 2019 MW 6.5 Ambon (Seram, Indonesia) earthquake and its implication for the earthquake nucleation process

We apply a template matching detection to report a swarm-like foreshock sequence concentrated near the northern edge of the strike-slip fault rupture of the 25 September 2019 MW 6.5 Ambon earthquake in Seram, Indonesia. The template matching helps to identify small earthquakes that the routine earthquake catalog has not listed. The magnitude of completeness decreases from 3.1 (Badan Meteorologi Klimatologi dan Geofisika – BMKG catalog) to 1.7 in the improved catalog. We detect 3201 foreshocks which are tens fold the number of foreshocks in the routine earthquake catalog. We did not find a significant temporal variation in the b-value of the frequency–magnitude distribution (FMD) of the foreshock seismicity prior to initiating the dynamic rupture of the mainshock. The foreshocks around the mainshock hypocenter start to be busy since the beginning of July 2019 and continuously accelerates, with a minor variation in the seismicity rates and b-values. Although possible, we did not suggest that the stochastic cascade effect plays a role in the mainshock nucleation process. We discuss and highlight the possibility of fluid triggering to explain the high b-values of foreshock seismicity.

Numerical analysis of surface foundation subjected to strike–slip faulting: model boundaries, pre-softening volumetric response, parametric study

The paper investigates strike-slip fault rupture propagation through dense sand and its interaction with surface foundations, employing 3D finite element (FE) modelling. Two soil constitutive models (implemented in Abaqus through user subroutines) are employed for this purpose: (i) a recently developed simple yet efficient model with a Mohr–Coulomb yield criterion, which incorporates post-yield isotropic frictional hardening and softening (MC–HS model); and (ii) the basic version of the more sophisticated hypoplastic model for sand. Both models are calibrated on the basis of monotonic triaxial compression tests (and an additional oedometer test for the hypoplastic model), conducted as part of this study. The numerical predictions are comparatively assessed against centrifuge model test results. In accord with the centrifuge model tests, the free-field analyses with the MC-HS model reveal a complex fault pattern at the ground surface, consisting of Riedel (R) shears. These are the surficial manifestation of complex 3D structures of helicoidal geometry, attributed to the spatial variation of shear stresses within the overburden soil due to the imposed bedrock offset. The development of R shears is primarily controlled by the pre-softening volumetric soil response in monotonic compression and soil dilation. The latter is underestimated by the basic hypoplastic model, thus predicting the formation of a single straight shear band instead of R shears. A parametric study is conducted employing the validated MC-HS model, exploring fault rupture–soil–foundation interaction. Foundation response is shown to be sensitive to the surficial fault pattern (R shears vs. single fault trace), but the mechanism (rotational vs. translational) and foundation distress are not affected to the same extent. A two-step design strategy is outlined, requiring a free-field analysis to capture the surficial fault pattern, followed by a minimum of four interaction analyses, varying the fault-normal and fault-parallel foundation location.

Experimental and numerical investigation for the rupture problem of a tunnel subjected to strike-slip fault

In this study, a model test and a DEM-FDM coupling numerical analysis were conducted to investigate the response and mechanism of a tunnel subjected to strike-slip fault rupture. The interaction of the tunnel with the fault rupture, the deformation pattern, and the strain evolution and crack propagation in the tunnel liner were observed in the test. With the experimental data, a DEM-FDM coupling model was constructed and calibrated. With this model, the response and mechanism of the tunnel subjected to strike-slip fault rupture were numerically investigated, to provide a deep insight into the design factors of the tunnel liner.

Offshore pipeline performance under strike-slip fault movements

Offshore pipelines often cross large areas with geomorphological, geological, and tectonic conditions that may pose a variety of geohazards, one of which is the co-seismic slippage of active tectonic faults. Ground movement induced by fault slippage imposes substantial straining on the pipelines, threatening their integrity. This paper presents the results of a series of large-deformation parametric finite element simulations of a partially embedded pipeline resting on a fine-grained seabed and subjected to the differential movement of an active strike-slip tectonic fault. Parametric computations were performed for different values of the angle between fault strike and the pipeline axis, shear strength at the seabed surface, and different contact conditions at the soil-pipeline interface. The pipeline is examined for both pressurized and non-pressurized conditions and for different values of wall thickness and pipeline embedment. The developed strains in the pipeline with the application of fault displacement are determined and compared with appropriate performance criteria for steel pipelines. It was found that the angle at which the pipeline crosses the fault trace is an important parameter. For a range of oblique intersection angles for which the pipeline is subjected to overall compression, pipeline buckling occurs at relatively small fault displacements. For other intersection angle values, local buckling is unlikely due to the pipeline stretching with the fault movement that reduces the compressive stresses. Pipeline safety against strike-slip fault rupture may be substantially improved by simply adjusting the routing at the location of fault crossing.

Geosynthetics reinforced interposed layer to protect structures on deep foundations against strike-slip fault rupture

In the present study, the interaction mechanism of a 10-story moment-resisting building frame sitting on the conventional piled raft foundation with a strike-slip fault rupture with a dip angle of 90̊ is studied via three-dimensional finite element numerical simulation using ABAQUS. In addition, an alternative composite foundation system with geosynthetics reinforced interposed layer between piles and raft is proposed to improve the safety and performance of foundation under strike-slip fault ruptures. The interposed layer is reinforced with two high tensile strength of the geotextile layer. The inelastic behaviour of piles under large ground deformations is simulated using moment-curvature relationships of the real reinforced concrete section of piles and ductility concepts. The performance of both composite and conventional piled raft foundations are evaluated in terms of the geotechnical and structural responses of foundations including rotational and translational displacements and shear forces of the raft, as well as shear forces and ductility capacity of piles. The obtained results show the superior performance of composite foundation with geotextile reinforced interposed layer in terms of a significant reduction in shear forces in the raft and piles, as well as ductility demand in the piles.

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.

Geofoam blocks to protect buried pipelines subjected to strike-slip fault rupture

This paper proposes using geofoam blocks to improve the safety of buried steel pipelines under permanent ground deformation due to strike-slip fault rupture. Since these geofoam blocks are deformable, they can compress during fault rupture and thus reduce the pressure imposed on the pipeline by the surrounding soil. This means that the pipe can sustain a higher level of tectonic deformations. For the pipeline system adopted in this study, the geofoam blocks consist of two 1 m thick blocks at each side and another on the top of the pipeline. The effectiveness of this configuration is then assessed in comparison to the conventional buried pipeline by three dimensional numerical simulations that consider the interaction between soil and structure and the impact of critical parameters such as the pipeline-fault trace crossing angle, geofoam blocks thickness and the internal pressure of the pipeline. The results indicated that the geofoam blocks reduced the axial tensile strain of non-pressurised pipeline from the unacceptable 4.16% to the safe level of 0.75% when the crossing angle was 135°. In addition, geofoam blocks successfully decreased the maximum ovalisation parameter and compressive strain of the non-pressurised pipeline from 0.237 and −25.8% to 0.065 and −0.47%, respectively when the crossing angle was 65°.

Multi-directional force–displacement response of underground pipe in sand

A methodology is presented to evaluate multi-directional force–displacement relationships for soil–pipeline interaction analysis and design. Large-scale tests of soil reaction to pipe lateral and uplift movement in dry and partially saturated sand are used to validate plane strain, finite element (FE) soil, and pipe continuum models. The FE models are then used to characterize force versus displacement performance for lateral, vertical upward, vertical downward, and oblique orientations of pipeline movement in soil. Using the force versus displacement relationships, the analytical results for pipeline response to strike-slip fault rupture are shown to compare favorably with the results of large-scale tests in which strike-slip fault movement was imposed on 250 and 400 mm diameter high-density polyethylene pipelines in partially saturated sand. Analytical results normalized with respect to maximum lateral force are provided on 360° plots to predict maximum pipe loads for any movement direction. The resulting methodology and dimensionless plots are applicable for underground pipelines and conduits at any depth, subjected to relative soil movement in any direction in dry or saturated and partially saturated medium to very dense sands.

Numerical evaluation of the effectiveness of flexible joints in buried pipelines subjected to strike-slip fault rupture

Buried steel pipelines transport large amounts of fuel over long distances and inevitably cross active tectonic seismic faults when seismic areas are traversed. Eventual fault activation leads to large imposed displacements on the pipeline, which may then fail due to local wall buckling or tensile weld fracture, having grave financial, social and environmental consequences. In this paper, flexible joints are evaluated as an innovative mitigating measure against the consequences of faulting on pipelines. Joints are introduced in the pipeline in the fault vicinity, aiming at absorbing the developing deformation through relative rotation between adjacent pipeline parts, which then remain relatively unstressed. The effectiveness of flexible joints is numerically evaluated through advanced 3D nonlinear finite element modeling. Extensive parametric analysis is carried out to determine the effect of pipeline – fault crossing angle, fault offset magnitude, joint angular capacity, burial depth and diameter over thickness ratio on the joint efficiency. The uncertainty regarding the fault trace is also addressed.

Underground pipeline response to earthquake-induced ground deformation

The principal causes of earthquake-induced ground deformation are identified and their interaction with underground infrastructure, primarily pipelines and conduits, is described. The coupled forces normal and parallel to underground pipelines arising from earthquake-induced ground movement are evaluated, including a review of measured stresses on pipe surfaces during large-scale testing, evaluation of frictional forces related to soil-pipe interaction, and the resolution of interaction forces along and across pipelines. Methods for characterizing soil reaction to pipe lateral and vertical movements are presented. The maximum downward pipe force is only about one-third the maximum force determined with conventional bearing capacity equations, thus requiring changes in current analytical and design practice. The analytical results for pipeline response to strike-slip and normal fault rupture are shown to compare favorably with the results of both large-scale and centrifuge tests of soil-pipeline interaction simulating these types of severe ground deformation.

Lateral soil–pipeline interaction in sand backfill: Effect of trench dimensions

Current analytical methodologies for the evaluation of soil pressures on laterally displaced pipelines, as in the case of differential (e.g. fault-induced) permanent ground movements, allow the use of sand fill material properties under the condition that the size of the trench is adequate so that the failure surface develops fully within the sand fill (i.e. “free field” response). The accuracy of this assumption is investigated in this paper by means of numerical analyses, which employ a number of advanced features, such as pipe-backfill interface elements, large strain formulation and mesh rezoning. Following verification against well-documented experimental data, the analyses investigate: (a) the shape and size of the failure mechanism, as well as, (b) the potential trench effects on soil pressures and pipeline strains in the case of a strike-slip fault rupture. It is shown that for small embedment depths soil failure extends to the ground surface, in the form of a general shear failure mechanism, while for larger depths it becomes progressively localized and surrounds the pipeline. It is also shown that, for most cases of pipeline diameter and embedment depth, common trench dimensions cannot contain the “free field” failure surface dimensions. Finally, analyses for limited trench dimensions, reveal that the ultimate soil pressure increases exponentially with decreasing trench width, leading to high bending strains in pipelines subjected to differential lateral ground displacements.

Validation of Fault Rupture-Response Spectrum Analysis Method for Curved Bridges Crossing Strike-Slip Fault Rupture Zones

AbstractIn response to the bridge damages observed in past earthquakes and the absence of practical analysis methods, a simplified analysis procedure named the fault rupture-response spectrum analysis (FR-RSA) method was developed in this research as an alternative to the onerous nonlinear response history analysis (RHA) method for bridges crossing strike-slip earthquake fault rupture zones. For validation of the FR-RSA method, this research investigated seismic responses of two representative curved bridges in California, including one three-span bridge and one four-span bridge. The selected bridges were analyzed using both the FR-RSA method and the nonlinear RHA method. Ground motion, earthquake fault rupture location, and fault orientation were varied in the analyses to expand the validation work under a broad range of the parameters. Result comparisons show that the FR-RSA method provides estimates of peak bridge displacement response that are close enough to the exact nonlinear RHA results in all con...

Numerical Modeling of Buried HDPE Pipelines Subjected to Strike-Slip Faulting

A systematic study of buried pipeline response to strike-slip faulting was performed wherein advanced computational simulations were conducted in parallel with a series of physical tests employing split-boxes within the geotechnical centrifuge at Rensselaer Polytechnic Institute and the full-scale testing facility at Cornell University. This article describes the numerical modeling and simulations of the experimental tests. The buried pipeline and the surrounding soil are modeled using nonlinear beam (shell) elements and elasto-plastic springs distributed along the pipeline, respectively. Using the finite element method, reasonable predictions are obtained for the axial and bending strain distributions measured during the tests. It is also shown that finite element analysis using pipe beam elements and a modified soil spring model can accurately predict the pipeline seismic behavior due to strike-slip fault rupture, especially when the pipe is subjected to combined bending and tension. In addition, existing closed-form solutions are evaluated.