Fault Displacement Hazard Analysis Research Articles

The Time-Dependent Method for Probabilistic Fault Displacement Hazard Analysis (PFDHA-td)

Coseismic surface displacement can cause major damage to buildings located on faults. Therefore, it is important to quantitatively evaluate the future surface displacement of active faults. The commonly used deterministic evaluation methods often tend to overestimate surface displacement values, so researchers are working toward probabilistic fault displacement hazard analysis (PFDHA). However, the PFDHA assumes that earthquakes occur equally in time, which is not consistent with the physical mechanism of earthquake occurrence. Elastic rebound theory and paleoseismic research results show that the accumulation and release of energy in the crustal medium have cyclical characteristics. In this study, using two parameters, the strong earthquake recurrence period (TRP) and strong earthquake elapsed time (tet), of active faults, the displacements of active faults with different TRP and tet under different exceedance probabilities are obtained. The calculation results indicate that the surface displacement hazard of the weakly active and extremely weakly active faults in the Holocene does not need to be considered; for the moderately and strongly active faults in the Holocene, the surface displacement result is lower than that provided by the deterministic method. According to the importance of the project, the calculation results of the PFDHA-td method under different exceedance probabilities are selected.

Probabilistic fault displacement Hazard analysis in an extensional setting: Application to a strategic Dam and methodological implications

We present a Probabilistic Fault Displacement Hazard Analysis (PFDHA) for a strategic dam located in the Upper Tiber Valley (Northern Apennines of Italy) claimed to be sited on a supposed capable fault (Montedoglio fault). We verify the seismic capability of the Montedoglio fault through detailed geological and geophysical analyses. We find no evidence for considering the Montedoglio fault as an active and capable structure, the fault being constituted by a system of discontinuous parallel faults, apparently inactive since more than 56 ± 3 ka, and likely unable to nucleate strong surface rupturing earthquakes. Since the dam lies on the hanging wall of the closest major active fault of the area (Anghiari normal fault, ∼1.5 km away), we investigate the likelihood of having distributed faulting at the dam's site in case of a strong surface-rupturing earthquake occurring on the Anghiari fault. We apply a probabilistic approach to obtain hazard curves of exceedance of vertical displacement at the dam's site for different rupture scenarios. We show that the mean hazard curve is always below an annual frequency of exceedance of 1 × 10−5, corresponding to displacement values below 1 cm over 100,000 years of return period. The study highlights several weaknesses and uncertainties in using PFDHA with state-of-the-art models, suggesting the need for improvements to enhance their applicability in earthquake engineering geology practice.

Coseismic surface ruptures of 20 strike-slip earthquakes measured from geodetic imaging data

Observations of coseismic surface ruptures are widely used for examining faulting mechanics and kinematics, and in fault displacement hazard analysis. Here, first, we provide new remote sensing observations of 20 historic surface rupturing continental strike-slip earthquakes (6.1 ≤ Mw≤ 7.9). To measure the near-field surface deformation pattern, we have processed a range of raw radar and optical images from satellite and aerial platforms with pixel tracking techniques, and in two cases using standard interferometric synthetic aperture radar (InSAR). We provide a range of observations, including surface displacement maps that constrain at least the horizontal component of surface motion (2D), and for three events the full 3D components. Second, we provide strain invariants for each event, which includes the finite dilatational strain, strain magnitudes, the vorticity, and maximum shear strain. Third, we provide a total of 134 surface fault rupture traces that are mapped manually from the displacement maps. Finally, we provide 2648 measurements of coseismic horizontal fault-parallel surface fault slip that are measured objectively using swath profiles with a function fitting method that we have developed.

Fault-displacement models for aggregate and principal displacements

New fault-displacement models (FDMs) are developed for the aggregate and principal net surface displacement using the database developed by the Fault Displacement Hazard Initiative Project. An FDM for the aggregate displacement is developed, which is then partitioned into principal and distributed displacements. The model for the aggregate displacement is first formulated in the wavenumber domain to incorporate seismology-based constraints for the extrapolation of the magnitude scaling of median displacements to large-magnitude events. The results from the wavenumber-domain model are then adjusted to fit the empirical moderate-magnitude scaling (M < 7) and the shape of the displacement profile at the ends of the rupture. Segments are used in the model development to better capture the complexity of the variability of the surface-displacement profile along strike, including regions with zero displacements. For applications in which segments cannot be identified, simplified FDMs without segments are developed that treat the number, lengths, and locations of the segments as aleatory variability. The principal-displacement FDM is then developed as an adjustment to the aggregate-displacement FDM. The segmentation and the magnitude dependence of the taper length of individual segments lead to non-self-similar scaling of the median profile along the entire rupture that can have a significant impact on probabilistic fault-displacement hazard analysis (PFDHA) for sites near the ends of faults. A key feature of the new FDMs is the use of a power-normal [Formula: see text] distribution for the aleatory variability, which leads to narrower distributions of the displacement for large-magnitude earthquakes compared to the commonly used lognormal distribution. For large-magnitude earthquakes, the expected maximum displacements computed using the power-normal distribution of the FDM are consistent with the observed maximum displacements along strike, supporting the narrower shape of the upper tail of the power-normal distribution for large-magnitude events.

Probabilistic fault displacement hazard analysis (PFDHA) for a strand of main boundary thrust (MBT) in Garhwal-Kumaon Himalaya

Probabilistic fault displacement hazard analysis (PFDHA) for a strand of main boundary thrust (MBT) in Garhwal-Kumaon Himalaya

Rapid Surface Rupture Mapping from Satellite Data: The 2023 Kahramanmaraş, Turkey (Türkiye), Earthquake Sequence

Abstract The 6 February 2023 Kahramanmaraş, Turkey (Türkiye), earthquake sequence produced > 500 km of surface rupture primarily on the left-lateral East Anatolian (~345 km) and Çardak (~175 km) faults. Constraining the length and magnitude of surface displacement on the causative faults is critical for loss estimates, recovery efforts, rapid identification of impacted infrastructure, and fault displacement hazard analysis. To support these efforts, we rapidly mapped the surface rupture from satellite data with support from remote sensing and field teams, and released the results to the public in near-real time. Detailed surface rupture mapping commenced on 7 February and continued as high-resolution (< 1.0 m/pixel) optical images from WorldView satellites (2023 Maxar) became available. We interpreted the initial simplified rupture trace from subpixel offset fields derived from Advanced Land Observation Satellite2 and Sentinel-1A synthetic aperture radar image pairs available on 8 and 10 February, respectively. The mapping was released publicly on 10 February, with frequent updates, and published in final form four months postearthquake (Reitman, Briggs, et al., 2023). This publicly available, rapid mapping helped guide fieldwork and constrained U.S. Geological Survey finite-fault and loss estimate models, as well as stress change estimates and dynamic rupture models.

Evaluating how well active fault mapping predicts earthquake surface-rupture locations

Abstract Earthquake surface-fault rupture location uncertainty is a key factor in fault displacement hazard analysis and informs hazard and risk mitigation strategies. Geologists often predict future rupture locations from fault mapping based on the geomorphology interpreted from remote-sensing data sets. However, surface processes can obscure fault location, fault traces may be mapped in error, and a future rupture may not break every fault trace. We assessed how well geomorphology-based fault mapping predicted surface ruptures for seven earthquakes: 1983 M 6.9 Borah Peak, 2004 M 6.0 Parkfield, 2010 M 7.2 El Mayor–Cucapah, 2011 M 6.7 Fukushima-Hamadori, 2014 M 6.0 South Napa, 2016 M 7.8 Kaikoura, and 2016 M 7 Kumamoto. We trained geoscience students to produce active fault maps using topography and imagery acquired before the earthquakes. A geologic professional completed a “control” map. Mappers used a new “geomorphic indicator ranking” approach to rank fault confidence based on geomorphologic landforms. We determined the accuracy of the mapped faults by comparing the fault maps to published rupture maps. We defined predicted ruptures as ruptures near a fault (50–200 m, depending on the fault confidence) that interacted with the landscape in a similar way to the fault. The mapped faults predicted between 12% to 68% of the principal rupture length for the studied earthquakes. The median separation distances between predicted ruptures and strong, distinct, or weak faults were 15–30 m. Our work highlights that mapping future fault ruptures is an underappreciated challenge of fault displacement hazard analysis—even for experts—with implications for risk management, engineering site assessments, and fault exclusion zones.

Fault displacement hazard estimation at lifeline–fault crossings: A simplified approach for engineering applications

Lifelines, such as pipelines, roads, and tunnels, are critical infrastructure and when crossing active tectonic faults, a reliable estimation of the fault displacement in case of an earthquake is required. The first and simplest approach is to use empirical fault scaling relations to compute the design fault displacement, but this may result in an unknown level of safety. Thus, the probabilistic fault displacement hazard analysis (PFDHA) is the appropriate tool to assess the fault displacement hazard within a performance-based framework. Based upon an established PFDHA model, we present a simplified approach for engineering applications focusing on the lifeline–fault crossing along with appropriate simplifications and assumptions to extend its applicability to numerous faults. The aim is to provide a structure-independent approach of PFDHA that can be used when a site-specific study is not required, not possible (e.g., absence of recent sediments for dating past events), or too cumbersome, e.g., for lifeline route selection. Additionally, an in-depth investigation is presented on the key parameters, such as maximum earthquake magnitude, fault length, recurrence rate of all earthquakes above a minimum magnitude, and lifeline-fault crossing site, and how they affect the hazard level. This approach will be the basis for deriving hazard-consistent expressions to approximate fault displacement for use within the Eurocodes. The latter is intended to serve as a compromise between hazard-agnostic fault scaling relations and a comprehensive PFDHA, which requires detailed calculations and site-specific seismological data.

Performance-based three-level fortification goal and its application in anti-dislocation countermeasures: A case study of Shantou Submarine tunnel

The dislocation momentum is the design basis for anti-dislocation to tunnel when a tunnel crosses an active fault. The influence of different dislocation levels on tunnel performances is not clear. Thus, based on seismic activity parameters at the site of interest and probability of fault dislocation, probability fault displacement hazard analysis (PFDHA) methodology was introduced in this paper to ascertain the fault dislocation level under different exceeding probabilities (63%, 10%, and 2%–3%). Then, based on the definition of different ground motion strength and fortification goals of the tunnel, a three-level fortification goal with different performance requirements of the tunnel was proposed. The first attempt to use the proposed indexes including the maximum dislocation of the tunnel and maximum relative deformation of the tunnel was tried to evaluate deformation and failure states with an experimental approach. Subsequently, the feasibility of the three-level fortification goal was further investigated according to the self-defined qualitative description and quantitative indexes in the segmental design and sectional expansion tunnels comprehensively. The results show that the fault dislocations relying on PFDHA at the site of the Shantou Submarine Tunnel are firstly ascertained as 0.04, 1.8, and 2.4 m respectively. Taking the fault dislocation as model input values into account, the dislocation mechanism of the tunnel under the three levels was revealed. More importantly, judging from the dislocation performance requirements of the three-level fortification goal, the tunnel deformation and failure states are mitigated by adopting the countermeasures. The sectional expansion design can well meet the requirements without the restriction of a strong earthquake, while the effectiveness of the segmental tunnel can be proved under frequently occurred and fortification earthquake. The final research results are expected to provide a new fortification goal for anti-dislocation hazard evaluation on expansion design in high-intensity seismic regions and segmental design in slight and moderate-intensity seismic regions.

Geomechanical Modeling of Ground Surface Deformation Associated with Thrust and Reverse-Fault Earthquakes: A Distinct Element Approach

ABSTRACTWe seek to improve our understanding of the physical processes that control the style, distribution, and intensity of ground surface ruptures on thrust and reverse faults during large earthquakes. Our study combines insights from coseismic ground surface ruptures in historic earthquakes and patterns of deformation in analog sandbox fault experiments to inform the development of a suite of geomechanical models based on the distinct element method (DEM). We explore how model parameters related to fault geometry and sediment properties control ground deformation characteristics such as scarp height, width, dip, and patterns of secondary folding and fracturing. DEM is well suited to this investigation because it can effectively model the geologic processes of faulting at depth in cohesive rocks, as well as the granular mechanics of soil and sediment deformation in the shallow subsurface. Our results show that localized fault scarps are most prominent in cases with strong sediment on steeply dipping faults, whereas broader deformation is prominent in weaker sediment on shallowly dipping faults. Based on insights from 45 experiments, the key parameters that influence scarp morphology include the amount of accumulated slip on a fault, the fault dip, and the sediment strength. We propose a fault scarp classification system that describes the general patterns of surface deformation observed in natural settings and reproduced in our models, including monoclinal, pressure ridge, and simple scarps. Each fault scarp type is often modified by hanging-wall collapse. These results can help to guide both deterministic and probabilistic assessment in fault displacement hazard analysis.

Probabilistic Fault Displacement Hazard Analysis Using Model of Seismic Source Characteristics at the Ikata Site Based on Guidelines for SSHAC Level 3

Probabilistic Fault Displacement Hazard Analysis Using Model of Seismic Source Characteristics at the Ikata Site Based on Guidelines for SSHAC Level 3

Probabilistic fault displacement hazard analysis for the north Tabriz fault

Abstract. The probabilistic fault displacement hazard analysis is one of the newest methods of estimating the amount of probabilistic displacement in fault surface rupture areas. Considering the strike-slip mechanism of the north Tabriz fault, Iran, using the earthquake method and historical earthquakes in 1721 and 1780, the surface displacement of the north Tabriz fault has been investigated, and the probabilistic displacement in different scenarios has been estimated. The north Tabriz fault's 50–60 km long section was selected as the source of possible surface rupture from its historical data. Two scenarios were considered according to probabilistic displacements, return periods, and magnitudes according to paleoseismic studies of the north Tabriz fault. For both scenarios, the probabilistic displacements for the exceedance rate of 5 % in 50, 475, and 2475 years for the probabilistic principle displacements (on the fault) of the north Tabriz fault have been estimated.

Probabilistic Fault Displacement Hazards along the Milun Fault

ABSTRACTCoseismic surface displacements can result in significant damage to structures located on or near a fault. To address this particular hazard, probabilistic fault displacement hazard analysis (PFDHA) has been proposed to estimate expected displacement on a fault and in its vicinity. To construct PFDHA, any new observed surface ruptures can be included. In 2018, an Mw 6.4 earthquake hit the city of Hualien, Taiwan, and caused surface ruptures along the Milun fault. Immediately after the earthquake, field investigations were carried out to investigate the surface ruptures, which provided crucial information for PFDHA. Based on our analysis of the surface displacement data in the Hualien event, we compared existing fault displacement prediction equations, and found that 86% and 65% of the observations from the free field and manmade structures, respectively, were within one standard deviation of the predictions. Based on our fault displacement model and its uncertainties, we analyze the fault displacement hazard in the Hualien region by incorporating epistemic uncertainties through a logic tree approach. Comparing with the occurrence probability of distributed surface faulting, most observations are within one standard deviation of the predictions, suggesting the applications of derived PFDHA.

Prospective Fault Displacement Hazard Assessment for Leech River Valley Fault Using Stochastic Source Modeling and Okada Fault Displacement Equations

In this study, an alternative method for conducting probabilistic fault displacement hazard analysis is developed based on stochastic source modeling and analytical formulae for evaluating the elastic dislocation due to an earthquake rupture. It characterizes the uncertainty of fault-rupture occurrence in terms of its position, geometry, and slip distribution and adopts so-called Okada equations for the calculation of fault displacement on the ground surface. The method is compatible with fault-source-based probabilistic seismic hazard analysis and can be implemented via Monte Carlo simulations. The new method is useful for evaluating the differential displacements caused by the fault rupture at multiple locations simultaneously. The proposed method is applied to the Leech River Valley Fault located in the vicinity of Victoria, British Columbia, Canada. Site-specific fault displacement and differential fault displacement hazard curves are assessed for multiple sites within the fault-rupture zone. The hazard results indicate that relatively large displacements (∼0.5 m vertical uplift) can be expected at low probability levels of 10−4. For critical infrastructures, such as bridges and pipelines, quantifying the uncertainty of fault displacement hazard is essential to manage potential damage and loss effectively.

Potential Fault Displacement Hazard Assessment Using Stochastic Source Models: A Retrospective Evaluation for the 1999 Hector Mine Earthquake

Surface fault displacement due to an earthquake affects buildings and infrastructure in the near-fault area significantly. Although approaches for probabilistic fault displacement hazard analysis have been developed and applied in practice, there are several limitations that prevent fault displacement hazard assessments for multiple locations simultaneously in a physically consistent manner. This study proposes an alternative approach that is based on stochastic source modelling and fault displacement analysis using Okada equations. The proposed method evaluates the fault displacement hazard potential due to a fault rupture. The developed method is applied to the 1999 Hector Mine earthquake from a retrospective perspective. The stochastic-source-based fault displacement hazard analysis method successfully identifies multiple source models that predict fault displacements in close agreement with observed GPS displacement vectors and displacement offsets along the fault trace. The case study for the 1999 Hector Mine earthquake demonstrates that the proposed stochastic-source-based method is a viable option in conducting probabilistic fault displacement hazard analysis.

Probabilistic fault displacement hazard analysis of the Anghiari - Città di Castello normal fault (Italy)

Fault displacement is a localized source of hazard for infrastructure located near active and capable faults, such as critical buildings and distributed facilities. This issue can be overcome through zoning and avoidance strategies, but facilities may sometimes not benefit from this option. In the last 20 years, several authors have developed a probabilistic approach to analyse this hazard, known as probabilistic fault displacement hazard analysis (PFDHA), for both principal fault and distributed rupturing. In this work, we apply the approach proposed by YOUNGS et alii (2003) to the Anghiari-Città di Castello fault, a NE-dipping normal fault located in the northern Apennines of Italy, which shows evidence of Quaternary activity. We explore two different rupturing scenarios to obtain displacement hazard curves and maps for different probabilities of exceedance in 200 years at different distances along and from the principal fault trace for both the principal and distributed rupturing. The expected displacement values for the principal fault rupturing are up to 130 cm for a return period of 10,000 years (2% in 200 years), and the distributed rupturing hazard is 3–4% of the principal fault rupturing hazard. It is null in the footwall of the fault and slightly variable in its hanging wall as a function of distance from the fault trace and fault tip. The variability of the distributed rupturing hazard within the first hundreds of metres from the principal fault can assist to define mitigation strategies for existing facilities located in proximity of the fault.

Probabilistic Fault Displacement Hazard Assessment (PFDHA) for Nuclear Installations According to IAEA Safety Standards

ABSTRACT In the last 10 yr, the International Atomic Energy Agency (IAEA) revised its safety standards for site evaluations of nuclear installations in response to emerging fault displacement hazard evaluation practices developed in Member States. New amendments in the revised safety guidance (DS507) explicitly recommend fault displacement hazard assessment, including separate approaches for candidate new sites versus existing sites. If there is insufficient basis to conclusively determine that a fault is not capable of surface displacement at an existing site, then a probabilistic fault displacement hazard analysis (PFDHA) is recommended to better characterize the hazard. This new recommendation has generated the need for the IAEA to provide its Member States with guidance on performing PFDHA, including its formulation and implementation. This article provides an overview of current PFDHA state-of-practice for nuclear installations that is consistent with the new IAEA safety standards. We also summarize progress in an ongoing international PFDHA benchmark project that will ultimately provide technical guidance to Member States for conducting site-specific fault displacement hazard assessments.

Reliability evaluation method for pipes buried in fault areas based on the probabilistic fault displacement hazard analysis

The tectonic fault poses a great threat to buried pipe segments. Buckling or rupture of pipes will ensue due to large strain induced by continuously increasing fault movements. In this study, a reliability-based methodology is conceptually proposed for designing new buried pipes or assessing existing pipes installed in fault areas. Uncertainties associated with the influencing factors of pipe structure and seismic loading (fault displacement) generated by earthquakes are considered. For pipe structural reliability, a developed back-propagation neural network (BPNN)-based surrogate model is utilized for the strain demand term in the limit state function for reliability calculations. Given statistical data for the basic variables including diameter, wall thickness, internal pressure, intersection angle or dip angle, and soil spring resistances, the conditional probability of failure can be obtained at a particular fault displacement by Monte Carlo simulation. Uncertainty of the fault displacement is estimated based on probabilistic fault displacement hazard analysis (PFDHA) having results given as probability of exceeding a certain fault displacement level for a specific site, then the occurrence probability of a specific fault displacement at a specific time can be indirectly obtained. The actual probability of failure (PoF) is calculated as an integral of fault displacement based on the total probability which is the product of the conditional PoF of pipe structure and occurrence probability of the specific fault displacement. This developed methodology is applied to a case study about a pipe project from China. Results show that the probability of failure increases with the elapsed time but stay within the safety margin for the next 30 years. Generally, the result of PFDHA is an essential input parameter in reliability analysis for pipes buried in fault regions. The multidisciplinary combination of structural reliability analysis and fault displacement hazard analysis is of practical significance for the reliability-based study of pipes in fault regions.

Probability of Occurrence and Displacement Regression of Distributed Surface Rupturing for Reverse Earthquakes

Probabilistic fault displacement hazard analysis provides a systematic approach to estimate the likelihood of occurrence and expected amount of surface displacement during an earthquake on-fault (principal fault rupturing) and off-fault (distributed rupturing). The methodology is based on for key parameters describing the probability of occurrence and the spatial distribution of the displacement both on and off-fault. In this work we concentrate on off-fault rupturing, and develop an original probability model for the occurrence of distributed ruptures and for the expected displacement distribution based on the compilation and reappraisal of surface ruptures from 15 historical crustal earthquakes of reverse kinematics, with magnitudes ranging from Mw 4.9 to Mw 7.9. We introduce a new ranking scheme to distinguish principal faults (rank 1) from simple distributed ruptures (rank 2), bending-moment (rank 21) and flexural-slip (rank 22) and triggered faulting (rank 3). We then used the rank 2 distributed ruptures with distances from the principal fault ranging from 5 m to 1500 m. To minimize bias due to the incomplete nature of the database, we propose a ‘slicing ' approach as an alternative to the 'gridding' approach. The 'slicing' approach is then combined with MonteCarlo simulations to model the dependence of the probability of occurrence and exceedance with the dimensions and position of the site of interest with respect to the principal fault, both along and across strike. We applied the probability model to a case-study in Finland to illustrate the applicability of the method given the limited extend of the available dataset. We finally suggest that probabilistic fault displacement hazard model will benefit by evaluating spatial distribution of distributed rupture in the light of spatial completeness of the input data, structural complexity and physics observables of the causative fault.

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.