Probabilistic Fault Displacement Hazard Analysis Research Articles

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

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.

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.

Probabilistic Evaluation of Off-Fault Displacements of the 2016 Kumamoto Earthquake

The 2016 Kumamoto earthquake occurred on April 16, 2016, and induced the complex distribution of surface ruptures and fault displacements, which revealed the difficulty of evaluating off-fault displacement hazards. The evaluation of off-fault displacements is necessary for the site investigation of an important facility, such as nuclear installations, but is difficult because off-fault displacements are thought to occur on unmapped or small-scale structures. A probabilistic fault displacement hazard analysis (PFDHA) assesses an off-fault displacement hazard as well as an on-fault one. Several PFDHA models have been developed from fault displacement datasets parsed by global-specific and Japanese-various faulting types. We developed a procedure to assess off-fault displacement hazards based on probabilistic and numerical simulation approaches. In the probabilistic approach, we constructed strike-slip and reverse-slip PFDHA models from a dataset of Japanese fault displacements. The off-fault components in PFDHA had a probability of non-zero off-fault displacement and an attenuation relationship. In the case of evaluating the site of an important facility, detailed field surveys were performed to collect numerous site-specific information. There is little site-specific data of off-fault displacements in Japan. The trench surveys were performed at off-fault displacement sites from the 2016 Kumamoto earthquake. The two trench sites were selected based on a linear low-coherence zone derived from the InSAR analysis, which emphasizes small-scale displacements. The excavation survey result at one site suggests a shorter recurrence interval than that of the active fault long-term evaluation. We also performed a probabilistic fault hazard analysis (PFDHA) of the trench sites by using the global strike-slip model and Japanese PFDHA models with and without the site-specific data. For the PFDHA results without site-specific data, the difference in the annual rates of exceedance between the global strike-slip and Japanese models increased with increasing fault displacements. This is because of the reduced decrease in the attenuation relationship of Japanese models. The differences in the annual rates of exceedance constrained with the site-specific data are independent of fault displacements due to variation in the probability of non-zero off-fault displacement between the global strike-slip and Japanese PFDHA models. These results suggest that the off-fault PFDHA models have high variability. In the case of PFDHA evaluation with several models, the individual PFDHA components are carefully selected by considering the individual effects. The site-specific short recurrence interval revealed by the trench survey leads to higher annual rates of exceedance.

Improved Implementation of Rupture Location Uncertainty in Fault Displacement Hazard Assessment

AbstractThis short note proposes an improvement to the implementation of uncertainty associated with rupture location from future earthquakes in probabilistic fault displacement hazard analysis. Location uncertainty leads to nonzero primary fault displacement near a mapped fault. With the improved implementation of location uncertainty, estimated fault displacement hazard at a given site is affected strongly by the dimension of the area considered (or the footprint size of the structure). A larger area near a mapped fault has greater potential of exhibiting primary fault displacement than does a smaller area at the same location. In addition, fault displacement hazard is affected by fault‐map quality and fault‐trace complexity. For a more accurately mapped fault with simpler geometry, larger fault displacement is expected directly over and in close proximity of the mapped fault. If fault location is highly uncertain and fault traces are complex, expected displacement is spread out in a wider zone along the mapped fault.

Performance Assessment of Buried Pipelines at Fault Crossings

A methodology for seismic performance assessment of onshore buried steel pipelines at fault crossings is presented. Probabilistic fault displacement hazard analysis is performed at first to determine the magnitude of the three fault displacement components in space. Next, three-dimensional (3-D) structural analysis of the pipeline via a nonlinear beam-type finite element model allows accounting for the different effect of imposed displacements in each axis. Finally, convolving of seismic hazard and structural response results in joint hazard surfaces of compressive and tensile strains that can be used to estimate the mean annual rate of exceeding any limit-state of interest under the influence of demand and capacity uncertainty.

Earthquake-induced crustal deformation and consequences for fault displacement hazard analysis of nuclear power plants

Readily available interferometric data (InSAR) of the coseismic deformation field caused by recent seismic events clearly show that major earthquakes produce crustal deformation over wide areas, possibly resulting in significant stress loading/unloading of the crust. Such stress must be considered in the evaluation of seismic hazards of nuclear power plants (NPP) and, in particular, for the potential of surface slip (i.e., probabilistic fault displacement hazard analysis - PFDHA) on both primary and distributed faults.In this study, based on the assumption that slip on pre-existing structures can represent the elastic response of compliant fault zones to the permanent co-seismic stress changes induced by other major seismogenic structures, we propose a three-step procedure to address fault displacement issues and consider possible influence of surface faulting/deformation on vibratory ground motion (VGM). This approach includes: (a) data on the presence and characteristics of capable faults, (b) data on recognized and/or modeled co-seismic deformation fields and, where possible, (c) static stress transfer between source and receiving faults of unknown capability.The initial step involves the recognition of the major seismogenic structures nearest to the site and their characterization in terms of maximum expected earthquake and the time frame to be considered for determining their “capability” (as defined in the International Atomic Energy Agency - IAEA Specific Safety Guide SSG-9). Then a GIS-based buffer approach is applied to identify all the faults near the NPP, possibly influenced by the crustal deformation induced by the major seismogenic structures. Faults inside these areas have to be tested for “capability” according to the same time window defined for the primary seismogenic structures.If fault capability is confirmed or, eventually, cannot be assessed, the next step is to implement an approach based on the potential to affect the safety of the NPP site in terms of fault geometry, and potential displacement.Finally, in the case where the fault can affect the safety of the site, the third step is the PFDHA or, in other words, the calculation of the annual probability of exceedance of the potential co-seismic fault displacement; this displacement is to be compared with the fault displacement threshold that will impact the safety of the NPP site.We also consider the effect of site vicinity tectonism on site vibratory ground motion and discuss an example in the light of the use of the GMPE.

Locating distributed faulting: Contributions from InSAR imaging to Probabilistic Fault Displacement Hazard Analysis (PFDHA)

Prediction of location and amount of slip for distributed faulting associated to strong earthquakes is a recently explored issue with major implications in terms of hazard assessment. Currently, the best practice involves the applications of Probabilistic Fault Displacement Hazard Analysis (PFDHA) whose results fit sufficiently well real data in the near-range of the primary fault but show considerable inaccuracies in the far-range. We believe that this inaccuracy descends from the biased earthquake databases used for regression analysis, whose data, relative to old earthquakes, were largely collected only by field surveys focused close to the primary fault (i.e., near-range).Remotely-sensed data (i.e., Interferometric Radar Imaging – InSAR) offer the opportunity to precisely measure the surface deformation induced by strong earthquakes and thus to explore its possible relation with distributed faulting. We analyze the L'Aquila earthquake case study (29th April, 2009, Mw 6.3) and explore the correlation between location and slip on distributed faulting and InSAR-derived deformation field. We find a significant correlation between occurrence of distributed faulting and profile curvature of the dislocation field, in spite of the distance from the primary fault. Moreover, distributed faults tend to occur within the area deformed by the earthquake, as imaged by InSAR data and whose extent is directly proportional to the earthquake magnitude (Mw), according to a dataset of 30 recent earthquakes.We then propose that these observations have to be incorporated into the present PFDHA practice as limit boundaries to possible scenarios of probabilistic analysis and that an integrated use of field-based and remotely data collection have to be implemented, following strong earthquakes.

確率論的断層変位ハザード解析の信頼性向上

確率論的断層変位ハザード解析の信頼性向上

Probabilistic Fault Displacement Hazard Analysis for Reverse Faults

We present a methodology for evaluating potential surface fault displacement due to reverse faulting events in a probabilistic manner. This methodology, called probabilistic fault displacement hazard analysis (PFDHA) follows procedures that were originally applied to normal faulting. We present empirical distributions for surface rupture, maximum and average displacement, spatial variability of slip, and other random variables that are central to performing PFDHA for reverse faults. Additionally, a sensitivity analysis is conducted on all independent variables in the PFDHA procedure. The Los Osos fault zone of central California is used as the test case, and results are presented in the form of a hazard curve. The influence each of the variables has on a hazard curve is quantified to provide direction for future research in PFDHA. It is seen that a distribution for slip spatial variability is the least influential term in the procedure, and a term for the probability of surface rupture has the most influence.

A Methodology for Probabilistic Fault Displacement Hazard Analysis (PFDHA)

We present a methodology for conducting a site-specific probabilistic analysis of fault displacement hazard. Two approaches are outlined. The first relates the occurrence of fault displacement at or near the ground surface to the occurrence of earthquakes in the same manner as is done in a standard probabilistic seismic hazard analysis (PSHA) for ground shaking. The methodology for this approach is taken directly from PSHA methodology with the ground-motion attenuation function replaced by a fault displacement attenuation function. In the second approach, the rate of displacement events and the distribution for fault displacement are derived directly from the characteristics of the faults or geologic features at the site of interest. The methodology for probabilistic fault displacement hazard analysis (PFDHA) was developed for a normal faulting environment and the probability distributions we present may have general application in similar tectonic regions. In addition, the general methodology is applicable to any region and we indicate the type of data needed to apply the methodology elsewhere.