the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Apr 2025
The impact of active and capable faults structural complexity on seismic hazard assessment for the design of linear infrastructures
Abstract. Since Active and Capable Faults (ACFs) may generate significant permanent deformation of the topographic surface, a careful evaluation of their spatial and geometric characteristics is essential for seismic hazard assessment when planning new linear infrastructures (e.g., roads, railway lines, pipelines). Although this is generally overlooked, the common structural complexity of fault zones leads to a non-uniform hazard along and across faults’ traces, because of deformation localization and partitioning. This study reviews the factors controlling fault rupture and propagation, specifically focusing on fault zone architecture and growth mechanisms. Four scenarios of physical interaction between ACFs and linear infrastructures are analysed. The fault-crossing scenario is likely the most susceptible to ground surface displacement, while the fault-parallel scenario needs evaluation of the width of fault damage zone overlapping with the infrastructure. Near-fault tip and transfer zone-crossing scenarios require assessment of the local deformation patterns. The importance of a structural geological approach toward the reliable assessment of seismic hazard related to ACFs, we review suitable investigations to derive appropriate geological deterministic constraints on the geometry, kinematics, slip and deformation style of ACF’s. Our approach may have significant impact on the legislation regulating the early stages of infrastructural design.
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RC1: 'Comment on egusphere-2025-506', Anonymous Referee #1, 26 Apr 2025
This is a useful and well-written paper about the impact of active and capable faults structural complexity on seismic hazard assessment for the design of linear infrastructures.
However, a moderate improvement is needed in the structure of the paper before its acceptance for publication. Some contents of sections 4 and 5 are more results than methodological explanations or discussion. Therefore, I recommend a new section, "5. Results," needs to be created where the authors may present their results, taking relevant material mainly from sections 4 and 5.Citation: https://doi.org/10.5194/egusphere-2025-506-RC1 -
AC1: 'Reply on RC1', Selina Bonini, 16 May 2025
We thank the Reviewer for the valuable comment and suggestions. We fully acknowledge the importance of clearly highlighting the original and innovative contribution of our work within the framework of seismic hazard assessment for infrastructure planning purposes. In this context, we would like to clarify that the main aim of the present study is to introduce and discuss the implications of the structural complexity of active and capable faults (ACFs) on seismic hazard evaluations, specifically in relation to the design of linear infrastructures. Our primary objectives are: (i) to propose conceptual scenarios illustrating the potential physical interactions between ACFs and linear infrastructures; and (ii) to analyse the key structural factors that govern the deformation patterns interfering with such infrastructures.
It is important to note that this work does not present new geological, structural, or geophysical data. Our primary focus is on the geometrical configurations that may arise from ACF-infrastructure interactions (Section 4). From this analysis, we then propose a practical workflow to the comprehensive parametrisation of an evolving ACF (Section 5). We believe that the current organisation of the manuscript effectively reflects our methodological approach and the conceptual nature of this contribution. Therefore, we would prefer to retain the present text organisation in the revised version.
Citation: https://doi.org/10.5194/egusphere-2025-506-AC1
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AC1: 'Reply on RC1', Selina Bonini, 16 May 2025
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RC2: 'Comment on egusphere-2025-506', Anonymous Referee #2, 02 May 2025
Referee comments for Bonini et al., 2025, preprint EGU preprint
General comments :
The definition of the IZ represents a key point of the proposed process of hazard assessment for linear structures, hence a proper scheme showing the IC dimention compared to the fault zone might improve the consistency of the concept. Its definition is suggested to be based on scaling law, which is a very good idea for a first order assessment. The issue is that those scaling laws present several orders of magnitude, and the definition of the considered dimension remains very coarse. I am wondering about the uncertainties related to the definition of those lengths, and how to i. constraint them and ii. Give some security range (kind if geometric safety factor), to correctly constrain the dimension of the zone, minimizing in the one hand the probability of missing some fault surface rupture and associated offsets, and in the other hand do not exaggerate the IZ size, as the cost possibly involved to ensure the safety of the structure may rise strongly.
Regarding section 5.2 and discussion about remote sensing and identification of fault damage zones using microtopographic technics, I think it is important to precise that this approach only works if the topography signal of the fault surface rupture and damaging has been preserved in the landforms. I mean that if erosion of anthropic activities exceeds the expression of the fault-related deformation, this approach will not work, and that this limit deserves to be mentioned. Hence here comes the geophysical approach (nondestructive) and paleoseismological and geotechnical approaches (destructive).
Another point is the organization of the sections in that chapter. Please make slightly more obvious the successions intro and scaling, RS, field geology and geophysics, then paleoseismology, dating and morphotectonics for slip rates assessments.
Specific comments and technical corrections :
L26, please specify the names of the Great Alaska and Niigita earthquakes
L52 : Why not add water adduction structures ? e.g. Laquilla EQ, that has been strongly affected by a waterpipe rupture.
L140: I suppose the processes here illustrated come from previous publications show them (e.g. Barnett 87, Peacock and Sanderson 91, 94). Would it be necessary to refer to the main ones in the caption ?
L155 : cumulative displacement is proportional to fault width with same order of magnitude ? They are proportional modulo a factor 102 to 103, what significance ?
L156 : Why 2 orders io magnitude ? Mean 100 km fault will have damage zone 10 km ? There are no references to explain this scaling relation.
L181: Maximum displacement along a single fault trace ? Cause if one considers the fault system (here the two main fault segments and the damage zone within the overlapping zone.
189 : is it representative to consider a stand-alone fault segment ? Could you please bring proper example ?
L220: 14 % ? Do the author precise a range of length when this relation is observable ? This might depend on the seismogenic width (previously names fault height) ? There is a quite big discrepancy here ; in what extent could this discrepancy be addressed for definition of relay zones ?
Figure 6 : the constant length model also corresponds to the characteristic slip model (Shwartz and coppersmith, 82). Is it necessary to precise it here ?
Figure 7 : regarding the coseismic diffuse rupture, on the right we observe in the transfer zone any left step ridel (RL strike slip indication), instead on the left (within the tip zone), they are right step (left lateral strike slip indication). It might be more coherent to maintain the same pattern in the surface rupture scheme.
L243: This sentence suggests you are prioritizing some parameters in the figure, but then it is not obvious that the different scenario presented in this figure allows you to choose parameters to prioritize. Maybe simply precise/reformulate the caption
Figure 8: Interesting. I found it hard to catch the location of the profiles displayed but I eventually understood
L249: certainly, but why ?
L253: Unless I am mistaken, linear correlation in a log-log graph describe a power law correlation and not a linear one.
L255: “it is reasonable to expect”, yes I suppose, but is there any references looking for cross-fault slip distribution (maybe from pixel correlation for instance) that may help to justify this assertion ?
L270: ‘’The length of the main slip surface’’ is a bit confusing. I might suggest reformulating.
L270 ‘’c.’’ ?
L272 : is there some relations describing the amount of displacement within the tip zones compared to the maximum surface slip observed ? This would help with assessment in the case of the near fault type scenario. Same question for the length of the tip growing ?
L294: Yes, accounting for bloc rotation in relay zones is necessary. Here, quantitative information related to blocks’ dimensions (and fractal aspect) would be useful. Also considering the rotation of tens of meter large blocks, this would generate at locale scale some surface rupture associated with offsets that could be analog to a classical surface displacement. Two processes can hence maybe be considered as analogs.
L300 : I do not understand this criterion. Is it a concept of ‘’Bandes de réserve’’, as buffer around the fault trace – a buffer that would be more pronounced on the hanging wall than on the footwall, according to previous observation on the relatively more damaged HW that FW ? In Morocco for instance, the regulatory Paraseismic Rules prescribe an arbitrary buffer zone 60 m from the fault trace and is associated to no implantation of new strategic and public-access buildings. Do you think any specific values might be appropriate for the carious scenario you defined here ? For instance, a relation between U, ang, damage zone width an length of the IZ ?
L311: I agree for structural architecture, but I would add that the surface rupture pattern also varies regarding to rupture type (e.g. supershear rupture will generate damages far away from main fault trace), rupture dynamics (propagation direction, directivity…) and local condition (water content, slope, ground cohesivity…). Those factors, combined, might reduce the ability to properly constrain the spatial distribution of coseismic displacement and extension of the damage zone.
L322; This affirmation seems to be contradictory with explanations given in L300, L170 and L271. In fact, if the damage zone is asymmetric for thrust (with more damage in HW dur to strain distribution) but symmetric in a SS fault, I do not understand the meaning of this concluding sentence.
L326: Those empirical laws correlate the amount of coseismic offset compared to magnitude or length and knowing the fault kinematics. They do not provide a direct empirical relation between the earthquake magnitude and the width of the core, and the fault damage zones (that as you explained before depending mainly on inheritance like local geology and structuration). For this, you must refer to the laws of figure 5. So, I would precise the sentence explaining that those laws can only give insight of the surface coseismic offset (mean and max), and that they depend of the fault kinematics.
L331: I follow the thinking. However, the mentioned laws bring uncertainty of three orders of magnitude (e.g. for a 1 m coseismic displacement, damage zone width might range from 0.1 m to 100 m. How to deal with such a large range to define
L334 : Color coded cell are often used for decision matrix. I suggest this as there are already green color on the ‘high’
L347 : Geophysical survey could also be interesting, if combined with geological and geotechnical analysis. Also Geotechnical care could be useful to discuss damage zones and maybe identify surface rupture
L364: This section brings interesting technics to assess the surface rupture pattern and needs to be more referenced for each.
L366 : To measure the height of fault scarp yes, but also horizontal displacement, cumulative or not. Also, it could be useful to precise the scales used for such surveys (dam, m, cm…).
L371 : It seems that there are two confusions here, i. between photogrammetry (which uses stereographic correlation of optical images) and Lidar scanning, and ii. Between aerial and terrestrial. Both technics are useful, so this sentence might be simply reformulated.
L375: please precise the parameters and bring examples (rises, crests, cross-correlation of depositional units in 3D paleoseismic trenches)
L377-78: This sentence is difficult to catch. What do you mean by slip surface(s), fault splays? Off-fault offset surfaces? Please reformulate and bring references.
L378: Also please change section for geophysics, and precise that correlations with field data will be useful to conclude on the observed contrasts.
L384: please give references
L395: You should mention OSL and radiocarbon dating and bring reference
L397: You should mention OSL and cosmonucleides dating (Be, Cl, He) and bring reference
L415-416: Please justify with existing examples or references that this interesting approach is properly compatible with the timing and budget requirement, as some dating, aerial acquisition, treatment and interpretation could be quite tight compared to delays usually running for infrastructure construction.
Citation: https://doi.org/10.5194/egusphere-2025-506-RC2 -
AC2: 'Reply on RC2', Selina Bonini, 16 May 2025
We thank the Reviewer for the valuable comment and suggestions that we will use to improve the text organisation of the revised manuscript and its scientific message.
Comment on the sizing of the interference zone (IZ): this work aims at introducing the IZ as a first order geometric relationship between an active and capable fault (ACF) and a linear infrastructure. The IZ concept strongly depends on the possible geometrical interference patterns between an ACF and a linear infrastructure (see our Figure 7). To provide an initial, indicative parametrisation of the ACF, we propose that fault scaling laws can be used. This helps assess the mappable area where the deformation effects associated with ACFs activity are expected to impact the infrastructure. We recognise that a reliable IZ characterisation requires more detailed levels and techniques of investigation, such those we propose in Section 5 and in Table 2 of the manuscript. This thorough level of investigation would avoid both an overestimation of the IZ and an underestimation of the fault dimensions (e.g., the width of its damage zone).
Comments on section 5.2: we will improve the description of the topographic techniques that can be used to the identification of orientation and distribution of the fault pattern deformation. We agree that we should also highlight the limitations of these techniques. Moreover, we will revise the initial part of Section 5.2 to better describe the sequence of used techniques to constrain an increased resolution of the structural complexity of fault zones.
Finally, we thank the Reviewer for the specific comments that we will consider for the revised version of the manuscript text.
Citation: https://doi.org/10.5194/egusphere-2025-506-AC2
-
AC2: 'Reply on RC2', Selina Bonini, 16 May 2025
Status: closed
-
RC1: 'Comment on egusphere-2025-506', Anonymous Referee #1, 26 Apr 2025
This is a useful and well-written paper about the impact of active and capable faults structural complexity on seismic hazard assessment for the design of linear infrastructures.
However, a moderate improvement is needed in the structure of the paper before its acceptance for publication. Some contents of sections 4 and 5 are more results than methodological explanations or discussion. Therefore, I recommend a new section, "5. Results," needs to be created where the authors may present their results, taking relevant material mainly from sections 4 and 5.Citation: https://doi.org/10.5194/egusphere-2025-506-RC1 -
AC1: 'Reply on RC1', Selina Bonini, 16 May 2025
We thank the Reviewer for the valuable comment and suggestions. We fully acknowledge the importance of clearly highlighting the original and innovative contribution of our work within the framework of seismic hazard assessment for infrastructure planning purposes. In this context, we would like to clarify that the main aim of the present study is to introduce and discuss the implications of the structural complexity of active and capable faults (ACFs) on seismic hazard evaluations, specifically in relation to the design of linear infrastructures. Our primary objectives are: (i) to propose conceptual scenarios illustrating the potential physical interactions between ACFs and linear infrastructures; and (ii) to analyse the key structural factors that govern the deformation patterns interfering with such infrastructures.
It is important to note that this work does not present new geological, structural, or geophysical data. Our primary focus is on the geometrical configurations that may arise from ACF-infrastructure interactions (Section 4). From this analysis, we then propose a practical workflow to the comprehensive parametrisation of an evolving ACF (Section 5). We believe that the current organisation of the manuscript effectively reflects our methodological approach and the conceptual nature of this contribution. Therefore, we would prefer to retain the present text organisation in the revised version.
Citation: https://doi.org/10.5194/egusphere-2025-506-AC1
-
AC1: 'Reply on RC1', Selina Bonini, 16 May 2025
-
RC2: 'Comment on egusphere-2025-506', Anonymous Referee #2, 02 May 2025
Referee comments for Bonini et al., 2025, preprint EGU preprint
General comments :
The definition of the IZ represents a key point of the proposed process of hazard assessment for linear structures, hence a proper scheme showing the IC dimention compared to the fault zone might improve the consistency of the concept. Its definition is suggested to be based on scaling law, which is a very good idea for a first order assessment. The issue is that those scaling laws present several orders of magnitude, and the definition of the considered dimension remains very coarse. I am wondering about the uncertainties related to the definition of those lengths, and how to i. constraint them and ii. Give some security range (kind if geometric safety factor), to correctly constrain the dimension of the zone, minimizing in the one hand the probability of missing some fault surface rupture and associated offsets, and in the other hand do not exaggerate the IZ size, as the cost possibly involved to ensure the safety of the structure may rise strongly.
Regarding section 5.2 and discussion about remote sensing and identification of fault damage zones using microtopographic technics, I think it is important to precise that this approach only works if the topography signal of the fault surface rupture and damaging has been preserved in the landforms. I mean that if erosion of anthropic activities exceeds the expression of the fault-related deformation, this approach will not work, and that this limit deserves to be mentioned. Hence here comes the geophysical approach (nondestructive) and paleoseismological and geotechnical approaches (destructive).
Another point is the organization of the sections in that chapter. Please make slightly more obvious the successions intro and scaling, RS, field geology and geophysics, then paleoseismology, dating and morphotectonics for slip rates assessments.
Specific comments and technical corrections :
L26, please specify the names of the Great Alaska and Niigita earthquakes
L52 : Why not add water adduction structures ? e.g. Laquilla EQ, that has been strongly affected by a waterpipe rupture.
L140: I suppose the processes here illustrated come from previous publications show them (e.g. Barnett 87, Peacock and Sanderson 91, 94). Would it be necessary to refer to the main ones in the caption ?
L155 : cumulative displacement is proportional to fault width with same order of magnitude ? They are proportional modulo a factor 102 to 103, what significance ?
L156 : Why 2 orders io magnitude ? Mean 100 km fault will have damage zone 10 km ? There are no references to explain this scaling relation.
L181: Maximum displacement along a single fault trace ? Cause if one considers the fault system (here the two main fault segments and the damage zone within the overlapping zone.
189 : is it representative to consider a stand-alone fault segment ? Could you please bring proper example ?
L220: 14 % ? Do the author precise a range of length when this relation is observable ? This might depend on the seismogenic width (previously names fault height) ? There is a quite big discrepancy here ; in what extent could this discrepancy be addressed for definition of relay zones ?
Figure 6 : the constant length model also corresponds to the characteristic slip model (Shwartz and coppersmith, 82). Is it necessary to precise it here ?
Figure 7 : regarding the coseismic diffuse rupture, on the right we observe in the transfer zone any left step ridel (RL strike slip indication), instead on the left (within the tip zone), they are right step (left lateral strike slip indication). It might be more coherent to maintain the same pattern in the surface rupture scheme.
L243: This sentence suggests you are prioritizing some parameters in the figure, but then it is not obvious that the different scenario presented in this figure allows you to choose parameters to prioritize. Maybe simply precise/reformulate the caption
Figure 8: Interesting. I found it hard to catch the location of the profiles displayed but I eventually understood
L249: certainly, but why ?
L253: Unless I am mistaken, linear correlation in a log-log graph describe a power law correlation and not a linear one.
L255: “it is reasonable to expect”, yes I suppose, but is there any references looking for cross-fault slip distribution (maybe from pixel correlation for instance) that may help to justify this assertion ?
L270: ‘’The length of the main slip surface’’ is a bit confusing. I might suggest reformulating.
L270 ‘’c.’’ ?
L272 : is there some relations describing the amount of displacement within the tip zones compared to the maximum surface slip observed ? This would help with assessment in the case of the near fault type scenario. Same question for the length of the tip growing ?
L294: Yes, accounting for bloc rotation in relay zones is necessary. Here, quantitative information related to blocks’ dimensions (and fractal aspect) would be useful. Also considering the rotation of tens of meter large blocks, this would generate at locale scale some surface rupture associated with offsets that could be analog to a classical surface displacement. Two processes can hence maybe be considered as analogs.
L300 : I do not understand this criterion. Is it a concept of ‘’Bandes de réserve’’, as buffer around the fault trace – a buffer that would be more pronounced on the hanging wall than on the footwall, according to previous observation on the relatively more damaged HW that FW ? In Morocco for instance, the regulatory Paraseismic Rules prescribe an arbitrary buffer zone 60 m from the fault trace and is associated to no implantation of new strategic and public-access buildings. Do you think any specific values might be appropriate for the carious scenario you defined here ? For instance, a relation between U, ang, damage zone width an length of the IZ ?
L311: I agree for structural architecture, but I would add that the surface rupture pattern also varies regarding to rupture type (e.g. supershear rupture will generate damages far away from main fault trace), rupture dynamics (propagation direction, directivity…) and local condition (water content, slope, ground cohesivity…). Those factors, combined, might reduce the ability to properly constrain the spatial distribution of coseismic displacement and extension of the damage zone.
L322; This affirmation seems to be contradictory with explanations given in L300, L170 and L271. In fact, if the damage zone is asymmetric for thrust (with more damage in HW dur to strain distribution) but symmetric in a SS fault, I do not understand the meaning of this concluding sentence.
L326: Those empirical laws correlate the amount of coseismic offset compared to magnitude or length and knowing the fault kinematics. They do not provide a direct empirical relation between the earthquake magnitude and the width of the core, and the fault damage zones (that as you explained before depending mainly on inheritance like local geology and structuration). For this, you must refer to the laws of figure 5. So, I would precise the sentence explaining that those laws can only give insight of the surface coseismic offset (mean and max), and that they depend of the fault kinematics.
L331: I follow the thinking. However, the mentioned laws bring uncertainty of three orders of magnitude (e.g. for a 1 m coseismic displacement, damage zone width might range from 0.1 m to 100 m. How to deal with such a large range to define
L334 : Color coded cell are often used for decision matrix. I suggest this as there are already green color on the ‘high’
L347 : Geophysical survey could also be interesting, if combined with geological and geotechnical analysis. Also Geotechnical care could be useful to discuss damage zones and maybe identify surface rupture
L364: This section brings interesting technics to assess the surface rupture pattern and needs to be more referenced for each.
L366 : To measure the height of fault scarp yes, but also horizontal displacement, cumulative or not. Also, it could be useful to precise the scales used for such surveys (dam, m, cm…).
L371 : It seems that there are two confusions here, i. between photogrammetry (which uses stereographic correlation of optical images) and Lidar scanning, and ii. Between aerial and terrestrial. Both technics are useful, so this sentence might be simply reformulated.
L375: please precise the parameters and bring examples (rises, crests, cross-correlation of depositional units in 3D paleoseismic trenches)
L377-78: This sentence is difficult to catch. What do you mean by slip surface(s), fault splays? Off-fault offset surfaces? Please reformulate and bring references.
L378: Also please change section for geophysics, and precise that correlations with field data will be useful to conclude on the observed contrasts.
L384: please give references
L395: You should mention OSL and radiocarbon dating and bring reference
L397: You should mention OSL and cosmonucleides dating (Be, Cl, He) and bring reference
L415-416: Please justify with existing examples or references that this interesting approach is properly compatible with the timing and budget requirement, as some dating, aerial acquisition, treatment and interpretation could be quite tight compared to delays usually running for infrastructure construction.
Citation: https://doi.org/10.5194/egusphere-2025-506-RC2 -
AC2: 'Reply on RC2', Selina Bonini, 16 May 2025
We thank the Reviewer for the valuable comment and suggestions that we will use to improve the text organisation of the revised manuscript and its scientific message.
Comment on the sizing of the interference zone (IZ): this work aims at introducing the IZ as a first order geometric relationship between an active and capable fault (ACF) and a linear infrastructure. The IZ concept strongly depends on the possible geometrical interference patterns between an ACF and a linear infrastructure (see our Figure 7). To provide an initial, indicative parametrisation of the ACF, we propose that fault scaling laws can be used. This helps assess the mappable area where the deformation effects associated with ACFs activity are expected to impact the infrastructure. We recognise that a reliable IZ characterisation requires more detailed levels and techniques of investigation, such those we propose in Section 5 and in Table 2 of the manuscript. This thorough level of investigation would avoid both an overestimation of the IZ and an underestimation of the fault dimensions (e.g., the width of its damage zone).
Comments on section 5.2: we will improve the description of the topographic techniques that can be used to the identification of orientation and distribution of the fault pattern deformation. We agree that we should also highlight the limitations of these techniques. Moreover, we will revise the initial part of Section 5.2 to better describe the sequence of used techniques to constrain an increased resolution of the structural complexity of fault zones.
Finally, we thank the Reviewer for the specific comments that we will consider for the revised version of the manuscript text.
Citation: https://doi.org/10.5194/egusphere-2025-506-AC2
-
AC2: 'Reply on RC2', Selina Bonini, 16 May 2025
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