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.

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.