Reviewer #1

General comments

This paper presents the first attempt of local seismic effects assessment in Bhutan. Considering the small amount of input data available (i.e., no instrumental records of past earthquakes, reduced geotechnical characterization of soil deposits, etc..) this study represents a first and relevant step towards a possible future deeper seismic hazard assessment. However, several critical problems need to be addressed and explained to let the manuscript be accepted for publication.

Response: We appreciate constructive comments from the reviewer. We have now assessed all the comments and we assure that all the issues raised by the reviewer will be duly addressed as follows:

Specific comments

1. Introduction: This manuscript focuses on the study of seismic hazard more in particular on seismic site effects, however few lines and only one reference citation on site effects is reported in the introduction. A wider review of past studies focused on this topic needs to be integrated in the manuscript.

Response: We appreciate the constructive comment from the reviewer. We will surely present a more critical discussion on the topic referring to several works. Meanwhile, published works in the study area is currently very limited, in particular on seismic site effects. Two of the studies conducted by Tempa et al 2020 and Tempa et al 2021 which covered parametric studies and shear wave profiling to estimate the site response and these has been critically upheld to complement the current study. Some of the field investigation, or any other research and its specifics to seismic site effects will be incorporated in the revision.

1. Lines 113 – 117: This sentence does not seem to be consistent with Figure 2 since the geological formations falling in the study area (black square in Figure 2) are not the same reported in the sentence.

Response: Thanks for pointing this out. We fully understand the inconsistency in the description of the geological formation of the study area. We will rectify the mistake in the revised version.

1. Authors performed a reconstruction of the groundwater table in the study area considering 29 borehole data without indicating the season during which the data has been recorded. Reasonably, the groundwater table position varies during the year. An evaluation of the possibility of grouping borehole by seasons could help to refine the map, particularly in the area between Dhamdhara, Pipaldara abd Kabreytar and in that close to Rinchending.

Response: Thanks for providing such insightful feedback. The investigation date is available, and it can be grouped as advised. We will do accordingly in the revised manuscript. A revised map with updated legends according to the seasons will be added where applicable.

1. Lines 258 -259: “[..] low, medium, and high […]” with respect to what? Please specify in text

Response: The authors intended to categorise the earthquake based on the level of PGA as low, medium and high in the study, so as to subsequently predict the seismic site effects as a function of amplitude parameters and deduce amplification factors. We will provide the basis for the selection of input motions and define the qualitative terms accordingly.

1. Authors reported in Figure 11 the Fourier Spectra of the considering earthquake as Fourier Amplitude vs Period. It is common use to represent Fourier Spectra as Fourier amplitude vs frequency, so this representation confuses the reader. It is opinion of this reviewer that just the X label is incorrect, but please check this figure and modify it consequently.

Response: We appreciate the feedback. We will update the figure with Fourier amplitude vs frequency in the revised manuscript.

1. Figure 12: This figure presents the variation of PGA induced by each earthquake at different depths in the soil. It could be more useful to present data by normalizing them to the maximum PGA of the earthquake input. Moreover, in case of Zone II the bedrock depth is fixed at 400m so Figure 12b should present data up to this depth.

Response: Thank you for the remarkable feedback. We will surely normalize the results with the max. PGA input and revise the manuscript accordingly. Also, we will plot the PGA variation up to the bedrock in both figures as suggested.

1. Authors performed a series of 1D linear-equivalent numerical modelling of eight soil columns representative of the study area and reported the results in Figures 13 and 14. They showed the response spectra at bedrock and on the surface. While results obtained by applying earthquake from M1 to M4 seem to be consistent, those obtained by considering M5 and M6 look anomalous. Furthermore, in the latter case the response spectra at the bedrock level are characterized by anomalous peaks at low period that are completely nullified at the ground level. I suggest the authors to check the signal processing of these earthquakes (M5 and M6) and verify the consistency with the input applied in the numerical simulations.

Response: We appreciate the reviewer for surfacing this issue. The authors will revisit the 1D model for all the sites and check the anomalous pointed out. If necessary, the analysis results could be updated to maintain the correctness if any. Also, we will provide a detailed discussion regarding the input motion as input strong motion characteristics may also lead to anomalies.

1. All the presented results need to be more deeply discussed. Moreover, considering the shaking level of the seismic input and the typology of numerical simulation, the topic of non-linear behavior of the soil material should be addressed. This could also help for a better interpretation of the results (i.e. Figures 17 and 18)

Response: Thank you for pointing out this. We truly feel that deeper insights are required. We will thus improve the discussion section juxtaposing the results with some published works. Also, we will add insights to each result. The non-linear behavior of soils in 1D model are usually characterized by the equivalent iterative model which takes into account the strain compatibility of non-linear behavior of soils. The current study does not cover experimental nonlinearity of soils. We will also add a robust description on equivalent linear and fully nonlinear soil behavior in the revised manuscript.

Technical correction

1. Line 24 -26: This sentence is not clear

Response: We will rewrite the sentence.

1. Line 86: Please specify which site effect you are investigating

Response: The current study in particular draws site effect in terms of amplification factor attributed mainly due to input motion amplitude parameters. To determine the amplification factor at the end, the spectral acceleration of surface and bedrock has been provided prior basis. The details will be discussed in the revision.

1. Line 186: This sentence is not correct.

Response: We will correct the sentence accordingly.

1. Line 189: This in-text citation is not present in the reference list

Response: We will cross-check text and reference sections in the revised manuscript.

1. Lines 359 - 360: This sentence is not clear.

Response: We will rewrite the sentence in the revised version.

1. Line 396 – 398: This sentence is not clear.

Response: We will update the sentence in the revised manuscript.

1. Are Baxa (Figure 2) and Buxa (Line 113) the same lithological group?

Response: Buxa is correct lithological group. We will update accordingly in Fig. 2.

1. Table 1: What “-do-“ stands for?

Response: The authors intend to indicate same test methods in Dhamdhara and Rinchending. The “-do-” will be removed and replaced with the test methods in the revised version.

1. Figures 1b: The legend is missed

Response: The Legend will be modified properly.

1. Figure 2: Please add the location of boreholes reported in Figure 5. Moreover, north direction and scale are missed.

Response: Borehole locations can be added with north and scale and Figure 2 will be updated.

1. Line 173 – 175: Acronyms should be explicitly reported in the manuscript.

Response: The acronyms will be reported in the revision.

1. Line 195-197. This sentence about liquefaction and corresponding potential is out of the paper topic. Please delete it.

Response: The sentence concerning liquefaction will be deleted as advised.

1. Figure 3: The legend is not clearly legible

Response: The legends of the Figure 3 will be modified.

1. Figure 7: The resolution of this figure is too low

Response: The Figure 7 has been used from a government report. We will recreate the figure in the revised manuscript.

1. Figure 10 – 11: To improve the manuscript readability, these figures could be merged in a unique figure composed of two columns, one devoted to time histories and another to the corresponding FFT spectra.

Response: The Figures 10-11 will be merged and presented in two columns or consolidated two figures.

1. Figure 12: Colors chosen for Earthquakes M4, M5 and M6 are M6 are too similar. Please use more distinguishable colors

Response: For Figure 12, contrasting color scheme will be implemented.

1. Figure 13: Please add “bedrock” and “ground surface” as labels in the graph

Response: The labels in Figure 13 will be changed to “bedrock” and “ground surface” in the revision as advised.

1. Figures 15 -16: Please specify how you calculated the red line FFT. Is it an average of the FFT values at each time step? Please specify in the text.

Response: The red line illustrated in the graph is an average value. The specification can be done either in the graph or in-text during the revision. We will add description regarding this in the revised version.

1. Figure 17b/d – 18b/d: How have you calculated the “Response spectrum intensity” and “Mean frequency”? Please specify in the text

Response: We will present the results as suggested by the reviewer in the revised manuscript.

1. All the figure’s caption should be improved

Response: As advised, the authors will re-visit the figure captions as a whole and make sure that they are appropriately described.

1. In-text citations need to be modified according to the journal guidelines.

Response: The authors will check according to the Journal’s guideline for submission and update it in the revision.

Thank you. 

Reviewer #2

Authors have presented a research on Sensitivity analysis of input ground motion on surface motion parameters in high seismic regions: A case of Bhutan Himalaya. This paper is most like a lecturing note has serious drawbacks in both poor presentations and applied technics. This paper deals with a very known approach without any new contribution. A critical drawback of this work is that the reliability of the collected geotechnical data was not comprehensively reviewed. The paper is well structured and written, however, considering the quality of the paper and uniqueness  of the research, I have concluded that the manuscript is not suitable for publication in Natural Hazards and Earth Science Systems.

 Response: We appreciate the reviewer’s efforts for putting forth such insightful comments and critiques. Despite the darkness observed by the reviewer in totality, we assessed all the comments and concerns raised by the reviewer and conclude that we can fairly meet the expectations of the reviewer. Thus, we would like to submit the revised version of the manuscript. The reviewer notes that the paper is like a lecture note, but we would like to draw the attention of the reviewer that limited work is done in Bhutan Himalaya, which makes understanding of seismic site effects pretty underrepresented when compared with the global landscape. To have a comprehensive discussion, we have tried to include as much details as possible as and when required. We agree that the reviewer on the use of very well-known approach but our data and study region are completely new and surely the eastern fringe of Himalaya, which is kind of hotspot for several moderate to strong earthquakes, can have benefit of this study. And regarding the comment from the reviewer on “without any new contribution”, we firmly object the idea and let you know that similar works are absent for the region. In terms of the query as raised on “reliability” we have used the government agency provided database and probably we are not accountable for reliability exhaustively. However, surely we will add comprehensive discussions on the collection process and mechanisms, citing pros and cons of the adopted procedure.  

• Abstract and introduction are very general and there is no significant in the scientific border. There is ample room to improve the introduction as “Introduction” is actually weak.

Response: We have noted the concern. We will present exciting abstract and introduction sections in the revised manuscript. Basically, developing a clear problem, approach, and critical discussions of the results together with the insights that could be instrumental for the region in the future. We will juxtapose published work with our own study to demarcate novelty and unique contribution too.

• Presenting facts is not sufficient for a journal paper, there needs to be more direction to the writing and evidence of critical analysis.

Response: We appreciate the reviewer for this wonderful comment. Indeed, we agree with the point. However, we do not believe that just facts are randomly reported in the paper. We will undoubtedly insert critical discussions despite facts and results in the revised manuscript.

• Authors highlighted anomalous damage patterns in various parts of Bhutan due to the earthquake but failed to present any data or photos etc. to highlight the damage.

Response: Thanks for your concern. Anomalous damage patterns cannot be shown directly with image rather can be reported citing the soil condition only. By anomalous damage, we mean to state that far field damage was sometimes more prominent than the near-field one. To this end, we cited anomaly. We will update the discussion in the revised manuscript.

• Some of the statements presented in the manuscripts are contrary to each other.

e.g. Abstract:....this study is the first attempt to quantify the influence of the 14 local site conditions in the eastern fringe of the Himalaya...

Introduction: In Bhutan, very few studies on local seismic response analysis have been 34 conducted so far. Some of the recent studies

Response: We appreciate the reviewer’s concern. We will assure consistency throughout the manuscript in the revised version.

There are many others..........

• I do not see any earthquake greater than Mw 7.0 in Figure 1, but authors mentioned that records of past earthquakes in Bhutan are available since 1713 (Mw 7.0). Authors highlighted at several places that Bhutan is one of the most seismically active regions in the world.

Response: According to literature review, the statement “earthquake greater the Mw 7.0 since 1973” has been indicative. However, authors could use only USGS database starting from early 1900. The authors will check and revise correctly.

• Page 2, Line 49: Local site conditions during historical earthquakes in Bhutan were identified as the main cause of structural damage. Any documents or reference or photos?

Response: The authors intended to mention damages being caused due to its geographical and geological settings. The sentence will be revised to align the aim of the current study. The damages of structures refer to the recent earthquake of April 2020 and September 2009 earthquake. We have some documental evidence only, which we re-interpreted to draw this conclusion.

• Page 5, Lines 129-140: Is this paragraph related to Seismicity and geological setting of the study area? There are some information which seem to be irrelevant for the article.

Response: The authors will improve this section based on the relevancy of the current study.

• Page 6: The groundwater table in the study area is shallow and varies between 0.5 m to 16.0 m. Are you still considered groundwater table at 16 meter as shallow depth? Please double check literature.

Response: The authors will check the depth variability interpretation through literature and revise the statement.

• Page 10, Line 195-196. The term liquefaction came out of nowhere.

Response: We appreciate this concern. The statement about liquefaction will be deleted in the revised manuscript.

• What about temporal variation of water table? Groundwater table is highly sensitive to rainfall. Did you consider it? It seems authors consider the groundwater table at the time of geotechnical investigation which can be random throughout the year. This could be attributed to wide range of groundwater table within small area.

Response: The investigation date is available. A revised map will have a legend according to the seasons; however, information regarding the investigation month is missing. We will add as much details as available in the revised manuscript.  

Table 1 shows more than 100 soil samples, but authors presented only 7 particle size distribution curves. Where is PSD curve for Rinchending?

Response: The authors presented average PSD of each site for holistic representation of particle size. The Figure 6 (Zone II) is the Rinchending area that comprises four sites. We will provide annotation in the revised manuscript.

• Table 1: The dry density of soil sample is higher than the bulk density for Rinchending. Even I do not believe the cohesion of the sample having SPT-N value higher than 100 is only 0.18 kg/cm². Where is plastic limit and liquid limit values?

Response: We appreciate the reviewer for pointing this out. We will present the precise geotechnical investigation data in the revised manuscript and make necessary correction to the current version.

• Soil at Dhamdhara is described as coarse-grained sand with gravel/cobbles and rock piece but authors reported PI value. PI values at Rinchending and Dhamdhara is not reliable based on soil descriptions.

Response: We will confirm with the geotechnical investigation report and make necessary changes accordingly.

• Double digit for shear wave velocity is not required.

Response: The authors will remove this double-digit presentation of shear wave velocity.

• Quality of Figure 7 can be improved significantly.

Response: We will recreate Fig. 7 in the revised manuscript.

• Authors should present the profile of peak ground acceleration (PGA) for the locations presented in Figure 5.

Response: In Figure 5, two bore logs belongs to Zone I (larger area than Zone II) and one bore log in Zone II. The profile of PGA is presented one each from the two zones.

• The manuscript currently lacks a cogent argument / thread. This stems from the introduction, which lacks an aim.

Response: We will restructure and at large rewrite the entire manuscript for coherence, clarity, and conciseness.

• Could the findings in the study be applied to any countries or only adopt to Bhutan? Please describe the contribution of this study from the viewpoint of local characteristics and universal ones.

Response: The conceptual framework remains valid globally for similar soil conditions. The significance of such studies can be incorporated for similar seismic regions with comparable soil types.

• Why not consider one or two ground motion from earthquake in Himalaya?

Response: Since the current study is one of the preliminary studies in Bhutan to study the seismic site effects, further in-depth studies can be conducted in future considering earthquake in Himalayan region as advised. Recent studies have also shown applicability of synthetic ground motion where instrumental records are not available as in the case of Bhutan.

• Irrelevant self citation. Similarity index is quite high. Some of the text were copied exactly from the following paper and other reports.

Tempa et al. (2021). "Shear wave velocity profiling and ground response analysis in Phuentsholing, Bhutan" , Innovative Infrastructure Solutions.

Response: The authors will restructure the sentences.

• Page 17, Lines 282-287: This is like a lecture note, a very well-known statement. 

Response: We will update the sentence.  

• Figure 12, why not PGA profile is presented up to bedrock? I would suggest to present PGA profile in terms of amplification ratio or factor by normalized PGA of input motion. It will help to visualize the results.

Response: The PGAs illustrated in Figure 12 will be normalized and presented up to the bedrock.

Thank you.