Local Site Effects Investigation in Durres City (Albania) Using Ambient Noise, after the 26 November 2019 (M6.4) Destructive Earthquake

Round 1

Reviewer 1 Report

The paper reports HV measurements in Durres City which had been stroke by a Mw6.4 earthquake.  The introduction is clear, as the geological context description.

The isofrequency and iso amplitude maps are coherent. The agreement between the observed and simulated peak frequencies is relatively good in absence of more data. However, it is not the case for the amplitude, as it is generally the case. I think that a better comparison with former similar works should be commented on and compared. Is there an influence of the latter earthquake on the result?

I think the manuscript will benefit from showing the spectrum of the Mw6.4 earthquake rather than just a few words. I guess the 0.2 Hz limit in the HV spectra is because of the 5s Lennartz limit. However, is this pertinent regarding the high of the buildings in the city?

The figure quality has also to be improved.

Some sentences, mainly at the beginning (abstract/introduction) of the paper are unclear. 

This paper is about microzonation mapping and is clear and well-structured.

I recommend its publication.

This is however purely technical, without any new research ideas. It will certainly be cited for further works in seismic hazards.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

General considerations

The research concerns the results of some ambient noise investigations in Durres (Albania) carried out after the November 26, 2019 earthquake.

In my opinion, the work could be interesting but the current version of the manuscript is quite far from the standards required by an international journal. In particular, its structure does not allow an easy understanding of the work and its logical sequence. Therefore, the manuscript must be arranged following the classical Introduction, Material and Methods, Results, Discussion and Conclusions structure. Furthermore, the aims of the research are not adequately discussed as well as the motivations behind it.

In addition, the manuscript presents a certain mismatch between what is written in the abstract and what is actually discussed in the main text.

Finally, the methodology and discussion of the results must be improved.

Specific points

Abstract. The authors begin the section declaring that: "Site characterization of metropolitan areas, especially after an earthquake disaster, is of paramount importance for interpreting spatial damage distribution… Such a case is the Durres city ...". However, the manuscript hardly refers to the relationship between the damage caused by the 2019 earthquake in Durres and the results of the microtremor investigations (see also subsequent comments).

Introduction. The section begins directly with the analysis of the case study, without introducing the reader to the general context in which the research is placed. Therefore, the authors will have to begin the section introducing the context analysis of the scientific problem. After that, the authors will introduce the case study, explaining the aims of the work and the usefulness of the results.

The section also requires a background relating to the use of ambient noise in similar contexts. I suggest some references to be analyzed [1-3].

At the end of the Introduction, the authors should summarize, for the benefit of the readers, the general structure of the work, indicating how the manuscript is arranged (subdivision into sections).

2. The November 26, 2019 Durres Earthquake (Mw 6.4).

The section title will be changed to better represent the content of the subsections. In addition, the section will be included in "Material and Methods".

The authors will include a subsection where discussing the regional geographical framework of the study area and the territorial, urban and demographic features of the city of Durres as well as the main features of the buildings, especially in the area where the highest damage due to the 2019 earthquake was recorded.

The subsection "Seismotectonic and geologic setting" should be renamed "Geological setting and seismotectonic aspect". Consequently, the contents of the section will be reshaped, discussing first the geological context and then the seismotectonic one. Furthermore, I suggest separating the discussion relating to historical and recent earthquakes from that relating to the analysis of the geological and seismotectonic aspects, adding another subsection whose title can be: "Historical and recent seismicity". In this subsection, the authors will also have to discuss in detail the macroseismic effects produced by the 2019 earthquake in Durres, going into the spatial distribution of damage. This is to contextualize the discussion of the results regarding the ambient noise investigations.

The initial discussion of section 2.1. (page 4) relating to the characters of the 2019 earthquake (mainshock and aftershocks) must be linked to the literature, adding the relevant bibliographical references.

The list of historical earthquakes and their effects in Durres should be summarized in a table.

Figure 1. The figure will include a box in which the city of Durres will be placed in the national geographic context of Albania.

Figure 2. The authors will change the caption from "Historical earthquakes ..." to "Historical and recent earthquakes ...". Additionally, the authors will indicate the source from which the epicentral earthquake data was taken. Finally, the map will include the location of the city of Durres.

3.1 Geological, geotechnical and geophysical data in the Durres region

Figure 3 is illegible.

Figure 4. To which macroseismic scale do the intensities indicated in the figure refer? Also, the maps are blank. Insert the main toponyms and the bars of the geographical coordinates.

3.2 Ambient noise data. The authors do not clarify how the choice of the measurement points of the ambient noise was made. Was the choice guided only by the damage caused by the 2019 earthquake (damage not adequately discussed, as already indicated above) or was it also guided by the geological features of the city? This aspect needs to be clarified.

To indicate the average, minimum and maximum spacing between the measuring points.

Which is the sampling rate used?

Figure 8. To include the geographic coordinate bar.

4. METHOD

"In addition, for certain sites where an estimated Vs profile was available ...". Which sites do the authors refer to? To indicate them on the map of Figure 8.

4.1 Data Processing and Analyzes of single station HVSR

Was applied an anti-trigger algorithm to remove transients or very low amplitudes? In which frequency range were the amplitude spectra computed?

"Certain criteria to select H/V ...". To detail all criteria used, also by a table, if necessary.

5.1 HVSR results

Figure 10. To include the geographic coordinate bar. Also, the text in the images is not legible.

6. DISCUSSION AND CONCLUSIONS

The discussion makes no reference to the relationship between the spatial distribution of damage and the results of ambient noise investigations. What is the relationship between the distribution of damage caused by the 2019 earthquake and the four categories proposed in the study? Can the damage recorded be a consequence of soil-building resonance effects?

 

References suggested

[1] https://doi.org/10.4430/bgta0013

[2]  https://doi.org/10.1007/s00024-020-02421-3

[3] https://doi.org/10.1016/j.measurement.2018.08.015

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Major comment: The main outcome of this paper is very weak. Performing micro-zonation study for the Durres city area is valuable, but just comparing the fundamental frequency with existed iso-bedrock depth is not new finding – many previous studies already showed that the HVSR is effective to find fundamental frequency and the fundamental frequency is related to the bedrock depth. Comparing empirical HVSR and theoretical HVSR is meaningful, but has not been developed for any other application. To be used as a potential data resource of H/V results for a micro-zonation study later, authors are recommended to include digital data of H/V including locations and H/V ratio per frequency of the survey.

Minor comments

1. The paper is about site amplification characteristics within the Durres city. Ch 2 is about historical seismicity around the city, which doesn’t need to be emphasized in this paper. The reviewer recommends greatly summarize the seismicity part.

2. Fig 4 (a) Please describe the meaning of legend items. 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors performed the required revisions.

However, further minor revisions are needed.

Statements in lines 40-42 and 105-106 require references.

Figure 1. I do not see the graphic bar scale related to the geological map and section.

Caption of Figure 1 will include the bibliographic reference of the Geological Map of Albania. Furthermore, the authors will include the reference considered to locate the hypocenter.

Author Response

Please, see an attachment the Reply to the Reviewer #2 and a second one the revised_version_2 of the manuscript.

Author Response File: Author Response.pdf