Probing environmental and tectonic changes underneath Ciudad de M&eacute;xico with the urban seismic field

Ermert, Laura; Cabral-Cano, Enrique; Chaussard, Estelle; Solano-Rojas, Dario; Quintanar, Luis; Morales Padilla, Diana; Fernandez-Torres, Enrique A.; Denolle, Marine A.

doi:https://doi.org/10.5194/egusphere-2022-1361

Preprints

https://doi.org/10.5194/egusphere-2022-1361

Preprints

10 Jan 2023

| 10 Jan 2023

Probing environmental and tectonic changes underneath Ciudad de México with the urban seismic field

Laura Ermert, Enrique Cabral-Cano, Estelle Chaussard, Dario Solano-Rojas, Luis Quintanar, Diana Morales Padilla, Enrique A. Fernandez-Torres, and Marine A. Denolle

Abstract. The subsurface materials of Ciudad de México have unique mechanical properties that give rise to strong site effects. We investigated temporal changes in the seismic velocity at strong-motion and broad-band seismic stations throughout Mexico City, including sites with different geologic characteristics ranging from city center locations situated on lacustrine clay to hillsite locations on volcanic bedrock. We used autocorrelations of urban seismic noise, enhanced by waveform clustering, to extract subtle seismic velocity changes by coda wave interferometry. We observed and modeled seasonal, co-, and postseismic changes, as well as a long-term linear trend in seismic velocity. Seasonal variations can be explained by self-consistent models of thermo-elastic and poro-elastic changes in the subsurface shear wave velocity. Overall, sites on lacustrine clay-rich sediments appear to be more sensitive to seasonal surface temperature changes, whereas sites on alluvial and volcaniclastic sediments and on bedrock are sensitive to precipitation. The 2017 M_w 7.1 Puebla and 2020 M_w 7.4 Oaxaca earthquakes both caused a clear drop in seismic velocity followed by a time-logarithmic recovery that may still be ongoing for the 2017 event at several sites, or that may remain incomplete. The slope of the linear trend in seismic velocity is correlated with the downward vertical displacement of the ground measured by Interferometric Synthetic Aperture Radar, suggesting a causative relationship and supporting earlier studies on changes in the resonance frequency of sites in the Mexico City basin due to groundwater extraction. Our findings show how sensitively shallow seismic velocity, and in consequence, site effects, react to environmental, tectonic and anthropogenic processes. They also demonstrate that urban strong-motion stations provide useful data for coda-wave monitoring given sufficiently high-amplitude urban seismic noise.

Received: 29 Nov 2022 – Discussion started: 10 Jan 2023

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Journal article(s) based on this preprint

23 May 2023

Probing environmental and tectonic changes underneath Mexico City with the urban seismic field

Laura A. Ermert, Enrique Cabral-Cano, Estelle Chaussard, Darío Solano-Rojas, Luis Quintanar, Diana Morales Padilla, Enrique A. Fernández-Torres, and Marine A. Denolle

Solid Earth, 14, 529–549, https://doi.org/10.5194/se-14-529-2023,https://doi.org/10.5194/se-14-529-2023, 2023

Short summary

Laura Ermert et al.

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-1361', Anonymous Referee #1, 07 Feb 2023

This paper evaluates the seismic responses to environmental factors, long-term subsurface deformation, and tectonic events by analyzing the autocorrelation of continuously recorded urban seismic noise. The authors discussed these diverse effects, from observations to model and physical interpretation, as well as site-dependent local effects and the impact of different materials. In addition, multiple types of seismic stations are used to investigate changes in the shallow to intermediate subsurface medium. They demonstrated the reliability of utilizing strong motion sensors for monitoring local deformation.

In general, the graphs are clear and well-organized, and the interpretation and discussion of the results are reasonably comprehensive. I have no doubts about the methods, no additional comments on the discussion or conclusion, nor on the article's writing, which I believe is publication-worthy.

Citation: https://doi.org/10.5194/egusphere-2022-1361-RC1
- AC1: 'Reply on RC1', Laura Ermert, 24 Mar 2023
  
  We thank the reviewer for the positive comments! We were happy to read that our argumentation and discussion have convinced the reviewer.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1361-AC1
- AC2: 'Reply on RC2', Laura Ermert, 24 Mar 2023
  
  Thank you for the detailed comments! They have been valuable in improving different aspects, in particular the presentation of the results. Please find a detailed response attached, and the changes in the re-submitted manuscript and supplementary material.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1361-AC2
RC2:
'Comment on egusphere-2022-1361', Alicia Hotovec-Ellis, 16 Feb 2023

In this paper, "Probing environmental and tectonic changes underneath Ciudad de México with the urban seismic field" by Ermert et al., the authors describe their efforts to observe and explain changes in the shallow seismic wave velocity across a city on highly variable near-surface geologic conditions. Overall, I found the paper to be a pleasure to read—equal parts rigorous and accessible. The authors are transparent with their methodology and assumptions, build on the wealth of previous observations (e.g., of shallow 1-D velocity structure to create site-specific sensitivity kernels) available to them, and have constructed a series of interpretations that testable and applicable elsewhere. I have no substantial comments on nor issues with the content of the paper itself. My only comments are for the presentation (e.g., wording, figure edits), which I hope will incrementally improve an already excellent article.
Find below a few comments, with line numbers where applicable:
(General) – I found it a little jarring to go between the English/Español versions of place names. I think mostly it’s the loss of the ´ in México that I notice most (which apparently was also dropped between the locations for ² and ⁴ in the author list). It’s a minor distraction, but I think it would be good to choose one name or the other (e.g., Ciudad de México or Mexico City) rather than use them interchangeably.
Line 51 – The phrase “not least due” was somewhat confusing to read the first time through. Perhaps “due largely” instead?
Figure 1 – The color choices for this map are somewhat confusing. First, I think the color for the lake zone should be something other than blue. I recognize that blue for lake zone makes some sense, but I think it evokes too much that standing water still exists there (when it does not). Brown instead? The blue symbols for the Tectonic Observatory sites also blend too much into the lacustrine blue, so whatever choice is made for the lake zone, these symbols should be contrast to it. Also some color other than green should be used for UNM if possible, for those with red/green colorblindness to prevent confusion with the RSVM sties. Yellow? If you cite Crameri et al. (2020) in Figure 2, you should be sure to apply those concepts to the maps/other figures as well.
Figure 2 – I only see one cyan/black line when I print the figure on paper. I can see clearly when the lines are supposed to be without the lines themselves, so perhaps arrows at the top of the figure centered on the time would be enough to illustrate the dates of these changes?
Line 114 – Obviously the cluster names for “day” and “night” are self-evident, but the difference between “noise” and “other” are not. Is “other” more like a transition between clear day and night? What constitutes “noise” in a way that it’d be correlated? Since you only end up using “day” during your work I don’t think this is a major issue, but as I was reading, I did wonder about it.
Figure 3 – Consider adding a color scale on the right side showing on the figure itself the color range and what it corresponds to.
Figure 5 – Similar comment as Figure 1, though I admit I do find the color mapping aesthetically pleasing despite the red/green split. I don’t think this figure is too much of an issue as you do have a clear delimit between which sites are in or out of the basin, and they are ordered clearly by elevation.
Lines 332-333 – You mention the full range of 10^-6 to 0.1 K^-1 back-to-back. Do you mean that basin sites had the full range of values that you observed? I just had to do a double-take that you hadn’t repeated yourself here.
Line 379 – You mention velocity drops upward of 10% here. Is this right? The largest drops I see in Figure 5 are of order 1%. The scale on Figure 8 also only goes up to 10⁰ and most sites do not approach even that. Please clarify if you mean that the 10% is referring to studies mentioned in the introduction (Lines 45-49) or if you observed this yourself, and if so where.
Figures 6/7 – Only thought here is the lake sediment color again (these sites aren’t on water!). I really like the presentation of the different components together like this!
Figure 8 – I’ll admit I found this figure difficult to interpret, other than to show the variety of observations at different frequencies and on different channels. I’d suggest changing the colors here to be ordered by frequency (light to dark, or vice versa).
Figure 10 – Same comment for color, though the main point of the figure is to illustrate the weak linear relation. I also found this figure oddly pixelated compared to the quality of the other figures.
Supplementary Figure 1 – Please use the same color scheme as Figure 2 here.
Supplement Line 52 – 25’000 and 75’000 to 25,000 and 75,000 to be consistent with the use of commas in Line 49, or vice versa.
Supplement Line 56 – Missing section number for “??”.
Supplementary Figure 2 – The dot-dashed red line is difficult to read. Consider instead a solid thin gray line or something similar instead?
Supplementary Figure 3 – In the titles for these plots explicitly include which site type they are rather than having your reader infer it.
Supplementary Figure 4 – Same red/green line color issue.
Supplementary Figures 5-6 – There is a lot going on in these figures, but I very much appreciate the transparency in showing everything—including where the inversions didn’t do a good job or converge. I printed these all out, and the figures are impossible to read if not on screen and zoomed in a lot. Is there a way to break these up to make them bigger when they are formatted into the supplement PDF? Also, same red/green choice.
Supplementary Figure 7 – Is color here by time?

I look forward to seeing this paper in print, and hope you find my comments useful.

Citation: https://doi.org/10.5194/egusphere-2022-1361-RC2
- AC2: 'Reply on RC2', Laura Ermert, 24 Mar 2023
  
  Thank you for the detailed comments! They have been valuable in improving different aspects, in particular the presentation of the results. Please find a detailed response attached, and the changes in the re-submitted manuscript and supplementary material.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1361-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-1361', Anonymous Referee #1, 07 Feb 2023

This paper evaluates the seismic responses to environmental factors, long-term subsurface deformation, and tectonic events by analyzing the autocorrelation of continuously recorded urban seismic noise. The authors discussed these diverse effects, from observations to model and physical interpretation, as well as site-dependent local effects and the impact of different materials. In addition, multiple types of seismic stations are used to investigate changes in the shallow to intermediate subsurface medium. They demonstrated the reliability of utilizing strong motion sensors for monitoring local deformation.

In general, the graphs are clear and well-organized, and the interpretation and discussion of the results are reasonably comprehensive. I have no doubts about the methods, no additional comments on the discussion or conclusion, nor on the article's writing, which I believe is publication-worthy.

Citation: https://doi.org/10.5194/egusphere-2022-1361-RC1
- AC1: 'Reply on RC1', Laura Ermert, 24 Mar 2023
  
  We thank the reviewer for the positive comments! We were happy to read that our argumentation and discussion have convinced the reviewer.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1361-AC1
- AC2: 'Reply on RC2', Laura Ermert, 24 Mar 2023
  
  Thank you for the detailed comments! They have been valuable in improving different aspects, in particular the presentation of the results. Please find a detailed response attached, and the changes in the re-submitted manuscript and supplementary material.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1361-AC2
RC2:
'Comment on egusphere-2022-1361', Alicia Hotovec-Ellis, 16 Feb 2023

In this paper, "Probing environmental and tectonic changes underneath Ciudad de México with the urban seismic field" by Ermert et al., the authors describe their efforts to observe and explain changes in the shallow seismic wave velocity across a city on highly variable near-surface geologic conditions. Overall, I found the paper to be a pleasure to read—equal parts rigorous and accessible. The authors are transparent with their methodology and assumptions, build on the wealth of previous observations (e.g., of shallow 1-D velocity structure to create site-specific sensitivity kernels) available to them, and have constructed a series of interpretations that testable and applicable elsewhere. I have no substantial comments on nor issues with the content of the paper itself. My only comments are for the presentation (e.g., wording, figure edits), which I hope will incrementally improve an already excellent article.
Find below a few comments, with line numbers where applicable:
(General) – I found it a little jarring to go between the English/Español versions of place names. I think mostly it’s the loss of the ´ in México that I notice most (which apparently was also dropped between the locations for ² and ⁴ in the author list). It’s a minor distraction, but I think it would be good to choose one name or the other (e.g., Ciudad de México or Mexico City) rather than use them interchangeably.
Line 51 – The phrase “not least due” was somewhat confusing to read the first time through. Perhaps “due largely” instead?
Figure 1 – The color choices for this map are somewhat confusing. First, I think the color for the lake zone should be something other than blue. I recognize that blue for lake zone makes some sense, but I think it evokes too much that standing water still exists there (when it does not). Brown instead? The blue symbols for the Tectonic Observatory sites also blend too much into the lacustrine blue, so whatever choice is made for the lake zone, these symbols should be contrast to it. Also some color other than green should be used for UNM if possible, for those with red/green colorblindness to prevent confusion with the RSVM sties. Yellow? If you cite Crameri et al. (2020) in Figure 2, you should be sure to apply those concepts to the maps/other figures as well.
Figure 2 – I only see one cyan/black line when I print the figure on paper. I can see clearly when the lines are supposed to be without the lines themselves, so perhaps arrows at the top of the figure centered on the time would be enough to illustrate the dates of these changes?
Line 114 – Obviously the cluster names for “day” and “night” are self-evident, but the difference between “noise” and “other” are not. Is “other” more like a transition between clear day and night? What constitutes “noise” in a way that it’d be correlated? Since you only end up using “day” during your work I don’t think this is a major issue, but as I was reading, I did wonder about it.
Figure 3 – Consider adding a color scale on the right side showing on the figure itself the color range and what it corresponds to.
Figure 5 – Similar comment as Figure 1, though I admit I do find the color mapping aesthetically pleasing despite the red/green split. I don’t think this figure is too much of an issue as you do have a clear delimit between which sites are in or out of the basin, and they are ordered clearly by elevation.
Lines 332-333 – You mention the full range of 10^-6 to 0.1 K^-1 back-to-back. Do you mean that basin sites had the full range of values that you observed? I just had to do a double-take that you hadn’t repeated yourself here.
Line 379 – You mention velocity drops upward of 10% here. Is this right? The largest drops I see in Figure 5 are of order 1%. The scale on Figure 8 also only goes up to 10⁰ and most sites do not approach even that. Please clarify if you mean that the 10% is referring to studies mentioned in the introduction (Lines 45-49) or if you observed this yourself, and if so where.
Figures 6/7 – Only thought here is the lake sediment color again (these sites aren’t on water!). I really like the presentation of the different components together like this!
Figure 8 – I’ll admit I found this figure difficult to interpret, other than to show the variety of observations at different frequencies and on different channels. I’d suggest changing the colors here to be ordered by frequency (light to dark, or vice versa).
Figure 10 – Same comment for color, though the main point of the figure is to illustrate the weak linear relation. I also found this figure oddly pixelated compared to the quality of the other figures.
Supplementary Figure 1 – Please use the same color scheme as Figure 2 here.
Supplement Line 52 – 25’000 and 75’000 to 25,000 and 75,000 to be consistent with the use of commas in Line 49, or vice versa.
Supplement Line 56 – Missing section number for “??”.
Supplementary Figure 2 – The dot-dashed red line is difficult to read. Consider instead a solid thin gray line or something similar instead?
Supplementary Figure 3 – In the titles for these plots explicitly include which site type they are rather than having your reader infer it.
Supplementary Figure 4 – Same red/green line color issue.
Supplementary Figures 5-6 – There is a lot going on in these figures, but I very much appreciate the transparency in showing everything—including where the inversions didn’t do a good job or converge. I printed these all out, and the figures are impossible to read if not on screen and zoomed in a lot. Is there a way to break these up to make them bigger when they are formatted into the supplement PDF? Also, same red/green choice.
Supplementary Figure 7 – Is color here by time?

I look forward to seeing this paper in print, and hope you find my comments useful.

Citation: https://doi.org/10.5194/egusphere-2022-1361-RC2
- AC2: 'Reply on RC2', Laura Ermert, 24 Mar 2023
  
  Thank you for the detailed comments! They have been valuable in improving different aspects, in particular the presentation of the results. Please find a detailed response attached, and the changes in the re-submitted manuscript and supplementary material.
  
  Citation: https://doi.org/10.5194/egusphere-2022-1361-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Laura Ermert on behalf of the Authors (24 Mar 2023) Author's response Manuscript

EF by Sarah Buchmann (24 Mar 2023) Author's tracked changes Supplement

ED: Publish subject to technical corrections (24 Mar 2023) by Michal Malinowski

ED: Publish subject to minor revisions (review by editor) (05 Apr 2023) by Susanne Buiter (Executive editor)

AR by Laura Ermert on behalf of the Authors (07 Apr 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (13 Apr 2023) by Michal Malinowski

ED: Publish as is (17 Apr 2023) by Susanne Buiter (Executive editor)

AR by Laura Ermert on behalf of the Authors (20 Apr 2023)

Journal article(s) based on this preprint

23 May 2023

Probing environmental and tectonic changes underneath Mexico City with the urban seismic field

Laura A. Ermert, Enrique Cabral-Cano, Estelle Chaussard, Darío Solano-Rojas, Luis Quintanar, Diana Morales Padilla, Enrique A. Fernández-Torres, and Marine A. Denolle

Solid Earth, 14, 529–549, https://doi.org/10.5194/se-14-529-2023,https://doi.org/10.5194/se-14-529-2023, 2023

Short summary

Laura Ermert et al.

Supplement

https://doi.org/10.5194/egusphere-2022-1361-supplement

Model code and software

Processing tools for seismic noise monitoring L. Ermert, M. Denolle https://github.com/lermert/ruido

Monte Carlo model for seismic noise monitoring L. Ermert https://github.com/lermert/cdmx_dvv

Laura Ermert et al.

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Short summary

Ciudad de México is built on a unique soil containing the clay-rich deposits of ancient lake Texcoco. Continuous, imperceptible shaking of these and deeper deposits by the traffic and other sources allows us to monitor changes in the subsurface seismic wave speed. Wave speed varies seasonally, likely due to temperature and rain effects; it temporarily drops after earthquakes, then starts to recover. Throughout the studied period, it increased on average, which may be related to soil compaction.


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