the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Update of the Seismogenic Potential of the Upper Rhine Graben Southern Region
Sylvain Michel
Clara Duverger
Laurent Bollinger
Jorge Jara
Romain Jolivet
Abstract. The Upper Rhine Graben (URG), located in France and Germany, is bordered by north-south trending faults, some of them considered active, posing a potential threat to dense population and infrastructures from the Alsace plain. The largest historical earthquake in the region is the M6.5+/-0.5 Basel earthquake in 1356. Current seismicity (M>2.5 since 1960) is mostly diffuse and located within the graben. We build upon previous seismic hazard studies of the URG by exploring uncertainties in greater detail, revisiting a number of assumptions. We first take into account the limited evidence of neotectonic activity, then explore tectonic scenarios that have not been taken into account previously, exploring uncertainties on Mmax, its recurrence time, the b-value, and the moment released aseismically or through aftershocks. Uncertainties on faults’ moment deficit rates, on the observed seismic events’ magnitude-frequency distribution, and on the moment-area scaling law of earthquakes are also explored. Assuming a purely dip-slip / normal faulting mechanism associated to a simplified 3 main fault model, Mmax maximum probability is estimated at Mw6.05. Considering this scenario, there would be a 99 % probability that Mmax is below 7.25. In contrast, a strike slip assumption associated to a 4 main fault model, consistent with recent paleoseismological studies and the present day stress field, Mmax is estimated at Mw6.85. Based on this scenario, there would be a 99 % probability that Mmax is less than 7.55.
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Sylvain Michel et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2023-359', Anonymous Referee #1, 03 Jul 2023
The article under review covers an interesting topic improving the results of existing literature. While the article is clearly written, in general, some aspects need to be addressed before publication.
General comments:
- While the article is generally linearly written and easy to follow, there are a few instances where some concepts are left hanging. A clear example is the shear modulus introduced at line 113 but whose value is defined only at line 194. While the fragmentation of the information may be inevitable due to the number of parameters present in the analysis, referencing the section where the parameters are discussed at length could benefit the readability.
- Some choices introduced as arbitrary could be better motivated (e.g. the linearity of the taper in line 183).
- The results following the analysis using the tapered and truncated seismicity model are presented and compared but they should be discussed more critically, showing which model should be considered for the following studies. Could the results from the two models be combined? How this would affect the results?
- While already done for some of the assumptions made, a systematic analysis of the results concerning the different parameters could improve the quality of the paper. How the variation of one (or more) parameter affects the results and, more importantly, how this should shape the uncertainty?
- Figures 4, 7, and 8 (as well as S13 and S15) could benefit from the addition of some sort of scale for the PDFs (even though I understand the difficulty due to the figures being already packed with information).
Targeted comments:
- Is the concept of α_s original or is it taken from previous studies? If the former applies, it should be discussed in more detail; if the latter applies, you should provide some references.
- In section 2.4 some references are needed relative to how to estimate the parameters from P_SM, as mentioned. In the same section, the variable P_barrier is introduced without being defined.
- The notation used in line 231 to define the Gaussian distribution N(90%, 25%) can be unclear. Since it refers to a parameter, I suggest changing it to N(0.9, 0.25).
- Section 5.1 provide a clear picture of the variability in the results due to different declustering methods but lacks a concrete discussion motivating how the selection of the algorithm used in the main analysis has been informed. Furthermore, it should be discussed how the results from different declustering algorithms should shape the uncertainty.
- While the concept in line 374 is clear, the length of future time series (centuries?) needed to improve the results doesn't provide any further information for future studies.
I also advise the authors to proof-reading the manuscript and the supplementary material: while no major need to be pointed out, there are a few grammatical errors and typos (e.g., the references in the Supplementary material are addressed as "Bibliographie").
Citation: https://doi.org/10.5194/egusphere-2023-359-RC1 -
AC1: 'Reply on RC1', Sylvain Michel, 05 Sep 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-359/egusphere-2023-359-AC1-supplement.pdf
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RC2: 'Comment on egusphere-2023-359', Anonymous Referee #2, 04 Jul 2023
The article focuses on the Upper Rhine Graben’s seismogenic potentials. Significance of the article is to improve the modeling of the seismogenic zones by including various parameters related to the fault modeling and seismicity of the region. In this regards, the article helps on constructing a better seismic hazard model for the region.
The paper has a good quality but there are some aspects of the paper that requires improvements. They are given in below.
Major comments:
- It would be better to provide a more expanded information about the truncated and tapered models. Maybe it is a very well known and used methods in the subject but it would help reader to understand the basic consent without reading another paper(s).
- Magnitude estimations are given in the second decimals which requires a great knowledge of the almost all the parameters in the study. However, there are lot’s of uncertainties in both data (eg. lack of knowledge about seismogenic depth) and method (eg. using a m0 and Aeq scaling law which has its own standard deviations). In this regard, providing earthquake magnitudes in second decimals as if there is such a good resolution in the study is not realistic.
- In the thermal gradient part of the Section 3.1 the thermal features are expected to increase linearly with depth. Is there any reference to justify this linear gradient in depth? Neither Freymark et al. (2017) nor Guillou-Frottier et al. (2013) has any model for the depths that are deeper than the drilling depths. Even though Freymark et al. (2017) had a model for density variations, in thermal data the study limits itself except for the Fig. 10F which does not provide a detailed model for the region.
- In the Section 3.1 seismogenic thickness of the southern par of the URG is defined by using temperature and salt basin assumptions. However, in the paper it is stated that in the southern URG there is seismicity. Can the authors add seismicity for the thickness modeling?
- In Section 3.1 and Section 3.3, relation between the section and their effect on the model parameters are explained by referring the variables in sections. It would be good to provide same information for Section 3.2.
- In line 267-268 what is the reason for choosing second peak in truncated model instead of the first one?
- In line 149, Pbarries is not defined.
- To sum up the study, a Table can be added into the conclusion part which shows the changing results for changing parameters. They are more or less presented in the text of conclusion. A table show the overall results which helps readers to summarize the study.
- As mentioned in Introduction and Figure 5, results of this study can be useful for nuclear power plant constructions. However, in the paper there is no indication of which model is better and should be preferred on hazard assessments. In a scientific point of view, all the variations in results are important but for the engineering perspective there must be a decision to make to choose a number to move forward. In the conclusion there is no such indications.
Minor details:
- Line 58 – “w” of M should be subscript to be in agreement with the other Mws.
- Line 128 – No need to say “according to global earthquake statistics”.
- Line 136 – No need to say “finally”.
- Line 138 – "since" is a conjunction, so it should always join two clauses.
- Line 170 – “aforementioned” can be moved before the “other”. “… by the aforementioned other faults”.
- Line 231 – What does percentage of the mean and variance of the scaling factor in numbers?
- Lines 275-278 – Word “thus” used in 3 consecutive sentences. Different wording can be chosen to text more readable.
- Please provide the DOI for all the references.
- In Figures 4, 7-8 it would be better to put a y-axis for Pmmax and and tau.
Citation: https://doi.org/10.5194/egusphere-2023-359-RC2 -
AC2: 'Reply on RC2', Sylvain Michel, 05 Sep 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-359/egusphere-2023-359-AC2-supplement.pdf
Sylvain Michel et al.
Sylvain Michel et al.
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