the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 06 Jul 2026
Long-term evolution and type-specific rainy-season activity of post-seismic geohazards in Southwest China
Abstract. Long-term evolution of post-seismic geohazards represents a critical yet complex challenge in earthquake-affected regions. This study systematically investigates the spatiotemporal patterns of post-seismic geohazard evolution following three major seismic events: the 2008 Wenchuan earthquake (Mw7.9), 2013 Lushan earthquake (Mw6.6), and 2017 Jiuzhaigou earthquake (Mw7.0), focusing on four representative counties (Wenchuan, Beichuan, Lushan, and Jiuzhaigou County) in Southwest China. The results show that: (1) post-seismic geohazard activity showed an intermittent clustered outbreak pattern; (2) geohazards were mainly concentrated in valley-related geomorphic units, with county-level differences characterized by reactivation–expansion, spatial inheritance, localization, and contraction; (3) monthly records excluding earthquake-month records showed a clear rainy-season concentration, with 78.1 % of geohazards occurring from June to August; and (4) Beichuan and Lushan showed clearer weakening trends, whereas Wenchuan and Jiuzhaigou remained in low-level persistent activity stages and should receive continued monitoring attention. These findings provide useful insights for long-term geohazard monitoring and risk mitigation in earthquake-affected mountainous regions.
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Status: open (until 30 Sep 2026)
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RC1: 'Comment on egusphere-2026-2643', Anonymous Referee #1, 18 Aug 2026
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AC1: 'Reply on RC1', Hongyu Duan, 28 Aug 2026
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We sincerely thank the reviewer for the positive and constructive assessment of our manuscript. We greatly appreciate the reviewer’s recognition of the study’s value, manuscript structure, figure quality, references, and overall presentation. The additional suggestions are helpful for improving the seismic background and clarifying the relationship between the initial seismic disturbance and subsequent post-seismic geohazard evolution. We have carefully considered these suggestions and will further revise the manuscript based on the available data and the scope of this study.
Comment 1: Whether the authors have identified an earthquake magnitude beyond which post-seismic risk is triggered.
Response:
Thank you for raising this important question. We have not identified a specific earthquake-magnitude threshold for long-term post-seismic geohazard risk. This study mainly examines the post-seismic evolution associated with the 2008 Wenchuan, 2013 Lushan, and 2017 Jiuzhaigou earthquakes and their corresponding study areas; therefore, the number of major earthquake events available for comparison is limited.In addition, several smaller earthquakes occurred during the post-seismic periods following these major events. However, these smaller earthquakes affected slopes and loose materials that had already been disturbed by the corresponding major earthquakes. Their geohazard responses may therefore reflect both renewed seismic disturbance and the pre-existing post-seismic disturbance, making them unsuitable as independent samples for identifying a magnitude threshold.
The available data are therefore insufficient to establish a generally applicable magnitude threshold. We will clarify this limitation in the revised manuscript. Future studies incorporating more independent earthquake events of different magnitudes and complete post-seismic geohazard records may help determine whether stable relationships or threshold behavior exist between earthquake magnitude and long-term post-seismic geohazard risk.
Comment 2: Consider site effects and any ground accelerations in relation to the types of disasters considered.
Response:
We agree that peak ground acceleration (PGA), local ground-motion characteristics, and site effects can influence the initial disturbance of slopes and may subsequently affect post-seismic geohazard development.However, event-specific strong-motion records and site-response data with consistent coverage across all study areas were not systematically collected when the geohazard database was established. The publicly available strong-motion data are mainly from a limited number of discrete stations and cannot provide a consistent and comparable PGA representation for the four county-scale study areas. Therefore, the available data are insufficient to establish a quantitative relationship among PGA, site effects, and different geohazard types. We will acknowledge this data limitation in the revised manuscript and identify it as an important direction for future research.
Comment 3: Indicate which types of landslides (collapse, flow, slide, etc.) are most affected by seismic events of high intensity and magnitude.
Response:
Thank you for this helpful suggestion. This issue is already addressed in the original manuscript. Specifically, Results Section 4.3 (Figure 10) compares the geohazard-type composition during the months of the major earthquakes. During the May 2008 Wenchuan earthquake, rock falls dominated in Wenchuan and Jiuzhaigou, whereas landslides dominated in Beichuan. During the April 2013 Lushan earthquake, landslides dominated in Lushan, while the August 2017 Jiuzhaigou earthquake was dominated by rock falls. These results show that earthquake-month geohazard peaks were generally dominated by rock falls and landslides.The Discussion further compares the immediate seismic response with subsequent post-seismic activity. Earthquake-month activity was mainly dominated by rock falls and landslides, whereas later rainy-season activity was dominated more by landslides and debris flows, indicating a shift from the immediate seismic response to rainfall-driven post-seismic reactivation. We agree that this conclusion can be stated more explicitly and will further highlight this type-specific transition in the revised Discussion and Conclusions.
Comment 4: Add data from the 2008 Wenchuan, 2013 Lushan, and 2017 Jiuzhaigou earthquakes.
Response:
Thank you for this suggestion. The current manuscript already provides basic information on the 2008 Wenchuan, 2013 Lushan, and 2017 Jiuzhaigou earthquakes in the “Study Area and Geological Setting” section, but these data are presented separately in narrative form.To improve the clarity and comparability of the seismic background, we will add a summary table compiling the main information for the three earthquakes, including occurrence date, magnitude, epicentral information, major faulting or rupture characteristics, and corresponding study area(s).
We again thank the reviewer for these constructive suggestions, which will help us further improve the manuscript.
Citation: https://doi.org/10.5194/egusphere-2026-2643-AC1
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AC1: 'Reply on RC1', Hongyu Duan, 28 Aug 2026
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RC2: 'Comment on egusphere-2026-2643', Anonymous Referee #2, 05 Sep 2026
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I thank the editor for the opportunity to review the manuscript entitled “Long-term evolution and type specific rainy season activity of post-seismic geohazards in southwest China”
I have to say that I was not convinced by the findings presented in the manuscript. The authors claim that they observe a “clear” relationship (e.g., lines 397–398), but they do not present any sound statistical, spatial, temporal or other quantitative method to support this claim. Additionally, no research questions or hypotheses are presented, while the stated objectives of the study are only partially examined.
In detail:
- The Introduction is confusing while in several places is See, for example, lines 57–68, and in particular lines 66–68. It is not clear whether the recovery period discussed by the authors refers to years, decades, centuries, or another timescale. Additionally, the authors refer to two key processes but do not explain why these processes are important or for what purpose they are being examined. Similar contradictions and phrasing issues appear in lines 45–47 and 76–85.
- This brings me to another important issue. Although the study has stated objectives, I do not see clearly defined research questions or hypotheses. In addition, part of the objectives remains unclear. For example, what exactly is meant by “non-earthquake-month geohazard activity”? The authors should at least explain this term.
- Throughout the manuscript, statements are made without sufficient support. See, for example, lines 96–102. This issue applies in particular to the entire Section 2 and also to parts of Section 3.
- The data issue is particularly vexing. There is no reference to the source of the data and no supplementary material is provided. Additionally, the authors describe the data textually in lines 137–142. Why not present this information in a table? This would make it much easier to read and understand.
- Regarding lines 143–148: is the distribution of the data normal or are extreme events distorting the results?
- The first earthquake examined occurred in 2008, but the precipitation analysis begins only two years earlier, in 2006. I think this is a very short period from which to draw sound conclusions.
- The findings are not sufficiently supported. Consider, for example, Figure 5 and line 185. I cannot understand the correlation or connection between precipitation and the other findings. How is this relationship demonstrated? Additionally, I cannot understand the distribution of events in the county by year. There is no statistical analysis of the proportions, and it is unclear how precipitation is linked to these patterns. The authors should revise this section and provide further explanation.
- Figures 6, 7, and others present continuous data while the raw data appear to be discrete. What interpolation method was used to convert the discrete data into continuous representations?
- The fact that there are more events in the year following an earthquake does not necessarily imply a causal or meaningful linkage. I would expect the authors to use a statistical or other quantitative method to support this notion. The authors currently present the distribution using bar charts, but I would expect to see something more consistent, for example an analysis based on proportions or Poisson tests.
- I would also expect the authors to perform spatial and/or temporal analyses. For example, where and when can a decay in post-seismic geohazard activity be observed?
- The authors reach conclusions that are not sufficiently supported by the findings of the study. See, for example, lines 384–390 and 397–400.
Citation: https://doi.org/10.5194/egusphere-2026-2643-RC2
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The manuscript addresses essentially technical, scientific, and probabilistic issues, which are integral to the topics covered by NHESS. The study examines the long-term evolution and seasonal patterns of post-seismic geohazards in the mountainous regions of western Sichuan, China. It focuses on four counties (Wenchuan, Beichuan, Lushan, and Jiuzhaigou) affected by three major earthquakes (Wenchuan 2008, Lushan 2013, Jiuzhaigou 2017). The study, which covers the geological and geomorphological context of China, can, however, be considered a model for internationally applicable research. The research findings, data, and maps reported in the paper may encourage fellow scientists to experiment with this research methodology elsewhere in the world, especially in seismically active areas affected by potentially destructive earthquakes, capable of also impacting slope stability. Therefore, the conclusions are substantial. The title clearly reflects the content of the document, the abstract is complete and provides consistent information about the study, which is intended for a broader, non-specialist audience, also taking into account the implications for civil protection. The size and readability of the figures are sufficiently relevant and appropriate to the data presented. The authors give due credit to previous work, spanning a sufficient period of time. In this regard, both the number and quality of references are appropriate, and the references are accessible for use by other researchers. The overall presentation is well-structured, clear, and easy to understand, especially for technicians and scientists in the field. The length of the paper is adequate and balanced for an international scientific context. The technical language is precise and understandable even by other researchers thanks to the use of good-quality English, which is fluent, simple, and easy to read and understand, even by a broad and diverse audience. The document is not accompanied by supplementary material.
Given its characteristics, the paper can be accepted without modification, but if the authors deem it appropriate, they could enrich the manuscript with: