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Rain- and Seismic-Triggered Mass Movements in Coastal Ecuador—A Case Study of the “El Florón” Landslide in Portoviejo

Earth 2025, 6(4), 156; https://doi.org/10.3390/earth6040156

by Melany Melgar^1,*

, Nayeska Ramírez-Cevallos¹

, Kervin Chunga¹ and Theofilos Toulkeridis^2,3,*

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Earth 2025, 6(4), 156; https://doi.org/10.3390/earth6040156

Submission received: 11 November 2025 / Revised: 3 December 2025 / Accepted: 7 December 2025 / Published: 11 December 2025

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

In this Manuscript, the predominant aims of the current research have been focused on identifying the lithological units of the subsurface using geophysical methods such as Electrical Resistivity Tomography (ERT), seismic refraction, Multichannel Analysis of Surface Wave (MASW), as well as Vertical Electrical Sounding (VES), and hereby characterizing strata with a high degree of weathering and structural discontinuities. The case study is relevant for rainfall- and earthquake-prone tropical slopes and shows a plausible retrofit concept; the paper can make a useful applied contribution. The specific opinions are as follows.

Please provide survey lines, acquisition/inversion details and the mapping from geophysical units to geotechnical layers.

Drainage is rightly emphasized but lacks design details (type, capacity, spacing, expected drawdown). A simple seepage–stability coupled sensitivity (with/without drains) would greatly strengthen the engineering claim.

The manuscript cites NEC compliance; consider adding a small parametric table showing FS under (i) pre-event, (ii) post-event back-analysis, and (iii) proposed works across static/pseudo-static for several k_h and water-level scenarios. This will clarify robustness beyond the single scenario already shown.

Author Response

Response Letter to the expert reviewer

Dear expert reviewer,

As authors of the manuscript entitled “Rain and seismic triggered mass movements in coastal Ecuador - a case study of the “El Florón” landslide in Portoviejo”, we appreciated a lot your suggestions and comments on the document, as we are certain and convinced, that they have been useful to enrich the fluency and clarity of the entire article. We also confirm that the writing in English has been thoroughly reviewed and accordingly improved. Below, we will detail the changes realized and you will be able to find them all exposed and answered since the responses to each suggestion and comments as well as given marked in the manuscript.

Comment:

Please provide survey lines, acquisition/inversion details and the mapping from geophysical units to geotechnical layers.

Response:

We appreciate your observation regarding the need to specify the survey lines, the acquisition and inversion details, and the correlation between geophysical units and geotechnical layers. In accordance with your recommendation, we have incorporated a more complete description of the geophysical acquisition design, including the number, location, and characteristics of the survey lines, as well as the technical parameters used during data acquisition and processing. Additionally, we added a dedicated section presenting the mapping between the identified geophysical units and the geotechnical layers of the stratigraphic model, thereby strengthening the integrated interpretation of the subsurface. The text has been incorporated into Section 3, Methods Applied and Field Investigation, subsection 3.2 Geophysical Prospection, being stated as:

“This section provides a general description of the methods applied to characterize the subsurface conditions. The study included a single Electrical Resistivity Tomography (ERT) line, used to identify contrasts associated with moisture variation, weathered materials, and lithological boundaries. In addition, three shear-wave velocity (Vs) profiles were collected to detect stiffness changes and the mechanical structure of the ground. These results were complemented by three geotechnical boreholes with SPT testing, allowing the correlation between geophysical units and the stratigraphy observed in the field. Together, these datasets form the technical basis for the detailed interpretation presented in the following sections.”

Comment:

Drainage is rightly emphasized but lacks design details (type, capacity, spacing, expected drawdown). A simple seepage–stability coupled sensitivity (with/without drains) would greatly strengthen the engineering claim.

Response:

We appreciate your valuable comment. In the revised version of the manuscript, a moisture-sensitivity analysis of the soil has been incorporated to strengthen the engineering justification of the proposed stabilization solution. Specifically, the variation of the safety factor (FS) was evaluated in response to progressive changes in groundwater depth, from 0 m (fully saturated condition) to –12 m. This analysis shows that the geotechnical solution maintains FS values above the limits required by NEC-15. These results confirm that the micropile and terracing system exhibits robust performance under extreme saturation conditions and does not rely solely on an idealized drainage scenario. The complete results of the sensitivity analysis have been included in Section 5.3 of the revised manuscript, together with the corresponding table supporting this evaluation.

Hereby we added within the manuscript the following section and additional table:

“The following section presents the sensitivity analysis aimed at determining the influence of groundwater-level variations on slope stability and evaluating the performance of the proposed stabilization system. Table 5 summarizes the evolution of the safety factor (FS) for groundwater depths ranging from 0 to –12 m, representing scenarios from full saturation to partially drained conditions. These results allow the identification of the critical saturation state and verify that the proposed stabilization system maintains stable conditions even when the groundwater level rises to the ground surface, an event typically associated with the clogging of surface drains during intense rainfall episodes. Under this most unfavorable scenario, the geotechnical solution preserves FS values above 1.05 under pseudostatic conditions, meeting the minimum requirements established by NEC-15, which are related to the horizontal seismic coefficient kₕ. In this way, the information synthesized in the table demonstrates the robustness of the design under hydrological variations, ensuring system functionality even under extreme moisture conditions.”

Table 5 : Variation of the safety factor (FS) as a function of groundwater-table depth

#	Depth of the groundwater level	FS
1	0	1.055
2	-1	1.060
3	-2	1.062
4	-3	1.064
5	-4	1.066
6	-5	1.068
7	-6	1.070
8	-7	1.071
9	-8	1.073
10	-9	1.074
11	-10	1.076
12	-11	1.077
13	-12	1.078

Comment:

The manuscript cites NEC compliance; consider adding a small parametric table showing FS under (i) pre-event, (ii) post-event back-analysis, and (iii) proposed works across static/pseudo-static for several k_h and water-level scenarios. This will clarify robustness beyond the single scenario already shown.

Response:

Table 6 will be corrected, so after this statement: “This improvement confirms the effectiveness of the implemented reinforcement by reducing ground displacements and ensuring slope stability under moderate seismic loads.”

…will be replaced by this:

Description of the analyzed geometry	FS static	FS pseudostatic kh= 0.354g
Description of the analyzed geometry	FS static	FS pseudostatic kh= 0.354g
Retrospective slope prior to the event	1.00	0.373
Slope after the event	1.290	0.522
Slope with a geotechnical stabilization solution	2.515	1.062

Once again and with all due respect, we are very thankful for your comments and corrections, which helped to see a few unclear parts and or even faults of our side within our manuscript. With your comments we were able to smooth the text, clarify missing parts or wrong spellings, which resulted to a much better than the initial version of this current study. Thanks a lot, on behalf of all authors

Reviewer 2 Report (Previous Reviewer 4)

Comments and Suggestions for Authors

Dear Authors,

- I sincerely appreciate the effort put into the revised manuscript. However, after careful review, I have some remarks in order to improve the quality of the manuscript.

- In the methodology, although several methods are used (ERT, MASW, ...), their integration is not always clearly explained.

- How were the failure surfaces validated by the geophysical and geotechnical methods?

- How were the shear strength parameters for the back-analysis selected?

- Please add the methodology flowchart.

- The Discussion section lacks synthesis and critical evaluation. A clearer causal sequence is needed. In other words, the authors should explicitly link rainfall anomalies, lithological weaknesses, structural discontinuities, and saturation conditions to the observed rotational sliding.

Add scales to all figures!

Author Response

Response Letter to the expert reviewer

Dear expert reviewer,

Dear Authors,

- I sincerely appreciate the effort put into the revised manuscript. However, after careful review, I have some remarks in order to improve the quality of the manuscript.

Comment:

- In the methodology, although several methods are used (ERT, MASW, ...), their integration is not always clearly explained.

Response:

Indeed, we appreciated your comment. In the revised version of the manuscript, we have clarified the integration of the geophysical and geotechnical methods employed in the study. A detailed explanation has been added on how ERT and MASW data were correlated with SPT results and laboratory tests in order to define lithological boundaries, identify saturated zones, and more accurately characterize the geometry and geomechanical properties of the failure surface. This additional content enhances methodological coherence and strengthens the interpretation of the stability models. The text has been incorporated in Section 3 “Methods Applied and Field Investigation,” subsection 3.2, after Figure 4.

Therefore, we added there: “The integration of geophysical and geotechnical methods was fundamental in the construction of the subsurface model. Electrical Resistivity Tomography (ERT) allowed to define the lateral and vertical distribution of geological units, as well as identifying saturated zones. Meanwhile, MASW tests provided shear wave velocity (Vs) values useful for the differentiation of layers with varying degrees of stiffness and characterizing lithological units. Both datasets were correlated with the results of SPT and laboratory tests, which allowed to validate geophysical anomalies and the determination of the strength parameters of each layer. This multidisciplinary approach facilitated the precise delineation of the fault surface and the characterization of the contact between the colluvial deposit and the bedrock, which controls the instability mechanism. This ensured the accuracy of the parameters used in the numerical modeling of slope stability under static and pseudo-static conditions.”

Comment:

- How were the failure surfaces validated by the geophysical and geotechnical methods?

Response:

Thanks for this valuable question. In the revised version of the manuscript, we have clarified the validation of the failure surfaces through an integrated geophysical–geotechnical approach. Electrical Resistivity Tomography (ERT) enabled the identification of resistivity contrasts associated with the colluvium–bedrock contact and highly saturated zones that coincided with the failure surface mapped in the field. Likewise, geoseismic testing (MASW/Vs30) confirmed stiffness changes along this interface. These findings were corroborated through geotechnical field inspections, test pits, and laboratory tests, which demonstrated the presence of a weakened horizon at the contact between the colluvial deposits and the weathered shales. This explanation has been incorporated into the Discussion section of the revised manuscript. Hereby we added at the end of subsection 4.4:

“The validation of the fault surfaces was realized through the integration of geophysical methods and direct geotechnical investigations. Electrical Resistivity Tomography (ERT) surveys allowed the identification of marked resistivity contrasts along the slope. There the colluvial soils (U1 and U2) exhibited values ranging from 12 to 28 Ω·m, indicating highly saturated zones, while the weathered shale and mudstone units (U3, U4, and U5) demonstrated resistivities between 13 and 22 Ω·m, corresponding to more competent materials at depth. These resistivity variations spatially coincided with the landslide fault plane identified in the field. Similarly, the geoseismic tests (Vs30) confirmed variations in subsurface stiffness, clearly delineating the contact between the colluvial soils and the underlying rock mass. The near-surface deposits presented shear-wave velocities between 180–310 m/s (U1 and U2), whereas the underlying weathered shale and mudstone units increased to 310–760 m/s (U3 and U4), reaching up to 900 m/s in the most competent unit (U5). This contrast enabled the precise location of the listric fault surface described in the kinematic analysis.

Complementarily, the field geotechnical inspection and the information obtained from test pits, undisturbed samples, and laboratory analyses corroborated the presence of a weakened zone at the interface between the shallow cohesive soils and the weathered shale units (U1–U4). The geometric projection of the main scarp, together with the structural analysis of the plane, allowed the determination of a rotational movement mechanism over a reactivated ancient fault plane, whose geometry coincided with the geophysical contrasts and the geotechnical parameters measured in situ.”

Comment:

- How were the shear strength parameters for the back-analysis selected?

Response:

We appreciate your observation, which allows us to clarify this issue. In the revised version, we have included a more detailed explanation of the criteria used to select the shear strength parameters in the back-analysis. The initial values were obtained from direct shear tests and subsequently adjusted iteratively in the stability model until a safety factor close to the observed failure condition (FS ≈ 1) was reached. This procedure follows the recommendations of the NEC-15 standard and commonly accepted methodologies for estimating soil behavior in landslide events. The added text is located in subsection 5.2 “Slope Stability Analysis,” of the revised manuscript.

There is has been stated after the first paragraph:

“For the selection of shear strength parameters used in the retrospective analysis, the initial values were those obtained from direct shear tests performed on representative samples of the materials involved in the instability. These values were subsequently adjusted iteratively within the numerical model, using the limit equilibrium method, until a safety condition equivalent to that observed during the event recorded in April 2023 was reproduced. That results into a limit equilibrium state with a FS of 1. This procedure allowed for the estimation of the soil shear strength during the collapse, following the recommendations of NEC-15 and the methodologies applied to the retrospective analysis of slope stability under actual failure conditions.”

Comment:

- Please add the methodology flowchart.

Response:

Great suggestion. You may see the new elaborated flowchart in the methdology section:

“Figure 4. Methodological flowchart illustrating the integrated geophysical–geotechnical approach applied to the characterization and stability analysis of the El Florón III landslide.”

Comment:

Response:

We appreciate your comment, as we all know, a discussion can never be too short. Therefore, we have strengthened Section 5 (Discussion) by adding a clearer synthesis of the results and an evaluation with an explicit causal sequence, directly linking rainfall anomalies, lithological characteristics, structural discontinuities, and saturation conditions with the observed rotational mechanism. This improvement enhances the coherence and critical interpretation of the findings through two additional paragraphs. Hereby, a first adding was incorporated at the end of Section 5 (Discussion), before the subtitle “5.1 Data and Numerical Modeling,” of the revised manuscript. A further, second adition was included at the end of subsection “5.3 Alternatives for Landslide Prevention,” before Section 6 (Conclusions).

First:

“The results obtained indicate that the rotational landslide at El Florón was conditioned by unfavorable geological and geotechnical characteristics present on the slope. A highly weathered colluvial deposit with low bearing capacity and a tendency to deform under moderate stress was identified. Furthermore, the orientation of the colluvium-rock contact towards the valley and the presence of structural discontinuities favor the formation of surfaces of weakness and a high susceptibility of the slope to instability. The integration of geophysical data and geotechnical tests allowed for the definition of the geometry of the fault surface and the variability in the strength properties of the colluvium, aspects that directly influence its stability.”

Second:

In summary, the increased rainfall in the months leading up to the collapse acted as the primary triggering factor, causing an increase in saturation and pore pressure in the surface materials, which led to a reduction in shear strength. Simultaneously, the weak geotechnical behavior of the colluvial deposit and the persistence of structural discontinuities facilitated the development of a rotational slide and the displacement of the material. The relationship between the rainfall anomalies, the geophysical evidence of high saturation, and the results of the slope stability analysis confirms the fault mechanism proposed in the present study.

Comment:

Add scales to all figures!

Response:

Realized

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

Reviewer’s Report on the manuscript entitled:

Rain and seismic triggered mass movements in coastal Ecuador 2 - a case study of the “El Florón” landslide in Portoviejo

The authors identified the lithological units of the subsoil using geophysical studies and investigated the deformation dynamics of the landslides using probabilistic and deterministic analyses. They also assessed the displacement moments of the post-landslide material using digital terrain models and direct shear tests for El Florón III, Portoviejo, Ecuador. I found this study and the results interesting; however, the presentation and literature review should be improved. Please see my comments below.

Line 12. It is not clear what the study is about and whether earthquake or seismic activity have occurred in the region. Please re-write the sentence to emphasize the motivation of the research.

From the abstract and conclusion, it is not clear what the objectives and contributions are. I suggest authors to state the objectives and clearly mention what has been done in your research including the methods and data used.

Introduction. The literature review on similar studies should be improved. For example, a severe seismic sequence occurred in Central Apennines, namely the Amatrice–Norcia–Campotosto seismic sequence (2016–2017) and the landslide activities that are further triggered by rainfalls are studied using InSAR technique in the following recent study, so please review and discuss:

Estimating Reactivation Times and Velocities of Slow-Moving Landslides via PS-InSAR and Their Relationship with Precipitation in Central Italy (Remote Sensing, 2024)

Likewise, the interconnection between rainfall and landslide activities are studied using InSAR technique in the following study that can be reviewed:

InSAR stacking to detect active landslides and investigate their relation to rainfalls in the Northern Apennines of Italy (Geomorphology, 2024)

Introduction. Last paragraph. Please first mention the research gaps, then highlight the main contributions of your research, preferably using a few bullet points. Then please provide an outline of how the rest of the research is organized.

Lines 180-209. I suggest renaming Section 2. “Materials” and then create two subsections 2.1 Study region and 2.2 Datasets. This way it is easier to follow what datasets you used in your research.

Line 167 and Figure 3. As you mentioned year 2012 experienced heavier rainfall compared to other years. How the precipitation may have influenced landslides in year 2012 need to be discussed. Likewise in 2021.

The study also lacks quantitative assessment. Some numerical results should also be included in the abstract.

In the discussion section, please elaborate on uncertainties involved in the input data, model parameters, etc. Please mention the limitations of your research and then provide future direction/recommendations. I also suggest reviewing the first article that I suggested above on how the authors used the sequential turning point detection (STPD) method to detect the dates of landslide reactivations and linked them to precipitation pattern changes.

Figure quality must be improved. Please enlarge the font size and ensure the figures have a resolution of at least 300 dpi. For example, Figure 3 has tiny font size and Figure 9 has poor resolution (the texts are blur).

Thank you and regards,

Author Response

Response Letter to the expert reviewer

Dear expert reviewer,

Reviewer’s Report on the manuscript entitled:

Rain and seismic triggered mass movements in coastal Ecuador 2 - a case study of the “El Florón” landslide in Portoviejo

Comment:

Line 12. It is not clear what the study is about and whether earthquake or seismic activity have occurred in the region. Please re-write the sentence to emphasize the motivation of the research.

Response:

We appreciate your observation. We have rewritten the corresponding sentence within the abstract in order to clarify that the landslide analyzed in this study was not triggered by seismic activity, rather than but by the given extreme rainfall during the 2023 wet season. The reference to the 2016 earthquake is maintained only as historical context and as a comparative framework to evaluate the susceptibility of the area to slope instability under static and pseudo-static conditions. This modification now explicitly emphasizes the motivation of the study, which is to characterize the geotechnical conditions and the factors controlling the reactivation of the rotational landslide in El Florón. You may find these changes, that have been incorporated in the very first lines of the abstract.

“On April 23, 2023, a rotational landslide occurred at El Florón III (Portoviejo, Ecuador), triggered by intense rainfall that increased saturation and water pressure in the pores of the colluvial materials. Therefore, the current research predominantly aimed to: (i) characterize the geological, geophysical, and geotechnical conditions that controlled the instability, (ii) identify and validate the fault surface, and (iii) evaluate a stabilization alternative in accordance with the Ecuadorian Construction Standard (NEC-15).”

We also added at section 5.1: “It is fundamental to clarify that the 2023 landslide was not triggered by seismic activity, but rather by saturation induced by heavy rainfall. Seismic conditions are included solely to assess the potential reactivation of the slope under future dynamic loads, considering the regional tectonic framework and national regulatory requirements for slope stability assessment.”

Comment:

Response:

We clarified the main aims right in the very first sentence of the abstract.

We also rewrote and reedited the complete section of the conclusions based on your suggestion:

“Landslides in Ecuador occur more frequently during periods of intense rainfall associated with El Niño and La Niña events. Under these conditions, the soils on slopes remain saturated for extended periods, increasing their susceptibility to failure and making it more likely that an existing mass movement will increase in magnitude during a seismic event. In this context, the landslide that occurred on April 23, 2023, was directly related to an anomalous excess of accumulated rainfall during the first four months of the year, reaching some 303 mm in March of 2023.

Through geotechnical characterization of the area, the geology is composed of colluvial and alluvial deposits overlying highly weathered Miocene shales and siltstones. This lithological configuration favored the development of a semicircular or silty landslide, which subsequently evolved into mudflows, primarily affecting silty-clayey soils with soft, highly plastic clasts and inclusions of completely weathered schist. These materials correspond to a "C" type profile, characterized by low cohesion and high plasticity under saturated conditions, which contributes to their high propensity for landslides and evolution into mudflows.

Furthermore, by integrating geophysical methods such as ERT, seismic refraction, MASW, and VES, along with numerical back-analysis, which allowed for modeling the landslide mechanism according to the data obtained, the stability analysis revealed that the current slope exhibits critical instability, with safety factors of 1.05 under static conditions and 0.336 under pseudo-static conditions, being values significantly lower than the minimums required by Ecuadorian regulations. The proposed design, based on a system of micropiles combined with stepped terraces, demonstrated a significant improvement in slope stability, achieving safety factors of FS = 2.51 under static conditions and FS = 1.062 under pseudo-static conditions. These fully comply with the requirements established by NEC-15. This also completely verifies compliance with the minimum requirements established by the standard, corroborating the efficiency of the proposed design in improving slope stability.

Finally, it is proposed to complement the stabilization by installing a surface and subsurface drainage system adapted to the new slope conditions. This system is essential to ensure the efficient evacuation of rainwater and infiltration, preventing the accumulation of pore water pressure and the loss of shear strength. Additionally, the application of chemical stabilization techniques is recommended, using hydraulic binders such as lime, to improve the mechanical properties and durability of the highly plastic soils present in the area.”

Comment:

Estimating Reactivation Times and Velocities of Slow-Moving Landslides via PS-InSAR and Their Relationship with Precipitation in Central Italy (Remote Sensing, 2024)

Likewise, the interconnection between rainfall and landslide activities are studied using InSAR technique in the following study that can be reviewed:

InSAR stacking to detect active landslides and investigate their relation to rainfalls in the Northern Apennines of Italy (Geomorphology, 2024)

Response:

In a scientific world filled with so many adequate studys, it is impossible to track always the very best fits for comparative works. Therefore, we are extremely thankful for the hint to great works related to our current study. Both recommended studies have been incorporated as references 10 and 11.

Comment:

Response:

We appreciate your comment. In the revised version of the manuscript, the last paragraph of the introduction has been restructured to first present the main knowledge gaps identified in previous studies and then highlight the original contributions of this research using a bullet-point format for improved readability. This modification enhances coherence and alignment with editorial requirements. The changes have been clearly and visible incorporated in the introduction of the revised manuscript.

You may notice such change in the addition and change of the final part of the introduction where we state:

“Despite advances in understanding landslides triggered by rainfall and seismic activity in Ecuador, significant research gaps remain, particularly regarding the combined effect of intense rainfall and seismic accelerations on highly weathered colluvial deposits in urban areas of the coastal region. Although recent studies in Italy have demonstrated the effectiveness of using InSAR satellite techniques to monitor slow reactivations related to rainfall and seismic sequences, the sudden failure at El Florón, which caused immediate structural damage, required direct geophysical and geotechnical investigations to determine the rupture mechanism and define urgent stabilization measures [10,11].

Based on the context, the current study provides a detailed characterization of the landslide of the El Florón area through the integration of geophysical and geotechnical methods and a back-analysis based on actual fault conditions, constituting a technical reference applicable to similar scenarios in the Ecuadorian coastal region. Therefore, this work focuses on (i) identifying the lithological units of the subsoil in the affected area, (ii) analyzing the instability conditions through back-analysis with real failure parameters and, finally, (iii) evaluating stabilization alternatives in accordance with current regulations. The final product may consist of acquiring dynamic parameters of the rock and soil that are relevant to numerous geological scenarios for the study area and similar regions worldwide.”

Comment:

Response:

We appreciate your suggestion. In the revised version of the manuscript, Section 2 has been renamed to be “Materials” to better reflect the data and inputs used in this research. Additionally, the content has been reorganized into two subsections: “2.1 Study Area”, describing the geographical, climatic, and geological context of El Florón III; and “2.2 Datasets”, detailing the sources and characteristics of the rainfall, geophysical, geotechnical, and topographic information employed in the analysis. These adjustments improve readability and traceability of the data sets. The changes have been implemented within the revised text.

Comment:

Response:

Thanks for this hint. In the revised version, a specific analysis has been added regarding the rainfall peaks in 2012 and 2021, explaining their potential influence on slope instability in Portoviejo. This clarification strengthens the interpretation of Figure 3 and the correlation between extreme rainfall episodes and landslide occurrence in the area. The new text has been inserted in Section 2.2 Datasets, immediately before Figure 3.

Comment:

The study also lacks quantitative assessment. Some numerical results should also be included in the abstract.

Response:

Realized.

Comment:

Response:

We appreciate your observation. In the discussion section, we have included a clear analysis of the main uncertainties in the input data, geotechnical parameters, and models used. We also added the study’s limitations, especially those associated with the limit equilibrium method and the scope of the available geotechnical characterization. Additionally, we have included recommendations for future research, highlighting the utility of advanced triaxial tests, finite element modeling, and monitoring techniques such as PS-InSAR and the STPD approach from the suggested article. These additions strengthen the discussion in accordance with your recommendation.

We added:

“The analysis presents uncertainties associated with the natural variability of colluvial soils and highly weathered shales, whose geotechnical parameters were estimated through basic laboratory tests and back-analysis, resulting in approximate ranges. This type of spatial variability in cohesive materials has been widely documented as a critical factor in predicting slope stability. The geophysical techniques used also have limitations. Hereby, MASW profiles have limited depth, while ERT models demonstrate restrictions in the resolution of lithological contacts, which limits the precise definition of the subsurface. Furthermore, the analysis lacks to incorporate a coupled hydromechanical model, therefore the slope's response to rainfall events is interpreted using limited spatial and temporal resolution rainfall data.

The limit equilibrium method allows for a preliminary estimate of the stability state, but it does not reproduce internal deformations or the temporal evolution of the landslide under varying conditions. The lack of advanced geotechnical testing and in-situ instrumentation limits the accuracy of the parameters used and restricts the validation of the slope's actual behavior. Although more sophisticated monitoring techniques exist, such as PS-InSAR, capable of detecting millimeter-scale deformations and analyzing reactivation processes, as demonstrated in recent studies relating landslide dynamics to precipitation patterns [10,11], this study focused on a previously characterized landslide in the area using accessible and complementary methodologies for analysis.

It is recommended to incorporate advanced triaxial tests to obtain parameters suitable for Finite Element Method modeling, which would facilitate the evaluation of internal deformations, stress redistribution, and reactivation processes. The installation of piezometers and inclinometers, along with the use of satellite data, including PS-InSAR and approaches such as the sequential inflection point detection (STPD) method, would allow for the correlation of potential reactivations with precipitation patterns and significantly improve landslide monitoring, following approaches like those applied in European studies [10-12]. Additionally, further MASW and ERT campaigns could validate subsequent changes at the site.”

Comment:

Thank you and regards,

Response:

All corrected and improved

Round 2

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

Dear authors

Thank you for addressing my comments and improving your manuscript.

Please use proper math format for your equations like 4 and 5.

regards,

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript focused on identifying the lithological units of the subsurface using geophysical methods such as Electrical resistivity tomography, seismic refraction, multichannel analysis of surface wave (MASW), as well as vertical electrical sounding, and hereby characterizing strata with a high degree of weathering and structural discontinuities. My comments are as follows:

Results are presented for a few “pre/post” geometries with one groundwater assumption and one pseudo-static coefficient. There is no uncertainty or sensitivity analysis (e.g., envelopes of FS vs. c–φ ranges, groundwater level, seismic coefficient), despite the text itself acknowledging sensitivity to c and φ. The paper should quantify how FS varies across plausible parameter bands and failure surfaces.
The conclusions suggest the solution “meets NEC-15” and “optimizes” geometry, but supporting evidence is limited to two FS numbers and a qualitative description of terracing and six micropiles; there’s no check on serviceability (displacements), global vs. local mechanisms, or construction staging risks.
You state minimum FSs per NEC-15 (1.50 static, 1.05 pseudo-static) and later report FS=1.48 post-slide as “under normal conditions,” which does not meet the stated minimum; this needs explicit discussion (why it is acceptable, or how mitigation addresses it).
Several figures (e.g., stability diagrams) appear without clear units/scales, boundary conditions, groundwater line, and failure surface search parameters. The location map should include coordinates and projection.
The conclusion rules out seismic triggering and attributes the slide to rainfall, but please provide the quantitative rainfall exceedance and a timeline that ties rainfall peaks to observed deformations; right now it is descriptive rather than analytical.
The manuscript reads as a project report rather than a reproducible scientific paper. It needs substantial language editing and re-structuring.
A parameter table for each stratum (γ, c′, φ′, unit weights wet/dry, E, ν, permeability; drained/undrained assumptions), with ranges used in sensitivity and uncertainty.
Full seismic demand derivation (why 0.30g vs 0.354g), and both static and pseudo-static checks tied consistently to the Ecuadorian Construction 641 Standard (NEC-15).
Micropile design basis (geotechnical vs structural, soil–pile interface parameters, group effects, capacity verification) with correct material properties.
A sensitivity/uncertainty section (tornado plots or probabilistic FS distributions).
The slope stability work hinges on a retro-analysis to force FS≈1 and then a few forward runs, but the paper does not disclose the full input set required to reproduce the results (complete stratigraphy per layer, strength/stiffness ranges, groundwater assumptions/time history, pore pressures, search settings, mesh/discretization choices, etc.). The text merely notes use of GeoStudio (R2, FEM module) and a Morgenstern–Price back-analysis to FS=1, without sufficient parameterization detail to check identifiability of the back-calculated strengths.

17 The paper states the pseudo-static coefficient per NEC-15 is 0.30g (85% of PGA 0.5g) and that this value was used in the numerical model; later, the “proposed solution” and stability checks are reported for 0.354g instead. The manuscript must reconcile which value was actually used and why.

18. Micropiles are given “unit weight 21.57 kN/m³, cohesion 2.94 kPa, φ = 45°,” leading to a shear capacity of 407 kN; however, those values look like soil parameters, not reinforced concrete / pile–soil interface parameters. The manuscript should clarify whether these are soil interface strengths, structural capacities from a separate design model, or placeholders—right now this undermines the credibility of the stabilization result.

Author Response

Response Letter to the expert reviewer

Dear expert reviewer,

Comments and responses:

Results are presented for a few “pre/post” geometries with one groundwater assumption and one pseudo-static coefficient. There is no uncertainty or sensitivity analysis (e.g., envelopes of FS vs. c–φ ranges, groundwater level, seismic coefficient), despite the text itself acknowledging sensitivity to c and φ. The paper should quantify how FS varies across plausible parameter bands and failure surfaces.

In this study, no uncertainty or sensitivity analyzes were performed. The text provides now a detailed account of your demand.

The conclusions suggest the solution “meets NEC-15” and “optimizes” geometry, but supporting evidence is limited to two FS numbers and a qualitative description of terracing and six micropiles; there’s no check on serviceability (displacements), global vs. local mechanisms, or construction staging risks.

The article was based on a retrospective analysis to develop a stabilization proposal. No serviceability assessments or global failure mechanisms were performed. This has been detailed in lines 729 - 736.

You state minimum FSs per NEC-15 (1.50 static, 1.05 pseudo-static) and later report FS=1.48 post-slide as “under normal conditions,” which does not meet the stated minimum; this needs explicit discussion (why it is acceptable, or how mitigation addresses it).

Thanks for this comment and observation. In this case, the FS at the time of the post-slide yielded a static value of 1.054. Therefore, given the minimum requirements established by the NEC, this event required a geotechnical solution. This has been now detailed in lines 623 – 626.

Several figures (e.g., stability diagrams) appear without clear units/scales, boundary conditions, groundwater line, and failure surface search parameters. The location map should include coordinates and projection.

Indeed, our mistake. Figures 7, 8, and 9 are now corrected.

The conclusion rules out seismic triggering and attributes the slide to rainfall, but please provide the quantitative rainfall exceedance and a timeline that ties rainfall peaks to observed deformations; right now it is descriptive rather than analytical.

Thank you, this has been now detailed in lines 716 – 719.

The manuscript reads as a project report rather than a reproducible scientific paper. It needs substantial language editing and re-structuring.

The article has been restructured as instructed by you.

A parameter table for each stratum (γ, c′, φ′, unit weights wet/dry, E, ν, permeability; drained/undrained assumptions), with ranges used in sensitivity and uncertainty.

In this study, only direct shear tests were performed. The text has been accordingly corrected.

Full seismic demand derivation (why 0.30g vs 0.354g), and both static and pseudo-static checks tied consistently to the Ecuadorian Construction 641 Standard (NEC-15).

Correct. This has been now detailed in lines 606 – 613.

Micropile design basis (geotechnical vs structural, soil–pile interface parameters, group effects, capacity verification) with correct material properties.

This has been now detailed in lines 685 – 696 of our manuscript.

A sensitivity/uncertainty section (tornado plots or probabilistic FS distributions).

No sensitivity analyzes were performed. This has been detailed in lines 708–718.

The slope stability work hinges on a retro-analysis to force FS≈1 and then a few forward runs, but the paper does not disclose the full input set required to reproduce the results (complete stratigraphy per layer, strength/stiffness ranges, groundwater assumptions/time history, pore pressures, search settings, mesh/discretization choices, etc.). The text merely notes use of GeoStudio (R2, FEM module) and a Morgenstern–Price back-analysis to FS=1, without sufficient parameterization detail to check identifiability of the back-calculated strengths. 619-622 y 666-669

Yes, indeed. This has been detailed between the lines 619 – 622 and 666 – 669.

The paper states the pseudo-static coefficient per NEC-15 is 0.30g (85% of PGA 0.5g) and that this value was used in the numerical model; later, the “proposed solution” and stability checks are reported for 0.354g instead. The manuscript must reconcile which value was actually used and why.

Responded accordingly and detailed in lines 606 – 613.

Micropiles are given “unit weight 21.57 kN/m³, cohesion 2.94 kPa, φ = 45°,” leading to a shear capacity of 407 kN; however, those values look like soil parameters, not reinforced concrete / pile–soil interface parameters. The manuscript should clarify whether these are soil interface strengths, structural capacities from a separate design model, or placeholders—right now this undermines the credibility of the stabilization result.

Yes, this has been responded in lines 685 – 696.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have presented an interesting and well-organized article with appropriate and thorough considerations.
There are no specific notes to suggest, so it is acceptable for publication in its current form.

Author Response

Response Letter to the expert reviewer

Dear expert reviewer, we are extremely thankful with your comment and appreciation, many regards on behalf of all authors

Reviewer 3 Report

Comments and Suggestions for Authors

I find the work of Melany Melgar et al. very interesting. The paper provides a detailed description of the influence of earthquakes and rainfall on landslide triggering in a coastal area of Ecuador. Field surveys and geophysical investigations were conducted to develop a hazard reduction model. Overall, I believe that the authors have achieved their objectives. Only minor changes or corrections are required, as can be seen in the attached text. et al. very interesting. The paper provides a detailed description of the influence of earthquakes and rainfall on landslide triggering in a coastal area of Ecuador. Field surveys and geophysical investigations were conducted to develop a hazard reduction model. Overall, I believe that the authors have achieved their objectives. Only minor changes or corrections are required, as can be seen in the text.

Comments for author File: Comments.pdf

Author Response

Response Letter to the expert reviewer

Dear expert reviewer,

Comments and responses:

PDF apart

The revisions by the Expert Reviewer have been addressed and indicated in the text via corresponding comments.

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Authors,

The authors of the manuscript raised an important topic in “Rain and seismic triggered mass movements in coastal Ecuador 2 - a case study of the “El Florón” landslide in Portov”. However, I have a fiew comments regarding this manuscript which are detailed below.

- This manuscript has presented results that are not something totally new and the Authors should review other papers that already raised the same topic. I mean that the outcomes of this study have been already proven in other regions and it should be somehow discussed here in order to show the novelty of this study. How about the novelty of your study? Could you please explain them here? Also, may I ask authors to list the main aims of the present study in the last paragraph of introduction. as now, it is clear for readers (Justify the choice of models and Geophysical methods used).

- It does not come clear, why description of this research is needed for reader? Please, highlight the justification of your study. Why it is important? Is it so, that no-one has done this type of study before? You mention more about 'what is already known', but you should write in the introduction 'what is not yet known' and that way justify the aim of your paper.

- My main concern is about the methodology and discussion; I believe that the authors perfectly explain the discussion of the results in terms of generating diagnostic information to fulfill the objective of the work. On the other hand, I would consider that the presentation of the results made in a beneficial way to the reader. For example, this manuscript has presented the results on prepared maps of which is not something totally new and authors should review/compare other papers (specially the newest ones) that already raised the points proved also here. I mean that the outcomes of this study have been already proven in other regions and it should be somehow discussed here in order to show the novelty of this study.

Further, due to the current quality of the paper, I recommend rejection.

Author Response

Response Letter to the expert reviewer

Dear expert reviewer,

Comments and responses:

Dear Authors,

Further, due to the current quality of the paper, I recommend rejection.

We appreciate the expert reviewer’s valuable comments. We have strengthened the scientific justification of the study in the introduction, highlighting the local and regional relevance of the “El Florón” case, which constitutes a representative event within an area with a high recurrence of rainfall- and earthquake-induced landslides.

Additionally, recent references from 2021–2024 on analogous studies in Latin America—such as those in Colombia, Peru, and Chile—were incorporated to contextualize the background and demonstrate the originality of the methodological application in Ecuador.

In this way, the new wording emphasizes “what is still unknown” about landslides in highly plastic clayey materials under combined saturation and seismic acceleration conditions.

In the Introduction section, a critical comparison has been incorporated with similar studies conducted in other regions (e.g., Pedernales – Manabí 2016, Chunchi – Chimborazo 2021, Alausí–Chimborazo 2023, and cases documented by Lacroix et al., 2020; Persichillo et al., 2018; Pollock & Wartman, 2020).

This comparison highlights the novelty of the present work in integrating probabilistic and deterministic analyzes applied to a coastal urban context with highly plastic soils, as well as in validating engineering measures adapted to the Ecuadorian construction reality—something rarely addressed in studies of the coastal region.

Based on the aforementioned, we are strongly convinced that the extended explanations and addings given within the manuscript of all of his/her doubts will convince the expert reviewer to reconsider his/her rejection into acceptance, as the given improvements are allowing a much better read and view of our detailed case study.

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Rain- and Seismic-Triggered Mass Movements in Coastal Ecuador—A Case Study of the “El Florón” Landslide in Portoviejo

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