the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Sep 2025
Coupled simulation of landslide, tsunami, and ground deformation for the 2017 Nuugaatsiaq event in Greenland
Abstract. We investigated the entire sequence of the tsunami event led by a massive landslide on June 17, 2017, in Karrat Fjord, near Nuugaatsiaq village, western Greenland to understand the causality of this cascade mechanism. The seismological analysis from seven stations across Greenland allows to estimate the landslide volume. Then, we conducted sequential simulations, consisting of (1) the landslide’s descent into the fjord based on topography, (2) tsunami generation and large-scale propagation, and (3) ground deformation caused by tsunami-induced sea level changes, considering both static and elasto-dynamic solutions. A 1 m-height of sea level change may lead to a ground deformation up to 0.1–1.0 mm along the coastline, and this can be detected by a seismogram. This event provided a rare chance to validate our integrated model using local seismic records alone in the case of no coastal measurement. While the timing of simulated processes matches observations well, uncertainties in landslide volume remain a key factor influencing tsunami amplitude and coastal impact. The detailed seismic signals captured both near and far from the source shed light on the multi-stage dynamics of such cascading events and offer valuable input for improving hazard assessment in fjord-like environments, and suggests that alert systems based on seismic data are feasible, allowing to reduce tsunami risks in fjords in polar regions.
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Status: open (until 14 Nov 2025)
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RC1: 'Comment on egusphere-2025-3803', Alexandre Paris, 09 Oct 2025
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AC1: 'Reply on RC1', Hideo Aochi, 27 Oct 2025
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Thank you very much for the careful review. We agree with your comment. Our reply to the main points is in the following.
- [novelty] We clarify our novelty in abstract. “The detailed seismic signals captured both near and far from the source shed light on the multi-stage dynamics of such cascading events. Such analysis will be performed systematically in real time to monitor the landside occurrence, giving an early estimation of potential tsunami and could be used in an early warning system. “
- [structure – methods ] We agree to modify the paper structure to separate the methods part and the result for a better readiness. The methods part consists of seismological inversion process, landslide-tsunami generation and propagation, and ground deformation.
The following is our reply to each comment. (The reviewer’s comment is in italic.)
Line 17: I'm not sure what you mean by 'understand the causality of this cascade mechanism', because it seems pretty clear what happened.
We change to “understand the sequential result of this cascade event. “
Line 38: close parenthesisWe correct.
Line 43: 'melting' -> thawing?We correct.
Line 44: 'huge' is not very scientific, huge compared to what?The ambiguous word is removed.
Line 45: what is your definition of megatsunami? does it really apply here? / Svennevig et al. are not the first to report this event, but I guess you put this reference because they summarized the previous ones?It was too much exaggerated. We remove the word of “mega”. Svennevig et al (2020) is not the first one, but a synthetic paper on this event. Other references will be added.
Line 55: tsunamigenicWe correct.
Line 61: do you mean in fjords in general?We mean general coastal region, including fjords. We change the expression to “along coastal area including fjords".
Line 65: remove the –Removed.
Line 68: you also modelled the landslide. More details about VolcFlow would be welcome. / modelling or modeling, the classic en-US/en-GB, be consistent in the whole paperWe will add more detail for VolcFlow. We write uniformly in British English.
Lines 75-76: you already said that in the introduction. I would remove this and add the references to Svennevig in the intro.We correct.
Line 84: KarratWe correct.
Lines 99-100: 'This is the main response of tsunamis', do you mean in general? Or this one specifically ?It is specifically on this waveform. We change the expression to “, which is the main response of this tsunami”.
Lines 98-101: instead of 'top', 'second' and 'bottom' panel, I would use the letters that you have on the figure.We change (b), (c) and (d).
Figure 1: maybe put the star in colour ? it's not easy to see in black like thisWe change the colour.
Lines 131-142: I have to admit I'm not qualified to review this paragraph. Just put a point at this end on line 142.We added a period (.) at the end of the paragraph.
Lines 170-172: could you add some examples of tsunami studies using FUNWAVE? I have Abadie et al. (2020) on La Palma in mind for exampleThe description of FUNWAVE is to be modified with some more references.
Lines 176-177: I would specify that you are using the Boussinesq model for the dispersion / Why start at 120 seconds? The landslide is faster than that, so the wave is already formed, what motivated the choice of this value?The simulation of VolcFlow results indicate that the avalanche ceased at about 120 s. To ensure the landslide-generated waves were fully developed, we extended the simulation to 120 s. Nearshore landslide tsunamis have wavelengths not much larger than the water depth (e.g., about ten times), so frequency dispersion and nonhydrostatic effects can be important. Boussinesq models provide more accurate wave speeds, evolution, run-up, and arrival times than the shallow water equations.
Line 182: where did you find the value of 49.7 Mm3?We precise that we re-estimated the volume of 49.7 Mm3 directly based on the bathymetry data used in Paris et al. (2020).
Lines 184-185: what do you mean by ‘our estimation varied by a factor of 2’?Our estimation varied up to twice 44.7 x 10^6 m^3.
Lines 131-137, 162-185 and 204-216: we are in a results section but for me, these lines describe the methods, not results, so they should be part of a methods sectionWe reconstruct the sections separating Method and Results.
Line 187: please explain what you mean by ‘coherent tsunami wavefront’We change the sentences to “We observe that the first tsunami wave front arrives in front of NUUG station at about 500 seconds, and the long-period harmonic wave oscillates until 1000 seconds. Then, the tsunami wavefield becomes dissipated. “
Line 189: like you said in the conclusion, this is due to the reflections in the fjord.We specify “due to the multiple reflections”.
Figure 4: please add axis units. Legend: kilometres is en-GBWe change to “kilometres”.
Line 209: close the parenthesisWe correct.
Line 213: ‘typical value for crustal bedrock’, give examples/referencesWe add the reference of the standard crust model CRUST1, accessible from https://igppweb.ucsd.edu/~gabi/crust1.html.
Laske, G., Masters., G., Ma, Z. and Pasyanos, M., Update on CRUST1.0 - A 1-degree Global Model of Earth's Crust, Geophys. Res. Abstracts, 15, Abstract EGU2013-2658, 2013.
Line 222: ‘These effects… are consistent with the observation’, I’m not sure to understand, what is consistent, the shape of the signal? the small amplitude (even with a factor 10)?We will clarify the expression.
“The first movement appears about 30 seconds after the landslide enters the sea. The body waves travel a distance of 30 km between the landslide site and NUUG station in about 5-10 seconds, so that the impact of this landslide process on the ground motions fades quickly within a minute, which is recognized in the observation (Fig. 6b). “
Lines 231-232: it does not seem like a new learning, we used this in Paris et al. (2019) based on the work of Okal, EA (2007). If I missed something, please explain it to meWe “demonstrate” instead of “learn”.
Line 233: seawaterWe correct.
Figure 7: too many pixels on this figure. Legend: remove respectively and use ‘left panel’ and ‘right panel’The computation was done on a grid of each 5 km, i.e. at the pixel centre. In order to show correctly the spatial variation, we plot directly the value with big pixel, instead of smoothing it.
Table 1: a small detail, here you write A.P. and in the text AP; did I miss the explanation for ‘smooth3’ and ‘smooth5’? / ‘It is worth noting… landslide volume’: I would remove this sentence from the legend and put it somewhere in the textSmooth3 and smooth5 are the averaged models over 3x3 and 5x5 grids, respectively. We clarify this in Table 1 caption.
Section 4.2: I don’t know what to think about this paragraph. It looks more like a review than a comparison with what you did. Either include more comparison with your work, or maybe move this paragraph in a restructured introductionWe summarize the available observations in Table 2 to compare. We will keep in Discussion.
Lines 299-300: I’m not a seismologist so my question is, how do you know that the signal is a landslide that collapsed? The signal of the 2017 event was first treated as a M4.2 earthquake, so no tsunami alert would be triggered for this magnitude. Would you identify areas of risks and lower the magnitude of alert in these areas? I’m curious about your thoughts on that.Thank you for this question. The source mechanism is different (moment tensor and single force) to identify the landslide and earthquakes, even if the initial estimation of magnitude is moderate. This is technically feasible , but not implemented systematically on any system nowadays.
Line 311: with the sentence construction we can think the ground deformation affected the villageWe correct. We do not need to cite here the village of Nuugaatsiaq.
Line 362: MadariagaWe correct.
We hope that our possible revision will make the paper clearer. Thank you again for your review.
Citation: https://doi.org/10.5194/egusphere-2025-3803-AC1
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AC1: 'Reply on RC1', Hideo Aochi, 27 Oct 2025
reply
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RC2: 'Comment on egusphere-2025-3803', Steven Gibbons, 23 Oct 2025
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Coupled simulation of landslide, tsunami, and ground deformation for the 2017 Nuugaatsiaq event in Greenland (Aochi et al.)
Reviewer: Steven J Gibbons
This paper describes an end-to-end numerical simulation of the 2017 Karrat Fjord, Greenland, event from rockslide, to tsunami, and to ground disturbance, validating the modelled ground motion against the seismic signal from a station operating about 30 km from the site of the rockfall. I have to state at the outside that I am not an expert on the Ground Motion Simulation aspect of this work, but the methodology surrounding the remaining parts of the paper appears sound and the modelled Ground Motion is to my eyes consistent with that recorded. I am confused about the purpose and motivation behind this paper as the event has already been studied extensively with Paris et al. (2019) performing both a landslide and tsunami simulation and demonstrating simply through side-by-side comparison of simulated water wave and seismograph that the tsunami is the cause of the ripples observed on the seismic station. In the abstract I read “… to understand the causality of this cascade mechanism” which to my understanding has already been resolved adequately. Aspects such as the relationship between landslide volume and wave height and the stability of the shape of the waveform under different release hypotheses are demonstrated here but, again, to my understanding were already adequately addressed by Paris et al. (2019).
I think a reframing of the work is necessary to make it clear what new is being demonstrated here. To my mind, the clearest aspect would be the workflow itself, predicting the size and form of a seismic signal that would be generated by a given slide scenario in order to assist in the post-event detective work for future scenarios where the origin of the wave itself may be less clear, but where there is sufficient seismic monitoring to allow a quantitative analysis. (i.e. to find the landslide parameters and tsunami wave heights that best fit available seismic data.) Is my thinking here correct? The ground deformation itself is not to me particularly significant (from a human or hazard point of view) – at 0.1 – 1.0 mm is only detectable by a seismometer and would be the least hazardous aspect of the event from the point of view of a person in the vicinity. If I have misunderstood the significance, please spell it out! I am not sure that it will be understood by the general readership if you don’t. I find that the abstract does not frame the purpose of the paper very well and I feel that a careful rewrite of this single paragraph would make entry into the paper far easier. (The sentence “A 1 m-height of sea level change may lead to a ground deformation up to 0.1 – 1.0 mm along the coastline, and this can be detected by a seismogram.” baffles me. Is the fact that 1m of water height can generate this ground deformation a result of the paper, or just something we ought to know? Seismologists know that the instruments can record such deformation.)
If I have missed significant finds about the event that are not covered in previous studies, please correct me and spell it out! (In line 67, we read “we first analyse the seismic data at NUUG and argue that a signal due to the tsunami can be identified.” – statements like this need to be addressed as this really has already been demonstrated.) I do not want to be too negative. I think that such a workflow – that models a process from collapse to seismic ground motion - is currently lacking. But I find the technical details describing the implementation too sparse for the readership to use this study as a guide to reproducing the workflow for this or other scenarios.
Line 45: I think the term “megatsunami” is unfortunate (but I know it has been used in earlier studies). I think it sensationalizes the event without having a formal scientific definition. (Wikipedia states “The term ‘megatsunami’ has been defined by media and has no precise definition, although it is commonly taken to refer to tsunamis over 100 metres (330 ft) high. We read – line 83, 84 – that “up to 90m” is appropriate for this event.) If must write “megatsunami” here, I would like it to be followed here by “, defined here as ….”. It would be nice to reach a consensus about what the word means so that in future it may provide a useful comparative term.
Figure 1: I would appreciate the starting time of the traces displayed ( 2025-06-17Z23:39? ) and the channel displayed. (I am assuming that this is a vertical component seismograph – is it BHZ, HHZ?). I think this is quite important for reproducibility. (The common convention for channel labelling is network.station.location.channel, e.g. DK.NUUG.--.HHZ )
Figure 2: There are two references contained in this Figure that do not appear in the reference list. (Yamada et al., 2013; Shi et al., 2012). There is no reference for the final box, «Boussinesq solution”). Boussinesq solution here refers to Ground Motion and not tsunami propagation?
Section 3:
In the inversion from the seismic data, have you accounted for the azimuthal orientation of the horizontal components?
You see for example on
https://ds.iris.edu/mda/DK/NUUG/--/BHE/?starttime=2010-07-20&endtime=2015-06-29
that the E-W component of station DK.NUUG is actually aligned at 169 degrees azimuth – i.e. almost North-South! (This is mentioned also in Figure 7 of Paris et al., 2019.)
This is unfortunate and a bane for seismologists but it has to be corrected for.(And it is easily corrected for using seismological software, e.g. obspy)
When I look at Figure 3, I think that the EW synthetic looks more like the NS observed and vice versa. But you would have to do the check to make sure that this is for real.
It could explain why your vertical component matches and your horizontal components don’t.Please check also the orientation on the components on which you did the inversion!
I have just spot-checked DK.KULLO
https://ds.iris.edu/mda/DK/KULLO/--/BHE/?starttime=2009-07-18&endtime=2599-12-31and I see that here the E-W component is apparently exactly at 90.0 degrees – whether that is true or not I’m not sure, but I think this information is the best we can get. If the same applies to all the stations in Figure S1 then you’re good to go (maybe state this explicitly in the paper that this has been checked).
Another approach to the inversion for the distal stations in Figure 3 would be a jack-knife procedure. Do the inversion with all the sets of 5 stations (with one left out) and use the results to calculate the ground motion for the 6th. This should give you confidence.
(I am quite overwhelmed by the good match of these stations displayed in Figure S1. I have never attempted a calculation of this kind myself so I do not know if you should expect this degree of matching. But, if so, it is very impressive.)
Section 3.2: Line 162. I note a lateral resolution of 100 meters for both landslide and tsunami. What is the lateral scale of the landslide? (i.e. how many pixels are resolving this sliding volume?) Have convergence checks been made in the landslide simulation? (i.e. if you double your resolution, is your solution essentially unchanged?) What is the spatial resolution of the GEBCO topobathymetry? I think it is coarser than 100m (?) – so I am assuming that a remeshing/interpolation has been done. This should be explicitly stated together with the method or software used.
In line 177, why and how is the FUNWAVE simulation only started at 120 seconds? Why not at zero seconds, or at least from the moment that the landslide touches the water? I sort of see in lines 185-186 that one tsunami model is switched to another at this time – but how? How is the matching performed? Is there some kind of discontinuity? I am assuming that this is difficult to implement (I wouldn’t know how to do this and I think it would be helpful to the readership to have this spelled out.) In a perfect world, scripts and input files and notes for the simulations themselves would be put on a repo.
Line 211: What does “The seismic waves usually propagate with a speed of a few kilometers per second, followed by static deformation.” mean? There is no permanent deformation to the best of my knowledge outside of the immediate source region. Or is there?
Figure 6: (lowpass filter for 0.001 Hz) means frequencies below 0.001 Hz – not above as indicated in the label for panel (b) To me, the likeness between (a) and (b) is good – the uncertainties influencing the tsunami height from the slide model are large (frontal area, entrainment … ) In panel (c), I see significant motion right at the start (t=0). What is this?
Are the simulations only performed for this time-window or is this the only time-window displayed in order to correspond with the seismic data displayed? I see time-series that are very much non-resolved. i.e. I would like to see it start from zero and end with zero. If there is no reason to show this, that is fine, but the numerical modeller in me wants to know what happens next. Is it resolved in a sensible way?
The waveforms in panels (c) and (d) seem exactly out of phase.
Figure 7: Please upload the figure to
https://www.color-blindness.com/coblis-color-blindness-simulator/
and see how it appears to people with different forms of colour-blindness! (I have done it.)
There are two things you can do: (1) change the colour palette to e.g. viridis or heat, and (2) change the scale to maximize the range (e.g. there is no value close to 1 cm)Table 1: I do not understand why the times are so different when the waveforms are so similar.
I think the “Data availability” section needs to be expanded greatly to cover also the software used for the different parts of the workflow.
volcflow, funwave etc.Are the codes fully open or, e.g. only available on request.
It would be a positive precedent to provide input files and running scripts for the simulations themselves for the sake of reproducibility. There is an increasing awareness of the need to make numerical simulations available, with examples such as the CINECA Simulation Data Lake:
https://sdl.hpc.cineca.it/app/home
but there are other possibilities such as https://zenodo.org/ and https://figshare.com/
Finally, there are many small grammatical and formulation issues. But I will not focus on them as I think there are more pressing issues that need resolving before these need addressing.
I hope that another reviewer is able to assess the Ground Motion Modelling aspect of this work as this falls outside of my expertise.
Citation: https://doi.org/10.5194/egusphere-2025-3803-RC2
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- 1
In this new study of the 2017 Karrat Fjord events, the authors modelled the landslide, the tsunami generated by this landslide and the ground deformation generated by the tsunami. Using the seismic signal of the landslide, they extracted a volume similar to previous studies. The tsunami propagation gives also similar results, and the wave amplitude depends on the landslide volume. Finally, they used two methods to simulate the ground deformation due to the tsunami. Both methods give similar results, matching in time with the observation but with smaller amplitudes.
The manuscript is globally well written, the figures are interesting, clear and support the text. However, it's a bit confusing, chaotic. Tell me if I'm wrong but the novelty of the study is the modelling of the ground deformation that could give an early estimation of the potential tsunami and could be used in an early warning system. So I think you could restructure the paper to highlight this, which is the main result. Also, in the 'results' section you present a lot of methods.
Here are some specific comments:
Line 17: I'm not sure what you mean by 'understand the causality of this cascade mechanism', because it seems pretty clear what happened.
Line 38: close parenthesis
Line 43: 'melting' -> thawing?
Line 44: 'huge' is not very scientific, huge compared to what?
Line 45: what is your definition of megatsunami? does it really apply here? / Svennevig et al. are not the first to report this event, but I guess you put this reference because they summarized the previous ones?
Line 55: tsunamigenic
Line 61: do you mean in fjords in general?
Line 65: remove the -
Line 68: you also modelled the landslide. More details about VolcFlow would be welcome. / modelling or modeling, the classic en-US/en-GB, be consistent in the whole paper
Lines 75-76: you already said that in the introduction. I would remove this and add the references to Svennevig in the intro.
Line 84: Karrat
Lines 99-100: 'This is the main response of tsunamis', do you mean in general? Or this one specifically ?
Lines 98-101: instead of 'top', 'second' and 'bottom' panel, I would use the letters that you have on the figure.
Figure 1: maybe put the star in colour ? it's not easy to see in black like this
Lines 131-142: I have to admit I'm not qualified to review this paragraph. Just put a point at this end on line 142.
Lines 170-172: could you add some examples of tsunami studies using FUNWAVE? I have Abadie et al. (2020) on La Palma in mind for example
Lines 176-177: I would specify that you are using the Boussinesq model for the dispersion / Why start at 120 seconds? The landslide is faster than that, so the wave is already formed, what motivated the choice of this value?
Line 182: where did you find the value of 49.7 Mm3?
Lines 184-185: what do you mean by ‘our estimation varied by a factor of 2’?
Lines 131-137, 162-185 and 204-216: we are in a results section but for me, these lines describe the methods, not results, so they should be part of a methods section
Line 187: please explain what you mean by ‘coherent tsunami wavefront’
Line 189: like you said in the conclusion, this is due to the reflections in the fjord.
Figure 4: please add axis units. Legend: kilometres is en-GB
Line 209: close the parenthesis
Line 213: ‘typical value for crustal bedrock’, give examples/references
Line 222: ‘These effects… are consistent with the observation’, I’m not sure to understand, what is consistent, the shape of the signal? the small amplitude (even with a factor 10)?
Lines 231-232: it does not seem like a new learning, we used this in Paris et al. (2019) based on the work of Okal, EA (2007). If I missed something, please explain it to me
Line 233: seawater
Figure 7: too many pixels on this figure. Legend: remove respectively and use ‘left panel’ and ‘right panel’
Table 1: a small detail, here you write A.P. and in the text AP; did I miss the explanation for ‘smooth3’ and ‘smooth5’? / ‘It is worth noting… landslide volume’: I would remove this sentence from the legend and put it somewhere in the text
Section 4.2: I don’t know what to think about this paragraph. It looks more like a review than a comparison with what you did. Either include more comparison with your work, or maybe move this paragraph in a restructured introduction
Lines 299-300: I’m not a seismologist so my question is, how do you know that the signal is a landslide that collapsed? The signal of the 2017 event was first treated as a M4.2 earthquake, so no tsunami alert would be triggered for this magnitude. Would you identify areas of risks and lower the magnitude of alert in these areas? I’m curious about your thoughts on that.
Line 311: with the sentence construction we can think the ground deformation affected the village
Line 362: Madariaga