Towards a standard typology of endogenous landslide seismic sources

Provost, Floriane; Malet, Jean-Philippe; Hibert, Clément; Helmstetter, Agnès; Radiguet, Mathilde; Amitrano, David; Langet, Nadège; Larose, Eric; Abancó, Clàudia; Hürlimann, Marcel; Lebourg, Thomas; Levy, Clara; Le Roy, Gaëlle; Ulrich, Patrice; Vidal, Maurin; Vial, Benjamin

doi:https://doi.org/10.5194/esurf-6-1059-2018

Articles | Volume 6, issue 4

https://doi.org/10.5194/esurf-6-1059-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

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From process to signal – advancing environmental...

https://doi.org/10.5194/esurf-6-1059-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 6, issue 4

Research article

|

16 Nov 2018

Research article |

| 16 Nov 2018

Towards a standard typology of endogenous landslide seismic sources

Floriane Provost, Jean-Philippe Malet, Clément Hibert, Agnès Helmstetter, Mathilde Radiguet, David Amitrano, Nadège Langet, Eric Larose, Clàudia Abancó, Marcel Hürlimann, Thomas Lebourg, Clara Levy, Gaëlle Le Roy, Patrice Ulrich, Maurin Vidal, and Benjamin Vial

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Final revised paper (published on 16 Nov 2018)
Preprint (discussion started on 21 Mar 2018)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of esurf-2018-23', Velio Coviello, 06 Apr 2018
RC2: 'Review of the MS "Towards a standard typology of endogenous landslide seismic sources" by F. Provost et al.', Anonymous Referee #2, 29 Apr 2018
AC1: 'Author response', Floriane Provost, 14 Jun 2018

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Floriane Provost on behalf of the Authors (06 Jul 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (12 Jul 2018) by Jens Turowski

RR by Velio Coviello (02 Aug 2018)

Suggestions for revision or reasons for rejection

I have read the point-to-point reply prepared by Provost and colleagues. I think the authors have done a good job of responding to the review comments. I appreciated their thorough justifications and the changes they made to the paper. There are no new major comments to the manuscript from my part. As such, I recommend the paper for publication after minor revisions. Please find here following my main comments to the revised manuscript. My final recommendations are not compulsory, authors (and the editor) will decide if accepting them or not, let me know what do you think.

1) The authors strongly support the use of the spectral information for the classification of landslide-induced signals detected at a distance < 1 km. In particular, they argue that “the source mechanism is a predominant factor controlling signal spectral content although the sensor to source distance plays a role in the contribution of certain frequencies to the signals amplitude”. This is probably ok but, in my opinion, the possible limitations of this approach deserve to be mentioned, especially if the ambition of the paper is to propose a general classification. We know that source proprieties have a strong control on the signal characteristics, this is self-evident. We also know that propagation through the geological media acts as a low-pass filter. However, not only the source-sensor distance but also attenuation and resonance effects can play an important role in shaping the spectral response. Imagine a number of sensors installed at the same distance from the source but in different conditions. The installation methods (directly in the ground, on a boulder, in a case placed on compacted deposits, etc.) and the geological context (sensor installed on bedrock, on fine deposits, on the landslide body, etc.) have a strong effect on both amplitude and frequency domains, in particular in case of low-cost and temporary monitoring networks. I think this can have an impact not only in terms of location error but also on the source characterization. In my previous review I reported some examples of these local effects, but there are many others published.
2) In their response about type of sensors, network geometry, and local effects, the authors summarize their thoughts with this statement: “Regarding the geological and geomorphological contexts, our assumption is that if we can observe similar signal features in different sites they can only be explained by the similarity of seismic sources”. Similarity is a classical and elegant attribute employed in many classifications of natural phenomena. Keep focusing on landslides, similarity is the baseline of the most adopted classification scheme proposed by Cruden and Varnes (1996), i.e. “similar landslides in similar materials are caused by similar processes under similar conditions”. However, I think that such a simple criterion could be in some cases misleading when the classification is only based on indirect measurements of the object of study, i.e. the inversion of landslide-induced seismic signals.

Minor corrections: the reference list still needs a careful review, still there are some contradictions on the number of test sites (13 or 14?), Table 1 still needs some correction (please refers to previous review round comments), the unit of measurement is missing in all seismographs, the bar scale is missing in all spectrograms.

Cruden DM, Varnes DJ (1996) Landslide types and processes. In: Turner AK, Schuster RL (eds) Landslides investigation and mitigation. Transportation research board, US National Research Council. Special Report 247, Washington, DC, Chapter 3, pp. 36–75.

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RR by Wei-An Chao (18 Aug 2018)

Suggestions for revision or reasons for rejection

The manuscript presents a standard typology of seismic sources including slopequake, rockfall, and granular flow based on the features of seismic signal and characteristics of its frequency content, leading a possibility of the forecast of initiation of landslide rupture. The revised version of the manuscript significantly improved in overall quality and I think that the subject is relevant to publication in Earth Surface Dynamics. However, there are several places where I think a bit more explanation and minor-to-moderate revision are needed. Detailed comments are listed below.

Abstract
(1) P1., Lines 6-8 “…We investigate the 1-100 Hz frequency band…”:
The signal features (e.g., duration, the dissymmetry coefficient, the number of peaks of the envelop function) used in the typology analysis highly depended the filtered seismic signals. How changes in the pattern of the proposed classification shown in Fig. 11 if the authors use a bandpass filtering with different frequency range, for example of 1-50 Hz. I also found the claim of the authors “The signal features are always computed on the trace with the maximal amplitude band-passed in the range [fc-50] Hz” (P12., Lines 4-5). Is there a mismatching compared to the 1-100 Hz stated in the abstract? The frequency content of a few source events can be higher than 50 Hz, such as resulting shown in Fig. 2(a), Fig. 3(c,e), Fig. 5(a,b), Fig. 7(e). If the authors applied a band-pass filtering of fc-50 Hz, it would be an unfair comparison in the classification scheme using signals recorded at different sites from variable sources. The author need to clarify above discrepancy.

1. Introduction
(2) P3., Line 2 “Schöpa et al., 2017”:
Please replace the reference of Schöpa et al. (2017) by “Schöpa et al. (2018) Dynamics of the Askja Caldera July 2014 landslide from seismic signal analysis: precursor, motion and aftermath, Earth Surf. Dyn., 6, 467–485, https://doi.org/10.5194/esurf-6-467-2018” in the manuscript.

3.3 MS processing chains
(3) P9., Lines 9-10 “…For this kind of signal, location methods based on the inter-trace correlation of the surface waves (Lacroix and Helmstetter, 2011)…”
A location scheme based on the cross-correlograms of inter-stations was proposed by Chen et al. (2013) for the determination of landslide source location. Please add the reference of “Chen et al. (2013) A Seismological Study of Landquakes Using a Real-Time Broadband Seismic Network. Geophys. J. Int., 194, 885-898, doi:10.1093/gji/ggt121.”

5. Methodology
(4) P11., eq.(2):
If I understand correctly the Amax should be replaced by “Tcorr”. The value of Amax is the maximal amplitudes of the waveform trace, which defined in the caption of Fig. 2.

6. Seismic description of the signals - typology
(5) P12-P16:
Why do the authors use the vertical trace in typology analysis only? Maybe some of events were recorded by vertical geophone. Did you try to use the horizontal components that generally less noisy? The seismic phases excited by the sliding stage are likely composed primarily of Rayleigh wave or shear wave, which have relative large seismic energy in the horizontal components. Considering both vertical and horizontal signals also helps us to comprehensively understand the possible source type in seismic wave generation. For example, the impacts of rockfall can excite higher seismic amplitudes in the vertical component.

6.3.2 Complex Slopequake
(6) P15., Lines 29-33:
Is the small-sized deeper earthquake (focal depth is relatively larger than inter-station distance) possible to be a seismic source of precursor signals? In cases of Fig. 9 a,b, the amplitude of precursor signals exhibits no obvious decay at different station sites. The amplitude ratio of vertical to horizontal for local deeper earthquake would be higher due to high incident angle of ray path of seismic waves. Three-component traces to discuss it would be helpful I think.

(7) P16., Lines 18-20, 31-32; P18., Lines 5-7; P19., Lines 31-32:
I also found the claim of the authors further investigations of precise source location and/or source mechanisms are needed to improve understanding different sources occurred at unstable slopes. However, the authors did not discuss more details in providing possible solutions to solve location and mechanisms of sources in accuracy. They (P16., Lines 18-20, 31-32; P18., Lines 5-7; P19., Lines 31-32) are weak statements in the current manuscript.

7. Discussion
(8) P17., Lines 29-30 “Harmonic signals have been also been documented recorded at the Pechgraben and Super-Sauze landslides Vouillamoz et al. (2017)”:
The sentence needs some adjustments regarding the English grammar, please make it more easily readable.

(9) P18., Line 8 “Harmonic coda are also observe for certain signals (Fig. 3d, Fig. 9c) at high frequencies …”:
It is not clear to me. Please highlight the portions of harmonic coda in the figures.

Figure 11.
(10) What is the meaning of n-value shown in upper right corner of each radar chart? Is n-value the number of used traces in classification analysis? Please clarify it.

Referee Report: PDF

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ED: Publish subject to minor revisions (review by editor) (03 Sep 2018) by Jens Turowski

AR by Floriane Provost on behalf of the Authors (13 Sep 2018) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (19 Sep 2018) by Jens Turowski

Dear authors,

thank you for the revised paper. I find that the reviewers' comments are adequately addressed. However, there are a large number of small language problems. These fall in two categories: first, typos and small grammatical errors - the list below is probably not exhaustive, so please check carefully through the manuscript. Second, there are some awkward and unclear phrases remaining, especially in the discussion. Please strive to improve these.

Note that the abstract conventionally is a summary of the article and as such is not part of the paper. Please make sure that abstract and manuscript can be read independently of each other. Currently, some information (e.g., used frequency bands, in response to a review comment) can only be found in the abstract. Please rewrite this accordingly and make sure that the abstract actually gives a summary of the most important results. As an example, it should give a brief description of the different classes you propose. Methodological detail is not necessary in the abstract.

I am looking forward to seeing your revised manuscript,

with thanks and best wishes, Jens Turowski

Abstract: the abstract is meant to be a summary of the article. It is NOT part of the paper (…but summarizes it). Within the abstract, please give a few more details on the classification and the relevant properties. (Re-)move details on the methods, if they are not relevant within the summary. For example, the information on the 1-50Hz frequency band is currently only given in the abstract, and not in the paper.
Discussion: the discussion currently contains many awkward phrases and could be clearer. I encourage you to carefully look through this section and try to improve it.
1.11 space missing between ‘proposed:’ and ‘slopequake’
1.11 I find the use of the word ‘gathering’ in this sentence unclear. Can you be more clear?
1.12 Please give a brief summary of the difference between Rockfalls and Granular Flows in the abstract.
1.16 The last sentence should not be part of the abstract and should be deleted.
4.21 …variety of signals is observed…
6.4 it might be good to repeat the definition of AE at this point
7.15 maybe change to ‘…can be very challenging…’
10.21 Somewhere in this chapter, include the information of the 1-50Hz frequency band.
11.6 ‘...average of on a moving window…’ – delete ‘of’
12.4-10 how does this fit with the information that you concentrate on the 1-50Hz frequency band, as mentioned in the abstract? Please clarify.
13.1 break
13.5 …and in the data reported by Hibert et al. (2011) and Dietze et al. (2017b).
13.7 …scaling laws have also been established…
13.21 Space missing before ‘The dissymmetry…’
13.25 ‘increase’
13.26 ‘rapidly’
15.10 ‘…it remains…’
17.2 ‘…can be differentiated…’
17.4 ‘…more examples…’
17.11 ‘Colombero et al. (2018) suggested…’
17.16 ‘…results of Colombero et al. (2018).’
17.20 ‘…rock fall signals…’
17.21 what does the number 12 refer to in the reference to Super-Sauze?
17.22 ‘…characterized…’
17.28 ‘…and Super-Sauze landslides (Vouillamoz et al., 2017).’
17.34 ‘Gomberg et al. (2011) hypothesized…’
18.5 ‘Systematic location of these events is needed… must be integrated… in the case that they…’
18.15 ‘Similar tremors have been found…’
18.28 unclear – what is meant by instabilities deformation?
18.29 ‘…currently prevent…’
18.30 (see also 18.23) either ‘First… second…’ or ‘Firstly… secondly…’
18.33 ‘…which remain…’
19.25 ‘…three main classes…’
20.8 clean up citations
Figure 5: typo in one of the location names; the caption misses a dot after Fig. (this repeats in other captions)

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AR by Floriane Provost on behalf of the Authors (30 Sep 2018) Author's response Manuscript

ED: Publish subject to technical corrections (08 Oct 2018) by Jens Turowski

ED: Publish subject to technical corrections (12 Oct 2018) by Niels Hovius (Editor)

AR by Floriane Provost on behalf of the Authors (17 Oct 2018) Manuscript

Short summary

Seismic sources generated by the deformation of unstable slopes are diverse in terms of signal properties and mechanisms. Standardized catalogues of landslide endogenous seismicity can help understanding the physical processes controlling slope dynamics. We propose a generic typology of seismic sources based on the analysis of signals recorded at various instrumented slopes. We demonstrate that the seismic signals present similar features at different sites and discuss their mechanical sources.