Subaqueous spreading: characteristics, evolution and its suitability as a paleoseismic proxy

Informations projet

SubSpread

N° de convention de subvention: 101003388

DOI

10.3030/101003388

Projet clôturé

Date de signature de la CE 23 Avril 2020

Date de début 11 Janvier 2021

Date de fin 10 Janvier 2023

Financé au titre de

• SPREADING EXCELLENCE AND WIDENING PARTICIPATION

Coût total

€ 148 049,28

Contribution de l’UE

€ 148 049,28

Coordonné par

UNIVERSITA TA MALTA
Malta

Periodic Reporting for period 1 - SubSpread (Subaqueous spreading: characteristics, evolution and its suitability as a paleoseismic proxy)

Période du rapport: 2021-01-11 au 2023-01-10

Résumé du contexte et des objectifs généraux du projet

The project ''SubSpread'' had the aim of investigating a specific type of subaqueous (marine and lacustrine) landslide (also called mass movements) known with the name of 'spreading', alternatively, in this document we will also use the term “spreading landslide”. Spreading is an extensional landslide characterising gentle inclined slopes. Its geomorphic signature is a 'staircase pattern' consisting in alternating topographic highs (ridges) and topographic lows (troughs or grabens). While onshore, spreading has been investigated in relation to earthquakes and clay landslides (or quick clay landslides, in particular in glacial and periglacial environments), within the subaqueous setting, this type of landslide did not receive an appropriate scientific interest. Prior to the launch of our project, investigations of subaqueous spreading were only related to the morphometric analysis of the Storegga Landslide, and to the general description of the physical process majorly inferred by case studies onshore. This type of landslide, as other marine or terrestrial landslides, can represent a hazard for nearshore or offshore infrastructures and therefore, our project tried to address these concerns in the following objectives:
1) Describe the morphological and geological aspects of spreading landslides in the subaqueous setting;
2) Study what are the trigger mechanisms of spreading and how does it develop;
3) Investigate whether the geological conditions of subaqueous spreading can be used to outline the evidence of past earthquakes.
The following sections will explain in detail the objectives and relative work packages that have been achieved, and what was not possible to address for those work packages that haven’t been fully completed.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

Work Package 1 (WP1) entitled as: ‘Identify the topographic and sedimentary signatures of submarine spreading’. The database generated by the work on WP1 is called “SubSpread” and published in Zenodo https://zenodo.org/record/7009251#.Y8FBMHbMJD8.
As proposed, this database included records about the morphology, the geology and the physiographic condition of the slides characterised by spreading.
A preliminary version of our results (R) from WP1 were presented atthe EGU 2021 conference. Completed results were then published in the scientific journal of ‘Geomorphology’, as a golden open-source contribution:
R1) Giona Bucci, M*., Micallef, A., Urlaub, M., and Mountjoy, J.: SubSpread: An integrated approach to understand the signature, mechanics and controls of subaqueous spreading, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13520, https://doi.org/10.5194/egusphere-egu21-13520 2021
R2) Giona Bucci, M., Micallef, A., Urlaub, M., Mountjoy, J., Barrett, R. A global review of subaqueous spreading and its morphological and sedimentological characteristics: A database for highlighting the current state of the art. Geomorphology 414 (2022) 108397, doi.org/10.1016/j.geomorph.2022.108397
Work package 2 (WP2) entailed the collaboration of the University of Malta and of the GEOMAR (Helmholtz-Centre for Ocean Science Kiel). WP2 had the aim of modelling the failure of spreading landslides and their development, by using a Coupled Eulerian-Lagrangian (CEL) method within the software package SIMULIA.
The mathematical model widely acknowledged by the scientific community for being the best approach at investigating spreading landslide is known as shear band propagation. This procedure studies the propagation of a shear surface through areas of weaknesses that are characterised by specific geologic layers within the slide. A fundamental assumption for this method in order to be applied is the occurrence of a gliding plane (or slipping surface) composed by clay, or clay and silt sediments, constituting the weak layer. Our work used geological information from the large subaqueous Tuaheni slide, offshore the East coast of New Zealand. A detailed geological correlation of the sediment and seismic surveys from this slide revealed that the slipping surface was not characterised by clay layers (as commonly documented in the literature onshore and offshore), instead sandy and silty sandy sediments were observed at Tuaheni site. As a consequence of this, a new modelling approach was needed.
More details about WP2 are provided in the Technical report (PR CORE 1).
A preliminary modelling exercise was published at the International Conference of Sealfoor, Landforms, Processes and Evolution in Valletta in 2022.
R3) Giona Bucci, M* Saadatkhah, N., Micallef, A. Subaqueous Spreading: state of the art, and first modelling attempts. International Conference of Seafloor, Landforms, Processes and Evolution; 4th-6th July, Valletta, Malta 2022 http://www.geomorph.org/wp-content/uploads/2022/05/R1292_SeafloorConference_Booklet.pdf
In conclusion, within the timeframe of this fellowship WP2 could not be developed as initially proposed. Subsequently, WP3 was modified from the original working plan.
Work Package 3 (WP3) originally aimed at using the geological information inferred by the investigation of spreading at Tuaheni (from WP2) and linking this with the occurrence of past earthquakes. Due to the changes occurred for WP2, WP3 had to be revised accordingly. Therefore, other potential activities were proposed, and for each of them new working plans were hypothesised. The details of which are fully explained in the technical report Part B attachment (PR CORE 1).
In conclusion WP2 and WP3 underwent a thorough revision from what the original proposed research was. In order to fulfil the unattained publication record within WP3, the fellow was engaged in coordinating another research study on sediment transport. This work is currently being developed within the hosting institution. It will represent an additional research output within six months from the conclusion of our fellowship.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

The research undertaken by this fellowship shed lights on the geological and hazardous aspects of spreading landslides as linked to some of the largest landslides offshore, and as such, as potential trigger of hazards to nearshore and offshore infrastructures. In most of the literature found and contained in our database quantitative information was missing. The modelling efforts undertaken within this project, that could solve research questions on the development of spreading landslides, are still at their preliminary stage. However, this research has clearly represented a stepping stone for the scientific community in highlighting the best approach possible for investigating subaqueous spreading landslides. We have now understood that the classical numerical method that is commonly used for investigating spreading onshore and offshore when clay layers are involved (the shear band propagation) cannot be extended to all types of spreading landslides, especially when sandy layers are involved. This finding leads to inquire a novel mathematical approach that will remarkably improve the understanding of the scientific community on how spreading develops and evolves. This research not only has been a chance of advancing the field of research within the earth sciences, for investigating a specific type of landslides but, it also represented an opportunity to make progresses in understanding the optimal conditions for the numerical modelling community of scientists who address complex research questions on failure mechanisms and landscape evolution.

Architecture of SubSpread Database