Global relevance of gas hydrate filled fractures for slope stability
Geophysics
Final Report Abstract
This project was funded within the priority program “International Ocean Discovery Programs” (IODP). Its main goal was to assess the global relevance of gas hydrate filled fractures for slope stability. The project had two main objectives, (1) to establish a geological and lithological framework for the TLC and to test with the laboratory experiment and modelling whether (2) gas hydrates filled fractures increase slope stability or gas hydrate filled fractures become weak layers at times of falling sea level or increasing bottom water temperature and act as preferred glide planes. The first geological and geophysical aim was to establish a high-resolution seismic stratigraphy for the TLC using CLSI. Especially the results from the second paper in work package 1 were a step forward in our capability to predict sub-surface physical properties and tie them to geological processes. At the TLC they allowed us to revalidate previous seismic interpretations, to tie potential weak layers to the 3D seismic imaging, and to discuss the impact of free gas beneath the TLC. Although such an approach generally is not novel our study is outstanding in the scientific community due to its comprehensive data set including 3D seismic data, MeBo and IODP cores, MSCL and LWD data. We were able to bridge the gap in resolution between the different measurements, as well as, to compare a site within the landslide with surrounding undeformed sediments, which is very unique in similar approach to study submarine landslides. The second objective was planned to be tested by triaxial shear tests. Unfortunately, technical problems in combination with the Covid-19 pandemic significantly hampered the progress of this work package. Despite these unpredictable circumstances we were able to develop a work flow for this novel system and perform first measurements, including a 3D analysis of the different material and structures of the samples. We plan to catch up on these experiments in near future. Additionally to the initial objectives, we were able to show with numerical modelling that fluid flow along reactivated normal faults is a plausible mechanism at the TLC. This mechanism can explain high amplitude anomalies adjacent to normal fault structures in the seismic data which indicate free gas. We interpreted this mechanism to be plausible as the calculated critical gas column heights match the observations in the seismic data. The parameter test within this study highlighted the relevance of the Poisson ratio. The determination of this parameter is therefore very important in future research as it will allow to further improve the significance of modelling geotechnical and faults mechanic processes. Apart from the technical aspect and the relevance of the modelling results for the failure mechanisms of the TLC, the results from the third work package are highly relevant for the field of micro seismicity, where the impact of fluid flow is controversial debated.
Publications
- (2018). Borehole stress indicators across the Hikurangi Subduction Margin: Preliminary insights from IODP Expedition 372. In: AGU Fall Meeting 2018, Washington, D.C., USA
McNamara, D. D., Wu, H. Y., Lee, H., Wallace, L. M., Lee, G., Heeschen, K. U., Elger, J. , Saffer, D. M., Barnes, P. und Pecher, I. A.
- (2019). Expedition 372A summary. In Pecher, I.A., Barnes, P.M., LeVay, L.J., and the Expedition 372A Scientists, Creeping Gas Hydrate Slides. Proceedings of the International Ocean Discovery Program, 372A: College Station, TX (International Ocean Discovery Program)
Barnes, P.M., Pecher, I.A., LeVay, L.J., Bourlange, S.M., Brunet, M.M.Y., Cardona, S., Clennell, M.B., Cook, A.E., Crundwell, M.P., Dugan, B., Elger, J., Gamboa, D., Georgiopoulou, A., Greve, A., Han, S., Heeschen, K.U., Hu, G., Kim, G.Y., Kitajima, H., Koge, H., Li, X., Machado, K.S., McNamara, D.D., Moore, G.F., Mountjoy, J.J., Nole, M.A., Owari, S., Paganoni, M., Petronotis, K.E., Rose, P.S., Screaton, E.J., Shankar, U., Shepherd, C.L., Torres, M.E., Underwood, M.B., Wang, X., Woodhouse, A.D., and Wu, H.-Y.
(See online at https://doi.org/10.14379/iodp.proc.372A.101.2019) - (2019). Fluid migration along reactivated normal faults in the gas hydrate system of the Tuaheni Landslide Complex off New Zealand. In: AGU Fall Meeting 2019, San-Francisco, CA, USA
Elger, J., Crutchley, G.J., Böttner, C., Gross, F., Mountjoy, J.J., Krastel, S., Barnes, P., Pecher, I.
- 2019. Site U1517. In Pecher, I.A., Barnes, P.M., LeVay, L.J., and the Expedition 372A Scientists, Creeping Gas Hydrate Slides. Proceedings of the International Ocean Discovery Program, 372A: College Station, TX (International Ocean Discovery Program)
Barnes, P.M., Pecher, I.A., LeVay, L.J., Bourlange, S.M., Brunet, M.M.Y., Cardona, S., Clennell, M.B., Cook, A.E., Crundwell, M.P., Dugan, B., Elger, J., Gamboa, D., Georgiopoulou, A., Greve, A., Han, S., Heeschen, K.U., Hu, G., Kim, G.Y., Kitajima, H., Koge, H., Li, X., Machado, K.S., McNamara, D.D., Moore, G.F., Mountjoy, J.J., Nole, M.A., Owari, S., Paganoni, M., Petronotis, K.E., Rose, P.S., Screaton, E.J., Shankar, U., Shepherd, C.L., Torres, M.E., Underwood, M.B., Wang, X., Woodhouse, A.D., and Wu, H.-Y.
(See online at https://doi.org/10.14379/iodp.proc.372A.103.2019)
