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Earthquake-induced instabilities in orogenic and volcanic environments


Project Description

Landslides and sector collapses are frequent consequences of tectonic earthquakes (Keefer, 1984, 2002), and represent an important secondary hazard, costing the economy ~$2 billion annually in damage and causing thousands of fatalities in the last century. Landslides constitute both coherent and disrupted or disaggregated slides including rock falls, soil slides, rock avalanches, rock slides, soil slumps and soil flows, varying in size and intensity. Recently, landslides induced by earthquakes such as the magnitude 7.8 Kaikoura (New Zealand) earthquake in November 2016, and the magnitude 6.6 Hokkaido (Japan) earthquake in September 2018 have brought the problem of earthquake-induced instability to the forefront of the attention of the geoscientific community. Earthquakes of magnitude 4 and above have been reported to induce ground shaking that can trigger instabilities, in cases up to 500,000 km2 have been affected by earthquakes above magnitude 9. Typically, the number of landslides and the area over which they occur also scale to the magnitude of the earthquake, although this is highly influenced by the local geology and morphology (Keefer, 1984). Areas of unconsolidated ground due to progressive deposition (sedimentary, volcanic), with steep morphology or with pre-existing planes of weakness such as slow-moving landslides are particularly prone to the effects of earthquake-induced shaking due to their residual shear strength (e.g. Schultz & Wang, 2014). However, landslides are not restricted to these areas and strain softening (the process by which a material progressively weakens during deformation) can occur in all geological materials; from top-surface soil to intact basement rocks.

It is thus vital that we understand slope stability in the event of earthquakes, and for this we must understand the mechanical and frictional rock properties of materials involved. This includes the complexity caused by stratification, in which different layers may have very different mechanical properties (e.g. Gudmundsson, 2006; Vidal and Merle, 2000), large-scale structures or discontinuities (Schultz & Wang, 2014) and saturation by groundwater or percolation of rainwater. The fluctuating stress field created during an earthquake interacts with local gravitational stresses, and in the case of an active volcanic system this may have yet further devastating consequences. Since the sector collapse of Mount St. Helens in May of 1980, the structural failure of active volcanoes has been widely recognised as a potentially devastating phenomenon – triggering eruptions or directing lateral blasts. Volcanoes are particularly susceptible to landslides because of their steep morphology, unconsolidated edifices, the presence of geothermal fluids and problems associated with the migration of magma that can result in progressive damage and vapour-phase deposition of minerals.
Project Summary
In this project, the properties of a wide range of materials collected at Mount St. Helens and from recent landslides in Hokkaido (Japan) and Kaikoura (New Zealand) will be experimentally investigated to understand the conditions which lead to failure during an earthquake, and the resulting consequences of such events. The successful candidate will employ a variety of approaches to tackle this question, including: fieldwork; physical property quantification such as porosity/ permeability; microtextural investigation by QEMSCAN; microstructural investigation by optical/ scanning electron microscopy and extensive mechanical testing.

Results of the mechanical investigation will be used to develop instability models which rely too heavily on estimated or averaged parameters such as dynamic elastic moduli, which could present significant errors in the calculation of slope stability. Heterogeneous layering is very important in terms of susceptibility to collapse, but modelling allows calculation of stress trajectories for any given anisotropy, loading and layering providing accurate constraints are available (e.g. Schaefer et al., 2013, 2015).

The successful candidate would aim to understand the physical and mechanical properties, and larger scale heterogeneity in order to interpret the relationship between the build-up of stresses, addition of temperature and any subsequent deformation this may incur. The student will enjoy working in a dynamic, international research group and will travel abroad for conferences and field work as well as to work alongside international project partners.

We encourage applications from students holding a first-class degree in Geophysics or Geology, ideally with experience in either rock deformation, geophysical surveys or extensive structural mapping and a keen interest in learning. This multidisciplinary work will employ a wide range of techniques and provide the selected candidate with a strong and varied set of skills to undertake a wide range of frontier research following their doctoral study.


Funding Notes

Full funding (fees, stipend, research support budget) is provided by the University of Liverpool. Formal training is offered through partnership between the Universities of Liverpool and Manchester in both subject specific and transferable skills to the entire PhD cohort and at each University through local Faculty training programmes.

References

• Keefer, D.K., 1984, Landslides caused by earthquakes, GSA Bulletin, vol. 95, no. 4, p. 406-421.
• Keefer, D.K., 2002, Investigating Landslides Caused by Earthquakes – A Historical Review, Surveys in Geophysics, vol. 23, no. 6.
• Schultz, W.H. and Wang, G., 2014, Residual shear strength variability as a primary control on movement of landslides reactivated by earthquake-induced ground motion: Implications for coastal Oregon, U.S., Journal of Geophysical Research: Earth Surface, v. 119, issue 7.
• Schaefer, L., Oommen, T., Corazzato, C., Tibaldi, A., Escobar-Wolf, R., and Rose, W., 2013, An integrated field-numerical approach to assess slope stability hazards at volcanoes: the example of Pacaya, Guatemala: Bulletin of Volcanology, v. 75, no. 6, p. 1-18.
• Siebert, L., 1992, Volcano hazards - threats from debris avalanches: Nature, v. 356, p. 658-659.
Vidal, N., and Merle, O., 2000, Reactivation of basement faults beneath volcanoes: a new model of flank collapse: Journal of Volcanology and Geothermal Research, v. 99, no. 1–4, p. 9-26.

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