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E329: Post-seismic deformation and the rheology of the crust and upper mantle (Lead Supervisor: David Al-Attar, Earth Sciences)

Supervisors: David Al-Attar (Earth Sciences) and Alex Copley (Earth Sciences)

Importance of the area of research:

Following an earthquake, the Earth continues to deform over a period of months to years. This process is known as post-seismic deformation, and can be measured using geodetic techniques such as GPS and InSAR. There are likely three main contributing factors to post-seismic deformation (i) afterslip, which is the continued slow motion on faults at depth, (ii) poroelastic rebound due to subsurface fluid flow driven by the pressure changes associated with coseismic motions, and (iii) viscoelastic deformation which results from the gradual relaxation of stresses due to solid-state creep. Both afterslip and viscoelastic deformation are very interesting from the perspective of solid Earth geophysics. The former process  gives information on the rheology and behaviour of faults, while the latter provides important constraints on the rheology of the crust and upper mantle, which is necessary for a broader understanding of the deformation within the continents.

Project summary:

There have been numerous studies of post-seismic deformation following earthquakes.  It has, however, proven difficult to differentiate between the three possible processes contributing to the observed deformation. Indeed, different studies have been able to explain the same observations using quite different models. However, due to ongoing improvements in  data collection, analysis, and modelling techniques it is timely to revisit these questions. Within this project, the student will develop of new techniques for modelling post-seismic deformation, and for solving the associated inverse problem.  The student will then revisit the classic earthquakes for which post-seismic deformation has been observed, and try to place robust constraints on the physical processes involved, and on the appropriate rheological parameters.

What the student will do:

The student will build on existing work done in Cambridge on viscoelastic deformation, with the first aim being the development of an efficient and flexible code for modelling post-seismic deformation within a layered half-space. They will then use the so-called adjoint method, which allows for the sensitivity of observations to underlying model parameters to be calculated in an efficient manner. There is also some scope to consider deformation within laterally varying earth models, or those having non-linear rheologies.

The student will learn to process and interpret relevant geodetic data for post-seismic deformation. These data will be used within an inverse problem to determine both the extent of any afterslip and the rheological parameters governing viscoelastic relaxation. A particular aim will be the quantification of uncertainty on the estimates obtained, this being vital for the correct physical interpretation of the results. All this work will also be placed within the broader tectonic setting of the earthquakes studied, and pertinent links with broader questions in continental tectonics will be addressed.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

Copley A., & Jolivert R., 2016. Fault rheology in an aseismic fold-thrust belt (Shahdad, eastern Iran).  J. Geophys. Res., DOI: 10.1002/2015JB012431

Copley A., 2014. Postseismic afterslip 30 years after the 1978 Tabas-e-Golshan (Iran) earthquake: observations and implications for the geological evolution of thrust belts. Geophys. J. Int., 197, 665—679.

Al-Attar D. & Tromp J., 2014. Sensitivity kernels for viscoelastic loading based on adjoint methods, Geophys. J. Int., 196, 34—77.

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