Seismicity and Structure of Subducting Slabs

This project aims to understand the distribution of seismicity associated with internal deformation in shallow subducting slabs. Subduction zones are well known to host the largest and most damaging earthquakes, but also a wide variety of smaller events. The distribution and style of this seismicity is essential for our understanding of the seismic hazard posed by subduction zones, and also provides critical information on the dynamics of the subduction process.

Subduction zones host the majority of the Earth’s seismic moment release. Whilst much of this is the result of motion between plates along the plate interface, significant seismicity also occurs within subducting plates. Although they rarely reach the size or frequency of earthquakes associated with the subduction megathrust, these earthquakes, often located deep beneath cities landwards of major subduction zones, have the potential to be devastating, as seen in the magnitude 7.9 1970 Ancash (Peru – the deadliest earthquake in South American history), the 2001 magnitude 7.7 El Salvador earthquake, and, more recently, the magnitude 7.1 2017 Puebla/Mexico City earthquake. In many cases, the occurrence of such earthquakes remains a surprise, with the capacity of the downgoing plate to host such large-magnitude earthquakes uncertain in many regions.

These earthquakes arise from the combination of the stresses derived from large-scale plate-driving forces, localised stresses arising from changes in slab geometry, and rheological factors relating to the structure and evolution of the subducting plate as it descends into the Earth’s interior. Critical to understanding the distribution of such earthquakes is our ability to accurately map out their location within the plate, in particular with respect to each other, and to the surface of the subducting plate. This project will initially focus on improving earthquake catalogues for a number of regional case studies (starting with Central and South America), accurately mapping out the seismogenic structure of the subducting oceanic plate, the location and mode of failure of active faults within the plate, and how the distribution of stress and strain vary within the plate. This will principally be done through the detailed analysis and modelling of global seismic data, incorporating locally-acquired data where available and useful. Many of the techniques required have been previously developed, but the student will tailor existing approaches to the requirements of the study and datasets available, and will be involved in the development of new approaches to the assessment of the seismic data as required.

The project will also aim to answer the questions of how these earthquakes relate to the geodynamic setting of the slab, its structure and rheological evolution, through the combination of seismological observations and geodynamic modelling. A final aim will be to understand the relationship between the largest earthquakes occurring in such settings (M7-8), and the background seismicity in their vicinity – in particular, addressing the issue of how these earthquakes activate such large sections of the seismogenic slab, and whether their spatial occurrence can be predicted, and incorporated into seismic hazard models.

Whilst the initial work will focus on Central and South America, the expansion to incorporate other tectonic regions, particularly in the event of important new data (either due to increased instrument coverage, or to the occurrence of particular earthquakes), is a further avenue for developing the project in later years.

The successful candidate will be part of the Tectonic Research group of the Institute of Geophysics and Tectonics (School of Earth and Environment) of the University of Leeds. The Tectonics Research group is a large and dynamic research group including Seismology, Structural Geology, Geomorphology, Quaternary Research and Remote Sensing. The PhD student will benefit from training from the Leeds-York-Hull Doctoral Training Partnership as well as from training at the university, and will be attending national and international conferences and workshops. Possibilities for attendance at fieldwork might arise in other projects at the Institute for Geophysics and Tectonics.