Sustaining large-scale earthquake ruptures in subducting slabs

We are looking to appoint a graduate student on a full scholarship the School of Earth and Environment to start on or before 1st October 2025.<br /> <br /> Subducting slabs continue to host large-magnitude earthquakes as they descend into the upper mantle. In this project, you will study the rupture process of some of the largest-magnitude of these intermediate-depth earthquakes, enhancing our understanding of the rheological controls on their occurrence, rupture extents and nucleation. You will use a range of data types, predominantly seismological, but drawing on strong-motion and geodetic data as and when possible to enhance our knowledge of these earthquakes.

<p style="margin-top:5px; text-align:justify; margin-bottom:11px">Large-magnitude intraslab events are common - in the 42 years to 2022, there have been 131 events with Mw> 7.0, 34 with Mw> 7.5.  These earthquakes typically represent the greatest hazard to the overlying regions, causing the most widespread devastation.  Additionally, they pose a slightly different set of geophysical problems, in terms of the parameters that control their occurrence, to other (particularly shallow, crustal) earthquakes.</p> <p>One of the critical aspects of intraslab seismicity is understanding the conditions under which it can host large-magnitude earthquakes, and the physics behind these large-scale ruptures.  Three questions of major significance arise: (1) how do slabs sustain such large ruptures; (2) how do these large ruptures relate to smaller-scale seismicity, and to the overall seismogenic structure; and (3) what are the rupture characteristics (e.g., stress drop, rupture speeds, and frequency content) of these larger-magnitude earthquakes. </p> <p>The relationship between small-scale intraslab seismicity and the largest intraslab events is complex.  In some cases, although smaller events appear to be separated into clearly defined DSZ’s, large earthquakes seem to be capable of rupturing through both planes of seismicity, and the usually-aseismic region in between.  In others, larger-scale seismicity is concentrated in regions where small-scale seismicity also extends through the slab, but this raises questions about the stress state of the slab in such places. Further questions arise over the maximum magnitude of the earthquakes the slab can host.  The coldest part of the slab, and hence that with the largest seismogenic cross-section, should be the outer rise region, immediately ocean-wards of the subduction zone. However, in a number of areas (e.g., Central America), both the total moment release and the maximum observed magnitude of intraslab events [Astiz et al., 1988; Melgar et al., 2018] are far greater than those in the outer rise [Craig et al., 2014], potentially indicating an increase in the seismogenic cross-section of the slab, despite its increasing temperature [Melgar et al., 2018]. </p> <p>This project will start determining well-constrained rupture models for these larger earthquakes (e.g., Figure 6), with a focus on estimating the correct rupture plane (and its geometry), rupture dimensions, rupture history, and source characteristics, particularly stress drop.  This will be done using a combination of globally-available seismic data, extensive regional strong-motion data (for areas where this is available, such as Central and South America [Arango et al., 2011]), and, where possible, geodetic data from both near-field GNSS instrumentation [Melgar et al., 2018b] and from satellite radar interferometry [e.g., Barnhart et al., 2014].  Techniques to do this are well-established, but are only rarely applied to intraslab events (e.g., Tarapacá, Chile [Kuge et al., 2010], Puebla, Mexico [Melgar et al., 2018]; Khash, Iran [Barnhart et al., 2014]; Peru [Luo et al., 2023]).</p> <p>You will apply a combination of seismological finite-fault modelling in a systematic way to this subset of earthquakes, and, particularly critical for addressing the questions outlined above.  Studies of large earthquakes cannot be fully automated, due to the variability in datasets, resolution, and problem complexity.  However, you will focus on the consistent and comprehensive application of these techniques to a wide range of events, to construct a detailed dataset for integration with the results of previous detailed work on smaller-scale seismicity in slabs. The approaches to do this are widely available [e.g., Ji et al., 2002; Melgar and Bock, 2015; Heimann et al., 2018], although some adaptation will be required to tailor them to an intraslab setting.  Combining finite-fault modelling with high-frequency back-projection [e.g., Koper et al., 2011] will allow a detailed assessment of the spatio-temporal evolution of the largest events and, particularly, an assessment of the degree to which they fail as a single asperity, or as cascading failures across multiple asperities.  Which mode dominates will have major implications for both the frequency content of the seismic waves generated (with large, smooth ruptures being enriched in longer period energy) and also the maximum magnitude of earthquake that is possible, addressing (3) of the questions outlined above. </p> <p>Determination of well-constrained rupture extents through finite-fault modelling will allow a detailed comparison of the sections of the slab that fail in large-magnitude earthquakes with the background seismicity and also the estimated rheological and internal stress state of the slab.  Detailed mapping of the rupture areas of a series of these larger-magnitude events within regionally-defined frameworks consistent with both the small-scale seismicity and with the rheological modelling of the slab will allow us to address (1) and (2) of the questions outlined above, and lead to an understanding of the preconditions necessary for slabs to host large-magnitude earthquakes.</p> <p>In later years, the project can follow a number of different potential avenues, depending on the skills and interests of the student, and the scientific progress made:</p> <ul> <li>Detailed studies of the source properties of smaller-magnitude intraslab events (e.g., stress drops) may offer a vital link to understanding the distribution of stress within the slab, and how this impacts on the nucleation and/or distribution of slip in large intraslab events.</li> <li>Integration of seismological results from large earthquakes with numerical models for the rheological structure of the slab will offer an avenue to understanding what controls.</li> <li>Intraslab earthquakes pose a different problem in terms of seismic hazard assessment to shallow crustal events or to events on the subduction interface [e.g., Hussain et al., 2020].  Exploring the potential impact of particular scenarios for major intraslab earthquakes offers a further avenue of investigation.</li> </ul> <p> </p> <p>References:</p> <ul> <li>L. Astiz, T. Lay, and H. Kanamori (1988).  Large intermediate-depth earthquakes and the subduction process, Physics of the Earth and Planetary Interiors, v53, pp80-166.</li> <li>W.D. Barnhart, G.P. Hayes, S.V. Samsonov, E.J. Fielding, and L.E. Seidman (2014).  Breaking the oceanic lithosphere of a subducting slab: The 2013 Khash, Iran earthquake, Geophysical Research Letters, v41, pp32-36 doi: 10.1002/2013GL058096.</li> <li>T.J. Craig, A. Copley, and J. Jackson (2014a).  A reassessment of outer-rise seismicity and its implications for the mechanics of oceanic lithosphere, Geophysical Journal International, doi:10.1093/gji/ggu013.</li> <li>S. Heimann, M. Isken, D. Kühn, H. Sudhaus, A. Steinberg, H. Vasyura-Bathke, S. Daout, S. Cesca, and T. Dahm (2018).  Grond – a probabistic earthquake source inversion framework, v1.0.  GFZ Data Services, doi:10.5880/GFZ.2.1.2018.003. </li> <li>E. Hussain, J.R. Elliott, V. Silva, M. Vilar-Vega, and D. Kane (2020).  Contrasting seismic risk for Santiago, Chile, from near-field and distant earthquake sources, Natural Hazards and Earth System Sciencs, v20, doi:10.5194/nhess-20-1533-2020.</li> <li>C. Ji, D.J. Wald, and D.V. Helmberger (2002).  Source description of the 1999 Hector Mine California, Earthquake, Part I: Wavelet Domain Inversion Theory and Resolution Analysis, Bulletin of the Seismological Society of America, v92, pp1192-1207, doi:10.1785/0120000916. </li> <li>K. Kuge, Y. Kase, Y. Urata, J. Campos, and A. Perez (2010).  Rupture characteristics of the 2005 Tarapaca, northern Chile, intermediate-depth earthquake: Evidence for heterogeneous fluid distribution across the subducting oceanic plate?, Journal of Geophysical Research, v115, doi:10.1029/2009JB007106. </li> <li>H. Luo, H. Zeng, Q. Shi, T. Wang, M Liao, J. Hu, and S. Wei (2023).  Could thermal pressurization ave induced the frequency-dependent rupture during the 2019 Mw 8.0 Peru intermediate-depth earthquake?  Geophysical Journal International, v232, pp115-127.</li> <li>D. Melgar, X. Pérez-Campos, L. Ramirez-Guzman, Z. Spica, V.H. Espíndola, W.C. Hammond, E. Cabral-Cano (2018a).  Bend Faulting at the Edge of a Flat Slab: the 2017 Mw7.1 Puebla-Morelos, Mexico Earthquake, Geophysical Research Letters, v45, pp2633-2641, doi:10.1002/2017GL076895.</li> <li>D. Melgar, A. Ruiz-Angulo, E.S. Garcia, M. Manea, V.C. Manea, X. Xu, M.T. Ramirez-Herrera, J. Zavala-Hidalgo, J. Geng, N. Corona, X. Pérez-Campos, E. Cabral-Cano, and L. Ramirz-Guzmán (2018b).  Deep embrittlement and complete rupture of the lithosphere during the Mw 8.2 Tehuantepec earthquake, Nature Geoscience, v11, doi:10.1038/s41561-018-0229-y.</li> </ul> <p><strong>Applicant Background</strong></p> <p>This project would suit candidates with a background in quantitative geology, geophysics, or physics with an interest in solid-Earth processes. Prior skills in coding are desirable, but not required. We encourage applicants from all backgrounds. </p> <p><strong>Training</strong></p> <p>The student will be based the Institute for Geophysics and Tectonics at the University of Leeds, and will collaborate with the co-supervisor at the Earth Observatory of Singapore, both remotely, and via visits to Singapore (as circumstances allow/require).  The student will receive training in observational earthquake seismology.  Within Leeds, they will have the opportunity to interact with the internationally-excellent research group in Tectonics, hosted within the Institute for Geophysics and Tectonics.  The School of Earth and Environment also hosts numerous staff from the NERC-funded Centre for the Observation and Modelling of Earthquakes and Tectonics (<a href="http://www.comet.nerc.ac.uk">www.comet.nerc.ac.uk</a>), with whom the student will be able to interact. Our current students come from many countries around the world and are well supported by a comprehensive programme of training and an inclusive supervision network.<span style="font-size:11pt"><span style="text-justify:inter-ideograph"><span style="line-height:107%"><span style="font-family:Calibri,sans-serif"><span style="color:black"> </span></span></span></span></span></p>

<p paraeid="{4efa8349-6078-45e4-9ef7-3104e110a3b1}{201}" paraid="255733758">To apply for this project you will need to make a formal application for research degree study through the <a href="https://www.leeds.ac.uk/research-applying/doc/applying-research-degrees" rel="noreferrer noopener" target="_blank">University's website</a>. You will need to create a login ID with a username and PIN.  </p> <p paraeid="{4efa8349-6078-45e4-9ef7-3104e110a3b1}{216}" paraid="2033294586">For ‘Application type’ please select ‘Research Degrees – Research Postgraduate’. The admission year for this project is 2025/26 Academic Year. You will need to select your ‘Planned Course of Study’ from a drop-down menu. For this project, scroll down and select ‘PhD Earth and Environment Full-time’. The project start date for this project is 1^st October 2025, please use this as your Proposed Start Date of Research.</p> <p>Please state clearly in the research information section that the research degree you wish to be considered for is <em>Sustaining large-scale earthquake ruptures in subducting slabs</em> as well as <a href="https://environment.leeds.ac.uk/see/staff/1216/dr-tim-craig">Dr Tim Craig</a> as your proposed supervisor.</p> <p>If English is not your first language, you must provide evidence that you meet the University's minimum English language requirements (below).</p> <p><em>As an international research-intensive university, we welcome students from all walks of life and from across the world. We foster an inclusive environment where all can flourish and prosper, and we are proud of our strong commitment to student education. Across all Faculties we are dedicated to diversifying our community and we welcome the unique contributions that individuals can bring, and particularly encourage applications from, but not limited to Black, Asian, people who belong to a minority ethnic community, people who identify as LGBT+ and people with disabilities. Applicants will always be selected based on merit and ability.</em></p>

Applicants to research degree programmes should normally have at least a first class or an upper second class British Bachelors Honours degree (or equivalent) in an appropriate discipline. The criteria for entry for some research degrees may be higher, for example, several faculties, also require a Master's degree. Applicants are advised to check with the relevant School prior to making an application. Applicants who are uncertain about the requirements for a particular research degree are advised to contact the PGR Admissions Team prior to making an application.

The minimum English language entry requirement for research postgraduate research study is an IELTS of 6.0 overall with at least 5.5 in each component (reading, writing, listening and speaking) or equivalent. The test must be dated within two years of the start date of the course in order to be valid. Some schools and faculties have a higher requirement.

<ul> <li style="margin-bottom: 11px;">We are offering 1 PhD scholarship in the School of Earth and Environment, funded by the Royal Society, for one Home fee rated candidate, covering a maintenance grant matching the UKRI rate (£19,237 in 2024/25) for four years, plus UK tuition fees, subject to satisfactory progress.</li> <li style="margin-bottom: 11px;">Full-time (4 years). The award will be made for one year in the first instance and renewable for a further period of up to three years, subject to satisfactory academic progress.</li> <li style="margin-bottom: 11px;">Awards must be taken up by 1^st October 2025. </li> <li style="margin-bottom: 11px;">Applicants must live within a reasonable distance of the University of Leeds whilst in receipt of this scholarship.</li> </ul> <p style="margin-bottom:11px"> </p>

<p>For further information please contact the PGR Admissions team via email: ENV-PGR@leeds.ac.uk.</p> <p> </p>