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Mapping the coupling properties of the subduction megathrust using seismic data


Key facts

Type of research degree
Application deadline
Ongoing deadline
Project start date
Saturday 1 October 2022
Country eligibility
International (open to all nationalities, including the UK)
Source of funding
Dr Tim Craig and Professor Sebastian Rost
Additional supervisors
Dr. Marianne Metois
School of Earth and Environment
<h2 class="heading hide-accessible">Summary</h2>

The properties of the subduction interface between plates vary in both space and time. In this project, you will develop techniques to map the properties of the subduction interface using remote observations of small-amplitude reflected seismic waves from intraplate earthquakes within the downgoing plate, which can be applied to subduction zones irrespective of local instrumentation, and in areas without the sub-aerial exposure needed for modern geodesy. This will allow us to probe the controls on spatio-temporal variations in the type of slip, in the presence of fluids along the subduction interface, and lead to an appraisal of hazard emanating from these subduction zones.

<h2 class="heading hide-accessible">Full description</h2>

<p>The plate interfaces of subduction zones generate the largest, most damaging earthquakes on Earth. However, along with major earthquakes, the plate interface can also accommodate the motion between plates through stable sliding or through periods of enhanced aseismic &ldquo;slow slip&rdquo;. Understanding the properties of this subduction interface, and how these may vary in both space and time is critical for understanding its behaviour, and its potential to produce large earthquakes in the future. Classically, the behaviour of the subduction interface has been characterised using geodetic techniques, which measure the motion of the Earth&rsquo;s surface above the plate interface, and use this to infer the slip behaviour of the interface. Established geodetic techniques are limited to terrestrial environments, limiting their resolving power in most submarine subduction zones, and leaving them unable to probe the behaviours of completely submarine subduction zones (e.g., Tonga-Kermadec, Bonin-Marianas). Sub-sea geodesy is in its infancy, and its prohibitively expensive, requiring extensive seafloor logistics and support.&nbsp;</p> <p>However, remote seismic data offer a way to map the rheological properties of the subduction interface, without the need for extensive near-field instrumentation (e.g., Song et al., 2010). Using well-located earthquakes occurring within the downgoing plate beneath the subduction interface, detailed waveform analysis suggests that it is possible to detect small-amplitude reflections and conversions from the overlying interface, allowing its elastic properties to be determined, and from these, its slip behaviour to be inferred.&nbsp;</p> <p>In this project, you will develop a set of seismological processing routines optimised for detecting these small- amplitude phases within the coda of off-interface earthquakes. This project will focus on technical development, and the construction of a test dataset, to span the Central American subduction zone. Central America is ideal for this technical development phase, as it is also geodetically well-instrumented, and known to display a range of interface behaviours. This will allow you to compare seismological results for the reflectivity of the subduction interface with other observational proxies, and allow you to determine what it is that a high-reflectivity subduction interface indicates &ndash; whether this is a proxy for interface coupling, or for the transient presence of fluids and/or slow slip, and thus what can be inferred about the slip behaviour of the interface using remote data only.&nbsp;</p> <p>Following this, the study will expand to encompass other regions, starting the northern New Zealand/Hikurangi, where a similar level of local instrumentation will allow the verification of our conclusions from Central America, before moving to application of submarine subduction zones, starting with a northwards progression from Hikurangi up towards Tonga.&nbsp;</p> <p><strong>References:</strong></p> <ul> <li>Song et al., (2009).&nbsp;&nbsp;<em>Subducting Slab Ultra-Slow Velocity Layer Coincident with Silent Earthquakes in Southern Mexico</em>, Science, v324, pp502+506, doi:10.1126/science.1165795.</li> <li>Radiguet et al. ,(2011).&nbsp;&nbsp;<em>Spatial and temporal evolution of a long term slow slip event: the 2006 Guerrero Slow Slip Event</em>, Geophysical Journal International, v184, doi:10.1111/j.1365-246X.2010.04866.</li> <li>Metois, Vigny, and Socquet (2016).&nbsp;&nbsp;<em>Interseismic Coupling, Megathrust Earthquakes and Seismic Swarms Along the Chilean Subduction Zone (38<sup>o</sup>&nbsp;&ndash; 18<sup>o</sup>S)</em>, Pure and Applied Geophysics, v173, pp1431-1449.</li> <li>Audet and Burgmann (2014).&nbsp;&nbsp;<em>Possible control of subduction zone slow-earthquake periodicity by silica enrichment</em>, Nature, v510, pp389-392.</li> </ul> <p>&nbsp;</p> <p><strong>Objectives:</strong></p> <p>In the course of this project, you will seek to answer three main observational questions:</p> <p style="margin-left:35.45pt;"><strong>Q1</strong>:&nbsp;&nbsp;How are high-reflectivity subduction zone interfaces related to coupling on the subduction interface?</p> <p style="margin-left:35.45pt;"><strong>Q2</strong>:&nbsp;&nbsp;How are high-reflectivity subduction zone interfaces related to transient slip phenomena in subduction zones?</p> <p style="margin-left:35.45pt;"><strong>Q3</strong>: Does the reflectivity of the subduction interface vary through time (e.g., through the presence of transient fluids)?</p> <p>You will work to map out the extent of high-reflectivity subduction zone interfaces around the world, starting with Central America.&nbsp;&nbsp;You will then compare these will geodetic data for the behaviour of the interface, the degree of coupling, and the presence of slow slip.</p> <p>&nbsp;</p> <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.&nbsp;&nbsp;Prior skills in observational seismology or geodesy are desirable, but not required.</p> <p>&nbsp;</p> <p><strong>Training:</strong></p> <p>The student will be based the Institute for Geophysics and Tectonics at the University of Leeds (UK), working with Dr. Tim Craig and Prof. Sebastian Rost, and&nbsp;will also spend time working with Dr. Marianne Metois at the Universit&eacute; Lyon 1&nbsp;(France).&nbsp;&nbsp;The student will receive training in observational earthquake seismology, geodesy, and numerical geodynamic modelling. &nbsp;Within Leeds, they will have the opportunity to interact with internationally-excellent research groups in Tectonics and in Deep Earth Dynamics, hosted within the Institute for Geophysics and Tectonics.&nbsp;&nbsp;The School also hosts numerous staff from the NERC-funded Centre for the Observation and Modelling of Earthquakes and Tectonics (<a href=""></a>), with whom the student will be able to interact.</p>

<h2 class="heading">How to apply</h2>

<p>Formal applications for research degree study should be made online through the&nbsp;<a href="">University&#39;s website</a>. Please state clearly in the research information section&nbsp;that the research degree you wish to be considered for is <strong>&ldquo;<em>Mapping the coupling properties of the subduction megathrust using seismic data</em>&rdquo; </strong>as well as&nbsp;<strong>Dr. Tim Craig</strong> as your proposed supervisor.</p> <p>If English is not your first language, you must provide evidence that you meet the University&#39;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.&nbsp;Within the School of Earth and Environment 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.&nbsp;Applicants will always be selected based on merit and ability.</em></p>

<h2 class="heading heading--sm">Entry requirements</h2>

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 Masters 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 School or Graduate School prior to making an application.

<h2 class="heading heading--sm">English language requirements</h2>

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.

<h2 class="heading">Funding on offer</h2>

<p>This project is part of a research grant from&nbsp;the Leverhulme Trust. &nbsp;Funding is available to cover the stipend (&pound;15,840&nbsp;for 2022/23*) and fees of a 4-year PhD studentship, along with associated research expenses. &nbsp;PhD stipends are not considered taxable income in the UK.&nbsp; *To be confirmed.</p> <p>&nbsp;</p>

<h2 class="heading">Contact details</h2>

<p>For initial enquiries about the project, please contact Dr. Tim Craig at <a href=""></a>.</p> <p>For information about the&nbsp;application procedure, please contact the Graduate School Office Admissions team at&nbsp;<a href=""></a>.</p>

<h3 class="heading heading--sm">Linked research areas</h3>