The inner workings of Slow Earthquakes and Slow Slip Events: New insights based on field, microstructural and -chemical evidence along with targeted experiments

In this exciting project, you will focus on the processes associated with the recently discovered Slow earthquakes and Slow Slip events. Until now, the processes that enable deformation at rates slower than “normal” earthquakes but faster than the commonly observed creep, remain elusive. You will tackle this problem by conducting targeted field work, perform in-depth microscopic analyses using state-of-the-art equipment and deformation experiments. Results promise to be of high relevance to society due high population densities in areas known geodetically and geophysically as being close to Slow Slip Areas.

Geophysical and geodetic observations over the past two decades have shown that our view of how plates deform along plate boundaries needs to be revised. We now recognise the importance of Slow Earthquakes (SEs) in which slip occurs more slowly than in regular earthquakes, but significantly faster than can be attributable to normal plate motion. SEs are abundant and should leave a distinct imprint in the geological record, as they accommodate deformation within large, 50 km scale plate boundary regions e.g. subduction zones. Their observed characteristics cannot, at present, be reconciled with our current understanding of how rocks deform: the extensively-studied ductile deformation processes are not compatible with the slip rates of SEs, yet classic brittle processes would result in recognisable seismic signatures that are not observed. At present, there are number of theoretical suggestions for the processes responsible for Slow Earthquakes. However, to determine what processes are actually involved, we need to search for evidence of the relevant deformation processes in the geological record.

In summary, despite SEs potential importance in the evolution of subduction zones and societal hazard, research to date has not revealed any striking geological signature that allow determination of the underlying processes of SEs [KFS’21], hampering markedly our understanding of this important phenomena. This project aims to use field observations and field analysis, as well as in-depth sample analysis, as a way to identify the possible mechanisms involved in Slow Earthquakes generation. Such analysis allows to pinpoint down the possible mechanisms and identify possible feedback mechanism that can explain the curious relationships of Earthquake Moment, duration and propagation speeds that have been identified (Fig. 1, [G&H’23]). Examples of field observations in former subduction zones include replacement veining and shear zones (Fig. 2).

In this project the student will work with leading scientist in Leeds and abroad to integrate latest techniques in characterizing deformation in metamorphic rocks and targeted experiments in order to understand the dynamics of the physiochemical processes at the core of Slow Earthquakes. As highlighted by [KFS’21] and [P’22] only a multi-scale and multi-disciplinary project can advance our understanding of SEs.
The project will address the following questions:
1) Distinguishing features: What features distinguish areas of inferred slow slip to areas known for very slow slip i.e. creep and very fast slip i.e. earthquakes? What are the defining signatures both in the field and at the microscale?
2) Processes: What physiochemical processes are responsible for the different slow slip geophysical signatures? Is there a “goldilocks” processes combination? Are different processes relevant at different scales?
3) Effects: How do the processes effect the long term behaviour of Slow Slip zones

In order to answers the question posed above, it will be necessary to combine different techniques and approaches.

1. Conduct field work in inferred slow slip areas: Investigate the large and small scale features, collect samples for later analysis
2. Analyse collected samples (e.g. nanoscale electron microscopy, microtomography) and geochemical techniques. One field area is New Caledonia (samples already existing, [T_etal’18; C&C’21]), while a second field area is to be determined (Option e.g. Santa Catalina (USA), HP-LT areas of E Australia, Syros, Greece). In each case, PT fluid conditions will have to be determined to assess the conditions under which deformation happened. As fluids are known to play a major part, we will be using chemistry as a tracer of fluid movement, hence analyses will be focussed on a combination of physical and chemical characterisation techniques. Specifically, you will quantify the signatures of inter- and intragrain deformation and any associated chemical or isotopic changes by combining state of the art Electron Backscatter Diffraction analysis (EBSD) and in-situ chemical analyses using a unique Focussed Ion Beam-Scanning Electron Microscope with time-of-flight detector at the University of Leeds. The spatial resolution, data analysis procedures and elemental and orientation precision of these highly advanced techniques allow for an investigation, in unprecedented detail, of the link between chemistry and deformation microstructures
3. Develop models of process dynamics derived from field and sample analysis.
4. Study the results from legacy “failed” experiments with known mechanical properties (e.g. [M_etal’02, CZT’19]). Here, slow fractures that closely resemble the known characteristics of SEs have been observed and captured in the resulting experimental samples, which are available in PP Hansen’s rock-deformation laboratory
5. Conduct well-constrained experiments of slow slip in the laboratory utilizing at the University of Minnesota (USA) followed by subsequent in-depth analysis of experimental samples. Experiment will use the isotope labelling technique that allows an examination of the chemical signature [S_etal’17]. Depending on the students interest analogue modelling similar to do that [B&M’01] can be conducted at University of Leeds.
6. Develop and test hypotheses linking the observations from the rock record into slow slip behaviours, relying on what we already know from the earthquake and Quaternary records on the environment of the studied rocks.
7. There is a potential to employ also numerical modelling to test the viability of the proposed processes to generate the geophysical signatures observed. Here collaboration with Dr. Jessica Hawthorne (University of Oxford) would be sought.
We expect the balance between these approaches to vary depending on the specific interests of the student. There is the potential to develop novel methods of integrating what you may observe in the rock record with physical models of slip; a challenging but important endeavour.

Potential for high impact outcome
Active tectonics and earthquake hazard is a pressing issue facing many countries. We are in a unique position at Leeds together with our international collaborators to bring together a range of observational, experimental and field approaches to answer important unresolved questions about the inner workings of Slow Earthquakes and Slow Slip Events and their potential link to large, devastating Earthquakes. The research topic has immediate relevance to improving our understanding of the link between slow slip and nature of seismic hazard. There will be ample opportunities to deliver the results of the project at international conferences in addition to UK meetings.
The project sits in an emerging research field with important fundamental research to be done but also important societal implications. Consequently, we anticipate the project generating several papers being suitable for submission to high impact journals.

You will be part of an active group of researchers and students at SEE that focus on earthquake dynamics including experts in active faulting and microstructural investigation of rocks and minerals. In addition you will have the benefit of the wide geochemical expertise in-house through Dr. Ivan Sarov and Dr. Dan Morgan. Specifically, the student will work under the supervision of Prof Sandra Piazolo and Dr. Laura Gregory and within the Tectonics group as well as the Rocks, fluids and melts groups of the Institute of Geophysics & Tectonics in the School of Earth & Environment at Leeds. The Institute also hosts the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET which provides a large group of researchers engaged in active tectonics research with whom the student can interact. This project provides a high level of specialist scientific training in: (i) geological field skills, (iii) Laboratory analysis including state-of-the-art microstructural and –chemical analysis (from outcrop to nanometer scale). As fluid presence and pressure is thought to be important we will also be trained in thermodynamic modelling to assess reaction induced fluid pressure variations [CMV’21]. The successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range from scientific computing through to managing your degree, to preparing for your viva (

Student profile
The student should have a strong interest in tectonics problems in metamorphic rocks with interest in both the physical and chemical processes and their interaction. The student should have,a desire to undertake laboratory and fieldwork overseas, and a strong background in a quantitative science (earth sciences, geophysics, geology, physics, natural sciences). Willingness and excitement for taking up the challenge to work at the boundary of mechanics, chemical and microstructural analysis utilizing a combination of technique (field analysis, in-depth microstructural analysis, experiments and/or numerical modelling) is a prerequisite.

References: [A&G’79] Gandhi, & Ashby, 1979, Acta Metallurgica, 27, 1565, [B&M’01] Bons, Bon & van Milligen. Geology, 29, 919-922 [C&C] Chapman & Clarke 2021, JMG, 39, 343; [CZT19] Carter, Zimmerman,Teyssier, 2019, JSG, 127, 103871; [CMV’21] Chapman, Milan, Vry, GRL, e2021GL096415; [F+’15] Frank et al. 2015, EPSL, 413, 135; [G&H’23] Gombert, & Hawthorne (2023). Journal of Geophysical Research: Solid Earth, 128(2), e2022JB025034. [H&R’13] Hawthorne & Rubin, 2013. JGR, 118, 3785; [H&B’18] Hawthorne & Bartlow, 2018, JGR, 123, 4243; [HZK’12] Hansen, Zimmerman, Kohlstedt 2012, Nature, 492, 415; [KFS’21] Kirkpatrick, Fagereng, Shelley 2021, Nature Reviews, 2, 285: [M_etal’02] Mei, Bai, Hiraga, Kohlstedt, 2002, EPSL, 201, 491; [PC’22] Penrose Conference The geological fingerprints of Slow Earthquakes, USA, March 2022; S’02] Schulson, 2002, ActaMat., 50, 3415; [S_etal’17] Spruzeniece, Piazolo, Daczko, Kilburn, Putnis, 2017, JMG, 35, 281; [T_etal’18] Taetz, John, Broecker, Spandler, Stracke, 2018, EPSL, 482, 33.