Geodynamics

How to make a subduction zone on Earth

Antoniette Greta Grima - edited by Diogo Lourenço March 14, 2019

How to make a subduction zone on Earth? Credit: shareicon.net, wikipedia.org.

Subduction zones are ubiquitous features on Earth, and an integral part of plate tectonics. They are known to have a very important role in modulating climate on Earth, and are believed to have played an essential part in making the Earth’s surface habitable, a role that extends to present-day. This week, Antoniette Greta Grima writes about the ongoing debate on how subduction zones form and persist for millions of years, consuming oceanic lithosphere and transporting water and other volatiles to the Earth’s mantle.

Antoniette Greta Grima. PhD Student at Dept. of Earth Sciences, University College London, UK.

Before we can start thinking about how subduction zones form, we need to be clear on what we mean by the term subduction zone. In the most generic sense, this term has been described by White et al. (1970) as “an abruptly descending or formerly descended elongate body of lithosphere, together with an existing envelope of plate deformation”. In simple words this defines subduction zones as places where pieces of the Earth’s lithosphere bend downwards into the Earth’s interior. This definition however, does not take into account the spatio-temporal aspect of subduction zone formation. It also, does not differentiate between temporary, episodic lithosphere ‘peeling’ or ‘drips’, thought to precede the modern-day ocean plate-tectonic regime (see van Hunen and Moyen, 2012; Crameri et al., 2018; Foley, 2018, and references therein) and the rigid self-sustaining subduction, which we see on the present-day Earth (Gurnis et al., 2004).

A self-sustaining subduction zone is one where the total buried, rigid slab length extends deep into the upper mantle and is accompanied at the surface by back-arc spreading (Gurnis et al., 2004). The latter is an important surface observable indicating that the slab has overcome the resistive forces impeding its subduction and is falling quasi-vertically through the mantle. Gurnis et al. (2004) go on to say that if one or the other of these defining criteria is missing then subduction is forced rather than self-sustaining. Forced or induced subduction (Stern, 2004; Leng and Gurnis, 2011; Stern and Gerya, 2017; Baes et al., 2018) is described by Gurnis et al. (2004) as a juvenile, early stage system, that cannot be described as a fully fledged subduction zone. These forced subduction zones are characterised by incipient margins, short trench-arc distance, narrow trenches and a volcanically inactive island arc and/or trench. Furthermore, although these juvenile systems might be seismically active they will lack a well defined Benioff Zone. Examples of forced subduction include the Puysegur-Fiordland subduction along the Macquarie Ridge Complex, the Mussau Trench on the eastern boundary of the Caroline plate and the Yap Trench south of the Marianas, amongst others. On the other hand, Cenozoic (<66 Ma) subductions, shown in figure 2, are by this definition self-sustaining and mature subduction zones. These subduction zones including the Izu-Bonin-Mariana, Tonga-Kermadec and Aleutians subduction zones, are characterised by their extensive and well defined trenches (see figure 2) (Gurnis et al., 2004). However, despite their common categorization subduction zones can originate through various mechanisms and from very different tectonic settings.

Figure 1: Map the Earth’s subduction zones and tectonic plates from W.K and E.H. (2003). See how subduction zones dominate the figure.

1. How are subduction zones formed?

We know from the geological record that the formation of subduction zones is an ongoing process, with nearly half of the present day active subduction zones initiating during the Cenozoic (<66 Ma) (see Gurnis et al., 2004; Dymkova and Gerya, 2013; Crameri et al., 2018, and references therein). However, it is less clear how subduction zones originate, nucleate and propagate to pristine oceanic basins.

Figure 2: The oldest, still active subduction zones on Earth can be dated back to 66 million years ago. These are self- sustaining mature subduction zones with well defined trenches and trench lengths (modified from Gurnis et al., 2004).

Crameri et al. (2018, and references therein) list a number of mechanisms, some which are shown in figure 3, that may work together to weaken and break the lithosphere including:

Meteorite impact
Sediment loading
Major episode of delamination
Small scale convection in the sub-lithospheric mantle
Interaction of thermo-chemical plume with the overlying lithosphere
Plate bending via surface topographic variations
Addition of water or melt to the lithosphere
Pre-existing transform fault or oceanic plateau
Shear heating
Grain size reduction

Some of these mechanisms, particularly those listed at the beginning of the list are more appropriate to early Earth conditions while others, such as inherited weaknesses or fracture zones, transform faults and extinct spreading ridges are considered to be prime tectonic settings for subduction zone formation in the Cenozoic (<66 Ma) (Gurnis et al., 2004). As the oceanic lithosphere grows denser with age, it develops heterogeneity which facilitates its sinking into the mantle to form new subduction zones. However, it is important to keep in mind that without inherited, pre-existing weaknesses, it is extremely difficult to form subduction zones at passive margins. This is because as the oceanic lithosphere cools and becomes denser, it also becomes stronger and therefore harder to bend into the mantle that underlies it (Gurnis et al., 2004; Duarte et al., 2016). Gurnis et al. (2004) note that the formation of new subduction zones alters the force balance on the plate and suggest that the strength of the lithosphere during bending is potentially the largest resisting component in the development of new subduction zones. Once that resistance to bending is overcome, either through the negative buoyancy of the subducting plate and/or through the tectonic forces acting on it, a shear zone extending through the plate develops (Gurnis et al., 2004; Leng and Gurnis, 2011). This eventually leads to plate failure and subduction zone formation.

Figure 3: Different ways to form a new subduction zone (from Stern and Gerya, 2017).

2. Where can new subduction zones form?

From our knowledge of the geological record, observations of on-going subduction, and numerical modelling (Baes et al., 2011; Leng and Gurnis, 2011; Baes et al., 2018; Beaussier et al., 2018) we think that subduction zone initiation primarily occurs through the following:

In an intra-oceanic setting through surface weakening processes

An intra-oceanic setting refers to a subduction zone forming right within the oceanic plate itself. Proposed weakening mechanisms include weakening of the lithosphere due to melt and/or hydration (e.g., Crameri et al., 2018; Foley, 2018, and references therein), localised lithospheric shear heating (Thielmann and Kaus, 2012) and density variations within oceanic plate due to age heterogeneities, where its older and denser portions flounder and sink (Duarte et al., 2016). Another mechanism proposed by Baes et al. (2018) suggests that intra-oceanic subduction can also be induced by mantle suction flow. These authors suggest that mantle suction flow stemming from either slab remnants and/or from slabs of active subduction zones can act on pre-existing zones of weakness, such as STEP (subduction-transfer edge propagate) faults to trigger a new subduction zone, thus facilitating spontaneous subduction initiation (e.g. figure 3) (Stern, 2004). The Sandwich and the Tonga-Kermadec subduction zones are often cited as prime examples of intra-oceanic subduction zone formation due to mantle suction forces (Baes et al., 2018). Ueda et al. (2008) and Gerya et al. (2015) also suggest that thermochemical plumes can break the lithosphere and initiate self-sustaining subduction, provided that the overlying lithosphere is weakened through the presence of volatiles and melt (e.g. figure 3). This mechanism can explain the Venusian corona and could have facilitated the initation of plate tectonics on Earth (Ueda et al., 2008; Gerya et al., 2015). Similarly Burov and Cloetingh (2010) suggest that in the absence of plate tectonics, mantle lithospheric interaction through plume-like instabilities, can induce spontaneous downwelling of both continental and oceanic lithosphere.

Through subduction infection or invasion

Subduction invasion/infection (Waldron et al., 2014; Duarte et al., 2016) occurs when subduction migrates from an older system into a pristine oceanic basin. Waldron et al. (2014) suggest that the closure of the Iapetus Ocean is due to the encroachment of old lithosphere into a young ocean. These authors suggests that subduction initiated at the boundary between old and new oceanic lithosphere and was introduced to the area through trench rollback. This process is thought be similar to the modern day Caribbean, Scotia and Gibraltar Arcs (Duarte et al., 2016). This suggests that the older subductions of the Pacific are invading the younger Atlantic basin, which might potentially lead to collision, orogeny and closure of the Atlantic ocean (Duarte et al., 2016).

Following a subduction polarity reversal

Subduction polarity reversal describes a process where the trench jumps from the subducting plate to the overriding one, flipping its polarity in the process (see figure 3). This can result from the arrival at the trench of continental lithosphere (McKenzie, 1969) or young positively buoyant lithosphere (Crameri and Tackley, 2015). Subduction polarity reversal is often invoked to explain and justify the two juxtaposed Wadati-Benioff zones and their opposite polarities, in the Solomon Island Region (Cooper and Taylor, 1985). Indications of a polarity reversal are also exhibited below the Alpine and Apennine Belts (Vignaroli et al., 2008). Furthermore, Crameri and Tackley (2014) also suggest that the continental connection between South America and the Antarctic peninsula has been severed through a subduction polarity reversal, resulting in the lateral detachment of the South Sandwich subduction zone.

Subduction initiation at ancient/ inherited zones of lithospheric weakness

Subduction zones can also initiate at ancient, inherited zones of weakness such as old fracture zones, transform faults, extinct subduction boundaries and extinct spreading ridges (Gurnis et al., 2004). Gurnis et al. (2004) suggest that the Izu-Bonin-Mariana subduction zone initiated at a fracture zone, while the Tonga-Kermadec subduction initiated at an extinct subduction boundary. The same study also proposes that the incipient Puysegur-Fiordland subduction zone nucleated at an extinct spreading centre.

In conclusion, we can say that subduction zone formation is a complex and multi layered process that can stem from a variety of tectonic settings. However, it is clear that our planet’s current convection style, mode of surface recycling and its ability to sustain life are interlinked with subduction zone formation. Therefore, to understand better how subduction zones form is to better understand what makes the Earth the planet it is today.

References:

Baes, M., Govers, R., and Wortel, R. (2011). Subduction initiation along the inherited weakness zone at the edge of a slab: Insights from numerical models. Geophysical Journal International, 184(3):991–1008.

Baes, M., Sobolev, S. V., and Quinteros, J. (2018). Subduction initiation in mid-ocean induced by mantle suction flow. Geophysical Journal International, 215(3):1515–1522.

Beaussier, S. J., Gerya, T. V., and Burg, J.-p. (2018). 3D numerical modelling of the Wilson cycle: structural inheritance of alternating subduction polarity. Fifty years of the Wilson Cycle concept in plate tectonics, page First published online.

Burov, E. and Cloetingh, S. (2010). Plume-like upper mantle instabilities drive subduction initiation. Geophys. Res. Lett., 37(3).

Cooper, P. and Taylor, B. (1985). Polarity reversal in the Solomon Island Arc. Nature, 313(6003):47–48.

Crameri, F., Conrad, C. P., Mont ́esi, L., and Lithgow-Bertelloni, C. R. (2018). The dynamic life of an oceanic plate. Tectonophysics.

Crameri, F. and Tackley, P. J. (2014). Spontaneous development of arcuate single-sided subduction in global 3-D mantle convection models with a free surface. Journal of Geophysical Research: Solid Earth, 119(7):5921–5942.

Crameri, F. and Tackley, P. J. (2015). Parameters controlling dynamically self-consistent plate tectonics and single-sided subduction in global models of mantle convection. Journal of Geophysical Research: Solid Earth, 3(55):1–27.

Duarte, J. C., Schellart, W. P., and Rosas, F. M. (2016). The future of Earth’s oceans: Consequences of subduction initiation in the Atlantic and implications for supercontinent formation. Geological Magazine, 155(1):45–58.

Dymkova, D. and Gerya, T. (2013). Porous fluid flow enables oceanic subduction initiation on Earth. Geophysical Research Letters, 40(21):5671–5676.

Foley, B. J. (2018). The dependence of planetary tectonics on mantle thermal state : applications to early Earth evolution. 376.

Gerya, T. V., Stern, R. J., Baes, M., Sobolev, S. V., and Whattam, S. A. (2015). Plate tectonics on the Earth triggered by plume-induced subduction initiation. Nature, 527(7577):221–225.

Gurnis, M., Hall, C., and Lavier, L. (2004). Evolving force balance during incipient subduction. Geochemistry, Geophysics, Geosystems, 5(7).

Leng, W. and Gurnis, M. (2011). Dynamics of subduction initiation with different evolutionary pathways. Geochemistry, Geophysics, Geosystems, 12(12).

McKenzie, D. P. (1969). Speculations on the Consequences and Causes of Plate Motions. Geophys. J. R. Astron. Soc., 18(1):1–32.

Stern, R. J. (2004). Subduction initiation: spontaneous and induced. Earth and Planetary Science Letters, 226(3-4):275–292.

Stern, R. J. and Gerya, T. (2017). Subduction initiation in nature and models: A review. Tectonophysics.

Thielmann, M. and Kaus, B. J. (2012). Shear heating induced lithospheric-scale localization: Does it result in subduction? Earth Planet. Sci. Lett., 359-360:1–13.

Ueda, K., Gerya, T., and Sobolev, S. V. (2008). Subduction initiation by thermal-chemical plumes: Numerical studies. Phys. Earth Planet. Inter., 171(1-4):296–312.

van Hunen, J. and Moyen, J.-F. (2012). Archean Subduction: Fact or Fiction? Annual Review of Earth and Planetary Sciences, 40(1):195–219.

Vignaroli, G., Faccenna, C., Jolivet, L., Piromallo, C., and Rossetti, F. (2008). Subduction polarity reversal at the junction between the Western Alps and the Northern Apennines, Italy. Tectonophysics, 450(1-4):34–50.

Waldron, J. W., Schofield, D. I., Brendan Murphy, J., and Thomas, C. W. (2014). How was the iapetus ocean infected with subduction? Geology, 42(12):1095–1098.

White, D. A., Roeder, D. H., Nelson, T. H., and Crowell, J. C. (1970). Subduction. Geological Society of America Bulletin, 81(October):3431–3432.

W.K, H. and E.H., C. (2003). Earth’s Dynamic Systems. Prentice Hall; 10 edition.

Conferences: Secret PhD Drivers

Kiran Chotalia - edited by Diogo Lourenço March 1, 2019

Welcome to Conference! Credit: picserver.org

Conferences are an integral part of a PhD. They are the forum for spreading the word about the newest science and developing professional relationships. But as a PhD student they are more likely to be a source of palpitations and sweaty palms. This week Kiran Chotalia writes about her personal experience on conferences, and lessons learnt over the years.

Kiran Chotalia. PhD Student at Dept. of Earth Sciences, University College London, UK.

My PhD is a part of the Deep Volatiles Consortium and a bunch of us started on our pursuit of that floppy hat together. Our first conference adventure was an introduction to the consortium at the University of Oxford, where the new students were to present on themselves and their projects for a whole terrifying two minutes. At this stage, we had only been scientists in training for a few weeks and the thought of getting up in front of a room of established experts was scary, to say the least. Lesson #1: If it’s not a little bit scary, is it even worth doing? It means we care and we want to do the best we can. A healthy dose of fear can push us to work harder and polish our skills, making us better presenters. Overcoming the fear of these new situations takes up a lot of your energy. But it always helps to practice. In particular, I’ve always been encouraged to participate in presentation (poster or oral) competitions. Knowing that you’re going to be judged on your work and presentation skills encourages you to prepare. And this preparation has always helped to calm my nerves to the point where I’m now at the stage I can enjoy presenting a poster.

Regular work goals that crop up in other professions are often absent, especially when we’re starting out. The build-up to a conference acts as a good focus to push for results and some first pass interpretations. At the conference itself, it makes sure people come to see your poster and you can start to get your face out there in your field. Lesson #2: Sign up for presentation competitions. AGU’s Outstanding Student Presentation Award (OSPA) and EGU’s Outstanding Student PICO and Poster (OSPP) awards are well established. At smaller conferences, it’s always worth asking if a competition is taking place as, speaking from experience, they can be easily missed. They also give you a good excuse to practice with your research group in preparation, providing the key component of improving your presentation skills: feedback. Lesson #3: Ask for feedback, not just on your science but your presenting too. If you’re presenting to people not in your field, practice with office mates that have no idea what you get up to. By practicing, you can begin to find your style of presenting and the best way to convey your science.

Me, (awkwardly) presenting my first poster at the Workshop on the Origin of Plate Tectonics, Locarno.

Sometimes, you’ll be going to conferences not only with your fellow PhD students, but also more senior members. They can introduce you to their friends and colleagues, extending your network, more often than not, when you are socialising over dinner, after the main working day. Lesson #4: Keep your ear to the ground. These events provide a great opportunity to let people know you are on the hunt for a job and hear about positions that might be right for you. At AGU 2018, I became the proud owner of a ‘Job Seeker’ badge, provided by the Careers Centre. It acted as a great way to segue from general job chat into potential leads. A memento that I’ll be hanging on to and dusting off for conferences to come!

One of the biggest changes to my conferencing cycle occurred last year after attending two meetings: CIDER and YoungCEED. Both were workshops geared towards learning and research, with CIDER lasting four weeks and YoungCEED lasting a week. Lesson #5: Attend research specific meetings when the opportunity arises. Even if they don’t seem to align with your research interests from the outset, they are incredible learning opportunities and a great way to expand your research horizons. By attending these meetings, the dynamic of my first conference after them shifted. There was a focus on catching up with the collective work started earlier in the year. Whilst the pace was the most exhausting I’ve experienced thus far, it was also the most rewarding.

Between all the learning and networking, faces start to become familiar. Before you know it, these faces become colleagues and colleagues quickly become friends. In our line of work, our friends are spread over continents, moving from institution to institution. They tend to offer the only opportunity to be in the same place at the same time. This also results in completely losing track of time and catching up into the early hours of the morning, so the next lesson is more subjective. Lesson #6: Know your limits. Some can stay out until 4am and rock up at the 8.30am talk. I wish I was one of these people but I have a hard time keeping my eyes open past 12.30am. Whatever works for you!

Me, presenting my most recent poster at AGU 2018 with my job seeker badge!

After the conference finishes, you are often in a place that you’ve never visited before. Lesson #7: Have a break. If you can, even an extra day or two of being a tourist is great treat after a hectic build-up as well as the conference itself. If staying for a mini holiday post-conference is not an option, make sure you take some time when you get home to rest and readjust before you get back to work and start planning for the next one.

Last but not least, Lesson #8: Don’t forget to have fun. The stress surrounding conferences and your PhD in general can at times be all consuming. Remember to enjoy the small victories of finally getting a code to run or finding time on the SEM to analyse your samples. At conferences, enjoy being surrounding scientists that are just starting out and the seasoned professionals with a back catalogue of interesting stories. And if you’re lucky enough to be at a conference somewhere sunny, make sure to get outside during the breaks and free time to soak up some vitamin D!

The Shanghai skyline after the Sino-UK Deep Volatiles Annual Meeting at Nanjing University.

Demystifying the Peer-Review Process

Adina Pusok - edited by Grace Shephard February 6, 2019

Magic Mirror on the wall, who is the fairest one of all? Demystifying the review process. Modified from unsplash.com @rawpixel

Adina Pusok

An important and inevitable aspect of being in academia is receiving a request to peer-review a paper. And much like the papers we write and submit, retaining structure and clarity for the review itself is important. This week Adina E. Pusok, Postdoctoral Researcher at Scripps Institution of Oceanography, UCSD, and our outgoing GD ECR representative, shares some detailed and helpful tips for writing a concise, efficient, and informative review. Do check out her very helpful Peer-review checklist PDF for download!

It is somewhat surprising that the peer-review process, a fundamental part of science (which prides itself on technical and objective methods), is usually left up to the individual reviewing scientist. Everyone agrees that there is little formal training in peer-reviewing, and many times it takes years until scientists become thorough and efficient reviewers (Zimmerman et al., 2011). Personally, I prefer to invest some of my time learning from other people’s experiences and best practices. For example, before my first review, I spent approximately two weeks researching material on how to deliver good reviews. But what are good reviews? And mostly, how does one write good reviews efficiently? In this blog post, I will attempt to synthesize some of the material I’ve come across, and share my personal guidelines that help me get through the peer-review process.

1. What is the peer-review process?

The peer-review process is in some ways like a legal trial. A judge (the editor) will take an informed and educated decision about the case (to publish/not to publish the manuscript in current form) based on the recommendations and arguments brought forward by lawyers (reviewers).

In reality, the journey of a manuscript (McPeek et al., 2009) through the peer-review process is as follows:

The manuscript is submitted to a scientific journal.
An editor reads the abstract/paper and decides whether it is suitable for potential publication at the journal.
If approved, it is assigned to an associate editor who will handle the actual review process.
The associate editor then compiles a list of potential reviewers, often partially based on recommendations from authors.
Those reviewers are asked whether they would be willing to review the paper in a timely fashion.
The reviewers then read the paper, consider the methods, data, analyses, and arguments, and write reviews containing their opinions about the paper, and whether the paper should be published in that journal.
The associate editor reads the reviews, usually two or more, and may write a third review, and makes a recommendation to the editor.
The editor then writes the authors a letter about the disposition of the paper.
Depending on the outcome, the manuscript will have successfully exited this journey (accepted for publication), or will have to restart the process again (by resubmitting a modified version to the same or a new journal).

Basically, each manuscript submission depends on the work of volunteers (editors, reviewers) (McPeek et al., 2009). Indeed, peer-review, which lies at the cornerstone of advancing science, is primarily a volunteering exercise (also referred as “community work”). But this process is such a valuable mechanism to improve the quality and accuracy of scientific papers, that some people think the system would collapse without it, as there would be little control on what gets published.

What’s the purpose of it?

The goals of peer-review are clear: to ensure the accuracy and improve the quality of published literature through constructive criticism. Hames (2008) points out that every peer-review process should aim to:

Prevent the publication of bad work.
Verify that the research was conducted correctly, and there are no flaws in the design or methodology.
Ensure that the work is reported correctly and unambiguously, with acknowledgement to the existing literature.
Ensure that the results have been interpreted correctly and all possible interpretations were considered.
Ensure that the results are neither too preliminary nor too speculative.
Provide editors with evidence to make judgments as to whether articles meet the criteria for their particular publications.
Generally improve the quality and readability of a publication.

2. Who gets to do it?

The editor decides who should complete the review based on recommendations from the manuscript authors (nowadays, it’s a submission requirement for most journals), relevant literature cited in manuscript, or their own professional networks. The reviewers are generally considered experts in a given field (extensive peer-review and/or publishing experience), qualified (typically awarded with a Ph.D.) and able to perform reasonably impartial reviews. For example, because I am an early career scientist, I have been asked to perform reviews mostly on topics relating to my Ph.D. work (both the methods and the science).

3. What do you get out of it?

While the peer-review process seems more of an obligation for the greater good of science and society, it has its own perks (albeit not many), and one can benefit from them:

Whichever way you look at it, the peer-review process will improve your scientific work. On one hand, authors receive valuable feedback from experts in their community. On the other hand, reviewers get to reflect on what constitutes high-quality science and incorporate lessons learned from reviewing into their own work.
Following the above point, reviewing does make you a better writer. You learn so many lessons from reading excellent to bad manuscripts, and in particular, you learn how to/not to write. It is very frustrating when you struggle with someone else’s unclear explanations or weak arguments. In my experience, that definitely makes you promise yourself to avoid those errors.
Reviewing trains your critical thinking, impartial judgment, and diplomatic skills. A review is not useful if it is not civil and contains personal or destructive criticism. In general, you learn to clearly argument your points and be diplomatic about the strengths and weaknesses of a paper.
You get to see the latest work before it is even published. Do make sure, though, that you respect the integrity of the review process and do not communicate any aspect of the paper to other people. In any case, this helps you stay on top of your field or expand/learn new science.
It does look good on your CV! Everyone agrees that community service (such as reviewing) is a positive for those aspiring for an academic career.
Most editors are senior scientists, and by entering the reviewers’ network, you become known. Better yet?! You become known as an expert in a certain field. Fortunately (or unfortunately), since academia relies heavily on prestige and reputation, that will pay off in the longer term.
Some journals will provide credit for your review, by acknowledging all reviewers once a year, or by awarding exceptional community service at meetings. While this is great for some, many scientists feel it is insufficient for the amount of work involved in reviews. Therefore, in recent years, it is possible to keep a general record of your reviews using ORCID and/or Publons (pay attention that only the journal and the year of each review is made public). This allows scientists to have something of a review index (complementing the usual publication index – e.g., Google Scholar).

4. How to undertake a peer-review?

Before I even started reviewing, I was somewhat familiar with what reviews looked like – I had already received them for my own submitted research papers. One of the first things I noticed is that each of the reviews had different styles: annotated PDFs or text files with line numbers, brief and not so useful/detailed reviews, short or long reviews etc. Since scientists receive little peer-review training, they are also likely to develop their own review style with time and experience. In principle, the style should not matter as long at the review is thorough, clear, and constructive.

There are many ways to complete a review, but just like writing an article, if you have a plan and structure, the entire process becomes easier and even more enjoyable. Moreover, establishing some good practices will ensure a robust review done in a timely manner. Plus, if you are like me (writing is not my favourite activity), you want to find ways to get the job done, as fast as possible and return to more exciting tasks. I find that checklists come in useful, whether it is about academic writing, presentations or reviewing.

Therefore, what I will attempt in this blog is to create a “Peer-Review Checklist“ that anyone can download as a PDF and help them navigate through the review process. It is a checklist I initially created for my own use, and I hope these tips in turn are relevant for first-time/early reviewers that are still in search of their styles. The checklist may also be useful to other experienced reviewers as a refresher. I would like to note that this is a suggested checklist and workflow, and depending on the journal or field, some elements may be different or missing. People should adapt the checklist to suit their needs, personal style, and the journal’s guidelines. I am also happy to receive suggestions (comments below/email), in order to improve the checklist over time.

Before I present the checklist in more detail, I want to highlight some resources that can help anyone improve their reviews:

Talk to colleagues, advisors, and friends about the reviewing process.
Pay attention to the reviews of your own papers. I actually modeled mine after one of the most constructive reviews I received.
Check journal guidelines. Many journals have extensive and good advice available online.
Published material (the most useful material that I found, especially Nicholas and Gordon, 2011, Stiller-Reeve et al., 2018a,b, and McPeek et al., 2009):

Peer-Review Workflow and Checklist

This checklist has been compiled from the advice of various articles and guides, and personal preferences. The aim is to give early reviewers a quick workflow of questions and tasks (that you can mark as completed) for any manuscript review. By following all the points, anyone can produce a constructive and thorough review in a timely manner.

Step 1: Pre-Read – Received an invitation to review

✓ Read abstract.

✓ Appropriate expertise.
Does my area of expertise and experience qualify me to critically evaluate the manuscript? Sometimes it will fit exactly with your expertise, whereas other times it will only just brush your field. One instance, I accepted a review that implemented a technical novelty in a method that I was familiar with. I decided it was still largely within my expertise, but I took the opportunity to learn something new. I made sure I went over the background studies, until I was comfortable asking questions and clarifying points. If you feel less confident, and your expertise allows you to comment meaningfully only on key sections of the paper, you can offer to review these areas and let the editor know you cannot comment on other aspects outside your expertise.

✓ Conflict of interest.
Can I provide a fair and unbiased review of this work? Am I able to evaluate the manuscript with an open mind, without being either negatively/positively predisposed? Check the journal’s guidelines for more specific guidance on avoiding conflicts of interest.

✓ Time and deadline.
Do I have time to write a complete review? Most journals suggest a timeline of a couple of weeks from the moment the invitation was accepted (usually 2-4 weeks). While this may seem sufficient time to return the review, most scientists have a large workload, and end up allowing only a few days for the review. Moreover, it can take more than 8 hours to provide a thoughtful, thorough, and well-referenced review (can depend on the paper type of course, so also pay attention to that). If you are unable to meet the deadline, contact the journal so that the editors can determine the appropriate course of action (some extensions can be granted at the discretion of the editors).

✓ Check journal guidelines and adjust your workflow.
It is better to do this early on in the review.

✓ Respond as soon as possible: Accept/Decline.
Explain to editor the reason for decline, and offer, if possible, suggestions for other reviewers.

Step 2: First Read – Gaining an overview

✓ Set up the structure of review
Prepare a document (I prefer to have a simple text file at hand) containing the following structure of the review:

R0. Review details
R1. Introduction (3 paragraphs)
R2. Major issues (numbered items)
R3. Minor issues (indicate line, figure, table numbers)
R4. Other suggestions (regarding supplementary material, etc.)
Notes (not included in final review)

✓ Read the entire paper. Take notes as you go
The first reading is to get an overall impression of the paper: motivation, approach, overview of results, and conclusions. Take some notes as you go. I usually like to print a copy and make annotations as I go along. However, don’t worry too much with corrections, spelling, punctuation, or references. It’s supposed to be a ‘casual’ reading (kidding).It might be a challenge, but at this point do your best to understand the paper. Some papers read (and are written) better than others, and it would be a shame to miss an interesting study, just because of language barriers. And it is perfectly normal (apparently!) to struggle reading a scientific article with “ultra-congested and aggressively bland” text. This article might help and amuse you: the 10 Stages of Reading a Scientific Paper.

✓ Go through all figures and tables
Do they complement the approach, results section, and conclusions?

✓ Readability
Sometimes it cannot be helped but to ask: is the English/writing so bad that you can’t understand the arguments? If the manuscript needs copyediting by a proficient English speaker before you can evaluate it on its scientific merits, it is legitimate to make such a suggestion to the editor at this stage. You can point out that you cannot give the paper a fair review in its current form, and suggest the paper to be withdrawn from review until the English is improved.

✓ Identify goals, method, findings, and relevance
The questions below might help:

What is the main question addressed by the research?
Is this question interesting and important to the field of study? How, specifically, will the paper contribute to the science?
Do the Abstract and Introduction clearly identify the need for this research, and its relevance?
Does the Method target the main question(s) appropriately?
Are the Results presented clearly and logically, and are they justified by the data provided?
Are the figures clear and fully described?
Do the Conclusions justifiably respond to the main questions posed by the author(s) in the Introduction?
Is the paper within the scope of the journal?
Is the paper potentially publishable based on its contribution to the field?

✓ Write introductory paragraphs (Section R1 – first 2 paragraphs) [“The study investigates/uses/finds/contributes”]
Answering the above questions will help you start the written review. In general, the most helpful review to everyone is one that first provides an overall summary of the main contributions of the paper and its appropriateness for the journal, and suggests what major items should be addressed in revision. This summary can also help you reveal what this paper is really about, if you weren’t sure until now. Or you might end up, writing back “It was difficult to understand the precise point(s) the authors were trying to make.”

The first paragraph should state the main question addressed by the research, and summarize the goals, approaches, and conclusions of the paper. Try writing one sentence for each of these points. The second paragraph of the review should provide a conceptual overview of the contribution of the paper to the journal. Some people suggest trying to also include here the positive aspects in which the paper succeeds, since there is enough space for negative aspects for the remainder of the review. The authors will have a sense of what they have done well, and will not be too discouraged.

✓ Evaluate whether the manuscript is publishable/or not (Section R1 – 3rd paragraph)

[“I recommend the manuscript not/to be published in Journal X with minor/major modifications, and I provide below the reason for my decision and some comments that are necessary to address….”]

You have three decision options: the manuscript is/has

publishable in principle -> Continue review to Step 3: Second Read.
major flaws, but addressable -> Return manuscript to authors for corrections, but document and substantiate the flaws, indicate willingness to provide full review if authors address them (continuing to Step 3: Second Read may still be helpful to reply to editor/authors).
fatally flawed/unsuitable -> Reject, but document and substantiate why. You consider the manuscript is flawed in a way that cannot be fixed and/or is unsuitable for publication in the target journal (high impact journals like Nature or Science reject most submissions solely based on the suitability of study to the journal).

Some manuscripts can have flaws that cannot be overlooked or improved easily. Examples of such fatal flaws might include drawing a conclusion that is contravened by the author’s own statistical evidence, the use of a discredited method, or ignoring a process that is known to have a strong influence on the system under study. Whatever the decision, remember to carefully explain your reasoning and provide clear evidence for it (including citations from other scientific publications).

Assuming there is no fatal flaw, you can continue to a second reading. Personally, I like to let the paper sit for a couple of days after the First Read, and let my mind digest the information. It will be surprising, but you allow some time for your brain to synthesize the major aspects (strengths and weaknesses) of the paper, and you want to focus primarily on those aspects in the next stage.

Step 3: Second Read – The science (major/minor points)

✓ Take detailed Notes (end of review file) indicating section, line, figure, and table numbers

Read the manuscript in detail from start to finish. Pay attention to assumptions, methods, underlying theoretical frameworks, and the conclusions drawn and how well they are supported. Refer to figures and tables when referenced in the text, making sure that the text and the graphics support rather than repeat each other, use your careful study of the figures at the end of the first reading to avoid too much disruption to the flow of your assessment.

I have found it useful to dump in the review file all the comments I have (brainstorming as I re-read the manuscript), including specific comments, thoughts or issues I want to return to. Indicate the line or figure numbers for all comments. There is a reason why most journals ask authors to add numbers to their submissions: to be specific about various comments and suggestions. For example, “line 189 contradicts the statement in line 20”, “paragraph 45-52 is unclear and convoluted, should be rephrased”, “Figure 2a needs X,Y labels”, etc. Plus, most of the review will have the important details written by the time you are done with the second reading. Another tip, it helps to classify your comments as major or minor flaws. Major flaws will need considerable time to explain or correct.

Note: some journals allow reviews as annotated PDFs – I found they are not that helpful because in the Reply-to-reviewers as manuscript author, I had to transcribe many of those comments again. Plus, a single read of the paper might not give enough insight into the strengths/weaknesses.

A sub-checklist:

Check every section individually (my preferred order): Introduction, Methods, Results, Discussion, Conclusions, Abstract, Other (e.g., Key points, Appendices). Make notes also on structure and flow of arguments.
Check method (i.e., equations, the experimental setup, data collection, details needed for reproducing results, and if that is not possible, is it stated why?).
Check all figures and tables, so that you understand all units, axes, and symbols. Do the figures reflect the main text?
Check References/referencing is done correctly.
Check any supplementary material.
Remind yourself the journal’s guidelines. Most importantly, does the manuscript comply with the journal’s data policy and best practices?

✓ Identify major and minor points (Sections R2 and R3)

Now it’s time to organize all those notes and comments. I usually sort them in 2 categories: major and minor issues (Sections R2, R3 of review). In general, the minor issues (e.g., line 21 – missing reference to the referred study, line 32 – sentence not clear, line 56 – typos) do not need further work at this stage.

Major points, on the other hand, require some work. First, organize major points clearly and logically, using separate numbered paragraphs or bullets to make each point clearly stand out. Make use of your numbered notes to provide evidence. It is the reviewer’s obligation to point out the weaknesses in the underlying science. If the methods are suspect, or if the authors over-interpret the data, or if they overlook important implications of their work, or more analyses are needed to support the conclusions, you should point that out as major points.

Is it possible to have too many major points? Could it be because they are not that major (overestimation of importance), or are they really major and cannot be overlooked? This might make you re-evaluate the review (major/minor, largely flawed). In general, I was not given more/found more than 10 major points in a manuscript, but exceptions can happen. Very importantly, try to advise the authors with concrete, actionable ways to address the problems.

✓ Add Other Points (Section R4 – Optional)

If there is anything else to add to the review, neither fitting the category of major nor minor points, such as suggestions for future work, add them at the end of review. If you have no further comments, it’s fine to leave this section empty.

Step 4: Final Read – The writing and formulation

Briefly read through the paper a third time, looking for organizational issues, and finalize the review.

✓ Check organization and flow of arguments

While you probably already noted down many of such issues (because if the manuscript is poorly written, then the arguments will often not make sense either), it’s still a good idea to quickly go over the writing and presentation (section headings, details of language and grammar). Suggest ways how to make the story more cohesive and easily reasoned.

However, was the paper hard to read because the paragraphs did not flow together? Did the authors use excessive and confusing acronyms or jargon? In these cases, I actually include improving the structure of the manuscript as a major point. However, do not feel obligated to catch every typo, missing reference, and awkward phrase – your scientific assessment of the paper is more important.

✓ Read and polish your own review
Read the review carefully, and preferably aloud, imagining you are the editor or the authors of the study. What’s the tone of your arguments? How would you feel receiving it back as the author? Will you find the review helpful and constructive? Or fair? This will draw your attention to how your criticisms might sound to the ears of the authors. Make sure to keep the tone civil and include both positive and negative comments.

✓ Upload your review using the link provided
I usually copy and paste my review (Sections R1-R4) in the provided boxes by the journal, or upload the polished review file.

✓ Answer specific questions regarding the manuscript and its presentationYou will probably also be asked specific questions or rate the manuscript on various attributes (answers in drop-down selections).

✓ Remarks to the editors
Any issues that the editors should be aware of can be indicated separately in Remarks to the editors, which remain confidential.

✓ Submit review to editor
You are done! You will probably hear back from the editor about their decision to accept or reject the manuscript. Important to understand, is that the editors take the final decision. Your role was only advisory in the whole process. However, you may be asked to review another version of the manuscript to assess whether the manuscript has been modified sufficiently in response to reviewers’ comments.

5. Etiquette of reviewing

I hope by now you have a clear idea of what constitutes the peer-review process and how to perform a review. Again, there are many ways how to undertake a review, but maybe you will find the checklist useful. It most surely requires considerable time and effort, but the checklist allows me to be confident that I gave my best consideration for the work submitted. By also ticking off tasks, I can perform the review in an efficient way, without worrying that I forgot something.

However, I am aware that we tend to be over-critical of other peoples work (and the workflow proposed here is quite lengthy). I’ve heard a couple of times the comment that “young scientists provide very lengthy and harsh reviews”. That has some grain of truth in it, as from a desire of being thorough, we might ask for extra-work for revisions that go beyond the scope of the manuscript or resources (time, material, etc.). We need to be aware of that, but at the same time invite authors to discuss potential avenues for the work.

What I will discuss next, is the etiquette of reviewing: what to do/not to do, fairness of reviews, providing/receiving criticism, and the Golden Rule of reviewing. As you will see below, they are interconnected with each other.

5.1 What to do/not to do when peer-reviewing

Top 3 To do:

– the review does not have to be long, but make sure you did a thorough and fair review, as you would want others to do it in return.

– be critical, argumentative, and straightforward: explain the problem, why it’s a problem, and suggest a solution.

– finish before the agreed upon deadline.

Top 3 Don’t do:

– be sarcastic, dismissive or other such tones. The review should be constructive and not offensive.

– be biased or let personal prejudices influence your assessment of the manuscript (e.g., poor English, excessive self-citations). In such cases, it’s better to decline to review and explain potential conflict of interest.

– write a too short review (even if it’s a great study). The authors might be happy to hear that, but the editor will not find it useful.

5.2 Working towards a transparent and fair peer-review process

Scientific peer-review is regularly criticized as being ineffective, broken or unfair. However, journals are generally committed to take active steps in order to ensure the fairness of the process. For example, most journals have clear ethical guidelines (i.e., AGU, EGU), and all participants in the review process are expected to uphold these guidelines.

While most of the review interaction happens privately between the authors-editors-reviewers, some journals (e.g., EGU journals, Nature Communications) have taken a step forward to make the peer review process more transparent, such that manuscript authors are given the option to publish the peer review history of their paper. This is great for making the process more open and fair! However, making things public can, in some cases, create unethical practices. For example, to ensure the impartiality and confidentiality of the peer review process, you should not discuss your review of the paper with anyone before or after publication. Also, apparently revealing yourself as a reviewer to the author or authors after review might create the wrong impression, as if you’re asking for favourable treatment in the future.

This last aspect brings the questions: “Should we reveal ourselves as reviewers or not?” and “Anonymous or signed review?” (see this perspective and another one). A senior editor and the author of Geoverbiage, Judy Totman Parrish, says that whether you sign your reviews is a personal decision, and that she has always signed her reviews in order to ensure the transparency, and the free exchange of ideas. She also says that she’s never experienced any backlash for any of the reviews she wrote.

I write my reviews anonymously, for exactly the same goal as above: to work towards a fair peer-review process. I find that there are many instances in which biases can form during the peer-review process (i.e., based on gender, age, nationality, but also experience, affiliation, or even prestige/prominent names) (see this article). My personal take on these issues, is that I believe reviews should be double-anonymous (authors do not know who the reviewers are, and reviewers do not know who the authors are), and the review history should be made public. I think this would reduce biases (probably not completely, as some authors/research groups can still be identified by the work submitted), while a transparent review history could ensure the fairness and civility of the review process. Also, with the rise of review statistics (ORCID and/or Publons), one can still be acknowledged for the work performed, without having to sign their names. This might not be possible in some fields (i.e., medicine or other fields where ethical guidelines are stricter), but in geophysics and geodynamics this shouldn’t be a problem.

5.3 Providing and taking criticism

This section might seem out of place for this blog post, but imagine for a moment that you are an author, and you’ve just put a lot of work to write the best paper so far. Your co-authors have read and re-read the paper, generating multiple improved versions with their comments. You finally submit the manuscript for review and, after a seemingly a long amount of time, you get the reviews back. Would you take the delivered message(s) as intended, or be hurt by it? With time you learn to not take things personally, but it’s unavoidable not to feel the tiniest bit affected by major criticism for the study you’ve worked so hard on.

The peer-review process puts you at the other end of writing papers. Therefore, I think scientists need to try their best to provide and receive constructive criticism, and identify and avoid destructive criticism (usually, directed at a person). What helps is to ask yourself: “Is it fair point? Could I use it to make a better version of the manuscript?”. If the answer is ‘yes’, then take the comment and use it to improve your work.

5.4 The Golden Rule

I would like to finish with the Golden Rule of reviewing. In their interesting read, McPeek et al. (2009) suggests reviewers to perform reviews with this in mind: “Review for others as you would have others review for you”.

I think as a more general rule, we can use some ancient wisdom: “Don’t do to others what you wouldn’t want done to yourself!”. It goes for reviewing and many aspects of life.

References:

Hames, I., (2008), Peer review and manuscript management in scientific journals: guidelines for good practice. John Wiley & Sons, https://onlinelibrary.wiley.com/doi/book/10.1002/9780470750803

McPeek, M.A., DeAngelis, D.L., Shaw, R.G., Moore, A.J., Rausher, M.D., Strong, D.R., Ellison, A.M., Barrett, L., Rieseberg, L., Breed, M.D., Sullivan, J., Osenberg, C.W., Holyoak, M., and Elgar, M.A., (2009), The Golden Rule of Reviewing, The American Naturalist, Vol. 173, No. 5, 155-158, https://www.journals.uchicago.edu/doi/10.1086/598847

Nicholas, K.A., and Gordon, W. (2011), A quick guide to Writing a solid peer review, EOS, Vol. 92, No. 28,  https://sites.agu.org/publications/files/2013/01/PeerReview_Guide.pdf

Stiller-Reeve et al. (2018), A peer review process guide, https://www.scisnack.com/wp-content/uploads/2018/10/A-Peer-Review-Process-Guide.pdf

Stiller-Reeve et al. (2018), How to write a thorough peer review, Nature, doi: 10.1038/d41586-018-06991-0,nhttps://www.nature.com/articles/d41586-018-06991-0

Zimmerman, N., R. Salguero-Gomez, and J. Ramos (2011), The next generation of peer reviewing, Front. Ecol. Environ., 9(4), 199, doi:10.1890/1540-9295-9.4.199, https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1890/1540-9295-9.4.199

Tomography and plate tectonics

Jonny Wu - edited by Grace Shephard January 23, 2019

Turning your conference poster into a dress is so last season, darlings - seismic tomography-inspired shoes will be the hottest trend at #EGU19 no doubt.

The Geodynamics 101 series serves to showcase the diversity of research topics and methods in the geodynamics community in an understandable manner. We welcome all researchers – PhD students to Professors – to introduce their area of expertise in a lighthearted, entertaining manner and touch upon some of the outstanding questions and problems related to their fields. For our first ‘Geodynamics 101’ post for 2019, Assistant Prof. Jonny Wu from the University of Houston explains how to delve into the subduction record via seismic tomography and presents some fascinating 3D workflow images with which to test an identified oceanic slab.

Jonny Wu, U. Houston

Tomography… wait, isn’t that what happens in your CAT scan? Although the general public might associate tomography with medical imaging, Earth scientists are well aware that ‘seismic tomography’ has enabled us to peer deeper, and with more clarity, into the Earth’s interior (Fig. 1). What are some of the ways we can download and display tomography to inform our scientific discoveries? Why has seismic tomography been a valuable tool for plate reconstructions? And what are some new approaches for incorporating seismic tomography within plate tectonic models?

Figure 1: Tomographic transect across the East Asian mantle under the Eurasian-South China Sea margin, the Philippine Sea and the western Pacific from Wu and Suppe (2018). The displayed tomography is the MITP08 global P-wave model (Li et al., 2008).

Downloading and displaying seismic tomography

Seismic tomography is a technique for imaging the Earth’s interior in 3-D using seismic waves. For complete beginners, IRIS (Incorporated Research Institutions for Seismology) has an excellent introduction that compares seismic tomography to medical CT scans.

A dizzying number of new, high quality seismic tomographic models are being published every year. For example, the IRIS EMC-EarthModels catalogue currently contains 64 diverse tomographic models that cover most of the Earth, from global to regional scales. From my personal count, at least seven of these models have been added in the past half year – about one new model a month. Aside from the IRIS catalog, a plethora of other tomographic models are also publicly-available from journal data suppositories, personal webpages, or by an e-mail request to the author.

Downloading a tomographic model is just the first step. If one does not have access to custom workflows and scripts to display tomography, consider visiting an online tomography viewer. I have listed a few of these websites at the end of this blog post. Of these websites, a personal favourite of mine is the Hades Underworld Explorer built by Douwe van Hinsbergen and colleagues at Utrecht University, which uses a familiar Google Maps user interface. By simply dragging a left and right pin on the map, a user can display a global tomographic section in real time. The displayed tomographic section can be displayed in either a polar or Cartesian view and exported to a .svg file. Another tool I have found useful are tomographic ‘vote maps’, which provide indications of lower mantle slab imaging robustness by comparison of multiple tomographic models (Shephard et al., 2017). Vote maps can be downloaded from the original paper above or from the SubMachine website (Hosseini et al. (2018); see more in the website list below).

Using tomography for plate tectonic reconstructions

Tomography has played an increasing role in plate tectonic studies over the past decades. A major reason is because classical plate tectonic inputs (e.g. seafloor magnetic anomalies, palaeomagnetism, magmatism, geology) are independent from the seismological inputs for tomographic images. This means that tomography can be used to augment or test classic plate reconstructions in a relatively independent fashion. For example, classical plate tectonic models can be tested by searching tomography for slab-like anomalies below or near predicted subduction zone locations. These ‘conventional’ plate modelling workflows have challenges at convergent margins, however, when the geological record has been significantly destroyed from subduction. In these cases, the plate modeller is forced to describe details of past plate kinematics using an overly sparse geological record.

Figure 2: Tomographic plate modeling workflow proposed by Wu et al. (2016). The final plate model in c) is fully-kinematic and makes testable geological predictions for magmatic histories, terrane paleolatitudes and other geology (e.g. collisions) that can be compared against the remnant geology in d), which are relatively independent.

A ‘tomographic plate modelling’ workflow (Fig. 2) was proposed by Wu et al. (2016) that essentially reversed the conventional plate modelling workflow. In this method, slabs are mapped from tomography and unfolded (i.e. retro-deformed) (Fig. 2a). The unfolded slabs are then populated into a seafloor spreading-based global plate model. Plate motions are assigned in a hierarchical fashion depending on available kinematic constraints (Fig. 2b). The plate modelling will result in either a single unique plate reconstruction, or several families of possible plate models (Fig. 2c). The final plate models (Fig. 2c) are fully-kinematic and make testable geological predictions for magmatic histories, palaeolatitudes and other geological events (e.g. collisions). These predictions can then be systematically compared against remnant geology (Fig. 2d), which are independent from the tomographic inputs (Fig. 2a).

The proposed 3D slab mapping workflow of Wu et al. (2016) assumed that the most robust feature of tomographic slabs is likely the slab center. The slab mapping workflow involved manual picking of a mid-slab ‘curve’ along hundreds (and sometimes thousands!) of variably oriented 2D cross-sections using software GOCAD (Figs. 3a, b). A 3-D triangulated mid-slab surface is then constructed from the mid-slab curves (Fig. 3c). Inspired by 3D seismic interpretation techniques from petroleum geoscience, the tomographic velocities can be extracted along the mid-slab surface for further tectonic analysis (Fig. 3d).

Figure 3: Slab unfolding workflow proposed by Wu et al. (2016) shown for the subducted Ryukyu slab along the northern Philippine Sea plate. The displayed tomography in a), d) and e) is from the MITP08 global P-wave model (Li et al., 2008).

For relatively undeformed upper mantle slabs, a pre-subduction slab size and shape can be estimated by unfolding the mid-slab surface to a spherical Earth model, minimizing distortions and changes to surface area (Fig. 3e). Interestingly, the slab unfolding algorithm can also be applied to shoe design, where there is a need to flatten shoe materials to build cut patterns (Bennis et al., 1991). The three-dimensional slab mapping within GOCAD allows a self-consistent 3-D Earth model of the mapped slabs to be developed and maintained. This had advantages for East Asia (Wu et al., 2016), where many slabs have apparently subducted in close proximity to each other (Fig. 1).

Web resources for displaying tomography

Hades Underworld Explorer : http://www.atlas-of-the-underworld.org/hades-underworld-explorer/

Seismic Tomography Globe : http://dagik.org/misc/gst/user-guide/index.html

SubMachine : https://www.earth.ox.ac.uk/~smachine/cgi/index.php

References

Bennis, C., Vezien, J.-M., Iglesias, G., 1991. Piecewise surface flattening for non-distorted texture mapping. Proceedings of the 18th annual conference on Computer graphics and interactive techniques 25, 237-246.

Hosseini, K. , Matthews, K. J., Sigloch, K. , Shephard, G. E., Domeier, M. and Tsekhmistrenko, M., 2018. SubMachine: Web-Based tools for exploring seismic tomography and other models of Earth's deep interior. Geochemistry, Geophysics, Geosystems, 19. 

Li, C., van der Hilst, R.D., Engdahl, E.R., Burdick, S., 2008. A new global model for P wave speed variations in Earth's mantle. Geochemistry, Geophysics, Geosystems 9, Q05018.

Shephard, G.E., Matthews, K.J., Hosseini, K., Domeier, M., 2017. On the consistency of seismically imaged lower mantle slabs. Scientific Reports 7, 10976.

Wu, J., Suppe, J., 2018. Proto-South China Sea Plate Tectonics Using Subducted Slab Constraints from Tomography. Journal of Earth Science 29, 1304-1318.

Wu, J., Suppe, J., Lu, R., Kanda, R., 2016. Philippine Sea and East Asian plate tectonics since 52 Ma constrained by new subducted slab reconstruction methods. Journal of Geophysical Research: Solid Earth 121, 4670-4741