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Paper of the Month — Seismic anisotropy

Paper of the Month — Seismic anisotropy

“SEISMIC ANISOTROPY AND MANTLE DEFORMATION: WHAT HAVE WE LEARNED FROM SHEAR WAVE SPLITTING?” (M. K. SAVAGE, 1999) commented by Dr. Jessica Johnson

 

Jessica Johnson from the University of East Anglia (UK) is our guest author of the PoM blog series of this month! She has chosen to comment on the paper “Seismic Anisotropy and mantle deformation: what have we learned from shear wave splitting?” (M. K. Savage, 1999). Firstly, let me introduce Jessica to discover why this paper is so important for her and then lets enjoy together her PoM!

At the University of Leeds, under the supervision of Prof. Neuberg, her MSci dissertation investigated the trigger mechanism of LP events at Soufriere Hills volcano, Montserrat. Jessica’s PhD thesis was titled “Discriminating between spatial and temporal variations in seismic anisotropy at active volcanoes”, and was carried out under the supervision of Prof. Savage and Dr. Townend at Victoria University of Wellington. She completed a two-year research fellowship at the Hawaiian Volcano Observatory (HVO), mainly working on shear wave splitting analysis at Kilauea and developing FEMs to explain unique patterns of ground deformation. Her second post-doctoral position was at the University of Bristol on a Marie Curie Incoming International Fellowship. Since 2015, she has been a lecturer in Geophysics at the University of East Anglia, where herresearch continues to focus around volcano geophysics.


“When deciding which paper to write about for this ‘Paper of the Month’, I flip-flopped between a classical paper and an important recent one. A lot of my research centres around seismic anisotropy (the variation of seismic wavespeed with direction) so I wanted to do the subject justice. However, the topic, and in particular the existence of temporal changes in seismic anisotropy, is hotly debated.

The first significant observation of large-scale seismic anisotropy was in 1964, when Harry Hess found that seismic refraction measurements in oceans showed that the P wave velocity of the upper mantle (Pn) was consistently higher for profiles recorded perpendicular to an oceanic spreading centre than for profiles recorded parallel to the spreading centre. The measurement of seismic anisotropy has since been found to be a proxy for determining the direction of maximum horizontal compressive stress (SHmax) in the crust; applied stress can cause microcracks to preferentially open parallel to the maximum compressive stress, creating an anisotropic medium with the fast direction parallel to SHmax. Measurements of seismic anisotropy have been used to detect fabric and stress in ice flows and in the Earth’s crust, flow in the upper mantle, topography of the core-mantle boundary and differential rotation of the inner core.

Even with this rich history of research behind it, and countless papers using and advancing the use of seismic anisotropy to understand the Earth at different levels (a google scholar search showed that over 100 papers have been published with seismic anisotropy or shear wave splitting in the title in 2016 alone), there is still much that is unknown about the phenomenon. As such, I have chosen what I consider a classical and extremely important paper by Professor Martha Savage: “Seismic anisotropy and mantle deformation: What have we learned from shear wave splitting?” It is a review paper, being published in Reviews of Geophysics, but it highlights some of the ongoing questions, which even 17 years on have not been completely answered. It is this aspect of the paper that I find so inspiring. This paper does not pretend to know all of the answers but it is an honest account of the state-of-the-art, which encourages the continued interrogation of the way we understand the Earth. I first read this paper when preparing for my PhD, and have referred to it frequently since. It is usually the first paper that I point new students towards as it not only gives a concise overview, but it is refreshingly still relevant. While Savage concentrates this paper on mantle deformation, most of the ongoing questions are relevant for seismic anisotropy studies on all scales.

Shear wave splitting in an anisotropic crust. Anisotropy is caused by preferentially aligned cracks due to a maximum horizontal compressive stress (SHmax). A vertically propogating shear wave that is arbitrarily polarised gets split into a fast wave with polarisation (φ) parallel to crack alignment, and a slow wave, which is polarised at 90° to φ. The waves are seperated with delay time δt.

Shear wave splitting in an anisotropic crust. Anisotropy is caused by preferentially aligned cracks due to a maximum horizontal compressive stress (SHmax). A vertically propogating shear wave that is arbitrarily polarised gets split into a fast wave with polarisation (φ) parallel to crack alignment, and a slow wave, which is polarised at 90° to φ. The waves are seperated with delay time δt.

In essence, the theme of this paper is the interpretation and inferences made from the measurement of shear wave splitting. Shear wave splitting occurs when a shear wave travels through a seismically anisotropic medium, splitting into two orthogonal quasi-shear waves orientated according to the fast and slow directions of anisotropy. Assuming that the seismic anisotropy has been measured accurately, its existence could be due to temperature and pressure, partial melt, stress, strain history, composition and/or orientation of the material. Savage explores the evidence for each type of anisotropic mechanism in different tectonic regimes and relates the evidence to the models. The paper walks through the analytical steps of deciphering the anisotropic signal. Even here, the paper points out that assumptions or inferences must be made such as the location along the wavepath that the anisotropy occurs, the homogeneity (or heterogeneity) of the anisotropy, or the anisotropic symmetry system.

In this 1999 paper, Savage suggests that the measurement of shear wave splitting is reasonably routine, and she concentrates mainly on the achievements and challenges associated with its interpretation. Today there are numerous studies that use freely available software, following traditional methods, to measure seismic anisotropy. Some of these recent papers have a “black box” feel about them in that the authors are assuming the method is so well tried and tested that it does not need to be addressed. However, Savage also alludes to the ever increasing capability in computing technology and the fact that understanding will likely change in the future.

As with many disciplines, it seems that the more we know, the more we realise that we don’t know. Researchers (myself among them) have found it necessary to go back to the measurements themselves and ask fundamental questions such as what exactly is being measured? What artefacts exist in the measurements? What factors interfere with the measurements? Is there observer bias in the measurements? Why is there so much scatter in the measurements?

Tomographic methods, high-density arrays, sophisticated modelling and decades of seismic data have helped the community come some way toward answering the Big Questions posed by Savage such as “Where is the anisotropy really occurring?”, “What causes the observed variations of splitting parameters?” and “Is anisotropy telling us about mantle flow or lithospheric deformation, or both (or neither)?”. All of these questions are currently being addressed within the community. Indeed, it is the continuing existence of these questions that causes so much of the controversy around the use of seismic anisotropy.

The measurement of seismic anisotropy has the potential to be an extremely powerful tool in understanding the Earth at all scales. Of particular interest to some is the capacity to use seismic anisotropy to independently measure and monitor in situ stress variations in the crust, both spatially and temporally. This ability would have implications for the monitoring of active volcanoes and earthquake-prone regions, assisting in risk mitigation efforts. In addition, stress monitoring in the crust would be useful in various engineering and energy sectors.

This important review paper should be the starting point for any scholar wishing to embark on a seismic anisotropy journey. Savage not only explains the phenomenon clearly and highlights important achievements, but applies the scientific method within the review paper to emphasise the caveats and future challenges. There is also a helpful mini-tutorial in the appendix to get you started!”

Reference

Savage, M. K. (1999). Seismic anisotropy and mantle deformation: What have we learned from shear wave splitting? Reviews of Geophysics, 37(1), 65–106. article. http://doi.org/10.1029/98RG02075


Is Savage (1999) one of your favorite classic paper as well? Do you want to add anything to Jessica’s comment? Use the space below to add your comment!
Are you an experienced seismologists and you want to be our next PoM author? Contact us at sm-ecs @ egu.eu

What was going on this week in the world of the ECSeismologists?

What was going on this week in the world of the ECSeismologists?

The 2nd TIDES training school!

About 60 ECSeismologists (42% women, 58% men; 67% PhD students, 33% others) gathered in Sesimbra (Portugal) from 19th to 23th Sep 2016 to be trained on seismic noise, from the physics of noise generation to seismic interferometry. Two of us had the opportunity to attend the school and we are happy to share our experiences in the blog!

But first, what is TIDES? Ok, apart from the thing the moon does to Earth? TIDES stands for TIme DEpendent Seismology, an EU COST action that aims to structure the EU seismological community for the development of data-intensive, time-dependent techniques for monitoring Earth active processes (e.g., earthquakes, volcanic eruptions, landslides, glacial earthquakes) as well as oil/gas reservoirs. TIDES is envisioned to connect European laboratories in Academia and Industry with complementary skills and will organise a series of workshops and advanced schools to train the next generation of scientists. 

The school in Sesimbra was the second training opportunity organised by the TIDES COST action (the first one was held in Jun 2015 in Bertinoro, Italy). At this year’s school, ECSs  were taught on ambient seismic noise generation mechanisms, correlations of scattered wave fields, and their applications to imaging Earth structure. For the occasion, a large group of  experts (Erhard Wielandt, Fabrice Ardhuin, Eléonore Stutzmann, Wayne Crawford, Michel Campillo, Céline Hadziioannou, Andreas Fichtner, Andrew Curtis, Roel Snieder, Christoph Sens-Schönfelder, Lapo Boschi, Florent Brenguier, Chris Bean and Thomas Lecocq) filled the schedule with engaging lectures.

Roel Sneider talking about measuring and interpreting time-lapse changes in recorded waveforms.

Roel Sneider talking about measuring and interpreting time-lapse changes in recorded waveforms.

 Most of the lectures were a combination of theoretical background and current research problems. The opportunity to deepen our knowledge on the subject through their teaching was of course invaluable. But also precious, from an ECS perspective, was the opportunity to listen to scientific discussions between the trainers! Particularly appreciated by the ECSs were the lectures in which the scariest equations of the seismic noise were explained step by step, those in which advice on “how to do” or “how to be a good noise seismologists” were dispensed and those where unanswered, open questions were introduced and discussed.

All ECSeismologists had the opportunity to actively contribute their share of knowledge and excitement to the school by presenting their research with short talks and posters. The training was completed by two hands-on practicals given by the PhD students Laura Ermert and Korbinian Sager.

ECS-rep Laura Ermert talking about noise processing and noise source imaging during on of the two practicals.

ECS-rep Laura Ermert talking about noise processing and noise source imaging during on of the two practicals.

The COST Action TIDES is organised in five Working Groups (“Forward problems, HPC applications”, “Seismic tomography, full waveform inversion, uncertainties”, “Applications in the natural environment and industry”, “Workflow integration of data and computing resources”, Seismic interferometry and ambient noise”). During the training school Yann Capdeville, Ana Ferreira, Chris Bean, Heiner Igel and Martin Schimmel led the meetings of the working groups where everyone (ECSs included!) was invited to share new research and collaboration ideas and existing useful information for people working in the different fields.

Believe it or not: The program also contained some live Fado (traditional Portuguese music) and a documentary on the highest wave ever surfed! Another evening passed quickly while Roel Snieder shared his insights – and asked for ours – on the art of being a scientist.

Susana Custodio joined the school on Thursday afternoon to talk about the historical and seismological aspects of the Lisbon earthquake, which occurred in 1755. She then guided a field trip to magnificent cliffs and dinosaur footprints belonging to two different periods of Jurassic and Cretaceous.

Dinosaur footprints in Cretaceous rocks seen by participants during the field trip.

Dinosaur footprints in Cretaceous rocks seen by participants during the field trip. [Picture taken by Martha Deen].

The enthusiasm of the organization committee was strong, so that the schedule of the school resulted slightly tight. But as we came here from all over Europe (and even from Australia, Saudi Arabia and Brasil) to learn new and exciting science, this made us feel like we actually reached the goal. Moreover, the beautiful beach and the amazing weather we enjoyed during meals and coffee breaks relieved our fatigues, as well as those of our trainers!

As you could imagine, with a diverse program such as this one, such a training school depends heavily on the engagement and initiative of those preparing it, and we felt very grateful to the people dedicating their time to the organization of this event, in particular Julie Baron (Grant Holder manager), Graça Silveira (local organisation), Andreas Fichtner (scientific organisation), Andrea Morelli (Chair of the COST Action). THANK YOU… and see you next year for the 3rd TIDES training school on Seismic Tomography!

Are you curious about the next training school? You can find more information at http://tides-cost.eu and on the facebook page https://www.facebook.com/cost.tides.20152018/?fref=ts

Your ECS-reps Laura Ermert and Laura Parisi

Science communication after disasters

Science communication after disasters

When events such as the Aug 28 2016 Amatrice earthquake occur, we seismologists are asked to answer scientific questions and to give an immediate judgment of the situation. Such questions may be asked by media officers during formal interviews or by friends and family members in person or even on the social networks in informal settings (sometimes only a few seconds after the earthquake’s occurrence). The choice of words and tone is not straightforward because in these catastrophic situations the public is very susceptible to misunderstandings. The public may even feel distrustful towards scientists that convey complex contents in a too technical language. While some experienced scientists may be used to answering such questions, Early Career Scientists often lack training to give answers to satisfy the righteous curiosity of the public and to avoid disengaging people with science.

Therefore, we invited three seismologists and three communication officers to discuss this topic with the SM ECS-rep team. First, we requested to talk about the scope and the manners of the scientific communication after an event like the Amatrice Earthquake in an official setting (e.g. press conference, official website or social media page of an institution).

Dr. Francesca Serra, communication officer at King Abdullah University of Science and Technology (KAUST), explained us some basics of communication in such case:

communication […] to be effective, should not be scientific, but designed to deal with both the actual risk (science) and the perception of the risk (social). For this reason the most appropriate communication should always be a “Risk Communication”, a communication that takes into consideration both aspects of risk perception. […] Risk Communication is […] an instrument for social inclusion, individual empowerment and joint control and management of hazardous situations.

In her discussion, Dr. Bárbara Ferreira, EGU Media and Communications Manager, highlighted the main role of the communication after such events: For authorities, decision makers and journalists, it is better to have good estimates in real or near-real time than perfect estimates a few hours after an earthquake because they need to act quickly to mobilise rescue teams, aid in recovery efforts, and to inform the public.

Dr. Anne Obermann, Senior Scientist at Swiss Seismological Service described how this rapid information dissemination is achieved in Switzerland after a major seismic event: We have an on-call service that is informed 24/7 about magnitude and location of earthquakes. Reports [..] are created automatically and accessible on the webpage within seconds, where it is well stated that this information has not been verified yet.  We then verify the accuracy […] and send out alerts to various federal offices, news agencies and other media. For earthquakes of public interest […] we post more extensive information on the website once we have more accurate information [..] that is updated constantly. Also, on the manners of the communication, she stated: In my opinion, in official statements/media interviews only scientific information should be communicated. I think there is no place for personal opinions or political topics in such a context, partly, because our expertise is limited and partly because we are representing our institute.

Prof. Andrea Morelli, Chief Scientist at Istituto Nazionale di Geofisica e Vulcanologia (INGV),  agreed with her on the style of the communication: First of all, when you are seen as talking on behalf of some laboratory or institution, you must always refrain from giving your personal feelings, and stick to a single, ‘official’, picture […] You should show that you are in control, and the news is clear. […] You may be asked a thorny question, that may be too difficult to answer in a sentence or two. Do not trust the possibility to have time enough to explain! The first sentence should do, in case rephrase the issue and precisely ask yourself the quick question you wish to answer.

Martin Mai, Professor of Earth Science and Engineering at KAUST, pointed out an important aspect of the communication: The scientific community continuously debates how to best communicate science and its implications, specifically if hazard and risk are the topics. Addressing the public after such devastating events is particularly difficult, and does not come natural to most of us, but requires practice and training.[…] I think that as scientists we have the responsibility to inform precisely about what is known and not known, and to abstain from speculations.

Map of the seismic sequence from Aug 24 2016 updated to Aug 27 at 18h00. The star represents the event of magnitude 6.0 occurred on 24 Aug at 3h32. Modified from https://ingvterremoti.wordpress.com/2016/08/27/sequenza-sismica-tra-le-province-di-rieti-perugia-ascoli-piceno-laquila-e-teramo-aggiornamento-delle-ore-18-00-27-agosto/

Map of the seismic sequence from Aug 24 2016 updated to Aug 27 at 18h00. The star represents the event of magnitude 6.0 occurred on 24 Aug at 3h32. Modified from https://ingvterremoti.wordpress.com/2016/08/27/sequenza-sismica-tra-le-province-di-rieti-perugia-ascoli-piceno-laquila-e-teramo-aggiornamento-delle-ore-18-00-27-agosto/

Our communication officers also advised on when communication should take place. They underlined again the need for rapid information after an event, but it was also mentioned that ideally, communication should take place all the time, not only in case of a crisis:

SERRA: Only before the hazard takes place it is possible discussing openly and with clear minds about the outcome and management of a possible hazardous event. After the event, as a matter of fact, the communication–technically speaking–does not refer any more to the risk but to the mitigation of the ongoing crisis, and for that we have the term Crisis Communication that follows different mechanisms and dynamics.

FERREIRA: If a potentially destructive earthquake happened in your country and you are the press or communications officer for the national geoscience institute (e.g. the INGV in the case of the Amatrice earthquake) you have to put out information about the event as soon as possible. By this I mean, as early as you have estimates for the main parameters of the earthquake, such as magnitude, depth and location, even if these estimates are not 100% reliable very soon after the event. […] when a destructive  earthquake happens, the news moves very quickly from focusing on the seismic properties of the earthquake (an area where you as a seismologist can comment on) to the fatalities and economic losses (which is likely not your expertise). If you don’t answer within a few hours of the event, you’ll likely have missed your opportunity to provide information the public is interested in.

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A very interesting facet of today’s topic is who should communicate. Here, two of our respondents agree with the fact that scientists, and in particular seismologists, should be the only ones answering to scientific questions.

MAI: Communicating with the public, with the media, requires training.  […] Public scientific communications regarding natural (or any) disaster should be in the hands of people (scientists/experts) who are trained to effectively disseminate information to a broad audience. […] As scientists, we should try to stick to our domains of expertise when communicating with the general public. Personally, I try not to answer questions that are far from my domain of expertise (like on political implications or decision making) since I think this may easily lead to confusion and misunderstandings, but of course other people will handle this aspect differently.

FERREIRA: Even if you are not an expert in the region where the earthquake happened, as a seismologist, you are qualified to answer questions about earthquakes. If a journalist reaches out to you for information and you say that you don’t want to answer any questions about an event in Italy because your expertise is in earthquakes in Nepal, it is likely they will simply  move on to the next geoscientist on their contacts list, who may not even be a seismologist! Do your best to answer questions accurately and clearly, and if you don’t know something or don’t have enough information to answer a specific question, don’t be afraid  to say “I don’t know”.

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A more specific side we asked to comment is the communication of the uncertainty.

MORELLI: Magnitude turns out to be a number to which people are particularly sensitive. How to balance confidence with uncertainty? […] It is then tricky to convey the idea of uncertainty if you want to appear dependable –sometimes your audience may think that you are unreliable if you are too cautious. One thing that you should point out, however, is that the picture you are giving reflects well the current state of knowledge, that will evolve with time as more data are added and better analyses come out. In this way, you are not saying that someone might do a better job, but just that more work is needed.

MAI:

Scientists should state that it may take time, more data, and further analysis to fully understand the size of the event and its consequences, and that after an hour or a day, we may still have only incomplete information. […] It is particularly difficult to communicate uncertainties, or even probabilities, as most of us don’t have an intuitive understanding how to interpret probabilities. Therefore, we should make an effort to clearly explain the facts, the data, the known details, to then make the transition to why other aspects of the event, its cause and consequences, are not yet, or only imprecisely, known.

FERREIRA: A way to deal with communicating uncertainty, is simply by stating that the values you are giving represent the best estimates for the data available at that moment and that they might change as more data becomes available. This is what the INGV does, for example.

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Then, we moved toward questions more specific for ECSs. In fact, soon after the Amatrice seismic event, we ECS in Seismology have been frequently asked by family, friends and non-seismology colleagues a very generic question about what happened in Amatrice. Our common reactions are, in this order: panic (is s/he testing my knowledge?), pride (s/he wants to know my opinion because of my degrees and scientific publications), confusion (from where should I start? what does exactly s/he want to hear from me?). Thus, we asked to our interviewees what kind of answer we should give to satisfy curiosity and keep the interest to science high. Here their answers:

MORELLI:

You are a geophysicist, you know the matter from inside: be relaxed. […] Often, questions quickly get to earthquake prediction: for many people this appears to be the only goal of the seismological community. Avoid the comparison with meteorologists (who of course make excellent forecasts) and talk instead about what we do know about earthquakes–it’s a lot! Never underestimate seismic hazard in any region, and always get into talking about prevention as the most important measure for mitigation.

FERREIRA: A thing to bear in mind when addressing  someone who is not an expert is to be conversational and speak at a level a 15-year old would understand. Avoid jargon: don’t talk about “focal mechanism” or “tensional tectonics” because your audience won’t know what those things are. Stick to terms you would  find on a newspaper article. You can find other tips on communicating with the media, which, to a certain extent, are also  applicable when speaking to family and friends, on the EGU website.

From "Communication as a Scientist" http://www.nature.com/scitable/ebooks/english-communication-for-scientists-14053993/communicating-as-a-scientist-14238273

From “Communication as a Scientist” http://www.nature.com/scitable/ebooks/english-communication-for-scientists-14053993/communicating-as-a-scientist-14238273

MAI: Again, we need to be honest about what we know, what we don’t know just yet, and what perhaps will not be known at all for a long time. Taking an earthquake as an example, I explain where it happened, and why (natural events → plate tectonics; for possibly induced earthquakes, this becomes more complicated), and why this particular one may have caused so much (or little) damage. Often the challenge then is, depending on your audience at that moment, to find the right tone and language, and the appropriate level of simplifications. As scientists, we are often “proud to show off with all the stuff we think we know”, but that may confuse the people whose questions we are trying to answer.

OBERMANN: When I talk with my family or friends, it happens that I am politically incorrect and do state my personal opinion, however, I try my best to communicate it as such. This is very important, as non-experts cannot differentiate between my opinion and facts. When I talk to the public–and the public starts for me as soon as unknown people are present–we should be much more careful and restrict ourselves to the science. An exemplary question to illustrate this: “Who is to be held accountable for the tragedy in Amatrice? Could this have been avoided?”. This is not on us to judge!

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Our doubts about communication after a disaster as the Amatrice earthquake were stronger when thinking about how to speak on social media. We then asked to Laura Roberts-Artal, Communications Officer at EGU with expertises in social media, gave us very useful advices: if you don’t feel comfortable preparing original content about the earthquake, that’s ok. What you can do is reshare information from reliable sources about the earthquake. The lay person won’t know where to look for good quality information, whereas you will. Not only will you be helping others to learn more, you’ll be playing an important role in stopping the spread of misinformation and scaremongering.

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We thank Andrea, Anne, Barbara, Francesca, Laura and Martin for their time, useful information and advices. Here there are their full answers.

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This post was planned and edited by the SM ECS-reps Laura Parisi, Lucia Gualtieri and Laura Ermert, in collaboration with all the ECS-rep team [sm-ecs @ egu.eu].


BIOGRAPHIES

Andrea Morelli  is a seismologist, Chief Scientist at Istituto Nazionale di Geofisica e Vulcanologia (INGV), he also teaches courses as Adjunct Professor at Università di Bologna. He studied in Bologna and Harvard University, and has previously worked in Rome at ING, and at Università di Urbino. His main interest is seismic tomography, and the study of earth structure at different scales. He has been involved in seismic instrumentation projects, in the Mediterranean region and in Antarctica.

Bárbara Ferreira is the Media and Communications Manager of the European Geosciences Union. She is responsible for the Union’s communication activities, from coordinating the EGU newsletter to members and overseeing the blogging and social media activities of the organisation, to publishing press releases for journalists and organising press conferences. She has a PhD in astrophysics from the University of Cambridge.

Anne Obermann is a seismologist at Swiss Seismological Service. She obtained her PhD degree in 2013 in Grenoble under the supervision of Michel Campillo and Eric Larose. Her research focused on monitoring and locating tiny perturbations in the subsurface using multiply scattered coda waves from ambient noise correlations. Since 2014 she is working for the Swiss Seismological Service at ETH Zurich, first as a postdoc and now as a senior researcher with focus on different aspects of imaging with ambient noise data and induced seismicity.

Francesca Serra coordinates the communications of the CEMSE Division, KAUST, since 2015. Prior to her affiliation with KAUST, Francesca worked for the SISSA of Trieste as manager of a science communication EU project funded by the 7th Framework Programme in collaboration with 8 European Institutes of Research. Before SISSA, Francesca worked for 9 years as senior officer at the Joint Research Centre of the European Commission both in Italy and in Belgium. Francesca is also an official organiser of TEDx, touring exhibitions and scientific events.

Laura Roberts-Artal is the Communications Officer at the European Geosciences Union. She is responsible for the management of the Union’s social media presence and the EGU blogs, where she writes regularly for the EGU’s official blog, GeoLog. She is also the point of contact for early career scientists (ECS) at the EGU Office. Laura has a PhD in palaeomagnetism from the University of Liverpool.

P. Martin Mai is professor in the Physical Sciences and Engineering Division at KAUST. He joined KAUST in June 2009 as founding faculty member. Prior to his affiliation with KAUST, Prof. Mai worked as senior research scientist at ETH Zurich, Switzerland. In 2015, he was elected Division President of the Seismology Division of the European Geosciences Union (EGU). His research interests include the physics of earthquakes and the complexity of earthquake phenomena, focusing on earthquake-source imaging, dynamic rupture modeling, and earthquake mechanics.

A seismologist on vacation

A seismologist on vacation

Beginning of this month, I was travelling to Germany to visit family and friends. One week out of the office, without interpreting wiggles or creating synthetic seismograms. But I bet that most of you know that vacation from science does not really exist, especially if an awesome opportunity comes along…

What do seismologists do during their vacation?

I was visiting a friend in Göttingen. Maybe you have heard about this German city beforehand – of course in the context of seismology. You might think of Emil Wiechert and his seismographs, Karl Zoeppritz and his equations, Beno Gutenberg or lots of other seismologist, who all worked in Göttingen.

Emil Wiechert (1861-1928) came to Göttingen in 1898 and started building the seismological observatory. Using the data of the seismographs, he carried out research to uncover the mysteries hidden inside the Earth. For years to come, important research was done by a lot of seismologist at the observatory. Beginning of the 21th century the golden times of the seismological observatory seemed to be forgotten and the site was on the verge of being teared down. But luckily in 2005 an association was formed that restored the site and takes good care of it now. The Wiechert’sche Erdbebenwarte Göttingen e.V. (Wiechert Earthquake Station Association) offers a guided tour on the first Sunday of every month between 2 and 5 pm to show the public around the observatory.

So I dragged my non-seismologist friend to the Erdbebenwarte – no, actually he was as excited as I was. All started with a very neat general introduction to seismology that was suitable for everybody, from the little kid to the grown-up seismologist. You could also listen to witty anecdotes about how the association struggled with German bureaucracy.

I don’t want to reveal too much because it is much nicer to experience it by yourself. But let me give you a sneak peek of what we saw and experienced there.

Exploration seismology in the early 20th century

Ludger Mintrop (1880-1956) dropped a 4-ton steel ball from a 15 meters height scaffolding to create artificial earthquakes to look inside the earth using transportable seismometers. Well, transportable seismometers at that time were still on the heavy side (~ 700 kg).

mintrop

Mintrops 4-ton steel ball. Photo by Wiechert’sche Erdbebenwarte e.V.

The association restored the scaffolding and now they drop the ball every time visitors are around. To hear and to feel the bump of the 4-ton steel ball was amazing. And the first thought that popped in my mind: “It would be a lot of fun to create seismograms the old fashioned way.” Of course, nowadays this is not efficient for us anymore, but I can dream, right?

The oldest working seismograph

Even though seeing the Mintrop ball fall down and feeling the impact was impressive, the best was yet to come: seeing the oldest, still working seismographs that already Wiechert had looked at.

verein-banner

Entrance to the seismograph room. Photo by Wiechert’sche Erdbebenwarte e.V.

The seismographs at this site were built in 1902 and 1904/05, and doing their duty already for way over 100 years.

“Every seismologist should kneel before this site.”

I was looking around when Wolfgang Brunk, our guide and chairman of the association, said those words and I decided it would have been too embarrassing for me to kneel down. But he is right, it is a very special place especially for seismologists. The doors were opened and we entered the room that houses the oldest working seismographs in the world.

seismograph

Inside the “holy grail” of seismology. The seismographs build in the beginning of the 20th century are still running. Photo by Wiechert’sche Erdbebenwarte e.V.

I enjoyed the guided tour a lot, definitely the best day in 2016 thus far. It is a very cool “scientific adventure park” for the whole family.

With love to detail the association did and still does an amazing job to keep Wiechert’s legacy alive and to bring the seismology in an easy and fun way to the people. Next time you are in Germany, you definitely have to visit the seismological station in Göttingen! You can either do that on the first Sunday of every month between 2 and 5 pm, or you contact the association to find the most convenient time for a private tour.

Are there similar sites that you visited during your vacation? Comment here! Maybe we can come up with a guide about “seismological vacation” worldwide.


Kathrin.SpiekerKathrin Spieker is one of the EGU ECS-representatives of the Seismology division. She is a PhD student in seismology at the Department of Earth Science of the University of Bergen (Norway) and investigates globally the crustal and upper mantle structure using passive seismic imaging with the focus on teleseismic converted waves. You can contact Kathrin via e-mail: Kathrin.Spieker@uib.no.

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