SM
Seismology

Seismology

Some reminders for EGU2017 General Assembly

With only 3 days left for the kick off of the annual European Geosciences Union General Assembly (2017), here is a quick-list to go through in time for EGU.

First, read this page for information concerning activities for Early Career Scientists at the GA:
https://www.egu.eu/young-scientists/at-the-assembly/

Sunday 23th April: The Opening Reception, 18.30-21.00 in Foyer E.
Mingle and tingle with the crowd, old, not so old, and young scientists, all in one place. A perfect place for a cheer and networking. A gathering point for early career scientists provides the opportunity to meet like-minded fellows, especially if it is your first time at the General Assembly or you are coming alone.

EU2017 mobile app
The EGU2016 mobile app is now available for most smart phones. Go to http://app.egu2017.eu  to download the app. 

Short Courses
With an ever increasing number of short courses held at the GA,  probably there is one good course for you. Many are held during breaks, purposely not to coincide with other sessions. The full list is here:  http://meetingorganizer.copernicus.org/EGU2017/sessionprogramme/SC

A quick look on the Seismology Program:  http://meetingorganizer.copernicus.org/egu2017/meetingprogramme/sm

  • Tuesday – Thursday: Meet the EGU Division President and the ECS Representative of Seismology
    Get a unique opportunity to meet with P. Martin Mai, the current president for the Seismology Division and L. Parisi. You are invited to stop at the EGU booth to ask EGU related questions or discuss ways you would like EGU to improve. Martin and Laura will be available on Tuesday and Thursday during lunch, 12:00-13:30 / Room EGU Booth
  • Medal Lectures
    Get the opportunity to listen to world class experts in various geosciences. Medal Lectures are special sessions that give merit to distinguished scientists. They are usually followed by insightful (and thought provoking)  presentations. These lectures are well attended and seats are quickly taken.

Note for seismologists: the Beno Gutenberg Medal Lecture by Hitoshi Kawakatsu on Wednesday, 26th April between 11:00–12:00 / Room K1. 

  • WednesdayDivision Meeting for Seismology (after the Beno Gutenberg lecture)
    In the Division Meeting for Seismology (SM), the division president will present the latest information on the state of the division, statistics for abstracts and sessions in 2016, and the news related to the various divisional activities. All members are invited, and encouraged to actively participate in the meeting. Lunch is provided.  Wed, 26 Apr, 12:15–13:15 / Room K1
  • Wednesday: Recent activities of the Seismology Division Early Career Representative(s) 
    What is a POM? Ever read a Seismology Blogpost? Are you aware of our facebook and Twitter initiatives? Do you have any comments/recommendations and/or concerns with regards to EGU and/or the Seismology Division? This is the right opportunity to share ideas with your ECS representative(s). We highlight all Seismology activities on a poster that will be presented on Wednesday 26th April, 17:30-19:00 – at EGU2017-13751. Hall X3. Come over and let’s talk!
  • Wednesday 26th April, 20h: SEISMOLOGY SOCIAL EVENT : Meet us for a drink at Mel’s Craft Beers & Diner, Wipplinger-straße 9, 1010 Wien.

  • Thursday: Consider attending our yearly own Short Course: Seismology for non-seismologistsThursday 27h April, 13:30-15:00, Room -2.91. A dedicated short course directed to non-seismologists or early career seismologists, with a particular focus how to integrate seismology within your own research. Every year this short course has been a success. We likely won’t turn you into a seismologist in 90 minutes, but would rather like to make you aware how seismological techniques can help you in geoscience.

Early Career Scientists’ Lounge.

In the Red Level of the conference centre you can find a place to take a break, grab a free coffee or soft drink and gather your thoughts away from the buzz of the Assembly. The lounge is also a great place to catch up with colleagues you haven’t seen in a while and perhaps strike up a new collaboration. On the notice boards you can find information about cultural activities on offer in Vienna. There is also the opportunity to provide feedback via suggestion boards.


By Koen Van Noten

Koen Van Noten is an earthquake geologist at the Geological Survey of Belgium. He investigates the influence of site effects on intraplate earthquake ground motions by Did You Feel It?” macroseismic data and near-surface geophysical techniques. Koen’s role as ECS is to encourage students to promote their results in seismology, geology and near-surface geophysics in various ways.

EGU Seismology Division 2017 visibility survey

Dear Seismology Division blogpost, Facebook and Twitter followers,

The EGU Seismology Division has prepared an online survey to investigate how members are following our division’s activities online. The data we will acquire through this simple survey allows us to learn how we can improve our visibility and to which activities we could further focus. The results will NOT be used for any commercial activities. They will be shown during next month’s GA in Vienna. All division members are encouraged to take part and to spread the word !

Visit the survey here:
goo.gl/CrR7N2

The online survey is an initiative of the Seismology ECS Team on behalve of Koen Van Noten, Laura Parisi, Matthew Agius, Laura Ermert, Lucia Gualtieri, Kathrin Spieker and Martin Mai (EGU Seismology Division President)

Visit the Blog: http://blogs.egu.eu/divisions/sm/
Facebook page: https://www.facebook.com/EGUSeismologyDivision/
Division on Seismology webpage: www.egu.eu/sm/home/
Twitter account: https://twitter.com/EGU_Seismo


By Koen Van Noten

Koen Van Noten is an earthquake geologist at the Geological Survey of Belgium. He investigates the influence of site effects on intraplate earthquake ground motions by Did You Feel It?” macroseismic data and near-surface geophysical techniques. Koen’s role as ECS is to encourage students to promote their results in seismology, geology and near-surface geophysics in various ways.

Paper of the month — The origin of volcano-tectonic earthquake swarms by Roman and Cashman (2006)

Paper of the month — The origin of volcano-tectonic earthquake swarms by Roman and Cashman (2006)

We are pleased to propose you a new Paper of the Month written by Dr. Derek Keir on volcano seismology.

Derek’s PhD thesis was on the “Seismicity of the Ethiopian rift” and conducted at Royal Holloway University of London under the supervision of Prof. Cindy Ebinger and Prof. Graham Stuart of the University of Leeds. Towards the end his PhD studies, the Dabbahu rifting episode started (September 2005) and formed much of the focus of his research for a decade. During 2006 and 2007 he worked as a teaching fellow at Royal Holloway, and then went on to a three year NERC fellowship at the University of Leeds during 2008-2010. He there worked with Prof. Tim Wright’s InSAR group to integrate seismic and geodetic constraints on dike intrusion. Since 2011, he has been a lecturer, and then from 2015 associate professor at the University of Southampton. Since 2016 he also holds the position of associate professor at the University of Florence. He works on a range of tectonic and volcanology problems, mainly in extensional settings.


I have decided to write about the 2006 Geology paper titled “The origin of volcano – tectonic earthquake swarms” by Roman and Cashman since it provides an exceptionally eloquent summary of how earthquake locations and focal mechanisms can be used to interpret magma dynamics, and why different volcanoes or volcanic settings show varying seismic characteristics. The paper was initially very useful for me personally since it was published near the start of the 2005-2010 Dabbahu rifting episode (e.g. Wright et al., 2005; Keir et al., 2009) and provided me, at the time very much a volcano novice, with a clear and concise picture of how to interpret the high-frequency seismic signals so commonly associated with magma motion. I have since recommended it as reading to a large proportion of my PhD and masters level students.

The use of earthquakes is an important tool in volcanology and volcano monitoring (Sparks et al., 2012), since the motion of magma in the Earth’s crust causes localised stress changes that can induce failure on new or pre-existing fractures near the intrusion. The majority of the earthquakes are called volcano-tectonic (VT) earthquakes because the individual waveforms have an appearance, with clear P- and S-wave onsets and high frequency content, the same or similar to regular tectonic earthquakes occurring on faults with slip not induced by magma motion (Roman and Cashman, 2006).

The location of these VT earthquakes can potentially provide clues to where magma is moving, and the earthquake focal mechanisms can provide clues to the type of fault slip, from which the orientation of the stress field can be inferred.

Despite the relatively simple idea that magma can stress the rock enough to cause an earthquake, variable and complex patterns of earthquakes in space and time can be observed around the magma bodies inside real volcanoes. The fundamental reasons for the variable distribution in space and time of VT earthquakes, and also the different types of focal mechanisms observed at different volcanoes were previously very difficult to discern in the published literature.

This paper starts off by providing the best summary I have read to date on three fundamental models of VT earthquakes by integrating the location of earthquakes relative to the associated intrusion with the orientation of the stress field and resultant focal mechanism. The paper describes that VT seismicity is commonly caused by stresses induced near the tip of a propagating intrusion, with the focal mechanisms consistent with the regional tectonic stress orientation. In this model the earthquake activity moves through time and tracks the position of the leading edge of the new intrusion.

The more important of the 2 alternative models is that for an inflating intrusion. In this model the earthquakes can be distributed all around the magma body, with no time migration. The compression created by the magma inflation against the wall rock can act against regional tectonic stresses to locally rotate the principal stresses, which can be inferred from a 90 degree rotation in earthquake focal mechanisms. The description of the various models is supported by a fantastic figure that incorporates all these elements, and is even directly useable in all three different types of regional stress fields by simply rotating the diagram.

The paper then draws in information from various examples of seismicity during volcanic eruptions in order to interpret fundamental controls and driving mechanisms of earthquakes, with links to magma rheology and dynamics. The major outcome is that the examples of a lack of hypocenter migration but with stress field rotation occurs before the eruption of magmas that undergo extensive crystallization during ascent and are commonly of intermediate composition. They suggest various mechanisms of increased normal stress at the intrusion wall that ultimately causes a stress field rotation including shear dilatency of magma and vesiculation of bubbles in the melt. In contrast, examples of migrating hypocenters with no stress field rotation are commonly associated with basaltic magma where stress changes associated with intrusion dilation are low compared to regional tectonic stresses. In such settings, amplification of regional stresses at the leading edge of relatively rapidly propagating intrusions causes the migrating earthquake pattern.

Since the publication of this paper the volcanology community has seen a rapid increase in the numbers of multidisciplinary studies at volcanoes that include ever more dense deployments of monitoring equipment and inclusion of satellite derived measurements of gas release and deformation (e.g. Sigmundsson et al., 2015). As predicted towards the end of the Roman and Cashman paper these new studies are providing ever better constraints on the forces associated with magmatic processes and how these interact with regional stresses in order to fully understand how magma interacts with rock. Despite these developments this paper still remains an extremely insightful piece of research that should be the starting point for all volcanologists wishing to use earthquakes to understand how magma moves.

 

References

Keir, D., Hamling, I.J., Ayele, A., Calais, E., Ebinger, C., Wright, T.J., Jacques, E., Mohamed, K., Hammond, J.O.S., Belachew, M., Baker, E., Rowland, J.V., Lewi, E. and Bennati, L, 2009, Evidence for focused magmatic accretion at segment centers from lateral dike injection captured beneath the Red Sea rift of Afar, Geology, 37, 59-62.

Roman, D.C., and Cashman, K.V., 2006, The origin of volcano-tectonic earthquake swarms, Geology, 34, 457-460, doi: 10.1130/G22269.1.

Sigmundsson, F., and 37 others, 2015, Segmented lateral dyke growth in a rifting event at Bardabunga volcanic system, Iceland, Nature, 517, 191-195.

Sparks, R.S.J., Biggs, J. Neuberg, J.W., 2012, Monitoring volcanoes, Science, 335, 1310-1311.

Wright, T.J., Ebinger, C., Biggs, J., Ayele, A., Yirgu, G., Keir, D., Stork, A., 2006, Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode, Nature, 442, 291-294.

Paper of the Month – Bubbles and seismic waves

Modified figure based on “Tiny Bubbles” by frankieleon 

Our paper of the month is  Bubbles attenuate elastic waves at seismic frequencies: First experimental evidence” (N. Tisato et al., 2015) commented by Luca De Siena.

Luca De Siena is Lecturer in Geophysics at the School of Geoscience, University of Aberdeen (UK). He received his PhD from the University of Bologna (Italy) with a scholarship from the INGV-Osservatorio Vesuviano for his work on seismic attenuation imaging of Mount Vesuvius and Campi Flegrei volcanoes. During his postdoc at the Institut für Geophysik, Westfälische Wilhelms Universität (Münster, Germany), Luca worked on the development of novel imaging techniques using stochastic wave propagation, whose application has led to novel attenuation and scattering models of Deception Island (Antarctica), Tenerife (Spain), and Mount St. Helens (US) volcanoes. His research interests include the development and application of attenuation and scattering tomography at lithospheric and mantle scales, and in sub-basalt/reservoir settings.

Luca will present us a paper by Tisato et al. that finally provides experimental evidence on the effects of fluids and gasses on seismic attenuation. The results nicely connect seismology with rock physics, and are important for any seismologist interested in using amplitude information to track fluids in settings, like volcanoes and reservoirs, where they represent a clear hazard/resource. The paper gives insight into processes that open a new seismology-rock physics research path, and better connects our Division with Geochemistry and Volcanology.


“Seismic attenuation is an outstanding tool to image the physical and thermal properties of the lithosphere, particularly in volcanic areas. But any seismologist studying and imaging attenuation in 3D is aware of a long-standing issue with researchers in different disciplines, such as petrology and volcanology: they want magma, and they will see it in our model. Since attenuation is so sensitive to hot structures and physical changes they will just pick an anomaly and model a sill.

Probably, also the seismologist wants that anomaly to be magma, in order to publish the highest-impact journals and be highly cited. For the average reader and the editor of these journals, there is in fact an ocean (of interest) between the “Seismic attenuation imaging of Yellowstone magma sill” and the “Seismic attenuation imaging of a high-attenuation domain under Yellowstone caldera that could be a magma sill/fluid reservoir/hot rock topping melting, please pick one”. The truth is we still have a long way to be able to characterize that domain in terms of magma/fluids/heterogeneity just by looking at seismic attenuation.

In their paper, Tisato et al. take a step towards this direction by concentrating on bubbles: in a laboratory, they prove that these microscopic objects are able to attenuate seismic waves at frequencies we use in the field. In addition, the best way to model this attenuation for imaging purposes is wave-induced-gas-exsolution-dissolution (WIGED), which I knew was an effective model to reproduce high seismic attenuation in magmas. Finally, a way to prove that magma fills all my low-Q areas? Not so much.

Bubbles are in fact crucial ingredients to model attenuation in fluids, and their relative percentage reduces and distorts seismic amplitudes in ways I have seen in seismic volcanic waveforms. I first read the paper with amazement at what our colleagues in rock-physics can actually pull out today. They can reproduce the physical processes I have been using throughout my career for imaging the Earth in their laboratories. The demonstration that the WIGED model is most effective to describe attenuation provides us with an ideal analytical input to image the Earth with attenuation, linking to petrological quantities related to the physical and chemical state of the Earth. The study thus provides us with an opening to multi-scale laboratory- field imaging techniques using attenuation.

The main strength of the work other researchers and industry will see is its application to fluid/gas monitoring. The use of seismic tomography based on WIGED is potentially a novel 4D technique better apt to monitor hazardous volcanic and reservoir structures. To me, the paper is the demonstration that seismology can aim to characterize the Earth and its complex processes at scales so far unexplored, once correct theoretical models and experimental evidences are provided, providing more reliable constraints to other disciplines.

The questions that came to my mind after reading it: Is the scale and level of heterogeneity in the laboratory the same I use in forward modeling? What if, with their results, I would be able to apply attenuation imaging to sample scale? And maybe use poroelasticity to link Q with porosity and permeability? A paper that lets you with so many ideas and is so good at connecting seismology with other disciplines is rare, and certainly worth reading.”


Reference: Tisato, N., Quintal, B., Chapman, S., Podladchikov, Y., & Burg, J. P. (2015). Bubbles attenuate elastic waves at seismic frequencies: First experimental evidence. Geophysical Research Letters, 42(10), 3880-3887.

Do you have questions, suggestions or comments? Please use the space below, or contact us on Facebook or Twitter @EGU_Seismo!

Are you an experienced seismologists and you want to be our next PoM author? Contact us at sm-ecs @ egu.eu

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