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Seismology

Seismology

When the Earth gets animated

Animations are a terrific way to engage students and to support public understanding of Earth Sciences. Yet, to make scientific research accessible, visual and fun is not easy. How do animations bring geophysics concepts to life? We asked the expert, Jenda Johnson (IRIS Education and Public Outreach)

When it comes to explaining Earth’s processes, animations come to the rescue.
Tectonic plates drifting on the asthenosphere, volcanos spewing lava and rubbles from their crater, earthquakes fracturing the crust and propagating till the Earth’s surface… Geoscience processes all deal with natural systems that change over time. Yet to understand dynamic subject matters is not easy-peasy, especially for learners, whether they be students or general public. To remedy this, graphic representation has increasingly been used as support [1], also thanks to the advancement in computer and software technology.
One of the reasons animations are now found so widely is the belief, shared among many, that animations can help learners understand complex ideas more easily. A recent study by Alessi and Trollip (2001)[2] has shown that mental representation is crucial for learners. Compared to static graphical representations, animations and simulations attract and capture attention; they facilitate science learning by reducing the level of abstraction of spatial and temporal information and the load of cognitive processing  [3], allowing the audience to build mental representation of unseen processes. Last but not least, their cosmetic appeal makes learners more motivated [4].
Animations are fully-fledged effective learning tools. But what is the educational strategy behind them? How can we create animations that are good for learning? Find out in our Interview with the Expert, Jenda Johnson.

 

Jenda Johnson has been working with the IRIS Education and Public
Outreach group since 2006. She produces geoscience animations,
videos, & interactive rollovers to depict geologic and seismologic
processes for teachers, students and general public. We asked her a
series of questions about her scientific, communication and graphics
expertise in making any geoscience project eye-catching, accurate
and clear for educational purposes.

 

 

 

What is your story, Jenda? Why Geology?
The truth is, I didn’t study Geology until I was 40 years old. I had had a career before that, but I had recently married a geologist and became surrounded by them. Being around geologists eventually prompted me to take a class of geology… mainly to understand the jargon of the people who came for dinner! Words like ‘andecite’ or ‘fractionation’ would no longer be a mistery to me. So I took a class, which then snowballed into getting a Bsc and a Msc in volcanic processes, and received a courtesy faculty position. But at that point my husband was transferred to Hawaii. Unfortunately, even though my master degree was in volcanic processes, there was no work for me there.”

 

That’s what drew you to science outreach?
“As a grad student, I was addicted to field mapping and research. I never envisioned a career into public outreach, honestly. But then I had to move away from research, where my heart was. I left the university and I joined the group that filmed lava flows in the Hawaii… And I got into filming for seven years! Starting thinking how to share that with the public and how much it can increase people’s interest in science: that’s what completely won my heart at that moment of my life.”
What about IRIS?
“Eight years later, when my husband and I returned to Oregon, I was contracted for a temporary position by IRIS. When I inquired as to what my job was, I was asked to figure out what was needed to help teach the public about earthquakes and seismology. Even though I had a seismology class as undergraduate, I never understood it very well. I also realized that the teaching material offered on the internet was not easy for the public to understand. Many people don’t see life in 3D: what they really need is a stepwise process of an animation.”

 Despite the apparent need for science outreach, achievements are still not sufficiently recognised. In times of an increasingly competitive funding climate, high-quality publications remain the currency of science and time spent on outreach activities equals less time for research.” says Dr Anne Osterrieder [6]

Scientists are now calling for increased public outreach and communication efforts. Why in your opinion?
“I do respect the outreach aspect of science at every stage of career. It is a tragedy that more students aren’t engaged by science, because when taught well it can be a fascinating journey into learning about the entire universe. In middle- and high-school geoscience education, too many teachers don’t fully understand geophysical processes, thus have a difficult time conveying an enthusiasm that hooks students to love science. Within academia, most focus only on his/her own research project, not taking time to share it with the public. Some component of outreach ought to be a part of every research projects: by describing your work in common language you can help the general public and the teachers understand your research, which results in interesting more people.”

 

Thanks to the establishment of several outreach activities in the last decades, the public knowledge of geoscience topics has improved. But still, some issues remain objects of debate among the masses. Is there still a topic on which science communicators should insist?
“I think that when there is scientific controversy, the major issues include misconceptions, lack of understanding, and a lack of ability to search for correct information. It is true that despite the numerous outreach activities, some topic still need to be explained. If I had to choose, my personal pet would be ‘predicting earthquakes’, which has been a hot-button topic. There are “conspiracy theorists” out there who believe that the government is hiding data. What I have always liked about seismology is that on the IRIS website all data is available in real time to anyone, especially if you subscribe to the data-management-system groups. Data is not hidden.”

 

Could you describe the process of creating an animation?
1) Research the topic. For complex topics I work with a Geophysicist to write out a story board that can be spoken aloud and that we can envision graphics for.
2) Collect photos and illustrations that others have made, and/or more commonly, make our own (use proper softwares).
3) Pull pieces together into an animation program.
4) Find science reviewers who are knowledgeable in the particular field of study to check for accuracy.
5) Have IRIS reviewers check to see that the animation works.
6) Get a narrator to read it.

 

Science disclosure is often the best compromise among scientific content, design and simplification of tough topics for the audience: what is your strategy? What is the aspect you focus more on when creating an animation?
“You need to find a common denominator that fills the gap between the science and the audience. In science animations, one of the mistakes often made is thinking that good art equals good science. Beautiful art may attract the general public but it doesn’t mean it is good science (but maybe that’s my excuse for not having artistic ability). Sometimes graphic artists are hired with no science background. They make very realistic pretty images but geophysical processes often can’t be shown to scale, because they are too huge or too small. So, I would say animation graphics should be designed with as little detail as possible to reduce information processing demands and let audience focus on the most important scientific aspects of the process.”

“People have fear of science: they have the fear they are not smart enough. And you want the audience to feel smart”

What are your key-points for an effective communication to the public?
“Know your audience. Try to address their level of knowledge: people need to be able to follow your presentation, what you are saying, and at the same time understand your slides. This can often be mentally challenging. Don’t underestimate that. Adjust language and graphic presentation accordingly. People have fear of science: they have the fear they are not smart enough. And you want the audience to feel smart.”

 

What is your suggestion for early career scientists to assertively communicate their science?
I remember as I was working on my master thesis, I enjoyed speaking with my peers. Accumulating and using a vast new scientific vocabulary can make you feel very powerful. But here I might caution you: be careful, adjust your speech depending upon who you are speaking or writing to. Keep in mind  that the words you chose can exclude your audience too. “If you can’t explain a process to your grandmother, you may not fully understand it” – that’s my motto. Do not try to impress your audience with all the fancy new words you have accumulated during your studies such that you use them to the exclusion of others following what you say.”

 

 

If you were to name a person who inspired you during your career, who would (s)he be?
“During this career (one of many!) in seismology outreach, I would definitely name Dr. Robert Butler. I began filming his workshops and now we work side-by-side on our trickiest animations. Robert had spent thirty years teaching at University of Arizona, he was made AGU fellow for his paleomagnetism research. He could have easily continued on that route. But quit it all to move to Portland and dedicated the rest of his career to teaching middle and high school science teachers about plate tectonics and earthquakes. He has received the highest marks in his workshop assessments, winning him a National Geoscience Teachers Award (NAGT). The way he uses his knowledge to teach teachers its really impressive and he taught me a lot: it is not ‘dumbing it down’, it is ‘clarifying it for the grandmothers!”

Jenda Johnson during one of her frequent backpacking trips on the mountains.

 

This post was written by Marina Corradini, with revisions from Walid Ben Mansour and Maria Tsekhmistrenko

 

 

Walid Ben Mansour is a post-doctoral research fellow at Macquarie University. He works on multi-observable probabilistic tomography for different targets (mining, seismic hazard). You can reach him at walid.benmansour[at]mq.edu.au

Maria Tsekhmistrenko is a PhD student at the University of Oxford. She works on the velocity structures beneath the La Reunion Island from the surface to the core mantle boundary. You can reach her at mariat[at]earth.ox.ac.uk

 

_________________________________________________________________________________
Jenda Johnson creates animations for IRIS to help Earth-science teachers understand complex seismologic processes, available here: www.iris.edu/earthquake. Member of the Board of Advisors at Oregon State University’s College of Earth Ocean and Atmospheric Sciences.  Among other collaborations: UNAVCO,  U.S. Geological Survey, Teachers on the Leading Edge (TOTLE), Cascadia EarthScope Earthquake and Tsunami Education Program (CEETEP), Hawai`i Volcanoes National Park, Haleakala National Park, EarthScope/USArray, High Lava Plains Seismic Array.

 

References:
  1. Lowe, R.K. (2004). Animation and learning: Value for money? In R. Atkinson, C. McBeath, D. Jonas-Dwyer & R. Phillips (Eds), Beyond the comfort zone: Proceedings of the 21st ASCILITE Conference (pp. 558-561). Perth, 5-8 December.
  2. Alessi, S.M. & Trollip, S.P. (2001).Multimedia for learning: Methods and development.Boston, MA; Allynand Bacon.
  3. Cook, M. P. (2006), Visual representations in science education: The influence of prior knowledge and cognitive load theory on instructional design principles. Sci. Ed., 90: 1073-1091. doi:1002/sce.20164
  4. Wouters, P., Paas, F. & van Merriënboer, J.J.G. Instr Sci (2010) 38: 89. https://doi.org/10.1007/s11251-008-9079-0
  5. https://www.theguardian.com/higher-education-network/blog/2012/feb/20/making-science-accessible

 

Scientific Talks: The Good, the Bad and the Ugly

Scientific Talks: The Good, the Bad and the Ugly

We’ve all been there at some point: being nervous, stuttering, or losing our train of thought because somebody looks so incredibly bored that you are afraid they might actually collapse. Then there’s saying something stupid or just plain wrong, or talking so fast and quietly that nobody understands what your results are.

These are certainly my lowest moments giving talks and I’ll save myself the embarrassment of referring to the time and place they happened.

 

Recently, I attended a conference and once again I witnessed the Good, the Bad and the Ugly. After a few short years in science I’ve already gathered a (substantial) list of faux pas that occurred during talks I’ve seen. Here are my absolute top 10 unsuccessful presentations in recent years:

  • Having the slide full of text (font size 8), reading directly from the slide, mumbling and not once looking at the audience.
  • All text written in bold and CAPITAL LETTERS. EVERYTHING THIS PERSON DID WAS TOO IMPORTANT FOR NORMAL FONT.
  • Figures directly drag and dropped from obspy, without labels (or font size 4) and then assuming everybody miraculously knows what the x and y axis are.
  • Animated animations with 10 figures on top of each other.
  • For the whole presentation not speaking into the microphone because the person is actually looking at the slide, explaining the important information without anybody hearing it.
  • Talking for 90% of the presentation about only one slide (which is not even relevant), realizing that time is running out and rushing through the rest of the slides which might have been interesting.
  • Squeezing 20 tiny figures very tightly into the final slide and only spending 15 seconds explaining them before time is up.
  • Generally coming unprepared.
  • A bright yellow background with pink colored font and green boxes for important information.
  • Comic sans. See this article for detailed information why comic sans should never be used.

 

 

…So, what makes a good talk?

 

Whenever I prepare a presentation, I try to follow the suggestions of my professor during my Masters. He had 5 golden rules for preparing a talk (here slightly modified):

  1. Keep the structure simple! Don’t try to squeeze in all the results of your project, unless they are important. Example: Introduction – Motivation – Methods – Results – Discussion. Done.
  2. Keep the slides simple! Not too cluttered with figures or text. Only put what you want to talk about, everything else that you will not talk about…Kick out! Text is there to support your argument, not to replace your talking.
  3. Remember the ‘1-slide, 1-minute’ rule: people don’t want to stare at the same slide for 5 minutes. Each slide needs to have some meaning, if you don’t talk about the slide, it goes in the bin.
  4. To check if a text or a figure is visually large enough, stand 60-100cm far from your desktop screen and see if you still can read the smallest font, if not make it bigger.
  5. Describe every figure you show and make sure to mention units and axis, even if the font is big enough – not everybody has a good eyesight. Make only very important statements or words boldit will stick in people’s minds better.

 

© Nienke Blom

 

These are the five basic rules of preparing the slides for a presentation. Now I want to add another, very important point.

After a recent week of talks at a conference the bulk of unsuccessful presentations were given by those who came unprepared, having dumped their latest research into one power-point presentation and made up their talks as they went along. On the other hand, often the best talks were from young researchers who might not have extensive results, but did have well-prepared, clean slides which were thought through and interesting even though some studies were at a preliminary stage. I enjoyed listening to those, because there were clearly some efforts put into these presentations.

 

Hence, my last point is: Prepare and practice your talk!

 

© Nienke Blom

 

 

This post was written by Maria Tsekhmistrenko, with revisions from Nienke Blom and Andrea Berbellini

 

 

Maria Tsekhmistrenko is a PhD student at the University of Oxford. She works on the velocity structures beneath the La Reunion Island from the surface to the core mantle boundary. You can reach her at mariat[at]earth.ox.ac.uk

Nienke Blom is a postdoctoral research associate at the University of Cambridge and works on seismic waveform tomography, developing methods to image density. She is the EGU point of contact for the ECS rep team. You can reach her at nienke.blom[at]esc.cam.ac.uk.

Andrea Berbellini is an Italian Post Doc at the University College London. He works on the source characterization from second-order moments and crustal tomography from ellipticity of Rayeligh waves. You can reach him at: a.berbellini[at]ucl.ac.uk

Seismology Job Portal

2 PhD positions 

[1] PhD/Postdoc in computational seismology and Lithospheric imaging by joint inversion of seismic data and gravimetric anomalies (Deadline for submission is 15-11- 2018) 

Goal: New methods for the joint inversion of seismic and gravimetric data, in order to obtain finely resolved 3D models of density at the regional scale. 

Scholarship: Funded by the OROGEN Program jointly organized by TOTAL, BRGM, and CNRS. 

Application:
https://www.seismosoc.org/job/laboratoire-get-geosciences-environnement-toulouse-toulouse-france-observatoire-midi-pyrenees-get-laboratory-at-cnrs-university-toulouse-p-sabatier-148-phd-posdoc-in-computational-seismolog/

 

[2] PhD project on the ECLIPSE Supervolcano project hosted at the School of Geography, Environment, and Earth Sciences, Victoria University of Wellington 

Goal:  seismic and geochemical/volcanological methods to study the seismic structure and eruption potential of supervolcanoes (particularly Taupo and Okataina calderas).  The  PhD project will involve a component of fieldwork.

Scholarship: The next deadline for PhD scholarship applications is 1 November 2018 in New Zealand dates (31 October in the US): successful scholarship applicants receive a NZ$23,500 stipend and all tuition fee payments for a term of three years.

 

Students wishing to apply should also contact Martha Savage (martha.savage@vuw.ac.nz) or Colin Wilson (Colin.Wison@vuw.ac.na) to discuss project options.

Application:
Full details regarding the application process are available from the Faculty of Graduate Research at http://tinyurl.com/VUW-FGR.

 

 

5 Post-doc positions

[1] Post Doctoral Fellowship, Seismology, Canada First Research Excellence Fund (Deadline for submission is 31-10-2018)

Goal:  Developing passive seismic techniques to image shallow structure using a combination of ambient noise and other seismic sources recorded by dense arrays. A primary goal of this research is to characterize induced microseismicity and improve understanding of the response of reservoir formations to perturbations such as injecting CO2 at sequestration sites and developing geothermal resources.

Scholarship: Canada First Research Excellence Fund and this is a joint project in collaboration with the University of Alberta.

The position is available immediately and the search will continue until the team is assembled. Anticipated start dates range from late 2018 to early 2019.

Application:
https://careers.ucalgary.ca/jobs/3050892-post-doctoral-fellowship-seismology-canada-first-research-excellence-fund

 

 

[2] Postdoctoral Opportunities at Rice University (Deadline for submission is 01-11-2018)

Goal:  We are seeking candidates with independent research interests that intersect with one or more faculty within our department.

Scholarship: Wiess and the Pan Postdoctoral Research Fellowships. The research fellowships will be supported for two years, pending satisfactory progress during the first year, and covers an annual stipend of $60,000 with a benefits package and an additional annual discretionary research allowance of $3,500.

Application:
http://jobs.rice.edu/postings/15058.

 

[3] Postdoc position available in marine seismic analysis and interpretation Department of Geology and Geophysics, Louisiana State University University (Deadline for submission is 07-11-2018)

Goal:  Processing interpreting and analyzing marine geophysical data from the South China Sea in order to generate an acoustic and sediment map of the entire basin.

Contact Peter Clift (pclift@lsu.edu) for more details

Application:
https://lsu.wd1.myworkdayjobs.com/LSU/job/LSU—Baton-Rouge/Postdoctoral-Researcher_R00029409-1

 

[4] Postdoctoral Research Position in Seismology at Colorado School of Mines (Deadline for submission is 01-01-2019)

Goal: high-resolution seismic models of the Middle East region. The project aims to combine waveforms with arrival times in adjoint inversions based on 3D wave simulations to improve data coverage in the study area.

Scholarship: Funded by AFRL (Air Force Research Laboratory)

Questions and requests for further information about the position can be emailed to Prof. Ebru Bozdag (bozdag@mines.edu). 

Application:
http://jobs.mines.edu/cw/en-us/job/493298/postdoctoral-fellow-seismology

 

 

[5] Postdoctoral Scholar, Earth and Environmental Systems Institute, Penn State University (Open Until filled)

Goal: modelling project investigating the use of seismic monitoring and time-lapse electrical resistivity in the critical zone observatory (czo) in central Pennsylvania. 

The postdoc will be co-supervised by Professors Susan Brantley, Andrew Nyblade and John Regan.

Application:
https://psu.jobs/job/82921

 

 

 

3 Faculty positions

[1] Assistant Professor of Seismology, Purdue University (Deadline for submission is 20-12-2019)

The Department of Earth, Atmospheric, and Planetary Sciences (EAPS), within the College of Science at Purdue University, invites applications for a tenure-track faculty position at the rank of Assistant Professor in the area of seismology.

Areas of specialisation: earthquake geophysics, and/or natural/active source seismic imaging

Questions related to this position should be sent to Douglas Schmitt (schmitt@purdue.edu) or Christopher Andronicos (candroni@purdue.edu).

Application:
 https://hiring.science.purdue.edu


[2] Faculty Position in Geophysics and Geochemistry (MIT) (Deadline for submission is 01-11-2018)

The Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at the Massachusetts Institute of Technology (MIT), Cambridge MA, invites qualified candidates to apply for a tenure-track faculty position.

Areas of specialisation: theory, observation, and/or experimentation and particularly encourage applicants whose work crosses traditional disciplinary boundaries.

Application:
https://academicjobsonline.org/ajo/jobs/11380

 

[3] Faculty Position in solid earth geosciences/engineering seismology (Deadline for submission is 17-12-2018)

The Center for Earthquake Research and Information (CERI) at the University of Memphis invites applications for a tenure-track faculty position at the Assistant Professor level to begin in August 2019.

Areas of specialisation: research interests related to Active tectonics, Continental/Lithospheric dynamics, Computational Geophysics, Exploration Geophysics, or Engineering Seismology.

More information about this position can be obtained by contacting the chair of the search committee, Eunseo Choi (echoi2@memphis.edu).

Application:
https://www.seismosoc.org/job/center-for-earthquake-research-and-information-at-the-university-of-memphis-149-tenure-track-faculty-position-in-solid-earth-geosciences-or-engineering-seismology/

 

Other positions

[1] Scientist, Seismology with Air Worldwide
Main responsibilities, but not limited to: Develop regional seismicity and probabilistic seismic hazard models using various types of available seismic, geological, geophysical, and geodetic information. Support AIR global earthquake models develop computer codes to address earthquake hazard related issues, collect and analyse earthquake catalogues, paleoseismic and geodetic information on faults. Collect and analysis geologic and geotechnical information for site response analysis. 

Application:
https://jobs.jobvite.com/air-worldwide/job/owQw8fwK

 

[2] Natural catastrophe specialist (earthquake) -Swiss Re
As a Catastrophe Perils Specialist you will be part of the Catastrophe Perils team which is responsible for Swiss Res global risk assessment framework and related client services in four locations across the globe. We are accountable for developing and disseminating Swiss Res view of Nat Cat risk. To achieve this, we develop and utilise state-of-the-art probabilistic models for assessing impacts of natural catastrophes such as windstorms, earthquakes and floods. We operate with a clear business mandate to grow Swiss Res visionary edge of natural perils (re)insurance in close cooperation with underwriters and clients.

Application:
https://careers.swissre.com/job/Armonk-Nat-Cat-Specialist-NY-10504/481361401/

 

Do you have a job on offer? Contact us at ecs-sm@egu.eu

 

 

The jobs listed on this page were gathered by Walid Ben Mansour

Palu 2018 – Science and surprise behind the earthquake and tsunami

On September 28, 2018, a powerful 7.5-magnitude earthquake and an unexpected tsunami shook the Indonesian island of Sulawesi, leaving behind catastrophic results and open questions among geoscientists. How come this event is having such an impact on the scientific community?

Figure 1. Map of Indonesia, showing the four Greater Sunda Islands, the location of the 2018-09-28, Mw7.5 Palu earthquake and its focal mechanism.

 

What we know so far

On Friday afternoon (at around 5pm Western Indonesian Time) the Minahassa Peninsula on Sulawesi island was struck by a Mw7.5 earthquake (Figure 1) [1]. The main shock occurred on the strike-skip Palu-Koro fault, one of the most active structure in Sulawesi [5]. The epicenter of the quake is located 27 kilometers northeast of Donggala, at a depth of 10 km [1]. By looking at the aftershocks distribution from within 4 days after the Mw7.5 event (Figure 2), we can approximately estimate a rupture extent ranging from a few kilometers to the North of the epicenter over about 200 km to the South [2]. The rupture area is thus roughly 200x20km, mainly located South of the hypocenter and ending in the city of Palu (Figure 2). Nothing surprising by now, but the intriguing part is coming.

Figure 2. Aftershocks distribution (coloured circles) from within 4 days after the Palu earthquake event occurred on 28 September. Hypocentral depth and magnitude are shown respectively with the colour scale and the circle size. The Palu-Koro fault is indicated in black. The mainshock event lies in the centre of a large aftershock cloud stretching over more than 200 km in N-S direction. Picture taken from Global Earthquake Monitoring Processing Analysis (GEMPA)[2].

By looking at the source time function of the Palu earthquake (Figure 3), we can deduce that the event took about 30s to rupture a length of 200km, suggesting a supershear rupture velocity. While most seismic ruptures propagate at speeds lower than the S-wave speed, supershear ruptures propagate at speeds between the P and S waves. Supershear ruptures are extremely rare events which, in the past, mostly propagated on very smooth part of strike-slip faults [12]. Coincidentally, first estimates of surface displacements along the Palu-Koro fault show a very sharp offset between the two sides of the fault, suggesting that the rupture propagated on a linear, very smooth segment of the fault.

 

“This is the most sharp and linear earthquake surface displacement I’ve seen since 2013 Balochistan eq! says geologist Sotiris Valkaniotis on his twitter account. And the image [Figure 3] has already gone viral on the net. Further study will be necessary to confirm if this event is in fact supershear.

 

Figure 3. On the left: source time function of the Mw7.5 Palu earthquake and its focal mechanism. The Palu earthquake took about 30s to rupture a length of about 200km along the Palu-Koro fault segment. Picture from GEOSCOPE Web Portal [3]. On the right: displacement map of the Palu-Koro fault. Colorscale from red to blue represents the North-South displacement in meters. Picture realized and posted by geologist Sotiris Valkaniotis on his twitter account.

 

Tectonic setting

Sulawesi is one of the Greater Sunda Islands [4], a group of four large islands within the Malay Archipelago including Java, Sumatra and Borneo (Figure 1). An intricate pattern of faulting scars the land: collisional orogenies, subduction zones, rift systems and transform faults pile up in this area [5], making the island prone to earthquakes.

Figure 4. Tectonic setting of the Sunda–Australia–Philippine–Pacific plates junction area. Arrows depict the far-field velocities of the plates with respect to Eurasia. Picture taken from Socquet et al. (2006)[5]

 

From a tectonic point of view, Sulawesi lies within the triple junction of the Australian, Philippine and Sunda plates and accommodates the convergence of continental fragments with the Sunda margin [5]. In particular, the southwestern part of Sulawesi rotates anticlockwise respect to the Sunda Plate; the northeastern Manado Block and the central North Sula Block move toward the NNW and rotate clockwise; the East Sulawesi is pinched between the North Sula and Makassar blocks (Figure 4).

 

Palu
The left-lateral strike-slip Palu-Koro fault is the main active structure in Sulawesi: it bisects the island and connects to the Minahassa Trench, where subduction occurs. The Palu-Koro fault zone accommodates 42 mm/yr and shows a transtensive behavior more complex than a simple strike [5]. This deformation is most likely explained by the presence of a pull-apart structure that may be localized around the Palu area (Figure 5)[5].

Figure 5. Sketch showing a transtensional state of a rock. It is unlikely that a deforming body experiences ‘pure’ extension or ‘pure’ strike-slip. Many tectonic regimes that were previously defined as simple strike-slip shear zones are by now assumed as transtensional. As such, transtensional regions are characterised by both extensional structures (normal faults, grabens) and wrench structures (strike-slip faults).

 

‘Surprise Tsunami’

Following the Mw7.5 earthquake, a series of tsunami waves hit Palu, Donggala and Mamuju decimating the coastline, flattening homes, destroying several inland areas in Central Sulawesi [watch the video below]. Indonesian Agency for Meteorology, Climatology and Geophysics (BMKG) initially issued a tsunami warning but eventually revoked it.

<< The decision was based on visual monitoring and further monitoring using the equipment [tsunami detection buoys] at sea for 30 minutes. The BMKG did not see any significant change in the sea level. That’s why they ended the alert >> BNPB spokesman Sutopo Purwo Nugroho said in a statement [6].

 

 

 

The eastern Indian Ocean basin is a region of high earthquake and volcanic activity, so tsunamis should come as no surprise. Yet, geoscientists are doubtful. Could the Palu earthquake alone have generated such a big tsunami wave?

 

Eighteen tsunamis have crashed in the area since 1900 by large shallow earthquakes [7] and among them we can’t forget the tsunami that hit the Indian Ocean following the December 26, 2004, earthquake in Sumatra [8]. The controversy about the ‘surprise’ tsunami however arises when we look at the tectonic setting of Sulawesi island and the devastating effects documented on the coastline.

 

Tsunami waves are generated by a sudden vertical motion of the seafloor. They are therefore mostly triggered by dip-slip earthquakes where the block of rock on top of the fault, also called the hanging wall, moves up, which pushes the overlying water column up [watch the animation below]. But the Palu earthquake occurred along a strike-slip fault, meaning the motion was mainly horizontal. It is therefore very unlikely that such a large tsunami could have been originated by earthquake rupturing alone.

This simplified animation illustrates the tsunamis generation in sudbuction zones. Tsunamis generally occur after a megathrust earthquakes and thus follow vertical movement in the crust. (© Marina Corradini)

 

Scientists’ best guesses?

¤ A submarine landslide: triggered by the main shock, a submarine tectonic displacement may have generated or augmented the tsunami waves.
¤ A complex bathymetry: the seafloor in the Palu Bay is not flat. If there is a slope, even an horizontal motion of the seafloor can produce an apparent vertical motion [9].

 

There is still no evidence that any of those hypotheses (landslide or seafloor slope) is the actual reason. They could be both too. Besides, the intensity of the tsunami seems to be more related to the shape of the Bay, which naturally acts as a funnel for the tsunami waves. As yet, a straightforward interpretation seems hasty and further analysis should come in aid.

 

 

Rescue and damages: what now?

The confirmed death toll from the Palu earthquake and tsunami has risen to 1,407 [10] together with thousand of buildings destroyed and over 61,000 people displaced [11]. The full scale of damages in the region can already be guessed by watching the dramatic pictures and videos spread online. First aid has already been mobilized through several nonprofit organizations and charities, and everyone’s help is essential in these circumstances.

 

This post was written by Marina Corradini, with revisions from Maria Tsekhmistrenko and Lucile Bruhat

 

 

Maria Tsekhmistrenko is a PhD student at the University of Oxford. She works on the velocity structures beneath the La Reunion Island from the surface to the core mantle boundary. You can reach her at mariat[at]earth.ox.ac.uk

Lucile Bruhat is a post-doctoral researcher at the Ecole Normale Supérieure (ENS) in Paris. She works on the description and understanding of the physical processes that underlie the earthquake cycle, through geodetic/seismological data analysis and numerical modeling. You can reach her on Twitter at @seismolucy

Acknowledgements:
The author thanks the IPGP Seismology and Tectonic Labs for the useful material and discussion.

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References :

[1] https://ds.iris.edu/wilber3/find_stations/10953070

[2] https://gempa.de/news/2018/9/28/tsunami-m75-earthquake-palu-indonesia/
[3] http://geoscope.ipgp.fr/index.php/en/
[4]  https://en.wikipedia.org/wiki/Greater_Sunda_Islands
[5] Socquet, A., W. Simons, C. Vigny, R. McCaffrey, C. Subarya, D. Sarsito, B. Ambrosius, and W.Spakman (2006), Microblock rotations and fault coupling in SE Asia triple junction (Sulawesi, Indonesia) from GPS and earthquake slip vector data, J. Geophys. Res., 111, B08409, doi:10.1029/2005JB003963
[6] http://www.thejakartapost.com/news/2018/09/29/central-sulawesi-quake-what-we-know-so-far.html
[7] Prasetya, G.S., De Lange, W.P. & Healy, T.R. Natural Hazards (2001) 24: 295. https://doi.org/10.1023/A:1012297413280
[8] https://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami
[9] http://adsabs.harvard.edu/abs/2003AGUFMOS21D..06L
[10] https://www.reuters.com/article/us-indonesia-quake-toll/death-toll-from-indonesia-quake-tsunami-rises-to-1407-agency-idUSKCN1MD0KH
[11] https://www.nytimes.com/interactive/2018/10/01/world/asia/map-tsunami-indonesia.html
[12] Bouchon, M., et al., Faulting characteristics of supershear earthquakes, Tectonophysics (2010), doi:10.1016/j.tecto.2010.06.011