# How do we make a scan of Earth's oceanic crust?

Milena Marjanović, Simon Besançon, Souradeep Mahato, David Hautemayou, Ted Luc

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## To cite this version:

Milena Marjanović, Simon Besançon, Souradeep Mahato, David Hautemayou, Ted Luc. How do we make a scan of Earth's oceanic crust?. Geoscience Communication, 2025, 10.5194/egusphere-2025-4799. doi:10.5334/gc2025

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Submitted on 28 Oct 2025

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Distributed under a Creative Commons Attribution 4.0 International License
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1 **How do we make a scan of Earth's oceanic crust?**

2

3 **Milena Marjanović¹, Simon Besançon¹,², Souradeep Mahato¹, David Hautemayou¹,³ & Ted**

4 Luc¹

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6 ¹Institut de Physique du Globe de Paris, Université Paris Cité, CNRS UMR7154

7 ²SIMON Now at: Laboratoire de Météorologie Physique, UMR6016 CNRS - UCA - OPGC, 4 avenue Blaise Pascal 63170 Aubière

8 ³DAVID Now at: Laboratoire de Physique de l'École normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, F-75005 Paris, France

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12 *corresponding author: Milena Marjanović; marjanovic@ipgp.fr

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14 **Abstract:** Like computed tomography (CT) scans used in medicine to look inside human bodies, marine seismologists conduct controlled-source experiments to understand the characteristics of the oceanic lithosphere (rigid outer Earth's layer) that covers >70% of the surface of our planet. While at sea aboard a research vessel, using the air compressed in an array of stainless-steel cylinders, we produce small earthquakes in the form of air bubbles that propagate through the water, Earth's crust, and mantle and return to be recorded by the instruments we place in the water column or on the seafloor. Although the technique was developed in the 1950s and has been extensively used by academia and industry for decades, it has remained obscured, primarily because it is conducted offshore, out of sight. To expose the less-known technique and show it as a possible career path, we designed a playful model that encourages interaction. Together with the model, we present fundamental Earth processes and the methods we use to explore them, followed by video materials we recorded at sea while collecting the data. Furthermore, to quantitatively evaluate our effort, we constructed age-adapted control quizzes completed by the participants before and after the workshop. These quizzes were designed to assess the student's understanding of the concepts, providing a clear measure of the workshop's effectiveness. We have already conducted the workshop package at several outreach events. Without any exception, the results of the quizzes show that students of ages(9-18 years improved their overall knowledge covered by the experiment. This result is a signal that supports the effectiveness of 'learning by doing' science in a playful, interactive way.

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34 **1. Introduction**

35 Seismologists record different types of seismic waves that propagate through the Earth's interior to understand its structure. For instance, by observing several records of an earthquake that struck a Croatian town ~40 km from Zagreb on October 8th, 1909, Andrija Mohorovičić noticed consistent, prominent blips originating at a depth of ~50 km kilometers depth. They were explained by the strong contrast in density between the crust and mantle, now known as the Mohorovičić discontinuity or Moho for short. Similarly, a few decades later, Inge Lehman, a Danish seismologist, by observing anomalous arrivals in the recorded seismic signal at the remote stations in Siberia and their mysterious difference in travel time, discovered that the Earth's core has two distinct parts: an inner, solid core and an outer, liquid core. In addition to revealing the structure of the Earth, these bursts of energy represent one of the most prominent natural hazards, unfortunately, many with casualties, especially when associated with large tsunami waves (e.g., Sumatra Earthquake in 2004), extensive fires (San Francisco in the USA, 1906) and even bringing humanity at the edge of a nuclear disaster (Tōhoku Earthquake in Japan, 2011). As most of those prominent earthquakes occur along the plate boundaries that are dominantly covered by the ocean (Fig. 1); number of instruments have been placed at its bottom for prolonged listening to the Earth's pulsation to provide the answer to the question of our time *when and where the next big one will occur?*

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<figure><img src="image_6.png" /><figcaption>**Figure 1** – Spilhaus global projection map offering a different view of the Earth's surface centered at Antarctica. With this projection we want to provide another view of our Blue Planet that places the ocean at its center. The tectonic plate boundaries are outlined and defined in Legend. The map is modified from Chen et al. (2023).</figcaption></figure>

In parallel with learning about the deep Earth's interior and hazard mitigation, to extract more detailed information about the Earth's outer shell, i.e., the crust and upper mantle, a new branch of seismic techniques that uses man-made, tiny earthquakes (controlled source or active seismology) has emerged. The first application was reserved exclusively for land surveying, mainly for mineral, oil, and gas exploitation. To produce these artificial tremors, dynamite explosions were used as the primary source of energy. In 1935, Maurice Ewing, the pioneering US marine geophysicist, with colleagues, started a new era in earth exploration of the subsurface by conducting TNT explosions in marine settings. This technique, initially used to image the thickness of ocean sediments, revealed a three-layer structure of the oceanic crust and quickly became the dominant tool in exploring the seafloor subsurface. It has been evolving ever since, with dangerous dynamite being replaced by air bubbles. However, as the surveys are conducted offshore aboard research vessels, the method has remained obscure and unknown outside of geophysical circles. To shed light and introduce this technique to new generations, we designed

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a model that depicts marine, controlled-source seismic data collection. Moreover, with this model, we aim to showcase the interdisciplinary context of the field, encompassing electrical and mechanical engineering, robotics, mathematics, physics, and, in recent years, artificial intelligence, while also highlighting its adventurous side of joining sea-going expeditions, open to everyone. We want to mention that for designing the model we obtained an EGU Public Engagement Grant in 2022.

<figure><img src="image_8.png" /><figcaption>**Figure 2** – Illustration of **A)** Multichannel seismic (MCS) and **B)** Wide-angle reflection-refraction seismic techniques.</figcaption></figure>

Communicating science to and engaging with the public are essential for establishing the link between science and society, making the research process more transparent and trustworthy, and the results more impactful and relatable to the public (e.g., Thomas & Durand, 1987; Stilgoe et al., 2019; Boon et al., 2022). However, it is not always clear what the best practices are for implementing this, i.e., what distinguishes high- from low-quality engagement/communication, with the latter carrying the risk of provoking a counter-effect (Reincke et al., 2020; Jensen & Holliman, 2016). Typically, the success of an outreach session would be only qualitatitevly expressed through an instantaneous reaction (aka “wow effect”), informal feedback (verbal or nonverbal) from the audience right after the event, and/or a personal feeling. Few, events are

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conceived to include quantitative evaluation. One of the most complete, but not widely known, guideline for evaluating the outreach activity is provided through IMPACTLAB (Land-Zandstra et al., 2023), which outlines ten different approaches, one of which is the entry/exit quizzes as a subgroup of the “Surveys method”, which we adopt here as in the guide it is recommended for assessing “detailed quantitative measure of acquired knowledge and understanding” acquired by the audience.

<figure><img src="image_10.png" /><figcaption>**Figure 3** – CUBI A in the lab, B under the water and C schematic representation of the instrument's main elements.</figcaption></figure>

## 2. Background

### 2.1 How does controlled source seismic work at sea?

In academia, we employ two primary types of controlled-seismic experiments: multichannel seismic (MCS) and wide-angle reflection-refraction (WAR) seismic (Fig. 2). The primary difference lies in the type of receiver used to record the seismic waves. Whilst the former uses >3-15 km long cable (i.e., streamer) with densely populated recorders (a few to tens of meters spacing) towed behind the ship at ~10 m below the sea surface, the latter uses ocean bottom seismometers (OBS) that are deployed on the seafloor at a few to tens of kilometres spacing. Typically, we would use MCS surveys to obtain high-resolution images (metric scales) of the subseafloor within a localized survey area. In contrast, WAR seismic would be used for more regional scanning of the subsurface at a somewhat lower resolution, ranging from several tens to hundreds of meters. The

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model we designed depicts the WAR seismic survey on which we will focus in the following sections.

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## 2.1.1 Ocean Bottom Seismometers (OBS)

The Ocean Bottom Seismometers (sometimes referred to Ocean Bottom Seismographs) or OBS for short exist in different forms and shapes depending on the laboratory in which they were designed. In this experiment we use the model of an OBS known as CUBI for Compact Underwater Bottom Instrument (Fig. 3). We need to mention that this model is preferentially used for recording the earthquakes, but we decided to use it here as it is the model that was developed and constructed at Institut de Physique de Globe de Paris - IPGP (where all the members of our team worked at the time of the model build up). The real dimensions of the instrument are 43 x 45 x 85 cm³; it's dry weight is about 35 kg without the weight (which adds ~15 kg). In the water without weight, it has negative buoyancy (-3 kg), which is obtained using well designed floating components (Fig. 3C). The maximum water depth at which this instrument can be deployed is 6 km below sea surface and its autonomy is guaranteed for 4 months using batteries that are cased in a glass sphere, which isolates the electronic components from contact with water and high pressures. The CUBI contains 2 sensors: a hydrophone (pressure sensor), and three-component sensor that measures vertical and horizontal displacements.

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**Figure 4** – Examples of A airgun cluster (aboard M/V Western Trident in 2015), B Air-gun array (aboard RRS James Cook in 2022) and C air-gun cylinder in the laboratory (aboard R/V Marcus G. Langseth in 2012). In panel D we show a snapshot of airgun firing under the water.

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### 2.1.2 Seismic source

To produce a quake at sea, instead of dynamite, nowadays, we use compressed air, which is pumped into airguns i.e., stainless-steel cylinders with chambers of different volumes (Fig. 4A-C) organized in several arrays. The total volume of the source can vary depending on the objective of the survey; typically, new generations of sources used in WAR seismic in academia are ~5000 in³ (or 82 liters). The position of each airgun within the array, as well as its volume is carefully designed to provide signals, which when superimposed result in the sharpest possible signal that propagates through the water and subsurface. An example of the compressed air released from gun-array under the water is shown in Figure 4D.

<figure><img src="image_14.png" /><figcaption>**Figure 5** – Schematic (A) and real (B) representation of the experiment. The white box in panel B marks the part of the experiment explained in detail in Figure 6.</figcaption></figure>

### 2.2 Building the model

As in all recipes, we first provide the main ingredients that constitute our model followed by detailed description of the role of each element and how the experiment is conducted. The schematic of the conceptual model and the final model are presented in Figures 5 and 6.
The main elements of the model:

* 300 l water tank,

* floating ship from LEGO CITY collection

* 3-D printed CUBI models

* electromagnetic box with 3 electromagnets and 3-D printed control box

* balloons

* pins for perforating balloons

* hydrophone

* laptop

* software for displaying the recorded signal

* large TV screenwhale model (from the same LEGO City set as the ship)

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165 • remotely controlled submarine toy

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167 For presenting the main principles of a WAR seismic survey, two components are essential: the
168 simulation of the source and its recording (Fig. 6). To effectively mimic the explosion of
169 compressed air under the ocean surface (as described in Section 2.1.2), we use a small balloon;
170 an inflated balloon is submerged into a large water tank and perforated to release an air bubble
171 that propagates through the water. Thus, the released signal, splashing the water within and often
172 around the tank (which is usually followed by the awe of the experiment participants), is then
173 recorded on a hydrophone. For this purpose, we used a water-proof piezoelectric microphone,
174 which detects different types of vibrations. The hydrophone is connected to a laptop with software
175 that displays the vibrations – we used either Audacity (an open-source digital audio editor) or a
176 MATLAB function. We must emphasize that with this model setup, we do not intend to record a
177 real seismic signal that can be further analyzed; instead, we want to demonstrate the central
178 concept.

<figure><img src="image_16.png" /><figcaption>179 **Figure 6** – Detailed layout of the experiment.</figcaption></figure>

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181 To depict all phases of seismic data collection and make the model more engaging, we add a
182 research vessel. here it is a floating ship model from the LEGO City collection (Fig. 6). In addition,
183 we include three 3-D printed models of CUBI (scale 1:7) and an in-house developed device. At
184 sea the OBSs are deployed from the surface and sink to the seafloor thanks to an attached weight
185 (Fig. 3C). After a period of seismic data recording, they are recovered by sending an acoustic
186 command that triggers the release of the weight. Freed from the weight, each OBS rises back to
187 the surface due to its built-in buoyancy. To simulate this mechanism in the experiment, we
188 designed simplified OBS models. Each model consists of a 3D-printed frame holding a sealed
189 plastic ball filled with air, providing buoyancy. Beneath the frame, a 3D-printed dummy sensor is
190 attached, weighted with an encased metal nut.

191 At the bottom of the tank, three electromagnets are installed, with their power cables routed
192 outside the tank to a control box. The control box is straightforward, consisting of three ON/OFF
193 switches that independently power each electromagnet. At the beginning of the experiment, the
194 magnets are switched ON. The three OBS models are then lowered by hand, one by one, until
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the nut contacts the magnet, effectively “anchoring” them to the seafloor. To recover the OBS, the procedure simply involves switching OFF the electromagnetic current. Once released, each OBS floats back to the surface autonomously, mimicking the real-world recovery process.

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## 3. Approach and methods

There are many examples of playful ways that our colleagues worldwide have designed to showcase research in Geology. For instance, every Fall, the Lamont-Doherty Earth Observatory from Columbia Climate School in the USA opens its doors to engage with the public through a wide range of ateliers, including demonstrations of deep-sea cores, "Gumby" safety suits, and the creation of volcanic eruptions (link from the 2024 program is available [here](#)). In France, the beginning of October is reserved for the Fête de la Science (FDS), an outreach event held nationwide. Traditionally, at our home institute (IPGP), this event is held every other year, with colleagues presenting inventive experiments and materials collected during expeditions across seven continents and five oceans. Some of the topics include talks on lost meteorites, the observation of the oldest ecosystems under the microscope, and a 360-degree view of Titan and Mars, to name a few (link to the latest FDS edition at IPGP can be followed [here](#)).

In Marine Geosciences, we typically use visual aids to depict the work we conduct at sea, which are ideal for presenting the processes and research activity we perform in the water column. For example, the videos recorded using submarine vehicles to collect rock samples are very efficient in depicting the activity. However, visual materials fall short when it comes to explaining indirect marine techniques, such as controlled-source seismic (Section 2.1); seismic data collection requires propagation of waves in the water column and subsurface, which are not visible in videos, which is posing a challenge when doing science communication.

Therefore, in addition to the video material and photos we collected at sea, we present a novel marine seismic model to bring the data collection offshore closer to the young audience. However, our approach is novel not only because we build a playful model, but also because, for the first time, we provide insights into the efficiency of the 'learning by doing' approach in explaining complex scientific concepts to primary and secondary school students. In fact, although many different experiments are conducted to promote science, we often lack a clear understanding of how impactful this activity is on students' retention of newly acquired facts and actual learning. To the best of our knowledge, no follow-up quantitative evaluation has ever been published in the domain of Marine Geosciences and hence no results are available. With this experiment, we provide an approximate measure of the effect of our outreach activity through entry/exit quizzes, detailed in Section 3.1.

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## 3.1 Constructing the quizzes

The experiment is accompanied by quizzes tailored to participant's age from 9 to 18. The quizzes are divided into three groups based on the age of the participants: Quiz 1 for 9-12 years, Quiz 2 for 13-15 years and Quiz 3 for the group > 15 years. The complete sets of quizzes in English are provided in *Supplementary material*; as we performed the events in France and Austria, the quizzes were also translated into French and German.

Each quiz group is composed of 5 questions that are either multiple choice or true/false. One example of the quiz question prepared for the age range 9-12 is:

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A marine geologist can discover clues about the formation of the Earth's crust by studying _________ (more answers are possible). The offered options are:

242 a) waves,

243 b) marine

244 c) animals

245 d) rocks
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246 e) ocean currents.

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248 Another example of the quiz questions for the age 13-15 years is:

249 What is the temperature of the deep ocean?,

250 with the offered responses:

251 a) 0-3°

252 b) 23-25°C

253 c) 0 -10 °C.

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255 The topics covered in the questions are all addressed during the presentation and experiment; therefore, no answer key was provided to participants after they completed the exit quiz. Although great care was taken in constructing the questions, which were adapted to the school program and age, and colleagues and collaborators reviewed the quizzes, it is essential to mention that they did not undergo an official quality control process.

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The results of the quizzes are summarized in Section 4 and are used exclusively to evaluate the effectiveness of the activity, not the initial knowledge of the participants. As we wanted to keep the quizzes anonymous and also emphasize the importance of working in a team, the results provided the overall performance of a group of students (i.e., they represent group scores).

3.2 Conducting the experiment and quizzes

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266 At the beginning of each session the participants were asked to complete the entry quiz, which
typically takes no longer than 5 minutes. As soon as the quizzes are turned in, we start with the
session. As every sea-going research expedition begins long before we board the research vessel,
our marine adventure in the lab also starts with the presentation of fundamental concepts behind
plate tectonics and its exploration beneath the ocean using seismic waves, with special emphasis
on the content covered in the quizzes. The explorers, equipped with the basic knowledge, are
then split into four teams: 1) principal investigators (PIs), 2) team in charge of the seismic source,
3) instrument team, and 4) signal imagery team. Typically, we have about 10-12 participants per
session. To determine the roles in the experiment, we conduct a small poll so that each participant
selects a note with a number that is linked to a specific position in the experiment. The experiment
starts with the two PI(s) placing the LEGO ship in the tank filled with water. The next step is to
deploy the OBS, which is done by three members of the instrument (OBS) team. Once the
instruments are deployed, the source team (up to four members) starts blowing up the balloons
that they submerge in the water and then explode using a pin. The released signal is recorded,
and the imagery team (up to three members) signals the timing of the shot, observing it on a large
screen. To explain the impact of controlled sources on the sea dwellers, we would occasionally
interrupt the "shooting" procedure by inserting a whale model from the LEGO City set. Therefore,
one of the seismic source team members has to be on watch and signal a pause in operation until
the whale leaves the survey area (here, the water tank), which is precisely the role of mammal
observers when we collect controlled source seismic data at sea. The final step of the experiment
involves recovering the OBSs that were released by cutting the electromagnetic current. The end
of the expedition is announced by the PIs, who drive a small submarine to check that none of the
instruments had remained on the seafloor. The whole procedure is recorded and provided in Video
supplement. For the events conducted at IPGP, after completing the simulation of a marine
seismic experiment, participants had the opportunity to learn more about the CUBI instrument
and its main components from the OBS team of engineers. By completing all of the proposed
modules (introductory lecture, conducting the simulation, and examining the instrument closely),
the participants were exposed to different aspects of professions involved in marine seismic. After
completing the experiment, the participants were kindly asked to repeat the quiz.
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<figure><img src="image_20.png" /><figcaption>Figure 7 – Analyses of the quiz results: the number of correctly answered questions before (blue) and the improvement after (green) the session: A cumulative results for each group and B results for each question within the particular group. The FDS 1-4 represent the results from the group of pupils who attended Fête de la Science (FDS) at IPGP; the “High-school” group represents the results of all high-school participants, and the UoV 1-2 shows the results from the event conducted at the University of Vienna. The bold number at the top indicates the total number of correctly answered questions after the session. The total number of participants is indicated by solid line and number in magenta. The specific group of the quiz (provided in Supplementary material) taken by the participants is indicated on the top of panel A.</figcaption></figure>

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## 4. Results and discussion

Here we describe the observations and results of the experiment conducted during three events. The first opportunity to present the experiment was during the *Fête de la Science* (Open House event in France) at the IPGP in early October 2024. The second session was organized with 32 high-school students who were invited to IPGP in December 2024. Finally, the third time, we conducted the experiment at the University of Vienna as part of Planet Earth Day in late April 2025. In Figure 7, we show the scores of the quizzes for all of the tested groups.

Here, we would like to mention the observation that was common for all three experiments. Namely, for the pins used to perforate balloons we intentionally selected two colors of the pin heads, pink and pastel blue. An interesting tendency was that while female participants did not seem to pay much attention to the pin color, male participants were dominantly selecting the pastel blue ones. This observation matches the results of a study conducted by Jonauskaitė et al.

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318 (2018), which shows that boys predominantly chose blue as their favorite color, which also seems to be liked by girls. In the following sections we describe each of the events and provide the results of the conducted quizzes.

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## 4.1 Fête de la Science (FDS) at the Institut de Physique du Globe the Paris (IPGP)

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323 The FDS 2024 event was named "Océan de savoirs" (Ocean of Knowledge), and therefore, it was the ideal time for the inauguration of our model. Typically, the IPGP communication team organizes visits for primary school students from several schools across the Paris area over two working days (Thursday and Friday); the event is also open to the public on the weekend. Here, we focus on the experience of working with school groups, as the experiment was conducted in its entirety (Section 3.2), including quizzes, which are challenging to conduct with the public.

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328 Over those two days, our atelier was attended by four groups of primary school students. Quiz 2 was distributed to FDS 1 and 2, which both had 8 participants, and to FDS 4 with 11 participants. The youngest group, FDS 3, had 11 participants and was given Quiz 1. The analyses of the quizzes clearly show that for the three groups (FDS 1, 3, and 4), the overall number of correct answers increased by about 50% after the experiment (Fig. 7A), demonstrating the positive impact of the activity. The improvement of the FDS 2 group was much lower (only ~10%), which is surprising as this group initially provided the overall highest score before the experiment.

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346 Upon examining the analyses of each question, it is noteworthy that some questions proved more challenging than others. For instance, for Quiz 2 (Supplementary material), question 4 regarding seismic waves was correctly answered by only ~50% of participants even after the session. This suggests that, despite being covered in elementary physics and explained during the experiment, the concept of wave propagation is not fully grasped by most students who participated. Another interesting observation from the same age groups comes from the analyses of the question regarding the temperature of the deep ocean (Quiz 2, question 5). About 75% of the participants from FDS 1 and FDS 4 provided an incorrect answer before the atelier; however, after the atelier, the situation was reversed, and 90-100% of the participants gave the correct answer. The complete analysis of the quiz outcome, broken down to each question, is provided in Fig. 7B.

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## 4.2 Experience with high-school students at IPGP

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364 This event was organized in collaboration with two physics professors from a high school located on the outskirts of Paris. In early December, 26 high school students participated in the activity, which included all the modules described in Section 3.2, followed by a specifically designed quiz aligned with their physics class curriculum, as confirmed by their professors (Supplementary material - quiz for ages >15). Thirty-two students attended the entire session, but six of them declined to take the quiz. To make the experiment efficient, the students were split into three groups, each with 10 students. As they came from the same school, followed the same curriculum in physics, and spanned the same age, we opted to present their results as a single group. Overall, we see an important improvement (~70%) in providing correct answers following the experiment.

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368 The main struggle was the second question regarding the types of seismic waves (see Quiz 3), which only 6 participants answered correctly. No improvement was seen after the experiment (Fig. 7B). In contrast, questions 4 and 5, which their professors identified as challenging, were answered correctly by almost all participants (25 out of 26).

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## 4.3 Planet Earth Day at the University of Vienna

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368 Through close collaboration between the University of Vienna (UV) and the European Geosciences Union (EGU), we were invited to participate in the Planet Earth Day at the UV with our experiment, with some modifications. The introductory presentation was conducted in German, led by two master' students from the UV, and the quizzes were translated into German. Due to
<figure><img src="image_22.png" /></figure>

logistical issues, the water tank was reduced to 150 liters, which also required the use of a smaller ship model. It is also important to mention that the event was open to the public, requiring registration, with four proposed sessions adapted to specific age ranges. The results of the quizzes are only available for the two groups, UoV 1 and UoV 2, who completed the Quiz 1 set. Unfortunately, the entry and exit quizzes from the other two groups were mixed up, and therefore, it was not possible to analyze them.

The results from the two groups show a significant improvement of ~60-80% after experimentation. However, it is worth noting that most of the kids were accompanied by a parent/guardian, which may have influenced the results.

Comparing the responses to individual questions from the FDS 3 participants at the Fête de la Science event with the answers from UoV 1 and 2 reveals both interesting similarities and differences. Unlike the FDS3 group, participants at the University of Vienna did not struggle with the definition of geology (question 1, Quiz 1; Supplementary material). However, they did exhibit similar difficulties with question 3, a multiple-choice question that may have been confusing for the youngest participants. Another possible explanation for the lower score (only <50% participants answered correctly after the session) was that the answer was not explicitly provided during the presentation, but was expected to be deduced from the whole activity, which may be challenging at an early age.

## 5. Final remarks

In recent years, Europe has seen an increase in excellent events organized to promote research, such as European Researchers' Night, national-level Open House events (e.g., Fête de la Science in France), and Pint of Science, to name a few. The common objective of these events is to develop interest, foremost among young audiences, in science (e.g., Strick and Helfferich, 2022). However, little is known about the impact these events have had on the participants and how effective they have been in communicating science to the general public. Some commonly known topics are proven to be very successful in public engagement activities; for instance, ateliers related to climate change or space exploration, have developed efficient ways to evaluate their impact that is often published (e.g., Moser et al., 2009; Vergunst et al., 2025; Smith et al., 2014). However, for Marine Geosciences, the landscape is quite different. Even though there are exceptional materials produced by scientists and artists (e.g., Project Seafloor Futures; Mae Lubetkin, 2024), they remain relatively unknown even among researchers in the field. As no adequate study has been conducted, we can speculate that one of the main reasons is that none of the work and experience is shared through publications, which, in turn, requires an evaluation component that is typically unavailable. Given the particular nature of the technique we wanted to expose, we opted for a hands-on approach combined with video materials; in addition, for the first time, we designed and applied an evaluation tool focused on the quantitative assessment of knowledge transfer.

As we continue to participate in the experiment through more outreach events across Europe, the feedback we receive from participants, especially the youngest ones and their teachers/guardians, is highly positive. As an anecdote, several primary school students participating during the FDS event at IPGP, provided grades for the experiment in their final quiz, and the notes ranged from 18 to 19 out of 20. Although the quizzes were not designed to test the initial knowledge of the participants, it is interesting to note that marine geosciences and associated processes, in particular, the concept related to seismic wave propagation are not well-known, as they are not covered by the core curriculum typically taught in primary and secondary school education. However, the results of the quizzes are encouraging and show that "learning by doing" is effective in helping students discover this lesser-known world, and we hope that some of the participants will develop a certain level of passion for marine sciences.

In designing the experiment, we primarily rely on our experience participating in the open house events. In fact, our prototype model (conducted for the first time by M. Marjanović in 2017
<figure><img src="image_23.png" /></figure>

at FDS - IPGP), involved only a small plexiglass water tank (~30 l). For this initial model, the main focus was on showing how the source works, therefore it involved only the underwater balloon explosion. The water was splashing everywhere, which was fun, but the personal sentiment was that the audience did not seem to receive the main message about seismic data collection. Several years of thinking and building the right team, as well as obtaining funding through EGU led to the model we have today.

Although the current model represents a significant improvement, one limitation is that we have only one hydrophone to record the shot, but we have three OBS models at the bottom of the tank, which sometimes leads to confusions. In addition, the hydrophone-microphone is often more sensitive to the movement of the participants than to the actual balloon' explosion. Currently, we are considering replacing it with piezoelectric sensors, placed close to each of the OBS models. In the future, we plan to upgrade the experiment to use sonar for simulating collection of bathymetry data. In addition, as the next stage of our project, we plan to properly film the experiment and make the material available online in multiple languages to reach students internationally. In parallel, we will also work on improving the quizzes and updating our presentation with the latest video material as we continue to collect it while at sea.

Acknowledgements:

We would like to thank the European Geoscience Union (EGU) and the Institut de Physique du Globe (IPGP) for the financial support of the model and for their assistance in organizing the events. In particular, we want to thank Emmelyne Mitard (now at INSU-CNRS), Pierre-Olivier Foucault (IPGP), Antoine Roux (now at INSU-CNRS), and Christina Orieschnig (EGU). We are also grateful to the colleagues from Vienna University, Heidi Wienhäupl and Nils Bezwoda, for preparing the materials we needed to conduct the experiment; we especially thank Xenia Hauser and David Fischer (UV), who conducted the event in German during the Planet Day event at the University of Vienna. We also thank the high school (led by Chloé Lardy), as well as all the participants in the experiment. To build the LEGO ship, we had great help from Elodie Lebas, Antoine and Jean-Guillaume Geignon. We are grateful to Samuel Howell (JPSL), who provided invaluable advice for the experiment's conception.

Data availability

No primary data sets were used in producing this article.

Ethical statement

For conducting of the quizzes, we closely followed the "Ethical Guidelines for Educational Research" published by the British Educational Research Association. Before the quizzes, we explained the process to the guardians (teachers and/or parents) and obtained their consent. All quizzes were anonymous, and the results do not reveal any personal details of the participants. Students had the right to withdraw from the quiz at any stage.

Video supplement

https://sdrive.cnrs.fr/s/33SgMcHtpwWRKYe

Author contributions

M.M. conceived the project; M.M. S.B. applied for the funding and built the model; S.M. conducted analyses of the quizzes's results; M.M., S.B., S.M., D.H., T.L. conducted the experiments; M.M wrote the initial draft of the manuscript with input from all co-authors.

Competing interests

The authors declare that they have no conflict of interest.
<figure><img src="image_24.png" /></figure>

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