This post was written by Yiran Li, a graduate student at Binghamton University in the seminar Science Communication for Scientific Ocean Drilling (SciComm for SciOD), Spring 2023.
For me, one of the key takeaways from graduate school was learning that being able to effectively communicate and share your research with others is just as important as the research itself, and that it is a crucial skill for integrating oneself into a collaborative research environment such as the one we have in the geosciences community. Participating in the SciComm seminar was an eye-opening experience for me. As a student of observational seismology, I had a general idea of what the International Ocean Discovery Program is through course works, but was completely unfamiliar with the aspect of community culture that advocates and invests in mentorship opportunities.
Many topics explored in this course were very new to me. It was really interesting to hear about journal studies that evaluate the effectiveness of different pathways in scientific communications, whether that’s interactions on social media or through outreach programs. I also empathized with the experiences of students who are just starting out in earth sciences, and how they discovered a community by participating in research opportunities – I had no idea that these literatures existed, and really appreciated the fact that there are published works highlighting the emotional aspects of pursuing careers in geoscience research. It helped me reflect over my own experiences as well. I hope to get more involved, and further explore more opportunities in science communication in the future.
Figure 1: A schematics of proposed slip style and stability around different parts of a megathrust system (Yao et al., 2017).
The great Tohoku earthquake that struck northeastern Japan in 2011 was one of the largest earthquakes ever recorded on the Earth. The 9.1 magnitude earthquake resulted in a devastatingly shaking tsunami that not only produced large death tolls and structural damages but also revealed that our understanding of how the large subduction zone faults behave needs to improve in order to better predict and mitigate future earthquakes. Integrated Ocean Drilling Program Expedition 343 drilled down to the slip interface near the earthquake epicenter in offshore Japan subduction zone with the aim of recovering both geophysical data and material samples around the fault surface (Figure 2). Geoscientists used these data to form a detailed understanding of what is happening to the earth material around the fault when large ruptures occur, incorporating many parameters like states of temperature and stress, sediment type, pre-existing fault structure, and fluid flow (Chester et al., 2013)
Figure 2: Drill sites around the Tohoku-oki earthquake epicenter in offshore eastern Japan. Core samples were collected from ~5 km inland from the trench, sampling the toe of the sedimentary accretionary prisms closest to the subduction zone down to the depth of ~840 m (Chester et al., 2013).
Megathrusts along subduction zones produce the largest earthquakes on the Earth due to the long fault length and relatively wide slip surfaces. The fault rupture associated with the 2011 earthquake reached over 62 m in slip along a 40 km long segment of the Japan Trench (Sun et al., 2017). The slip was considered unusually large for an event that took place at shallow depths in the Earth near the subduction trench, where the fault surface was generally believed to be stable (Figure 1, Yao et al., 2013). While the occurrence is less frequent, shallow rupture events of this magnitude need to be monitored because the slip can breach and significantly displace the seafloor, which will cause tsunamis.
The deepest points in the Earth’s ocean are subduction trenches, where the downgoing oceanic plate bends and sinks beneath the overriding continental plate (Figure 1). The JFAST project reached one of the deepest water depths amongst all of the expeditions in the International Ocean Discovery Program (IODP Expedition Statistics) in order to tap into the shallowest portion of the subduction megathrust. In total, five boreholes were attempted at Site C0019 (Figure 2), three of which successfully reached the target fault surface (Chester et al., 2013). Multiple types of data were carefully collected over the course of a month. In addition to successfully recovering the cores, the expedition also performed real time well logging while drilling (LWD) to retrieve in situ conditions of the sediment and materials surrounding the fault surface. High-resolution electrical images also illuminated the structures and lithological properties in the borehole and enabled the identification of plate boundary fault zones (Figure 3, top). In particular, the patterns of the beddings and fractures inferred from the borehole images showed multiple faults that comprise the fault zone and drastic change in sediment structures as they are sheared by plate motion (Figure 3, bottom). Finally, temperature sensors were directly deployed along the fault interface in Hole C0019D during expedition 343T to measure the remaining frictional heat produced from the slip event 16 months prior (Figure 4).
Figure 3: The fault zone was reached at ~720 m below the sea surface (Chester et al., 2013). (top) borehole images and well logs taken along the fault zone and (bottom) combined interpretation of bedding structures near the fault zone (Chester et al., 2013).
References
Expedition 343/343T Scientists (2013). Site C0019. In Chester, F.M., Mori, J., Eguchi, N., Toczko, S., and the Expedition 343/343T Scientists, Proc. IODP, 343/343T: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.343343T.103.2013
Sun, T., Wang, K., Fujiwara, T., Kodaira, S., & He, J. (2017). Large fault slip peaking at trench in the 2011 Tohoku-oki earthquake. Nature communications, 8(1), 14044.
Yao, H., Shearer, P. M., & Gerstoft, P. (2013). Compressive sensing of frequency-dependent seismic radiation from subduction zone megathrust ruptures. Proceedings of the National Academy of Sciences, 110(12), 4512-4517.
Figure 4: Borehole opening at the seabed (6897.5 m deep!), where the tubing pipe of the temperature observatory is being lowered down and installed along the fault zone to measure frictional heat released from the Tohoku earthquake (Photo galleries, JAMSTEC).
Figure 1. The location of New Zealand with respect to the complex tectonic boundaries between the the Pacific plate and the Australian plate (Barnes et al., 2019). Cooler, darker colors represent deeper areas of the ocean, whereas warmer colors represent shallower regions around New Zealand.
New Zealand is tectonically complex, hosting both subduction and strike-slip fault zones associated with the plate boundary between the Pacific plate and the Australian plate. The country is thus geologically active, with many potential natural hazards that require investigation and close monitoring (Figure 1, Barnes et al., 2019). The need for improved mitigation also presents an opportunity to better understand the Earth processes prevalent in active tectonic settings. Between 2017–2018, International Ocean Discovery Program Expeditions 372 and 375 set out to collect data (cores, well logs, and in-situ geophysical measurements) at the Hikurangi Margin in northern New Zealand, with primary goals of better understanding the mechanisms and behaviors of gas hydrate-bearing landslide (Barnes et al., 2019) and slow slip events on subduction faults (Saffer et al., 2019). A combined total of six sites were sampled between the two expeditions, with two in the Tuaheni Landslide Complex (TLC) and four in a transect across the Kermadec Trench near the Hikurangi Margin.
Submarine landslides are often the byproduct of catastrophic destabilization events like earthquakes. If severe, the resulting slope failure can sometimes significantly displace the seafloor, even causing tsunamis (Harbitz et al., 2014). However, the submarine Tuaheni Landslide Complex in the offshore Hikurangi margin is unusual, showing evidence of slow, continuous downslope movement of sediment rather than discrete events. Furthermore, the onset of landslides seem to correlate with the edge of gas-hydrate, with a general shift in the styles of seafloor deformation above and below the depths where the gas hydrates are stable (Figure 2, Mountjoy et al., 2014). The cores and well logs collected from Expedition 372 were used to test several hypotheses on how exactly the gas hydrates are related to the observed gradual landslides.
Figure 2. A seismic subsurface image (Mountjoy et al., 2014) showing the cross section of submarine landslides at the Tuaheni Landslide Complex. The lateral change in deformation style across the locations of gas hydrates (strong amplitude in the seismic section) can be inferred from the different faulting style.
Hikurangi Margin is also well documented for another tectonic phenomenon that is observed along the subduction zones, called slow slip events (SSEs). Unlike the devastating megathrust ruptures that release strong seismic energy from sudden movements along the fault surface, SSEs release energy gradually, over a course of weeks or even months (Saffer et al., 2019). While not necessarily an immediate natural hazard, the phenomenon is a relatively recent finding and garnered increased attention from the research community in the last two decades as the observational techniques improved and densified. Hikurangi margin hosts a region of well-studied SSEs with regular occurrences, where the fault (Pāpaku fault) is at shallow depths, accessible by drilling (Saffer et al., 2019). The goal of Expedition 375 was to reach and sample the fault zone, through coring, wireline logging, and installment of geophysical observatories (Figure 3).
Figure 3. An interpreted seismic subsurface image (Barker et al., 2019) of the drill location relative to the Papaku fault.
Recent studies have begun to shed light on the mechanisms behind the above phenomena using the core and geophysical data retrieved by Expeditions 372 and 375. For example, the cores from Expedition 375 reveal highly variable lithologies near the slow slip fault surface, ranging from marine clay and carbonates to volcaniclastic and conglomerate rocks (Figure 4). The large variety of material with different compositions and grain-sizes also means different deformational responses to the stress as they are carried into the Earth on the subducting plate, and by extension, the different slip behavior (Barnes et al., 2020). Computer numerical modeling has also previously shown that fault surfaces with variable materials might favor transient slow slips over large, sudden ruptures (Saffer et al., 2015), compatible with the observations made from the borehole data.
References
Barnes, P. M., Pecher, I. A., LeVay, L. J., Bourlange, S. M., Brunet, M. M. Y., Cardona, S., … & Wu, H. Y. (2019). Expedition 372A summary. Texas A&M Univ. https://doi.org/10.14379/iodp.proc.372A.101.2019
Saffer, D. M., Wallace, L. M., Barnes, P. M., Pecher, I. A., Petronotis, K. E., LeVay, L. J., … & Wu, H. Y. (2019). Expedition 372B/375 summary. Proceedings of the International Ocean Discovery Program, 372, 1-35. https://doi.org/10.14379/iodp.proc.372B375.101.2019
Harbitz, C. B., Løvholt, F., & Bungum, H. (2014). Submarine landslide tsunamis: how extreme and how likely?. Natural Hazards, 72, 1341-1374.
Mountjoy, J.J., Pecher, I., Henrys, S., Crutchley, G., Barnes, P.M., and PlazaFaverola, A. (2014b). Shallow methane hydrate system controls ongoing,downslope sediment transport in a low-velocity active submarine landslide complex, Hikurangi Margin, New Zealand. Geochemistry, Geophysics, Geosystems, 15(11):4137–4156.https://doi.org/10.1002/2014GC005379
Barker, D.H.N., Henrys, S., Caratori Tontini, F., Barnes, P. M., Bassett, D., Todd, E., and Wallace, L. (2018). Geophysical constraints on the relationship between seamount subduction, slow slip and tremor at the north Hikurangi subduction zone, New Zealand. Geophysical Research Letters, 45(23):12804–12813. https://doi.org/10.1029/2018GL080259
Barnes, P. M., Wallace, L. M., Saffer, D. M., Bell, R. E., Underwood, M. B., Fagereng, A., … & IODP Expedition 372 Scientists (2020). Slow slip source characterized by lithological and geometric heterogeneity. Science Advances, 6(13), eaay3314.
Saffer, D. M., & Wallace, L. M. (2015). The frictional, hydrologic, metamorphic and thermal habitat of shallow slow earthquakes. Nature Geoscience, 8(8), 594-600.
Figure 4. Core and borehole data from site U1520, showing variable lithology of the material being transported into the plate boundary fault zone (Barnes et al., 2020). On the right panels, numbered 1–8, are images of the cores that were drilled during IODP Expeditions 372/375.
