Category: Science Posts

By Collin Brandl

A major goal of this Early Career Scientist training expedition is giving the participants (a total of 19 “principal investigators” ranging from graduate students to postdocs to faculty) the chance to experience every part of what goes into a full seismic research expedition. One of the most important aspects is being the Chief Scientist during your shift, which means that you are in charge.

At the beginning of our watch group’s first shift in the ship’s computer lab (read: control center), from noon to 8 p.m. on Tuesday, our six-person group had to decide on our roles for the day. Graduate student Emily Schottenfels had already been involved in a meeting on the bridge with the Second Mate, so it felt right for her to be the Chief Scientist of our shift; I became the Co-Chief.

One might expect the Chief and Co-Chief Scientists to be figureheads of the watch, especially because we are just students. However, that is definitely not the case. Almost immediately, Emily and I had to run (safely) up the bridge to deliver an update with some changed latitude and longitude coordinates and an updated operation plan.

After this, Emily and I patrolled around the computer lab to make sure all the operations were running smoothly, especially once the gear was deployed and data was being acquired. We also had a discussion with Masako Tominaga and Anne Trehu, two of the project lead scientists, and Lee Ellet, a Scripps’ shipboard geophysical engineer, about the parameters for collecting seismic data. We needed to decide on the source spacing, the sampling rate, and how long we would record for. Ultimately, we chose for the ship to use the acoustic source and then move forward for 25 meters before using it again while we record from that point for 8 seconds and measure the signal every .5 milliseconds. Luckily there were no major issues that arose during our watch, just a few fishing boats that the ship needed to avoid.

Unfortunately, the smooth seas did not last for long (figuratively speaking). As we awoke on the second day of the cruise, we were slowly brought up to speed about some issues that occurred overnight. Luckily, we sailed with an exceptional crew and geophysical engineering team that worked quickly and effectively to solve the problem. It turns out that an important aspect of being the Chief Scientist is working with a variety of people across different groups to keep the expedition running smoothly. Coordinating with Lee, his engineers, and the crew in the engine room was very fast paced but rewarding. By the end of our second day, everything was back to normal and the data was coming in great.

By the end of both shifts/days, I can sincerely say that being the Chief Scientist (or Co-Chief) is badass. The opportunity to be out here at sea and to be in charge of “science-ing” helps to illuminate the future of someone interested in marine geology and geophysics research. You have to make a lot of split-second decisions, communicate a lot of messages to the science crew, and make sure every operation/scientist is running smooth. I am so happy to be here, to be learning, and to have had the chance to be in charge.

— Collin Brandl is a graduate student at the University of New Mexico

Por Estefania Ortiz

Hace dos años, antes de convertirme en estudiante de posgrado, nunca habría pensado que estaría en el mar en una expedición de investigación sísmica. Desde que empecé mi programa de posgrado en la Universidad Texas A&M, tuve la oportunidad de participar en grandes proyectos de investigación: explorando la geología de la secuencia Ofiolita de la Cordillera de la Costa en California y Canadá usando métodos geofísicos, realizando experimentos de magnetismo de nanoescala en la Universidad de Minnesota y Cambridge (Reino Unido), y aprender más sobre las propiedades físicas y químicas de las rocas y cómo interactúan con los fluidos en la Universidad de Leicester (Reino Unido). Ahora estoy a bordo del R/V Revelle (mi primera vez en el mar), recogiendo datos sísmicos multicanal a lo largo del geológicamente complejo Margen de Cascadia.

Para mi investigación de tesis de maestría, mi principal proyecto de investigación se centra en tratar de mejorar la comprensión de cómo medir las señales climáticas registradas en los sedimentos del fondo marino, utilizando una variedad de conjuntos de datos geológicos y geofísicos del Océano Pacífico Ecuatorial Oriental. Esta región del Pacífico se encuentra a pocos grados del ecuador, en el fondo liso sin alterar, en una zona donde se pueden encontrar “altas tasas de acumulación de sedimentos” (0.02 milímetros por año, una pizca de polvo). Esta región tiene unos 400 metros de sedimento sin alterar la capa antes de llegar a la roca dura subyacente a los sedimentos, que registra una gran cantidad de información sobre las condiciones climáticas del pasado que se remonta a hace 28 millones de años. La información extraída de estos sedimentos puede ser utilizada por paleoceonógrafos (científicos que estudian la historia de los océanos) para reconstruir el clima pasado y las condiciones del océano, esta información se utiliza para ayudarnos a entender las condiciones climáticas actuales y esperadas.

Para lograr mi meta de investigación, utilizo datos sísmicos marinos, que son como un ultrasonido de la tierra que me ayuda a imaginar kilómetros bajo el fondo del océano, y muestras de sedimentos recolectadas desde el fondo del océano. Yo, analizo mis muestras de sedimentos para comprender una pequeña área del océano y uso las imágenes sísmicas para correlacionar mis datos a grandes áreas del océano. Con estos datos, busco patrones en mis muestras de roca e imágenes sísmicas para entender cómo el movimiento de sedimentos podría afectar las señales climáticas registradas en los sedimentos medidos.

Sin embargo, para mi proyecto de investigación, no tuve la oportunidad de recopilar mis propios datos sísmicos. Por lo tanto, solicité ser parte del crucero de entrenamiento sísmico ECS con el fin de ganar experiencia en el campo marino. Durante esta expedición, esperaba aprender de geocientíficos de alto nivel cómo diseñar eficientemente mi propio proyecto, incluyendo los desafíos involucrados con la adquisición, procesamiento e interpretación de datos sísmicos marinos.

La expedición ha superado mis expectativas. Desde el primer día nos dieron importantes roles que son cruciales para el éxito de nuestra expedición, incluyendo ser jefe científico, co-jefe científico (roles con mucha responsabilidad incluyendo liderar el equipo científico, comunicarse con el equipo de adquisición de datos sísmicos y el capitán del buque, y asegurar que el trabajo propuesto sea razonable y alcanzable con los recursos disponibles), y procesador sísmico (encargado de evaluar la calidad de los datos adquiridos y procesar los datos sísmicos recogidos a imágenes del subsuelo). Rápidamente aprendimos que la comunicación y la resolución creativa de problemas son la clave para adquirir con éxito datos sísmicos y ayudar a la tripulación del barco a navegar el Revelle a áreas de interés.

El Crucero de Capacitación Sísmica de ECS me ha enseñado cómo trabajar como parte de un equipo en un ambiente de ritmo acelerado y cómo comunicarme exitosamente con compañeros de equipo para lograr los objetivos de investigación. Después de mi experiencia de entrenamiento, me siento más confiada en mi habilidad para ser una científica principal en futuras expediciones marítimas y continuar contribuyendo a la comunidad científica. Mis experiencias de investigación únicas no serían posibles sin el apoyo de la National Science Foundation y un grupo de mentores dedicado que han estado liderando este esfuerzo de capacitación.

— Estefania Ortiz es un estudiante en la Universidad Texas A&M

By Fani Ortiz

Two years ago, before I became a graduate student, I would have never thought I would be at sea on a seismic research expedition. Since I began my graduate program at Texas A&M University, I have had the opportunity to be involved in great research projects: exploring the geology of the Coast Range Ophiolite sequence in California and Canada using geophysical methods, conducting nanoscale rock magnetism experiments in the University of Minnesota and Cambridge (UK), and learning more about physical and chemical properties of rocks and how they interact with fluids at the University of Leicester (UK). Now I’m aboard the R/V Revelle (my first time at sea), collecting multichannel seismic data along the geologically complex Cascadia Margin.

For my master’s thesis research, my main research project focuses on trying to improve understanding of how to measure climate signals recorded on seafloor sediments, by using a variety of geological and geophysical data sets from the eastern equatorial Pacific Ocean. This region of the Pacific is located a few degrees from the equator, on smooth unaltered seafloor, in an area where “high sediment accumulation rates” (.02 millimeters per year, a sprinkle of dust) can be found. This region has about 400 meters of unaltered sediment cover before we reach the hard rock underlying the sediments, which records a wealth of information about past climate conditions going back to 28 million years ago. The information extracted from these sediments can be used by paleoceaonographers (scientists who study the history of the oceans) to reconstruct past climate and ocean conditions, this information is used to help us understand current and expected climate conditions.

To accomplish my research goal, I use marine seismic data, which is like an ultrasound of the earth that helps me image kilometers under the ocean floor, and sediment samples collected from the ocean floor. I then analyze my sediment samples to understand one small area of the ocean and use seismic images to correlate my data to large areas of the ocean. With this data, I look for patterns in my rock samples and seismic images to understand how sediment movement might affect the climate signals recorded in the measured sediments.

However, for my research project, I did not get the opportunity to collect my own seismic data. So, I applied to be a part of the Seismic ECS Training Cruise in order to gain marine field experience. During this expedition, I hoped to learn from senior geoscientists how to efficiently design my own project, including the challenges involved with the acquisition, processing, and interpretation of marine seismic data.

The expedition has exceeded my expectations. From day one we were given important roles that are crucial to the success of our expedition including being chief scientist, co-chief scientist (roles with a lot of responsibility including leading the science team, communicating with the seismic data acquisition team and ship’s captain, and making sure the proposed work is reasonable and attainable with the available resources), and seismic processer (in charge of assessing the quality of the data acquired, and processing the seismic data collected to images of the subsurface). We quickly learned that communication and creative problem solving are key to successfully acquiring seismic data and helping the ship’s crew navigate the Revelle to areas of interest.

The ECS Seismic Training Cruise has taught me how to work as part of a team in a fast-paced environment, and how to communicate successfully with teammates to accomplish research objectives. After my training experience, I feel more confident in my ability to be a chief scientist in future marine expeditions and to continue contributing to the scientific community. My unique research experiences would not be possible without the support of the National Science Foundation and a dedicated mentor group who has been leading this training effort.

— Fani Ortiz is a graduate student at Texas A&M University

By Jessie Saunders

Off the Pacific Northwest coastline lies the Cascadia subduction zone, a region of the Earth where one section of the Earth’s crust (the Juan de Fuca Plate) moves underneath another part of the crust (the North America Plate). Subduction zones produce the largest earthquakes ever recorded, and because most of these subduction zones are underwater (Cascadia included), these earthquakes can also generate deadly tsunamis. Despite this hazard, there are portions of the Cascadia subduction zone offshore Oregon where we do not have information about the structure of the two plates where they connect. Such information can add to our understanding of the tsunami hazard for the Pacific Northwest. Part of the mission of our research expedition on the R/V Revelle is to image the structure of the two plates at the trench where they connect and help fill in some of the present data gaps.

Tsunamis caused by large subduction zone earthquakes are some of the most destructive natural hazards on Earth. In addition to the sudden change in the seafloor caused by the earthquake, if an earthquake occurs close to the trench, it can trigger an underwater landslide in the sediment layers at the trench above the shallow section of the fault. Such landslides cause more water to be displaced and add to the height of the tsunami waves that hit the coastline closest to the location of the landslide. This occurred during the devastating magnitude 9.1 Tohoku-oki earthquake that happened in 2011 offshore Japan. The earthquake ruptured into the shallow portion of the subduction zone by the trench and caused an underwater landslide on the northern edge of the earthquake’s rupture area.

Like Japan, the Cascadia subduction zone offshore the Pacific Northwest has experienced large subduction earthquakes in the past and will experience them in the future. The historical earthquake record for this region shows evidence of large tsunamis and underwater landslides, so it is important to develop accurate tsunami early warning systems for the coastal populations in this region.

Local tsunami warning systems in development for Cascadia are using land-based seismic networks (seismometers and accelerometers) and geodetic networks (GPS) to rapidly estimate the characteristics of earthquakes such as starting location, magnitude, and the amount of motion on the fault. These earthquake characteristics can then be put into a tsunami model which calculates the expected wave height and the time it will take for the wave to reach the coastline. This information is the basis for the early warnings issued to the coastal communities of the Pacific Northwest. However, such warning systems will have a difficult time estimating any additional effects caused by underwater landslides because the landslides would occur close to the trench and far from the early warning network’s instruments.

One way to improve tsunami early warnings is to identify regions along the trench that are more likely to collapse in a landslide. If an earthquake occurs close to one of these regions, the warning of the incoming tsunami could be modified to say that there is the possibility of an underwater landslide and that the people closest to the possible slide area should evacuate to even higher ground.

Right now, there is not a lot of data for the near-trench region offshore Oregon that can be used to identify potential future landslide locations. Our expedition on the R/V Revelle will help fill in some of the gaps. This mission targets a past underwater landslide offshore Oregon. By imaging the structure of the slide, we can learn about the conditions that caused the landslide at that location. After we image this region, we will travel northward and image sections of the deformation zone near the trench that have not experienced a large underwater landslide. We hope to use the information from the landslide to assess the possibility of landslides in these locations. These data will greatly improve tsunami early warnings when the next “really big one” occurs.

— Jessie Saunders is a Ph.D. student at Scripps Institution of Oceanography

 

By Irina Filina

A large destructive earthquake in the Cascadia Subduction Zone is long overdue. The earthquake, often referred as a megathrust, is expected to produce a tsunami that will affect the western coast of the U.S. and Canada. With this in mind, the region’s coastal population is training to get ready for this event and scientists are working to better understand what it may be like.

In Newport, Oregon, just before boarding the R/V Roger Revelle for this scientific expedition, we had to participate in a mandatory tsunami drill. We walked together to the highest elevation in the port area, which is a designated point for people to gather in case an earthquake and tsunami happen. The necessary supplies of food and water are stored at this muster point, allowing the people affected by tsunami to wait while the water level drops off. Posters with directions and estimated walking times to the muster point are established on the way to the location. These posters serve as mitigation to the expected hazard; they definitely will be crucial for the people affected when this expected earthquake hits the northwest coast of the U.S., and may save many lives.

The megathrust in the Cascadia Subduction Zone is associated with the area where the young, oceanic Juan de Fuca plate is sliding under the continental part of the North American plate. In order to assess the hazards, mitigate the damage, and make improved predictions about this potentially devastating event, it’s necessary for scientists to have a reliable and detailed geologic model of the Earth’s lithosphere – the uppermost rigid layer of the planet. This subsurface model consists of information about the thickness and lithological composition of the rocks of both plates, usually organized in layers, such as sedimentary strata, various crustal units, and the upper mantle.

In order to develop a geologic subsurface model, a variety of remote sensing geophysical techniques are used, such as seismic sounding and potential fields (gravity and magnetic) surveying. All of these techniques share the same underlying principle – they use the measurements of some physical phenomena at the Earth’s surface to derive geological information about the rocks in the subsurface. Different methods focus on different physical phenomena – acceleration due to gravitational force is measured for gravity prospecting, the strength and direction of the Earth’s magnetic field are recorded in magnetic surveying, while the ground motion (onshore) or water pressure (offshore) is measured for seismic sounding.

Seismic reflection sounding is the most widely used geophysical method scientists use to map the variations in thickness and lithology of the subsurface layers. This method uses artificially created sound waves that spread through the rocks in the subsurface and are reflected and or refracted at each contact between the different rock layers. The resultant complex pattern of reflected and refracted seismic waves is recorded at some distance from the source of seismic wave.

Interpreting these various seismic arrivals can be challenging and they don’t always provide an interpretation scientists are confident in. In this case, the other geophysical measurements, which record information about the same subsurface, may be integrated with seismic sounding data to constrain the resultant geological model. One of these complementary geophysical techniques is gravity surveying, which is sensitive to variations in the densities between various rock layers in the subsurface. Another technique is magnetic field analysis, which maps the changes in rocks’ magnetic mineral content, described by a physical property named magnetic susceptibility.

A focus of my scientific research is combining records from various geophysical methods together in order to derive a reliable subsurface model that honors all the recorded datasets. During this expedition, the data for all three geophysical methods – seismic sounding, gravity and magnetic readings – are being recorded simultaneously. The integrated analysis of all three datasets together results in a more detailed geological model: the seismic sounding provides the depths to various subsurface layers, while the potential fields allow constraining the lithologies of different geological units (rock layers) based on the derived physical properties, such as densities and magnetic susceptibilities. As the derived geological model should agree with all three datasets, the overall confidence in the result will increase greatly.

The geological model of the Cascadia Subduction Zone that’s created using the data collected during this expedition will improve our understanding of the structures and overall structural architecture of the lithospheric plates involved in the anticipated megathrust. Using this integrated geophysical approach that combines three different methods will result in much more robust and confident subsurface models. These, in turn, will lead to more confident and reliable earthquake prediction and hazard assessments that will help keep citizens of this region safe.

— Irina Filina is an assistant professor at the University of Nebraska-Lincoln

By John DeSanto

So there’s this movie Hollywood came out with a few years back called “San Andreas.” The latest in a proud tradition of dumb, “bad science” summer disaster flicks, I find this movie absolutely fascinating because it is a film about a giant earthquake that gets a fair bit wrong about giant earthquakes.

Take the tsunami, for instance. While it is awesome to see San Francisco leveled by an unstoppable 150-foot wall of water, it is also unlikely to happen because (a) tsunami-causing earthquakes happen near the tsunamis they cause, and (b) the San Andreas fault is many miles inland in the middle of a desert. Also, an earthquake on the San Andreas fault would be very serious, but not nearly as powerful as depicted in the film. It’s too bad, too, because there is a major city in the lower 48 states that is at risk of suffering an earthquake and tsunami as large as, say, the pair that hit Japan back in 2011. It’s not San Francisco or L.A. It’s Seattle.

See, there are these rocks around Seattle that could only have ended up where they are if they were washed ashore by a tsunami, and a big one at that. Although there were likely indigenous people living in the region when the tsunami (and earthquake that presumably caused it) happened, they had no written language, so that disaster and its impact on them were not recorded in the annals of history. For scientists who are concerned with understanding the risk of a large earthquake and/or tsunami happening in Oregon and Washington State, this is pretty frustrating because it tells us that a major earthquake and tsunami must have happened and probably could happen again, but any further details are a little difficult to come by.

How do we go about figuring out where and what could happen? Well, the earthquake we’re worried about caused a tsunami, so it will probably happen offshore. But it also turns out that not all earthquakes cause tsunamis, they need to either be very shallow under the seafloor or near underwater cliffs that can break in landslides. This means that if we had a map of the seafloor we could identify the “problem areas” offshore that could cause a tsunami if an earthquake happened there.

Hey, we do have a map of the seafloor! I’ll just pull out my phone, open up Google Earth and… oh. There are a lot of strange tracks on the seafloor, and they are really detailed. It turns out these tracks are actually real. They are places a ship went to and directly measured the seafloor depth using an instrument called a multibeam sonar, which uses peculiar sounds (called “chirps” because they sound like a bird chirping… every 10 seconds, nonstop, 24/7) to take a picture of the seafloor beneath the ship. The parts of the seafloor that look very smooth are actually our best guess of what the seafloor looks like based on satellite data. But because the satellite data is not as detailed as the multibeam data we think of it as a “hole” in the seafloor map.

Simply put, if we want to figure out where a tsunami could come from, we need to go out on a ship and collect more multibeam data!

While surveying the seafloor, we may also collect seismic data to help us identify which “problem areas” of the seafloor have a nearby fault that can cause a large earthquake. All of a sudden, we would have a much better picture of where large earthquakes and tsunamis could come from and how large they could be.

So here I am out at sea, one of a large group of rugged scientists (almost like in the movies), collecting the multibeam data we need for our map of the seafloor and the seismic data we need to find the faults that could produce a large earthquake. The ocean is pretty vast; this survey will literally be a drop in the bucket. However, every little bit of data helps us present a clearer picture of the earthquake and tsunami risk faced by the residents of Oregon and Washington State. This information is incredibly valuable because it will help us to prepare for the worst-case scenario, saving lives and property in the future.

Perhaps the most disappointing thing about disaster flicks is that there is often evidence a disaster will happen, but no one seems to take it seriously. In reality, this could not be further from the truth. Although the evidence for a large earthquake and tsunami striking Oregon and Washington is subtle, it is certainly real. We’re treating that evidence very seriously so we are not caught off guard in the future.

— John DeSanto is a P.h.D student at Scripps Institution of Oceanography

By Srisharan Shreedharan

Subduction zones are regions on the earth’s crust where a tectonic plate (usually the oceanic plate) ‘subducts’ or shears under another plate (usually the continental plate). Subduction zone earthquakes, which happen in many locations globally, can be incredibly devastating depending on their size and potential to cause large tsunamis. This is more so since many of the world’s population centers, such as San Francisco, Tokyo, and many cities in New Zealand, are situated close to subduction zones.

As a graduate student interested in the evolution of subduction ‘megathrusts’ or large subduction zone earthquakes, I study them by conducting small-scale rock friction experiments. I am looking at how friction is different in various locations along the subduction zone and what this means for future earthquakes in these regions.

Earthquakes occur on faults, which are simply the interface between the two plates, in the context of subduction zones. Faults, with their not-so-smooth surfaces, thick sediment layers, and fracture zones display a variety of frictional behaviors. Frictionally, faults can be velocity strengthening or weakening. This means that with an increase in fault slip speed (like during an earthquake), the friction of velocity strengthening faults increases. This prevents an earthquake from further propagating because there is now an increased resistance to sliding on the fault. On the opposite end, velocity weakening faults have reduced friction values as their speed increases, and they further promote earthquake rupture, which can grow into very large hazards. If these quakes occur on oceanic faults, the earthquake can even reach the seafloor and create large tsunamis like during the 2011 Tohoku earthquake and the 2004 Sumatra earthquake.

Equipped with this knowledge, I conduct experiments in my lab where I shear, or slide, two small pieces of rock against each other and change their relative velocities to observe how they behave frictionally. I conduct my experiments in a large hydraulic press, which is essentially two hydraulic rams providing a force along the rock-rock interface and perpendicular to it. Sometimes, this results in the creation of stick-slip instabilities, which are really cool small-scale manifestation of earthquakes (or labquakes!).

There is evidence (based on the type of experiments I described earlier) that smectite, a type of clay, exhibits velocity weakening behavior over the pressure – temperature regimes necessary to propagate earthquake rupture near the seafloor close to the subduction zone. Scientists have studied subduction zones around the world for many decades now, and they have recently discovered that not all subduction zone earthquakes reach the seafloor. Based on these two observations, my work here at the Cascadia Margin is to image beneath the seafloor at different locations along the margin. I am looking for changes in fault structure over time. To do this, I plan to re-survey a region, which was last surveyed over two decades ago. Fault displacement/shift, if any, will give me more insight into how close to the seafloor the earthquakes from the past 20 years may have propagated. My survey line also goes over a scientific site that was last visited over 40 years ago.

I will combine the new seismic data from this survey with the existing data to accurately describe the many layers of rock and sediment that will invariably show up in my sub-sea floor images. I plan on using these datasets as a baseline to comment on the presence/absence of sediment layers (eg. smectite) in other seismic images acquired during the cruise. This will help me make an informed judgement about the potential for large tsunamis at various locations along the west coast.

In many ways, laboratory and field studies go hand in hand, especially in the context of earthquakes. Not all kinds of data can be collected in the field due to time constraints, instruments sometimes break down and there are field constraints such as bad weather. Experiments conducted on a much smaller scale provide us with the flexibility of exploring a larger set of parameters to explore. This helps build an intuitive understanding of how larger scale hazards like earthquakes and tsunamis work in nature. It also helps us build testable hypotheses and theories that we can back up — or refute — based on field scale observations. Ultimately, these experiments and studies help us, as a population, build better early-warning instruments, create more robust building codes in extremely earthquake-prone areas, and create tsunami resistant structures in coastal areas.

— Srisharan Shreedharan is a Ph.D. student at Penn State University

By Brendan Reilly

Greetings from the Oregon Margin. This isn’t my first time here. In June 2017, I sailed on another expedition, Oceanus cruise 1706B, organized by fellow Early Career Scientist (ECS) Seismic Cruise participant Mo Walczak, to collect sediment cores, which have layers of sediment, or mud, that have accumulated on the seafloor. The cores we were after on that expedition would contain an environmental history of the Columbia River watershed going back over ten thousand years.

We recovered around 5-10 meters of mud from a number of locations. Each layer in these sediment cores represents a period of time slightly older than the layer above it and records information about the environmental conditions of that time. Reconstructing these conditions will build on our understanding of the relationship between Pacific Northwest water resources, ecosystems, and environment and Earth’s climate during times warmer and cooler than present.

As on this current expedition, the researchers in the Oceanus science party were almost entirely early career scientists, including three Research Experience for Undergraduates (REU) students, one undergraduate who missed her graduation ceremony to participate, seven graduate students, and two post-docs. In the months since returning with those cores, the REU students have studied the microfossils, physical properties, and geochemistry of these sediments. These preliminary data indicate that many of the basins we cored contain high resolution records of Columbia River discharge and past oceanographic conditions of the Oregon Margin.

We used these initial data to target the most promising sites for survey with the Scripps Multi-Channel Seismic (MCS) system during the ECS Seismic Cruise. Our initial results suggest that these basins contain hundreds of meters of sediments, potentially extending back millions of years. This is significantly deeper than the subbottom profiles we were able to image with the ‘chirp’ subbottom imaging system we used previously. The chirp uses a higher frequency sound wave than the MCS system we are using during ECS Seismic Cruise. This allows for a higher resolution image of the upper tens of meters, but it cannot penetrate as deep as the lower frequency MCS system.

A challenge we’ve encountered is finding sites with high accumulation rates of mud, without much influence by erosive turbidity currents, or flows of sediment that travel downslope on the seafloor. Their deposits, turbidites, have been useful in investigating the earthquake history of the Pacific Northwest, but can complicate interpretation of sediments for environmental history. Careful survey, like we did in June 2017 and are doing during the ECS seismic cruise will help identify the perfect sites for further work.

We have learned a lot so far about the nature of the deeper Oregon Margin sedimentary deposits from the ECS Seismic Cruise and have started discussing our plans for the next steps to investigate them further. A rewarding aspect of the cruise has been developing new research questions that could be addressed collaboratively with my fellow ECS participants in the future. While this project is a large undertaking, ultimately, what we learn will contribute to our understanding of how the Pacific Northwest has changed in the past and how that information can be used to plan for changes that may happen in the future.

— Brendan Reilly is a Ph.D. student at Oregon State University

By MItch Lyle

Forty-four years ago this month I first went to sea for science; now I am on about my fortieth research expedition. It’s a long process to explore and map the seafloor. I’ve spent my entire career on this research and am now passing the torch by helping to train the next generation.

I watch the young scientists here on the R/V Revelle for their first expedition and think back to my early trips. The objectives of this expedition are to gather important data on how the Oregon continental margin is constructed and also to pass practical experience to the younger scientists. Gathering data at sea is a different skill set from working in the lab or on land: things break, time is short, and ship time is expensive and hard to get. Scientists must learn to be flexible but still get the critical scientific information they need.

On Revelle we are mapping the seafloor and using seismic reflection, or sound pulses, to image the shape of sediment layers that lie below the seafloor. The sediment geometry tells us how the sediments were deposited as they were eroded from the land. The sites we find that show the sediment has quietly accumulated are good spots for us to later return and collect sediment cores, which contain climate history going back tens of thousands of years. Since earthquakes bend and compress the sediment layers, the shape of the layers gives clues about how earthquakes happen and how they have uplifted or changed the coast.

The survey technology we use has vastly changed since 1973. The new technologies make life much simpler. GPS positioning now enables us to locate the ship to a few feet at any moment. In the 1970s we had a position fix every few hours from transit satellites but had to guess at what happened in between these. We often were actually miles away from where we thought we were, which of course was not very good for our maps.

And, we didn’t really have computers—a smartphone is much more powerful than the big boxes we took to sea in 1973. So, everything was recorded on paper and perhaps digitized later. Yet scientists still use the paper traces of seismic reflection records we collected then because for many places, these 40 or 50-year-old paper records are the only data available on a given location. To use these data, we scan the records into special programs and orient them with respect to newer digital data like we are collecting today.

In 1973, we mapped the seafloor with an echo sounder, which gave us one line of soundings directly beneath the ship. Then we’d digitize the depth to the ocean bottom at 5-minute intervals from the paper records while we were off watch. The chief scientist for the project would look over our work and hand it back to us to do over again if we were sloppy. Today, we use a process called swath mapping, where we can get a fan of depths from 120 spots on the seafloor simultaneously and can map for more than a mile on either side of the ship. As the ship follows the planned track line, it paints a map of the seafloor that’s wide enough to cover an entire submarine (underwater) volcano. These data are recorded to computer servers on board and their positions are referenced automatically. Still, hands are needed to sort through the data files, edit the traces, and remove fliers. It isn’t all automatic.

I am impressed how the young scientists can adapt to the digital world, having grown up interacting with devices. They smile at the all-thumbs approach of older generations. And they jump right in to make the maps, process profiles and get done in a matter of days what used to take months of post-expedition work. Now we can go so much faster from raw data to interpretation to paper to database.

These young scientists will need such skills in their careers because close to 90 percent of the ocean has not been mapped to the scales that we need. Marine geologists get jealous of NASA researchers studying Mars, who have maps that can image to a couple of feet. Most of the ocean is mapped at a scale of five to ten miles—enough to find the big seamounts and trenches, but not enough to image current channels or seafloor faults. On the bright side, almost every time we go to sea we find something new, so doing marine geology is never boring.

— Mitch Lyle is a Research Professor in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University and a Principal Investigator for this Early Career Scientist Seismic Training Cruise.

 

By Brandi Lenz

I am a first year Ph.D. student in the School of Earth Sciences at THE Ohio State University under the supervision of Dr. Derek Sawyer. I study marine geohazards, such as submarine landslides. I have worked with high-resolution marine two-dimensional and three-dimensional seismic data from my undergraduate research projects and completed a reflection seismology course. However, I have not had the opportunity to participate in marine acquisition and processing. It is important that I gain this experience early in my career so that I have a better understanding of the data I will be working with and will be able to teach others on how it is acquired, processed, and interpreted.

Our study area for this expedition is the Cascadia Margin, and we are collecting data on it offshore Oregon. The area is tectonically active and at risk for many geohazards such as earthquakes, tsunamis, and submarine landslides. It is the perfect place for me to study submarine landslides on an active margin. Submarine landslides are similar to landslides that occur on land, but they occur underwater and are often much larger.

Scientists have noted that there seems to be an absence of slope failures or submarine landslides in the Astoria fan region, which is the northern portion of our study area. I think this is because only the bathymetry, or changes in the depth of the seafloor, has been measured and studied in detail, and there are not a lot of existing seismic profiles that go through the region. This means the data is probably biased to slides with distinct head scarps, the steep section of the slope from where a landslide begins to fail, and more recent events. Collecting seismic profiles is essential if we want to understand the history and frequency of these events. Seismic profiles allow us to “image” below the sea floor and will help us see older events.

The Astoria Fan has higher sedimentation rates than elsewhere along the margin. It consists of mostly clay and silty-clay sediments. Large landslides usually occur in areas of weaker fine-grained sediment and have the potential to create or enhance tsunami events. My hypothesis is that landslides will be less frequent outside the fan due to a lower sedimentation rate, which allows seismic strengthening to occur. Seismic strengthening can increase the shear strength of sediments by exposing them to low-magnitude earthquakes. This causes the sediments to become stronger or more consolidated over time, and therefore less susceptible to submarine landslides.

It is a delicate balance though. Earthquakes are also considered to be one of the main triggers for these underwater landslides. Seismically strengthened sediments can still fail, but it’s more than likely this would require a higher magnitude earthquake. Seismically strengthened sediments probably have a different style of failure. They likely fail in a more blocky cohesive way, which is important to understand because they could have the potential to create tsunamis. Other scientists have already identified and characterized several submarine landslides on the Cascadia Margin, especially the southern portion of our study area. It includes a known, large-scale slope failure, the Heceta slide, which is believed to have produced a large tsunami.

Once seismic profiles are acquired inside and outside the fan, we can identify submarine landslides in the subsurface to get an idea on how frequent these events actually are. Seismic strengthening has not thoroughly been explored with seismic data yet, so I am excited to see what we can learn from it. Also, we are going to have a few seismic profiles of the Heceta slide and a nearby slump feature. I am hoping these profiles will help us better understand this large catastrophic slide and the mechanisms associated with its failure.

This research opportunity has benefited me greatly and will help advance my developing career as a scientist and educator. The expedition has given me valuable experience that will assist me with my continuing research in marine geohazards and provide me with interesting data I can use in my dissertation. This whole expedition has been life changing, especially since I have lived in land-locked areas my whole life and never spent any time out at sea. I finally know what it’s like to be on a research vessel (and get seasick!), acquire and process seismic data, and collaborate with other scientists with different backgrounds and point of views. If I had to describe this seismic training cruise in one word it would be “AMAZING!”

— Brandi Lenz is a Ph.D. student at The Ohio State University