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The science party for PICTURES includes five biologists (called PSO, for Protected Species Observers) who are charged with scanning the ocean around the ship to detect the presence of protected species. They take photos, identify the different species and keep detailed logs of their observations. The National Oceanographic and Atmospheric Administration (NOAA) has developed a well-defined and strict protocol to protect whales, dolphins, sea lions, seals, sea turtles to protect them from the sound generated to image the subsurface. This protocol includes the requirement that the sound level be ramped up gradually and that it be cut down when protected species are detected within a specified radius that depends on the water depth, source strength and type of animal. This leaves gaps in the data – a small price to pay to share the ocean with its majestic inhabitants.

Because our seismic source is on 24/7, the marine mammal specialists work shifts around the clock (like the rest of the science party). From dawn to sunset, two observers are outside on the observation tower, which provides a spectacular view of the ocean, the ship, and occasionally the Chilean coast, where desert mountains reach the sea. One observer is always stationed in the main lab, with their passive acoustic monitoring system (PAM), which enables 24/7 monitoring. The PAM records signals from a hydrophone (an underwater microphone) that is towed by the ship and records the sounds of the sea e.g. airgun shots, higher frequency chirps for mapping the seafloor (referred to as “the bird” because of the bird-like sound it makes) and, of course, the conversations of whales and dolphins. These sounds are displayed as spectrograms on two computer monitors as well as listened to with earphones.

So far during PICTURES, we have seen many marine mammals and sea turtles. The PSOs are always willing to answer questions from the geophysicists about marine life, or to simply chat and tell jokes. 🙂

– Carsten Lehman, November 2016

(Science Objectives translation prepared by the German members of the PICTURES cruise)

Ziele der Fahrt

Der westliche Teil des südamerikanischen Kontinentes ist eine aktive Subduktionszone, an der sich die Nazca Platte mit einer Geschwindigkeit von etwa 7 cm im Jahr unter die südamerikanische Platte schiebt. Dieser Vorgang führt zu häufigen Erdbeben. Aufzeichnungen dieser Beben über lange Zeiträume ergab unter anderem, dass die Beben entlang der Subduktionszone nicht überall gleichmässig verteilt sind, sondern das sogenannte seismische Lücken („seimic gaps“) vorhanden sind. In diesen Lücken sind starke Erdbeben lange überfällig. Eine dieser Lücke im Grenzgebiet zwischen Chile und Peru wird mit dem „Integrated Plate boundary Observatory – Chile“ (kurz: IPOC) seit 2007 kontinuierlich überwacht. Mithilfe des Observatoriums wurden viele Daten über Erdbeben und den Spannungszustand der tektonischen Platten aufgezeichent. Damit konnten auch wichtige Erkenntinsse aus dem Stark-Beben in der Nähe von Iquique vom 1. April 2014 (Magnitude von 8,1) gewonnen werden: Trotz der starken Erschütterung wurde nämlich dabei nur der nördliche Teil der seismischen Lücke geschlossen, was eine im Süden weiterhin unter starker Spannung stehende Plattengrenze hinterlässt. Zwei Besonderheiten richteten die Aufmerksamkeit der Wissenschaftler auf dieses Beben-Gebiet: (1) Eine ausgedehnte Zeitspanne mit Beben in den Monaten und Wochen vor dem Hauptbeben und (2) eine starke Korrelation zwischen diesen Vorbeben mit Veränderungen des lokalen Schwere- oder Gravitationsfeldes. Schwankungen im Schwerefeld deuten auf geologische Veränderungen in der Zusammensetzung der Erdkruste hin. Die Ziele des Projektes PICTURES sind deswegen darauf ausgerichtet, diese Veränderungen entlang der Region der seismischen Lücke zu finden und zu charakterisieren. Dazu werden geophysikalische Messtechniken eingesetzt, die der nicht-invasiven Abbildung des menschlichen Körpers ähneln, wie z.B. Ultra-sound oder tomographische Verfahren wie CAT-scans. Eine Kernfragestellung für die Wissrenschaflter ist dabei wie die ungewöhnlichen Änderungen im Schwerefeld hervorgerufen werden, und ob sie sich auf die Entstehung und Ausbreitung von Erdbeben auswirken.

Diese Abbildung zeigt auf der linken Seite die historische Abfolge von Erdbeben in Nord-Chile und Süd-Peru seit 1868. Die vertikalen Linien zeigen die vermutete Ausdehnung der Zone entlang der Plattengrenze, mit den stärksten Beben in rot eingefärbt. Auf der rechten Seite ist eine topographische Karte der Region um Iquique zu sehen. Die schwarze Linie mit Dreiecken zeigt die Plattengrenze und Bewegungsrichtung an (nach Osten). Die gefärbten Konturlinien vor der Küste von Iquique und Pisagua beschreiben die Laterlverschiebungen innerhalb des Erbebengebietes in Intervallen von je 1m. Die weiß-gestrichelte Linie zeigt das Segment, in dem die seismische Lücke geschlossen wurde und die weiße Linie im Anschluss die Bereiche, wo sie weiterhin besteht. Wäre die gesamte seismische Lücke während eines großen Erdbebens geschlossen worden, so wäre wahrscheinlich ein Beben mit einer Stärke über Magnitude 9 möglich gewesen.

-contributed by Michael Riedel, Jan Handel and Florian Petersen

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The objective of PICTURES is to generate images of faults and other structures beneath the seafloor. Although we have to wait until the end of the cruise to recover the Ocean Bottom Seismometers and get our hands (and computers) on the data, we get the multichannel seismic (MCS) reflection data in real time and have been having a wonderful time processing the data to generate pictures. These data are recorded on a long (up to 12.5 km!) tube that is towed behind the ship and contains thousands of hydrophones. The hydrophones record minute pressure changes generated as sound waves from our seismic source bounce off the seafloor and structures beneath it. The cartoon below shows ray paths of reflected waves recorded on the hydrophone streamer and refracted waves recorded at distances beyond the streamer by OBSs or sonobuoys (expendible floating buoys that contain a hydrophone and send data by radio back to the ship). For this cruise we are using OBSs rather than sonobuoys because they stay at a fixed place on the seafloor and can record data to much greater distance.

The seismic reflection data are rearranged in the computer to generate images like the one shown below, which shows the oceanic crust of the Nazca plate being thrust beneath the continental margin of Chile. Although it looks like the underthrust (i.e. subducted) crust is flat beneath the accretionary prism, this is an illusion. The vertical axis in this image is the time it takes for the acoustic energy to travel from the energy source to the reflector and back to the streamer. To convert this axis to depth, information on the speed of sound is needed, and sound travels more quickly in the accretionary prism than in the ocean. The speed of sound in water is approximately 1500 m/s. A rough guess of the speed of sound in the accretionary prism is 3500 m/s. We therefore estimate that the Nazca plate crust is at about 7 km depth at the trench and at about 9.5 km depth at the eastern edge of this image. The OBS data will provide more detailed information on the speed of sound beneath the seafloor that will be used to improve the imaging.

And for a contrasting view, here is an image we just got this morning showing a large seamount or ridge entering the subduction zone.

We are scrambling to process the data as fast as it comes in to get a first look at the data. Check back again for more pictures from PICTURES.

– Anne Tréhu, November 2016

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Eating a good meal is very important, but luckily here on the R/V Langseth we have a team of top cooks. They always have a lot of ideas to share with us, with cuisine from America to Asia, and everywhere in between. There are always several choices between different dishes just in case you do not like one (so spicy !!). And never forget the delicious dessert!

The meals are always ready on time, at the same time, every day. It’s the superb moments around these meal times that get everyone out of work to talk and laugh. Sometimes these are the only moments of the day that we see the people who work in different parts of the boat than us. Truly, these moments of sharing and socializing are really important for everyone!! Even if you miss a meal or find yourself hungry for snack, there is always something to eat so you’ll never die of hunger 😀 – the salad bar, sandwiches, leftovers from meals and sweets (yummy cakes and cookies!)

I knew as I left France that my biggest problem was figuring out how I will spend 2 months at sea without candy or chips. It was a real concern for me, so I made sure to buy some candy for myself before leaving (but only one box) :D. Luckily, soon after the boat departed, I was surprised with more and more candy every day – all thanks to Tom, who truly thought about everyone when it came to sweets. During our shifts we eagerly wait for Tom to know what surprise he will have for us that day :D. Even when we work on deck he never forgets and always comes with candy or chocolate for everyone. This is not something he does for himself – he is always giving away more candy than he eats himself. Tom, we really appreciate you <3

But we also cannot forget Todd! It is impossible for 4am to pass without seeing Todd sit before his computer with the best pistachios in front of him, sharing them with everyone. Todd has more pistachios in his suitcase than clothes 😀 He prefers the peppered ones, but I prefer the salt. This makes sharing no problem for us!

– Sara Hussni-Alhisni, November 2016

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An OBS records earthquakes and other seismic and acoustic signals in the deep ocean. The instrument package includes two sensors – a seismometer to record vertical and two components of horizontal ground motion and a hydrophone to measure sound. In addition, batteries, a very accurate clock and a data logger are included in a tube that can withstand very high pressures. The instrument is dropped overboard and falls freely to the seafloor. When it is time to recover it, an acoustic signal is sent to the release system to decouple the anchor from the rest of the instrument. Without the anchor, the OBS is buoyant and floats to the sea surface, where it is fished out of the ocean and the data are downloaded to the computer. The steel anchor rusts on the seafloor and dissolves after several years. Some OBSs have a back-up timed release in case the acoustic release malfunctions.

To make it easier to find the OBS when it surfaces, it is normally equipped with a radio sensor and a blinking light source. These devices have a pressure sensor inside which ensures that they switch off below a specified water depth to preserve battery power while on the ocean bottom.

Here are pictures of the two types of OBSs used during PICTURES:

The main difference between the two OBSs shown are the way the components are assembled and the type of flotation. The SIO-OBSIP OBS uses pressure-resistant glass balls in a yellow plastic shell, whereas the GEOMAR OBS uses syntactic foam, which allows it to go as deep as 8000 m. The deepest OBS during PICTURES is at 7070 m, and the shallowest is at 674 m water depth. Both types of instruments can be left on the seafloor for up to 1 year to record earthquakes.

– Jan Handel, November 2016

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I really should start keeping track of how many times people not only ask me “What do you do out there?!” but how common it is to have it followed up by some quippy comment like “Do you have scurvy yet?” or “How many people have had to walk the plank?” I can’t lie, we are definitely rationing the fresh fruit, but the salad bar is holding on strong. I have never been on a boat for more than 10 days, and this is going to be 49. Seven weeks of constant motion, of constant science, of constant ocean. I really didn’t know what to expect about how my life would drastically change for that time period…

So what is it really like? Well, it’s kind of like a happy, low security prison (we get one 15-minute phone call a week) or like living in a really small town where you greet the same faces every morning. Some days are very busy, filled with logging data on watch in the main lab, assembling and releasing OBS, deploying the streamer and source for active seismic, and other prep on deck. The science going on here is ever changing, with a constant influx of a truly monumental amount of data. Everyone wants to be involved when something new is taking place, and it is easy to fill the day when there are physical tasks going on. However, as we settle into the active source seismic process, there is often much more downtime to fill. Learning the routine of a boat that is operating 24 hours a day certainly involves learning how to balance that work with something else.

For mental relaxation and fun there is plenty available for entertainment. There is a small theater with ample movies, as well as a server with films or TV shows to watch in your cabin. On the first night before leaving port we watched The Life Aquatic, a classic Wes Anderson film perfect for priming us with expectations for this voyage. Now that we are underway, a lot of people have a TV show they are binge watching with the hours to kill they wouldn’t have back at home to power through season after season of Shameless or Grey’s Anatomy (two currently battling examples). Later at night you can often hear boisterous card games and conversations going on in the mess hall. There are few times when many peoples’ shifts overlap, and a large game of cards seems to be like a consistent means to celebrating those times.

Getting out of the windowless seismic lab and outside is also necessary when there are no jobs to do that force you out on the deck. To that end, we have each started to find our favorite places on the boat to sit. Getting a little sun, enjoying the sea breeze, listening to the airguns, looking for whales, and reading a book that isn’t some data processing manual are definitely peaceful ways to get outside. However, after the first week, finishing the only book I brought, I quickly realized I should have brought more. Thankfully, people are willing to share and there is a small library with an assortment of books.

Many of us also try to make time for a visit to the ship’s gym every other day or so, which is in a container on deck. This is one of the best ship gyms I have seen, with an elliptical, rowing machine, treadmill, stationary bike, and an assortment of weights. The motion of the boat, especially when we are caught in a period of increased side to side rolling, makes using the gym quite the sweaty adventure. Never before have I had a treadmill come with such a good view as well as a warning about using it. I personally try to make going to the gym a daily staple, pretending that I’m getting in my daily bike commute and after work run that I would be used to at home. It helps to balance all the good food that I have little willpower to avoid, and the challenge of running completely hands free on the treadmill provides a goal yet to be achieved.

Finally, holidays and birthdays do not go unnoticed on the ship either. Halloween was full of as much candy as any other year, though only one person dressed up (the head PSO Cassi was Princess Leia). Everyone did get involved decorating the lab with paper pumpkins and skulls, and we are phasing into a new round of decorations for Thanksgiving later this month. The crew and science party are making photo collages of their loved ones to post on the wall in the lab, a chance for people to feel especially thankful of their family, their animals, and their significant others. We have also had a few birthdays to celebrate, which provide opportunities to embrace working with what you got, using found decorations like the Spongebob Squarepants birthday banner and having the kitchen make a cake with fake candles made of toothpicks. Having people from so many different countries, birthday signs in English, Arabic, German, Russian, and Spanish were hung to surprise Kathy at her midnight watch, along with a seismic reflection birthday card. Welcoming Jan to his very early shift with “Happy Birthday” on the monitors as well as a bowlful of his favorite chocolate ice cream. We might be a little nerdy about how we do it, but I’d say we really know how to enjoy our time at sea and weeks are passing by more smoothly than I ever expected.

– Emma Myers, November 2016

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The western boundary of South America is an active subduction zone, where the Nazca plate is being thrust beneath the South American plate at a rate of approximately 7 cm/yr. Earthquakes occur along this boundary frequently, resulting in a long record of activity that led to the identification of several “seismic gaps,” sections of the plate boundary where a large earthquake is overdue. One of these gaps ruptured in 2010 with the M8.8 Maule earthquake. Another gap, in northern Chile and Peru, has been monitored by the Integrated Plate boundary Observatory – Chile (IPOC) program since 2007. Consequently the onshore region was well instrumented for monitoring earthquake activity and strain accumulation when a M8.1 earthquake struck on April 1, 2014. This earthquake, however, only partially filled the gap, leaving a long stretch of un-ruptured plate boundary to the south. Two features of this earthquake caught our attention: an extended and well-characterized sequence of seismic events in the months and weeks prior to the mainshock, and a striking correlation between this sequence and anomalies in the earth’s gravity field. Tiny perturbations in gravity are indicative of geologic differences in the composition (and therefore, the density) of the earth’s crust. PICTURES is designed to image this region using techniques that are analogous to those used for non-invasive imaging of the human body (a combination of a CAT scan and an ultrasound) in order to understand the geologic origin of the gravity anomalies and their impact on how earthquakes nucleate and propagate.

This map shows the earthquake history of northern Chile and southern Peru since 1868 on the left. The vertical lines show the estimated north-south extent of the rupture zone in different earthquakes, with the largest events highlighted in red. The map on the right shows the topography of the seafloor, with dark blue being as deep as 7000 m and the pink and grey showing shallow seafloor on the Iquique Ridge. The black line with triangles shows the plate boundary where the Nazca plate plunges beneath South America and the arrow shows the direction of motion. The colored ovals just offshore Iquique and Pisagua show a model for the slip during the April 1, 2014 earthquake, with contours at 1 m intervals. Light green shaded areas are the rupture areas of other recent earthquakes. The dashed white line shows the segment of the plate boundary that ruptured during the 2014 earthquake, and the solid white line shows the remaining gap. Had the entire gap ruptured at once, it could have generated an earthquake as great as ~M9. (adapted from Schurr et al., Nature, 2014)

The places we call home are spread across the globe, and most, though not all, of these are far from the coastal city where our adventure will begin. We assemble gradually over two or three days in the northernmost city in Chile, the lovely port town of Arica. Known as La Ciudad De La Eterna Primavera, or “the City of the Eternal Spring,” the climate here is a rare “mild desert,” an arid region with moderate temperatures year-round. While we are in port the weather is warm and breezy, although the water at the beaches is cold and lifeguards turn away swimmers due to strong currents.

In the center of town is El Morro de Arica, a large hill overlooking the coastline. El Morro oversaw the destruction of Arica in 1868 when an earthquake of magnitude 8.5-9 and the resulting tsunami destroyed the city, and watched again in 1877 as another large earthquake shook the region, this time sparing Arica. Not far west into the Pacific Ocean is the Peru-Chile trench, where the Nazca plate is subducting beneath the South American plate. The trench has a long and prolific history of earthquake activity recorded in the rocks, oral traditions, and written history of Chile. A Mw 8.2 earthquake in April, 2014 in the Pisagua/Iquique region ruptured part of an area that had been quiet for longer than usual, and provided the background for the project we are about to undertake.

From our vantage point atop El Morro we watch as the research vessel R/V Marcus G. Langseth approaches the port of Arica. Soon to be our home for the next seven weeks, she floats slowly into the port after loading most of our equipment in Florida. The science party moves onto the ship on Saturday morning, amid two cruise liners full of tourists visiting the city to eat empanadas and saltenas, and browse the stalls of native crafts and modern souvenirs set up on the weekends. The chief scientist on our cruise is Dr. Anne Tréhu, a professor in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University in the U.S. The other lead scientists are Dr. Emilio Vera from Universidad de Chile, Santiago and Dr. Michael Riedel from GEOMAR in Germany. I am a post-doctoral research associate at Oregon State. Five graduate students from the U.S., Chile, Germany, and France, three engineers/technicians from Scripps Institute of Oceanography, and one engineer from GEOMAR complete the PICTURES science party. We will be joined on the cruise by the LDEO Chief Science Officer and the technical staff under his direction, protected species observers, and the maritime crew of the R/V Langseth. Together we will travel over 4500 km, recording geophysical data across the source region of the 2014 Pisagua/Iquique earthquake and westward across the trench.

-Kathy Davenport, October, 2016