(Please begin at the bottom of the page to follow our adventures from the beginning)

 

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

(Please begin at the bottom of the page to follow our adventures from the beginning)

 

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

 

 

 

 

The map below shows the location of ocean bottom seismometers (OBSs) that we have deployed since leaving port on October 23. These instruments will sit on the seafloor until the end of November, while we generate small seismic sources in a grid above them. The data from this experiment will be used to construct an image of the earth’s crust beneath the seafloor. The instrumentation and the scientific background for this experiment will be discussed in upcoming posts. Fifty of the OBSs are being supplied by the Scripps Institution of Oceanography in La Jolla, California, as part of the U.S. Ocean Bottom Seismic Instrument Program (OBSIP). Nineteen are being supplied by GEOMAR, in Germany. Fourteen of these were recovered from the seafloor after being there for the past year recording aftershocks of the April 1, 2014 Iquique earthquake.