David Clemens-Sewall

July 16th, 2013

Hey guys! Sorry for the long hiatus. Things got quite busy after I returned from the boat. Also, the cable which I need to download photos off my camera mysteriously went missing while I was on the ship. Anyways, photos and more stuff about the boat will be coming as soon as a replacement cable arrives later this week.

For now, however, I'm going to tell you a little bit about the data I have been/will be working with. My project is focussed on resolving inconsistencies in the locations of a swarm of earthquakes which occurred over four days in 2008 near Explorer Ridge off the coast of Vancouver Island. The earthquakes themselves have been located by the Canadian National Seismic Network (CNSN), the Advanced National Seismic System (ANSS), and by Dr. Dziak's group using data from the Navy's Sound Surveillance System (SOSUS). Both the CNSN and ANSS locations are derived from land-based seismometer networks in Canada and the US respectively. The SOSUS network is an array of hydrophones, originally designed to detect foreign submarines, which also record acoustic waves generated by submarine earthquakes. Due to its national security purpose, the data from the SOSUS hydrophones is classified, hence I will only be examining the locations reported by the Dziak group.

Fortunately the seismographs for the CNSN and ANSS locations are in the public domain. P and S arrival picks have already been made for the Canadian data and I hope to be able to use those picks in my analysis. The instruments in the Canadian array are about half broadband and half extremely short period and preprocessing has already been done. In case you're not well versed in seismometer jargon, broadband and and extremely short period refer to which range of the seismic spectrum the instruments "hear". By analogy you can think about how human ears can pickup sounds in the range from 12 Hz to 20 kHz whereas bat ears are most sensitive to higher pitched sounds in the 15 kHz to 90 kHz range (see [url=http://en.wikipedia.org/wiki/Hearing_range]http://en.wikipedia.org/wiki/Hearing_range[/url]). Since these datasets are public it is possible that many other researchers have used them. However, to my knowledge no one else has published about these earthquakes using this dataset.

In addition to the land-based networks, I have been examining data from ocean bottom seismometers that were part of the Central Oregon Locked Zone Array (COLZA) experiment. This data, too, is publicly available but I am unaware of anyone outside of our lab group using it to examine these earthquakes. A previous IRIS intern in my lab has gone through the data and examined the T-phases (acoustic waves generated by submarine earthquakes which travel through the ocean). I will be filtering and processing the data and hope to be able to glean some insights about its usefulness in relocating these types of earthquakes.

Okay, that's pretty much it for my datasets. As soon as the camera cable comes in I'll upload photos from the boat and the mountain we climbed this weekend!

July 2nd, 2013

Have you ever wondered how we recover instruments from the bottom of the ocean? It's okay if you haven't, I hadn't either until about a week ago. The process doesn't involve highly trained dolphins, but in some cases is almost as cool:

Let's start with a description of the instruments. Each ocean bottom seismograph (OBS) is composed of three pieces: battery, seismometer, and recording electronics. Each piece is housed in its own, bright yellow, pressure cylinder--which weighs about 100 pounds. To make matters worse, in shallow waters (less than 1000 m depth) we need to protect the instruments from trawl nets. Thus all of the shallow water instruments are defended by square pyrimidal armored steel plate structures about as wide as I am tall. I couldn't even guess how much these weigh but to move them around the ship we need to use one of the ship's cranes.

So how do we pick these up? Well, many of the instruments have buoys attached to them by long lengths of rope. When our ship nears the instrument we send an acoustic pulse which tells the instrument to release its buoy. Then the buoy floats up to the surface and we can drag the instrument up using the rope attached to the buoy. No highly trained cetaceans necessary. A lot of the time this goes swimmingly. However, sometimes corrosion or biology prevents the buoy from releasing. That's when (cue the heroic music) Jason is deployed.

Jason is an approximately cubic,  unmanned, submersible robot. It's sides are a bit longer than I am tall. The front bristles with an array of cameras and two hydraulic arms. Six thrusters, positioned throughout the body, provide Jason with full maneuverability. The robot remains connected to the ship via an umbilical cord-like tether which goes another submersible named Medea (evidently someone at Wood's Hole was a greek mythology buff). Medea is lowered from the ship via winch and steel cable and remains close to beneath the ship while Jason is free to explore the bottom to the limit of its tether. The arrangement seems a bit complicated, but is probably the best way to reduce the risk of Jason getting tangled in cables and being lost to the deeps.

The Jason team (a group of engineers and pilots on board with us) controls Jason from a special, NASA command center like room on deck. There, three pilots sit in front of a bank of about 15 computer monitors displaying various video feeds from Jason and Medea. The three pilots work together to control Jason, Medea and the ship with a collection of computers and joysticks. Behind the pilots sit the scientists (including me). We get to control the science camera with a joystick--an xbox controller, truly--and are responsible for logging events of interest. Getting to sit in the room and observe is quite exciting (I'll upload photos as soon as I return).

It turns out I have to go and help with a recovery now so I will have to describe the actual Jason dives (the exciting part) the next time I get a chance with the internet.

To be continued.........

June 30th, 2013

Hey guys!

I thought I might provide a little bit of background about why we're on this research cruise. This expedition is a part of the Cascadia Initiative, a multi-year endeavor to better understand the seismicity and structure of the Cascadia subduction zone off the coast of Oregon, Washington and Vancouver Island. A subduction zone is where two plates collide and one, usually a denser oceanic plate, sinks (subducts) beneath an overriding plate, usually a lighter continental plate. The best analogy I can think of is in airports at the ends of the moving sidewalks (you know, where that same peevish robotic voice in every airport says "The moving walkway is approaching the end. Please watch your step") where the moving walkway (our subducting plate) bends down beneath the stationary floor (our overriding plate). There are a lot of great images for this on the internet if you're finding it tough to visualize. Subduction zones matter. Vast numbers of people live near them and they are capable of generating tremendous earthquakes. We know the precise date in 1700 A.D. that the last great quake (a magnitude 9!) shook the Cascadia subduction zone from Japanese records of a devastating tsunami. To accurately determine the locations of small earthquakes in subduction zones (which inform our understanding of their structure) we need to place seismometers off-shore on the ocean bottom to augment the land-based stations. On this cruise, we are picking up seismometers which were deployed here a year ago and have been recording the seismicity for the past year.

Anyways, that's the (extremely short) version of why we're out here. If you're curious for more detail please comment below and I'll happily reply. More posts about ship living, robots, dolphins and whales will be coming soon (or at least as soon as I have more uniterrupted time to write). And yes, I have a lot of photos but they will have to wait until I'm back on land, and not on satellite internet, to upload.

Cheers!

David

June 25th, 2013

This morning at 10 am sharp the Atlantis pulled away from our mooring so smoothly I didn't notice we had started moving. I think it's safe to say that that was probably the last time I will be unaware of the ship's motions. We steamed out through a channel cut in the Columbia bar and quickly met the tumultuous waves of the Northern Pacific. The Columbia bar is a large sandbar formed by the vast volumes of sediment pouring out of the mouth of the Columbia river and it presents a significant navigational hazard. For this reason, ships such as ours are taken through the channel by a pilot--an expert in navigating the bar. However, his task complete, we had no further use for our pilot and made him walk the plank!

Just kidding, he climbed off the side of the ship on a rope ladder of his own accord and jumped to a waiting speedboat! His task complete, he waved goodbye and headed off to track down threats to England... err, go pilot other ships into the harbor.

Anyways, even without the Bondesque stunt life aboard the ship has been quite exciting. The ship has been tossing up and down and occaisionally rolling from side-to-side quite dramatically. Elizabeth (the other intern in Anne's lab) and I practiced jumping in time with the pitching of the ship to gain extra moments of hang time! Imagine jumping a mere inch off the deck and landing what feels like seconds later. (Okay, written out that's a lot less cool than it felt but I hope you get the idea.) Seasickness has affected certain members of our party more so than others. A couple of people are still huddled at the rail of the ship but everyone's starting to do better. For my own part, I've tried not to believe in seasickness. In general, I've found that my attitude mentally can have an enormous influence over how I feel physiologically. Hence I have remained confident that seasickness does not affect me. After all, my queasy stomach is most likely due to engorging myself on the excellent ship's food.

Next up: I'll have my first early watch shift from 4-8 tomorrow morning and hopefully I'll see my first OBS recovery!

June 25th, 2013

Greetings blogosphere!

I'm currently sitting in the science computer lab of the R/V Atlantis research ship. Around me are no less than 20 computer monitors, two tv's, three ordinary printers, two poster plotters (I think that's what they're called, essentially very large printers), racks full of circuitry and servers, four fire hydrants, and--just for good measure--two analog clocks. I will undoubtedly post a lot more about the Atlantis in the coming weeks but for now it will have to suffice to say that it is the largest and coolest (I spent part of today examining the vehicles which discovered the corpse of the Titannic) vessel I have ever been on; and it hasn't even left port yet!

Tonight I would like to share with you my goals for the summer. I've broken these down into three sections: before the cruise, during the cruise, and after the cruise.

Before the cruise (aka this past week):

• Familiarize myself with the town of Corvallis and the OSU campus.
• Determine/define the project I will be working on this summer.
• Begin learning the techniques I will use for my project.
• Join a summer league team to play ultimate frisbee with, generally get to know the ultimate community.
• Find people with whom to go adventuring on weekends.
• Get to know graduate students and the other interns.

During the cruise:

• Fulfill all of the duties expected of me as a watchstander
• Eat well and maintain adequate amounts of sleep (this may seem spurious but failing to acheive this severely hampers my ability to do anything else)
• Help with as many different projects as i can to learn as much as I can
• Write regularly for this blog.
• Make friends with the crew.

After the cruise:

• Finish all of the blog posts from the cruise and upload my photos.
• Learn how to do earthquake relocations and do it for the relevant earthquakes.
• Look at the resolution and location from t-phases (these last two goals will make sense once I describe my project in a later post).
• Write abstract and draft poster for conference.
• Go mountain biking 5 times a week (I can dream, right?)
• Climb a big mountain.
• Go whitewater kayaking.
• Decide (at least preliminarily and subject to change) if I want to pursue graduate school in geophysics.

And finally, (this past week notwithstanding) I intend to write regularly for this blog. Communication of my experiences, passions (science, the outdoors, ultimate frisbee, ice cream, to name a few), and visions is a skill which I keenly want to improve. There is, of course, no expectation that you will continue to read anything that I write. But I hope to engage you such that you want to keep reading.

For the next two weeks I am going to be on a research cruise picking up ocean bottom seismometers off the coast of Oregon. I will only have sporadic access to slow satellite internet, so I don't know how often I'll be able to upload my posts. For now I'm going to head down to my folding bed in the belly of the ship afore I lose any more coherence. We set sail on the morrow!

May 30th, 2013

Hi guys, I'm David, I am a junior from Dartmouth College, I grew up in Pittsburgh PA and my favorite flavor of ice cream is chocolate chip cookie dough. I think that one day someone should make chocolate chip cookie dough with coffee ice cream instead of vanilla but I digress. We are almost finished with our orientation week and it has been quite a busy one! I think my favorite part of this week has been getting to meet people from a much broader spectrum of earth sciences than I have before. Before this week I had only met one geophysicist (hi Leslie!) and yesterday I got to go hiking with a volcanologist. Anyways, I have to wrap it up now but stay tuned for more updates.

Ps. Did I mention I've never written a blog before? All four of you reading this are witnessing a historic moment (hi Michael, Katie and parents)