The Pacific-North America plate boundary in Southern California is a rare example of recorded subduction of an oceanic spreading center. This process most likely plays a regular role in the plate tectonic cycle. However, our understanding of the physical properties of the oceanic plate on the western side of the boundary remains limited. Existing seismic data for the boundary typically ends at the coastline due to the fact that onshore data collection is typically easier. As a result, current models for deformation and mantle flow lack data from nearly half the plate boundary.
This summer I will help deploy 34 OBSs on a research cruise as part of a year-long passive broadband OBS experiment off the coast of southern California. Specifically, my part of the project will be to collect and analyze existing data on the bathymetry, gravity, and magnetic fields and to develop maps to be used during the cruise. Looking at the bigger picture: The long term goals of this project are to collect data that will further our understanding of fault structure, stresses, seismicity, surface geomorphology and the interaction between the crust and lithospheric mantle on the western side of the transpressional Pacific-North America plate boundary.
I survived the research cruise! It was such an awesome experience to be working at sea (I did not even get seasick). We deployed 24 broadband OBSs and 10 short-period OBSs and conducted some bathymetry surveys. Ship life is 24/7 and quite unique. People sleep at all times during the day and I worked 4 am - 8 am and then 4 pm - 8 pm each day. I must say I probably will not miss waking up at 3:30 am each morning but I do feel strange walking on a steady surface. 😊 Working a shift meant writing logs every fifteen minutes noting our depth, latitude, longitude, heading, ship speed, wind direction, wind speed, sea and air temperature, and any cool bathymetry or important events. Sometimes we would have to wake up our computer tech to deploy the magnetometer or wake up the OBS crew thirty minutes before we reached a station. We also edited some multi-beam bathymetry data and helped pick point for bathymetry surveys. On my shift, we were usually deploying an OBS which involved writing down the OBS serial numbers, noting any conditions or problems that may have on impact on retrieving the OBS a year from now, finding the OBS's initial descent rate, and calculating an ETA to the bottom of the ocean. We would have to communicate with the bridge and let them know when to raise the bow thrusters and start moving again. After each OBS successfully landed on the sea floor, the ship would start a diamond shaped survey around the OBS to make sure communication with the instrument was clear. At the end of the survey, the OBS crew would send a disabling signal that put the OBS into sleep mode.
We returned to one OBS site at the very end of the cruise to try retrieving it so we could take a quick look at the data. There had been an earthquake on 08/23 the instrument should have recorded. The OBS is recovered with an acoustic release. Once we returned to the deployment site, the OBS crew transmitted a a "hey, wake-up" signal. The OBS sent a return pulse and by timing how long it took the OBS to respond, we could estimate how far away it was from the shift. A code was then sent to make the OBS release from its anchor and float to the surface. I think the best part was everyone running to the bow to see if they could spot its little flag rising to the surface.
After looking at maps of all of our stations and digitizing faults, it was exciting to actually visit the site and know that we were filling in several gaps in the gravity and magnetics maps. Some of the faults had never been mapped to 100-meter resolution before! On the fun side of things, I saw dolphins, seals, whales, and porpoises! I loved climbing down into the bow dome which has these underwater windows. Of course to get there meant climbing down this shaft and doing a ninety degree ladder switch, but it was well worth it! 😊 Most of our trip was cloudy but we did catch a few gorgeous sunsets and the moon rising over the water. I will certainly miss all of the interesting people and friends I made on the trip.
While on the ship, I wrote my AGU abstract so could Monica could edit it. I still have a lot of work to complete! In the next two weeks, I will continue developing on my velocity model for the uppermost mantle and crust in the Channel Islands region. My project will follow me back to Rowan and I hope I can complete everything for AGU!
The R/V Melville.
Main Lab! An OBS logger case is sitting on the table.
Our typical station in the main lab. Jen and Natsumi are at the science command central.
Short Period OBSs awaiting to be deployed.
Short Period OBS ready for deployment! 24 Broadband OBSs are in the background.
Deploying a Broadband OBS.
Jon getting the maggie (our magnetometer) ready.
The ladder to the bow dome!
Me in the bow dome!
Sunset at Sea!
Well, we depart for San Diego tomorrow at 6 am to finally start our research cruise. The time just zipped by! I spent the past week and a half finalizing and printing my plots, marking our stations on charts, and making notes of which legs of our trip we will want to toss the maggie overboad (apparently the magnetometer's adorable nickname is maggie). On the side, I've been continuing working on my ray tracing model and drafting up an abtract for AGU. I still have four weeks left, which seems like a big chunk of time, but I know it will be gone in a flash. It was kind of strange trying to write an abstract when I haven't really confronted the whole "results" part yet. Hopefully, in my downtime on the ship, I can add some meat to it and get a better feel for the direction I want to take. I should have internet access on the ship (which means blog updates at sea) but I am not exacly sure of its reliability. My first goal is to avoid/minimize seasickness (preferably just avoid). I have never been seasick but I hear terrible things. Nonetheless, I am quite excited!! I've packed Captain Crunch, starbursts, and dramamine. I'm ready to go!
I am already half way through this week and I have not even blogged about last week. Time flies. I have been using mb-system to check out the Murray and Arguello Fracture Zones and San Pedro Basin Fault to see how well they have been mapped. If we can deploy the OBSs on schedule, we will probably map these features. I’ve been getting used to looking at multi-beam bathymetry and navigation data and cleaning up noisy ship tracks. The only slight drawback is the survey files can be large and it takes my code quite a while to compile. Last week I went to UCLA with Dr. Kohler to pick up a new laptop we will be taking with us on the cruise. UCLA was a monster campus compared to Rowan! I spent some time today copying final plots and making sure all of our programs run correctly on the new laptop.
On another note, I am also starting a kind of spin-off project that might follow me back to Rowan and I am excited! I am going to do my best to explain it but Dr. Kohler just told me about it yesterday and I will discuss it further with her in the next few days!
So to set up the scene here: I was sad that I would not really be getting to work with that data that we are collecting on this cruise. It ‘s a year long experiment and when we return to Caltech, I will be getting ready to head home anyway. Dr. Kohler proposed I try to develop a model that will predict what the travel time curve for our OBS stations and a few onshore stations will look like through the zone of compression. I have to pick a hypothetical seismic event (we are starting very simple and giving it a back azimuth of 270 degrees so the ray paths will arrive in the east-west direction). My first baby step is to make a grid of crustal thickness and corresponding velocity for each receiver location. I have to take into consideration the high velocity anomaly in upper mantle below the Transverse Ranges and account for rays traveling through topography and different elevations. I am going to back project rays from the receiver through the layers (using Snell’s law, woot) to the earthquake. I’m starting with a simple layer model with an even grid and then once I’m comfortable with that, we will revamp it and make it cooler. The kind of long term goal is to perhaps set us up with some travel time residuals in the future. I think my programming weapon of choice will be C… Well, that is all I know for now! Oh and I cannot wait for the research cruise....only a couple of weeks!
The first third of my internship is officially completed. I thought I should take a moment to look back on my initial plan and see where I stand. I am comfortable using Linux and GMT. I am still reading papers on previous work and background on the area where we will be deploying the OBSs but I do feel I have a much stronger foundation on the subject. I finished looking at magnetic and gravity datasets and managed to create some nice plots! WOOT! I learned about the corrections made to raw data and the instruments we will be using on the cruise. Currently, I am finishing the mb-system tutorial and figuring out how to edit and process multi-beam bathymetry data. I’m encountering fun things like pitch and roll corrections and sound velocity profiles. There is just so much to learn and time keeps flying!
As a whole, I feel I am where I should be. I deviated slightly from my original plan by finishing the magnetic and gravity maps before moving onto mastering mb-system but I think my progression still worked. I have four weeks until the cruise and I am heading toward producing ship track bathymetry maps. If I keep to the plan, in the next two weeks I will be ready to develop the final version! Then, I can prepare for two weeks on the high seas! On a personal note, I am really enjoying this internship and sunny California!!
And the Caltech turtles!
Well, a fourth of my internship is completed. Time is just cruising along! I have a great book on marine geophysics and I’ve been reading about the corrections made to raw magnetic and gravity field data and learning about the instrumentation we will be using on our cruise. Since I have been looking at datasets and mapping, I figure I should know what I’m working with and how it is collected.
Most of the week I have been datum hunting! I looked at databases for magnetic and gravity field ship track data and added to my maps. I went a little cross-eyed after staring at the computer for hours. (A small price for thorough and complete data!) I think I have exhausted most of my online resources so *fingers crossed* my gravity and magnetic maps are practically finished. I have a cute script and I love awk! I have a few minor adjustments to make like adding labels to the plotted OBS stations. So to recap: I have ship track maps of the free-air gravity field and residual magnetic field of the area we will be deploying the OBSs. I also made a low resolution but still kind of fun etopo1 topography map and a magnetic intensity map from the GeoNet data repository. The latter two maps do not have any holes in the data so they are nice to look at. I found a few additional ship tracks with raw magnetic and gravity data. I will plot them to see if they fill in any gaps in the map and check with Dr. Kohler if it is worth making the necessary corrections to add them to the final maps.
I should hopefully have final versions of magnetic and gravity field maps this upcoming week which is ahead of schedule! Yay! I will then move onto learning MB-System and plotting multi-beam bathymetry data.
Well, I have completed week two. I spent some time familiarizing myself with GMT and making some topographic maps (I am pretty comfortable with it now). Once equipped with GMT, I started looking at magnetic field ship track data from the National Geophysical Data Center. I wrote a script and made my first plot of a residual magnetic field along the ship track. A small but exciting triumph! (I will try to upload it once I’ve made a bit cuter.)
I also met with Dr. Kohler to discuss my reading and ask questions. I am battling through the terminology and picking up some geology along the way. There is just so much to learn! The paper I’m currently reading (in case you were interested: “Geophysical evidence for the evolution of the California Inner Continental Borderland as a metamorphic core complex”) is particularly interesting because it looks at both offshore and onshore seismic and gravity data centered on the Los Angeles Basin. Although still fairly close to shore, this paper does address some offshore data collection and analysis in an area we will be working in. I think it gives some nice background.
As for this upcoming week, I plan to continue looking at magnetic field data to get a better idea of what the area’s residual field looks like and improve the quality of my plots. As always, I will keep on reading.
Oh and on the fun side of the spectrum, I ventured back into LA, saw Rodeo Drive, and then went to fireworks at the Rose Bowl. Awesome! 😊
Well, I survived my first week! I spent most of the time reading, rereading, and then…some more reading. (Which is great for me since I am typically a bookworm). I just hope my brain is absorbing everything. I am learning about the geologic history of the area, previous studies, and familiarizing myself with the terminology. My first week was really one giant introduction to the project. Dr. Kohler showed me the route for the research cruise and the proposed OBS sites. (Apparently, the Navy might make us move a few sites). I looked at maps of the bathymetry/topography of the area to find some possible deep water sites to test the equipment. I started learning about magnetic field and gravity data collection and the types of corrections made to raw data. I am pretty comfortable using unix and have moved on to conquering GMT. This week, I will hopefully start working with “baby” data sets and writing my own script. I plan to begin looking for magnetic field and gravity data relevant to the project.
On a fun note, I went to Santa Monica this weekend! It was lovely there and I cannot tell you how much I love palm trees. In the process, I conquered the LA bus system...a great achievement. On the way back from Santa Monica, I managed to sit next to that guy. (You know, the one guy on the bus that decides to sit next to you and brief you on his conspiracy theories. Well, his goldfish predicts earthquakes. We might want to look into that). All in all, I am having quite the adventure. 😊 Here are some pictures of Caltech's campus.
Well, I just flew into L.A. and finally started my internship at Caltech today! The campus is so beautiful and on a totally random note, there are palm trees everwhere! Since I spent most of the day getting introduced to the campus and the project, I figured I would type up my plan of attack for the summer and some expecations.
I hope in the following two weeks I can become pretty comfortable with the software I'm using (Linux, GMT, and MB System). I want to read as much papers as I can on previous work relating to my project and build up my background knowledge on the geology and history of the area where we will be deploying the OBSs.
The next part of the internship, I want to start finding and working with datasets relevent to our area. I want to create maps of datasets and most importantly, actually understand what I'm looking at.
In the two-three week period before the research cruise, I want to be ready to prepare some very pretty final versions of bathymetry and gravity maps and write some cute code.
Then I will be off on a boat!!!
As for expectations, I hope this internship helps me figure out what direction I want to take after my undergrad studies (I have less than a year AHHH!) and gives me some valuable research experience.
I am at orientation week and typing my first official blog. I am quite excited for the summer but also equally nervous. Orientation has been very informative although I realize I have so much to learn! New Mexico is beautiful and I am really looking forward to our upcoming day in the mountains. I cannot wait to start working on my project. California here I come!