Em is a student at The College of New Jersey currently completing his research at University of California - Riverside under Dr. Heather Ford.
The Basin and Range Province is a region in the western US where there is a significant amount of tectonic extension. This region encompasses most of Nevada, and trickles down through the border into Mexico. In some parts of the Northern Basin and Range, there is estimated extension up to 250 km. If strain in the crust caused by this extension was vertically uniform, we would see large variations in Moho depth that reflect the topography. Since this is not observed, we are looking for evidence of viscous flow in the lower crust using seismic anisotropy. Seismic anisotropy is the directional dependence of seismic velocities. In other words, seismic waves move faster on one axis than they do on another. This effect can be produced by melt, alignment of cracks, or the alignment of anisotropic minerals. We will be using PS receiver functions to image anisotropic boundaries in the crust and upper mantle beneath 6 long-running USArray stations in the region.
At this point I’ve really become acclimated to Riverside. One of my biggest challenges this summer has been transportation. I’m used to mass transit at home, being from the immediate New York City area. The bus system here is ridiculous. There are multiple bus companies with different fees to remember and their schedules don’t work together at all. Luckily, my first week here I bought a crappy cruiser bike. But during week 4, I got a flat tire on the way home from frisbee one night. I have now replaced the tire tube three times, and have had to call in several favors in the process: borrowing tools, tire pumps, or rides to the bike shop. My office is walking distance from my house, but this obstacle prevented me from going to frisbee and the climbing gym on the other side of town. Every time I changed the tube it popped again. I finally decided the tire might be the problem during week 6, and my friend happened to have a used (but not frayed) tire I could use. I installed the new tire before surfing last Sunday and am happy to report that it’s going well and I’ve been mobile all week! I have to say that it’s been a learning experience though, because I’ve never run into problems with my bike at home, but now I’ve learned how to fix one. Other less dramatic bike issues include, but are not limited to: one working brake, two working gears, and a busted seat. There’s nothing I could do about the seat besides replace it, but I did get my other brake and another gear working!
Another challenge I’ve faced this summer has been my limited knowledge of geology jargon, since I’m coming from a physics background. When reading papers, I find myself looking up definitions and schematic drawings every couple sentences. So papers are slow-going, but I’ve found my discussions with Heather really productive. On my own I try to understand the paper as best I can, and come prepared with questions or anything I felt needed more explanation.
I have found coding to be one of my strengths this summer, and the UNIX tutorials have definitely aided that. But even so, a lot of time this summer has been spent debugging old codes and trying to troubleshoot something. Once again, Google has become a close friend through these tough times. It’s easy to get really frustrated with these things, and sometimes I can spend a late night banging my head against a wall just to find that the problem was easier to fix in the morning with fresh eyes. Now I like to take walks outside when I start hitting a wall.
Cooking has always been a challenge for me, even though I’ve lived on my own and cooked for myself for a year now. Cooking at college was hard because I had a different schedule every day and lived with 7 other people. I would also stress recipes too much, and wouldn’t cook without having a recipe in mind. You can see how this would be stressful. And if I was lacking an ingredient, I wouldn’t cook at all. I was very good at letting my food go bad. I noticed myself doing the same thing at the beginning of the summer, so I started being more creative. Every day on the way home from work I pass a market where I’ll buy whatever veggies look good, throw them in a pan, and add chicken or pasta or both. Sometimes it’s really good and sometimes it’s just okay, but I’m feeding myself a lot better, wasting less food, and cooking has even become fun!
Last weekend my friend Stephen and I climbed Mount Baldy, whose elevation is 10,064 ft. It was an 11.3 mile hike with 3,900 ft elevation gain. That's definitely the highest altitude I've experienced, and the most elevation gain as well. It's safe to say I am still feeling it three days later. We almost didn't go because there was a forest fire and we weren't sure if the trail would be closed. It was an incredible view--we could see the Pacific ocean and the southern tip of the Sierras despite the smokey haze. Six hours later, we stopped at a brewery as a reward on the way home.
^My friend Lindsey and I riding our bikes home from frisbee when I got a flat. Couldn't complain about the scenery while we waited for a lift. Smog makes for pretty sunsets.
^One of the evenings spent learning how to change a tire. My roommate's kitten was very interested in watching me from the other side of the screen and eventually started to climb the screen with his claws and got stuck. That roommate moved out. I miss her kitten very much.
^The peak is on the right. This is the Devil's Backbone, which was very exposed. That's my friend Stephen, who is clearly in much better mountain-climbing shape than me.
^Things on the way up
^The top!!! I didn't bring enough water because I am silly and impractical, but hey I made it!
^Panorama view facing south. You can see the sand fire and smokey layer in LA to the west. We were able to see the skyline of LA as well.
Week 6 I finished picking P-arrivals, and began generating receiver functions! Hip, hip, HOORAY!! But this weird thing kept happening: at most of the stations, the number of receiver functions was inconsistent as I set different maximum frequencies. Take a look at some of the weird data I got below.
Figure 1: Initial receiver functions for station BMN plotted by back azimuth (direction of earthquake in degrees from North), with a maximum frequency of 0.5 Hz. Top plot is the radial component, bottom plot is transverse component. Vertical axis is time in seconds, which can be converted to depth. Blue peaks show depths where there was an increase in seismic velocity, red peaks where there was a decrease. Notice how some back azimuths have data on the transverse component, but not on the radial component. (???)
Figure 2: Same as Fig. 1 but with a maximum frequency of 0.75 Hz. Notice how there are receiver functions in the 120-140 back azimuth range for the radial component where there weren't for 0.5 Hz above.
Figure 3: Same as Fig. 1 and 2 but with a maximum frequency of 2 Hz. Now the transverse component is losing data. What's going on???
Figure 4: Receiver functions from the same data set plotted by epicentral distance in kilometers (Distance from the earthquake), with a maximum frequency of 0.5 Hz. For whatever reason, nothing was showing up on the radial component, no matter the frequency.
We puzzled over why this was happening, and decided to sort through the waveforms further to eliminate the possibility that I’d let through bad data. Turns out that was exactly the problem. Despite my meticulous sorting, there were many subtle hiding squirrels. When I sorted one of the stations again, the receiver functions turned out normal! RESULTS, finally! So I continued sorting through the stations once again in SAC. Here's a peek at what BMN looks like now:
Figure 5: After getting rid of some 'squirrels' in the data set, receiver functions plotted by back azimuth with a maximum frequency of 0.5 Hz. This can be compared to Fig. 1, which had tons of inexplicable holes. Here, the holes are present on both the radial and transverse components, and suggest that there weren't any earthquake events in the data set coming from those directions. Inside the green box is quite possibly evidence for anisotropy. You can see there are a couple flips from positive to negative around 4-5 seconds, which is also the apparent depth of the LAB, which we can see in Fig. 6.
Figure 6: Receiver functions plotted by epicentral distance with a maximum frequency of 1 Hz, with the cleaner data set. In the green box you can make out the Moho (boundary between crust and mantle) in blue, and the LAB in red (Lithosphere asthenosphere boundary).
Over the weekend we had another comedy night, and Sunday I went surfing for the second time! I rented a different board this time--slightly smaller and hard instead of soft. I found it a lot easier to maneuver through crashing waves, and got beat up slightly less. I actually took a few waves into shore! But I still couldn’t get my front foot up and did this on my back foot and front knee. Hey, it’s still fun even if I look silly!
Surfing at Trestles, a famous SoCal surf spot. Saw a lot of amazing surfers out there.
Week 5 was a short week because of Independence day and I took Friday off for travel. This week I began picking P-wave arrivals using SAC. Since I was now looking at all three components at once (r, t and z), instead of just z, I was able to weed through data further, because sometimes the r and t components were quite squirrelly, and looked nothing like the z components. I have henceforth referred to them as “squirrels”. I see seismograms behind my eyelids when I go to sleep. How am I supposed to sleep when I’m subconsciously trying to pick P-wave arrivals?!
^This is a particularly nice-looking P-arrival in SAC
The weekend after week 5 I travelled back to Oakland--this time the train to LA was late so I missed my Megabus and spent 4 hours in downtown LA. Then the next Megabus's AC broke 2 hours into the normally 7 hour drive... the journey totalled at 15 hours this time. But it was all worth it, because I got to see Louis CK perform standup Saturday night! I’m not good at keeping up with TV shows or watching any of the movies I’ve listed recommendations for in my phone’s notepad, but I LOVE standup. I even started comedy night here at my friend’s house some Saturdays. We sit in the backyard and watch standup specials on a projector screen. Hannah is also a huge Louis fan, and once again, he was hilarious. Before the show, we spent the day in Berkeley, which was a really nice area with cool record shops. The campus was beautiful as well, and I was happy to see big climb-worthy trees, something I miss in Southern California. The next day we went to Six Flags with Fast Passes. Highly recommended experience: we only waited 5 minutes for anything, and we got to go on everything at least twice.
^Waiting for Louis in the Golden State Warriors' stadium. "The last time this stadium was this full something terribly sad happened..." -Louis CK
^OMG A TREE (Berkeley Campus)
During week 4 I finished chucking bad data (or so I thought… more on that later) from PQL. On Tuesday we discussed Complex subduction and small-scale convection revealed by body-wave tomography of the western United States upper mantle by Brandon Schmandt and Eugene Humphreys, in which they explain a seismic tomography model of the western US. I was especially intrigued by their method of determining partial melt from the P-wave velocity to S-wave velocity ratio. Thursday we discussed Vertical mantle flow associated with a lithospheric drip beneath the Great Basin by John West et. al., which integrated seismic anisotropy and tomographic models to argue the existence of a lithospheric drip beneath the Great Basin trending in the direction of the North American plate motion. Very cool stuff!
California is a weird place. Riverside should be a desert but there is green everywhere thanks to the sprinklers that go off constantly and spray all over the pavement. That stuff irks me. I really like it out here though. Maybe because I’m doing seismology, hanging out with scientists, and going to the climbing gym in the evenings, but the west is pretty sweet. I’m in love with the dramatic landscape and open rock faces. The super-hot afternoons are balanced by the cool mornings and the lack of humidity is wonderful.
The weekend after week 4:
Saturday: I went on a short day hike near my house in the Box Springs.
Sunday: I went with a couple of grad student friends to BLM land, where people go to shoot deadly weapons. I never thought I’d shoot a gun in my life, but on Independence Day weekend I had the opportunity to shoot quite a few. Again, California is a weird place. I had no idea what BLM land was, but apparently nobody wants it, and people go there to shoot at things like old refrigerators and soda bottles. It was an interesting experience.
Monday: On the Fourth of July, one of my friends from Frisbee invited us all for a barbecue. It was really nice to eat burgers right off the grill. I also saw fireworks from my front yard when I got home.
^My workspace, equipped with a brand new iMac. I'm in an office that leads to Heather's office. Sometimes I share the office but everyone has been at field camp or away all summer.
^Box Spring Mountain Park. I pass this scene every morning on the way to work. It's only 100 ft from my house, and a great place to run in the morning or evening when the sun isn't too hot.
^This is a scene from the top of the same mountain on Saturday. Cloudy days like this are rare, and I actually found myself looking for a jacket.
I haven’t updated my blog in a while… I guess you could say I’ve been busy trying to get the most out of my experience here. When we left off I was still looking through seismograms on PQL. Wow, those were the DAYS! During week 3 I continued sorting through seismograms in PQL, and I read and discussed two papers with Heather. On Tuesday we discussed Implications for continental structure and evolution from seismic anisotropy by Paul Silver and Winston Chan, which explains the shear-wave splitting method for seismic anisotropy. Even though this isn’t the method we’re using, I found it really interesting/informative. On Thursday we discussed a rather long paper Western United States Extension: How the West was Widened by Leslie Sonder and Craig Jones. I came to the western US this summer knowing basically nothing about the geology here, so this actually helped a lot. Heather gave me this paper along with a few other shorter articles and a link to a page with animations showing the geologic evolution globally and regionally and they’re really cool. Here’s the link: http://emvc.geol.ucsb.edu/1_DownloadPage/Download_Page.html
Week 3 I also developed an elevator speech for my project. I’ve had to explain it enough times to grad students in other departments at this point that I think I have it down. My analogy for anisotropy is the video game Frogger. It’s easier and faster to move in the direction of traffic, but moving perpendicular to it is difficult and takes longer, much like the differing velocities of seismic waves through anisotropic rock on different axes. It has already proved useful when I have to explain to someone why I’m here when they find out I’m from New Jersey and have no idea what an acai bowl is. This skill will be very valuable in the future, because what’s the point of doing research if I can’t explain to anyone what I’m doing?
After week 3 I embarked on a 12-hour journey. I took a bus to a bus to downtown Riverside, where I took a train to downtown LA, where I took a megabus to Oakland, where I took a train to a grilled cheese restaurant. My friend Hannah from New Jersey is working in Oakland this summer, and I made the trip up there for San Francisco Pride! The grilled cheese Friday night was pretty good, but at Pride I got a RAINBOW grilled cheese. Infinitely better. We also went to Black Sands beach, where we hiked down to the tiny shore from these huge sea cliffs. There was a beautiful view of the Golden Gate Bridge.
^Oakland grilled cheese vs. Rainbow grilled cheese. Left picture is me immediately post-12 hour journey--no idea where the energy is coming from.
^Black Sands trail. My friend Hannah is in the last one. You can see the Golden Gate Bridge in the background.
I have now finished my second week at UCR, and am in the midst of a record-breaking heat wave! The first couple weeks here have been very mild-- highs in the 70s and 80s. But over the weekend the temperature steadily rose to 90s, then 100s, then breaking into the 110s Sunday and Monday! Supposedly these temperatures aren't normal here this time of year; they usually come in August or September.
I was able to escape the heat Saturday by going to the beach! I went surfing at San Clemente, where it was ~80 degrees as opposed to the 100s of Riverside. It was my first time surfing and also first time seeing the Pacific. Surfing was a lot of fun, but also a lot of work! I spent most of the day getting beat up due to my developing ability to "turtle" as they say, which means flipping upside down with your board to let a wave crash and pass over you. But I was so bad at anchoring the board that the wave would just pick both of us up and not so gently put us down wherever it so pleased. I did catch half of a few waves, which was enough to keep my resilience. Apparently the surf was really difficult too--very choppy, unpredictable breaks, and the afternoon onshore winds (it took us half the day just to find a beach that wasn't packed) making them break more quickly-- so I didn't feel too bad about my ability. Disclaimer: I was given a crash course on the physics of surfing; these are all terms I picked up only Saturday.
In other news, yesterday's record breaking 112 degree temperatures caused two forest fires 40 miles from UCR, and it surprisingly made a very beautifully ominous sunset as the sun descended behind the smoke cloud to the west. I climbed partway up Box Springs Mountain near my house after work to watch. I forgot sunscreen.
When we left off last week, I had just finished preprocessing the data, and was about to start looking at squiggly lines. Well I'm still looking at squiggly lines, yay! Originally my tools were this: PQL (which crashes a lot and takes a long time), or a Python script that needed debugging. I actually got the Python script running in about half a day, and was flying through data: a seismogram would pop up, I would type "y" for good, or "n" for bad, and the script would do all the sorting for me. But after a certain date at each station (in the 2004-2007 range), the script would stop working due to some kind of dimension problem in matplotlib, and I ended up going back to PQL. Hence why I'm still on this step. However, I've developed a reasonably efficient system, and only experience about 3 crashes per station. Not so bad. And I think I'm getting a better idea of what good and bad data looks like as time goes on, especially since PQL gives me the ability to zoom in and compare to other seismograms. Another reason why it's taking longer: I've become more critical.
I'd like to say a couple things about the data set I'm using. I am using 6 stations in the Basin and Range that I selected because they've been running/archiving data for more than ten years, and their locations within the Basin and Range are reasonably spread out. I requested the data from IRIS, so I'm not the first to work with it. Four of the stations are from the US National Seismic Network (US ELK, MNV, TPNV, and WVOR), one is from the Leo Brady Network (LB BMN), and the last is from the Caltech Regional Seismic Network (CI NEE). I've been getting pretty beautiful data from all of them, but the US stations have been the easiest to work with so far. Their azimuths were aligned with North and East to begin with (even though I had to rotate later), they retain the same sampling rate throughout (0.025 s), and generally don't give me too much trouble. CI NEE, on the other hand, was the only station whose sampling rate changed (from 0.05 to 0.025 s), and since most of the data was recorded at 0.05 s, I had to decimate the data recorded at 0.025 s. This slower sampling rate won't pose an issue, luckily, because the we are filtering for data between 0.2 and 3 Hz, and even a 0.05 s sampling rate allows us to record data faithfully up to 40 Hz. CI NEE was also the only station with really weird azimuths! It's "North" component was at 14 degrees from north from 1993-1998, then in 1998 it changed to 49 degrees! Why on earth would you want to do that? Maybe there's a seismic method that I've yet to discover that involves mislabeling your directional components.
After going over the internship self-reflection rubric with Heather, I have deemed "formulating a research question that could be answered with data" one of the skills to really focus on this summer. I think it's important not only to understand the research I'm doing, but also be able to recognize what methods can be used to answer certain scientific questions. I want to have a broader knowledge of the field, so that when it comes time to conduct my own research, I can recognize what methods could be used to study some feature. This is an especially pressing task for me, because I will be applying for the NSF Fellowship in the fall, and the application requires a written proposal. In order to develop this area, I am going to be reading papers outside of my research to broaden my understanding of the region and other seismic methods.
This is a little late, but last week was my first week at UC Riverside! I'm getting accustomed to the area: ridiculously priced organic markets, a constant view of Box Springs Mountain, gutterless rooves, and my newfound Californian allergies. Heather took me on a tram up to San Jacinto from Palm Springs the day before work started, so I was able to meet her before jumping right in. The change in temperature and vegetation as you ascend the mountain is incredible. It was about 106 degress at the bottom, and 70 at the top!
The first task I took on was identifying long-running seismic stations in the Basin ad Range; we wanted 6 stations that had been running for at least ten years. There are surprisingly few in the region, so there was a lot of prioritizing involved. I then made a sod request for the data, which Heather conveniently had a script for. After that, things got much more tricky.
At first, preprocessing involved scrolling and squinting through ~20 years of earthquake data files at six different stations. Each earthquake produces three files that correspond to the axes of the seismometer: E, N, and Z. And many earthquakes produced any number of duplicate components, missing components, and components of mismatching sizes. After a day or two of manually sifting through the files, I decided to write some scripts that would do it for me, which proved to be an incredibly educational process. This small skill seriously came in handy when I had to start checking azimuths, rotating to radial (direction of earthquake) and transverse (perpindicular to earthquake) components, checking sampling rates and decimating them for uniformity, and finally filtering for the frequencies we want. That's where I am now. Data is all ready to go, and I get to start looking at squiggly lines tomorrow! (Which supposedly will make my eyes bleed as well)
After a week of struggling with files, I can see how the time can get away from me doing research, so it might be wise to set some goals for myself:
On a less academic note, I met some grad students who share my love of nature at Ultimate Frisbee pickup, and they took me camping in Joshua Tree National Park last Thursday. We slept under the stars, and I saw the Milky Way for the first time. Even more surreal was waking up to the magnitude 5.2 earthquake near the San Jacinto fault! I was laying on the ground only about 60 miles from the epicenter. At this point the coyotes started yelling and the Milky Way was directly overhead. Then we woke up at dawn and booked it to work.
^I took this from the tram about halfway up San Jacinto
^Top of San Jacinto
^Playing Ultimate in Riverside. I still can't get over the ever-present view of that mountain, though people will insist it's a "pile of dirt".
^Our campsite waking up in Joshua Tree
It's day 5 of orientation, the last day before we leave. New Mexico is not the desert I expected. I had no idea there were mountains, or that my allergies would continue to thrive. The field experiences we've had have been awesome--I've never climbed a mountain that high. And the lectures have answered a lot of questions I've had about the field, especially coming from a physics background, and succeeded in getting me excited for the summer.