This figure pulls together my summer research nicely, but needs quite a bit of explaining. This summer I was comparing magnetotelluric (MT) data and p-wave seismic tomography residuals to get a better understanding of the Rio Grande Rift. I was helping out with installing MT sites across the rift. These sites were arranged in 3 lines that transect the rift -- one northern line near Denver, Colorado, one middle line near Taos, New Mexico, and one southern line near Las Cruces, New Mexico. I modeled some MT data from 9 sites on the northern line creating models of resistivity versus depth. I also have produced p-wave travel time residuals over the rift with 22 events, and averaged all the residuals at each site to produce average travel time residuals. Each MT site was matched with the closest (in location) average residual time. This figure depicts the last resistivity layer of the MT models ("at infinity") and the corresponding p wave travel time residuals versus longitude of the northern line. The bottom plot shows the slow area below the rift (around the center of the line) while the top plot shows higher resistivity (lower conductivity) under the rift. While its accepted that the rift's upper mantle is slow, it is expected that areas of slow velocity have high conductivity. This is because higher temperature, more hydration, and more partial melt all cause slower velocities and higher conductivities. Changes in composition, however, can either produce slow or fast velocities and low or high condictivities. This figure raises some questions and definitely requires further investigation, but sums up my summer nicely by combining MT and P-wave tomography.
So I've done a lot since I've last posted to this blog. I've picked about 25 events and made residual maps, spent another intensive week in the field, and learned a ton more about MT.
It's exciting that my residual maps support other tomography models, and that different back azimuths show a distinct seismically slow area under the Rio Grande Rift. Here's one of my residual maps:
During this second field trip we were in southern New Mexico, sometimes within a mile from the Mexican border (which is a measly little black fence). We were told by a farmer that we were in drug smuggling territory, but everyone we met was super nice and we never felt unsafe. We even ran into border patrol a couple of times when we were out in the middle of nowhere installing sites, which surprised us both. There were some close calls with thunderstorms and tarantulas, but it made for some great pictures:
Oh yea, and we saw this car in the desert:
While I'm at CU, I'll be using MATLAB, dbxcor and GMT. Currently, I'm using MATLAB to better understand the processing and modeling of MT data by playing with a forward modeling program. I will soon be using dbxcor to process US Array seismic data of the Rio Grande Rift area to make a P wave tomography model. This model will be compared to the numerous different tomography models out there and will also be compared to the MT model to better define why certain areas below the rift are slow. The IRIS EMC website is a rally helpful tool to look at the different tomography models and see what the cross section slices look like where the three MT lines are located. GMT will be used to make various maps such as a residual maps from the various earthquakes used in my tomography model and maps of the earthquake locations themselves.
After my second week of digging holes and endless off-road driving, my first field trip is over. During the week, I really got the hang of things and installing sites is no longer daunting. I love how field work is an adventure, and you never know what obstacles will come your way, who you'll meet or where you'll go. I'm already ready to go back, even though the destination is the-middle-of-nowhere New Mexico.
I've started my three week session at CU, which so far consists of Unix.. and Unix. My goals for the week are to get a better grasp on GMT and begin to figure out how to process seismic data with dbxcor.
I've spent one week out in the field in New Mexico without internet so this is my first opportunity to post to the blog. One of my goals for this summer is to get field work experience, and I'm definitely getting a lot of it. I've been traveling to various towns across New Mexico installing a line of magneto telluric (MT) sites with a grad student at UC, Danny Feucht, and two other interns from Colorado. My mentor Anne Sheehan just joined us last night. Installing an MT sight includes a lot of digging in the New Mexican heat, but I really enjoy working outside and visiting different places. I have another week of field work and then I go to boulder to work on analyzing earthscope data of the Rio Grande Rift. Hopefully the combination of seismic and MT data will give a good subsurface picture of the rift.
When I'm in Boulder at UC, my goals are to learn how to analyze and process seismic data and learn more about seismology and tomography. Three weeks in Boulder will be a nice break from field work and will be a good opportunity to learn more about the theory behind what I'm doing, diferent areas of geophysics that could help solve mysteries of the Rio Grande Rift, and the overall bigger picture. When I go back into the field I will only be with another intern so a goal is that we an successfully install MT sights as a two-person team.
Orientation has introduced new concepts and techniques that I think will be useful for my research this summer. Deploying the siesmometers on the first day gave me insight into how field experiments are set up. This will help me when I am in the field even though the intruments will be different. The class time has refreshed my memory of material I have already learned and given me a good starting point to learn material I haven't yet been exposed to. Maureen Long and Sandra Saldana's talks especially interested me. They each gave a very different perspective on careers in geophysics and gave me a lot of thinking to do about my future.