Tuesday, December 15, 2015

Long Time, No Blog

Well, it has been a LONG time since I have posted on my blog, ~ 2.5 years. I did not even realize it had been that long until I checked this evening.

A lot has happened over the last 2.5 years, here are a just few examples:
  • Just this past October I successfully defended my Ph.D. at the University of New Hampshire. My dissertation is entitled "The Relationship Between Oceanic Transform Fault Segmentation, Seismicity, and Thermal Structure." I'll post a link to it once it's available online, and I'll include the abstract below
  • In September, 2014 my first paper related to my PhD research was published:
    Wolfson-Schwehr, M., Boettcher, M.S., McGuire, J.J., and Collins, J.A., 2014, The relationship between seismicity and fault structure on the Discovery transform fault, East Pacific Rise: Geochemistry, Geophysics, Geosystems, v. 15, no. 9, p. 3698–3712, doi: 10.1002/2014GC005445.
  • On October 23, 2013 I gave a talk at the USGS Menlo Park. I admit that standing up on the podium, in front of all the flags and facing many of my committee chair's colleagues (she was a Mendenhall Fellow there), was a bit intimidating. Everyone there was very welcoming, however, and I really enjoyed the day. The talk is available to watch online here
  • On October 30, 2015 I gave my second web-streamed talk at the University of Texas Institute of Geophysics. This was my first post-defense talk, and it was definitely more relaxed than many of my others. It was quite fun to be flown down from northern Cali for a couple days and to get to tour the facilities and meet with many of the researchers. This talk is also available online, and can be watched here.  
  • In 2013 I co-convened my first AGU session on oceanic transform faults, and in 2014 I did it again! It was really nice to be able to bring the oceanic transform fault community together, and we're hoping to make this a biennial occurrence. 
  • And, on a personal note: In Aug. 2014, I gave birth my son, Lincoln. He's our first child, and such a joyous addition to our family. 

So that pretty much catches you up on all the major things I believe. I know I have said this before, but I am going to recommit to this blog once again and try to update on a regular basis. It's AGU week now, so that should give me some good material to blog about.

Oh, and here is the abstract for my dissertation:

Monica Wolfson-Schwehr
University of New Hampshire, December, 2015

Mid-ocean ridge transform faults (RTFs) are typically viewed as geometrically simple, with fault lengths readily constrained by the ridge-transform intersections. This relative simplicity, combined with well-constrained slip rates, make them an ideal environment for studying strike-slip earthquake behavior. As the resolution of available bathymetric data over oceanic transform faults continues to improve, however, it is being revealed that the geometry and structure of these faults can be complex, including such features as intra-transform pull-apart basins, intra-transform spreading centers, and cross-transform ridges. To better determine the resolution of structural complexity on RTFs, as well as the prevalence of RTF segmentation, fault structure is delineated on a global scale. Segmentation breaks the fault system up into a series of subparallel fault strands separated by an extensional basin, intra-transform spreading center, or fault step. RTF segmentation occurs across the full range of spreading rates, from faults on the ultraslow portion of the Southwest Indian Ridge to faults on the ultrafast portion of the East Pacific Rise (EPR). It is most prevalent along the EPR, which hosts the fastest spreading rates in the world and has undergone multiple changes in relative plate motion over the last couple of million years. Earthquakes on RTFs are known to be small, to scale with the area above the 600C isotherm, and to exhibit some of the most predictable behaviors in seismology. In order to determine whether segmentation affects the global RTF scaling relations, the scalings are recomputed using an updated seismic catalog and fault database in which RTF systems are broken up according to their degree of segmentation (as delineated from available bathymetric datasets). No statistically significant differences between the new computed scaling relations and the current scaling relations were found, though a few faults were identified as outliers. Finite element analysis is used to model 3-D RTF fault geometry assuming a viscoplastic rheology in order to determine how segmentation affects the underlying thermal structure of the fault. In the models, fault segment length, length and location along fault of the intra-transform spreading center, and slip rate are varied. A new scaling relation is developed for the critical fault offset length (OC) that significantly reduces the thermal area of adjacent fault segments, such that adjacent segments are fully decoupled at 4OC . On moderate to fast slipping RTFs, offsets 5 km are sufficient to significantly reduce the thermal influence between two adjacent transform fault segments. The relationship between fault structure and seismic behavior was directly addressed on the Discovery transform fault, located at 4S on the East Pacific Rise. One year of microseismicity recorded on an OBS array, and 24 years of Mw 5.4 earthquakes obtained from the Global Centroid Moment Tensor catalog, were correlated with surface fault structure delineated from high-resolution multibeam bathymetry. Each of the 15 Mw 5.4 earthquakes was relocated into one of five distinct repeating rupture patches, while microseismicity was found to be reduced within these patches. While the endpoints of these patches appeared to correlate with structural features on the western segment of Discovery, small step-overs in the primary fault trace were not observed at patch boundaries. This indicates that physical segmentation of the fault is not the primary control on the size and location of large earthquakes on Discovery, and that along-strike heterogeneity in fault zone properties must play an important role. 

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