My primary work as a doctoral student was the characterization of strain accumulation and release in the southern Walker Lane/northern Eastern California Shear Zone (ECSZ).
The Walker Lane is a right-lateral shear zone in eastern California/western Nevada that accommodates approximately 25% of the Pacific-North America plate motion. The long-term and short-term slip rates on faults in some parts of the Walker Lane are not consistent. In particular, contemporary GPS slip rates are nearly double the late Pleistocene geologic slip rates summed across the Walker Lane at ~37°N. Since plate motions are essentially uniform over these time scales (up to 2 Ma), discrepancies in long- and short-term slip rates require a mechanism or explanation. One possibility is that there is a strain transient in the region, in which current slip rates are higher than the long-term average. However, since the long- and short-term slip rates in the Walker Lane immediately adjacent to this region are equivalent, this is not a likely explanation. A second possibility is that strain is being transfered to the northeast of the Walker Lane, into a zone of extension called the Silver Peak-Lone Mountain extensional complex. A third possibility is that the observed geologic slip rates in Owens Valley are underestimated and are actually faster than previously thought.
In order to test these possibilities, we established a dense network of GPS monuments across the Walker Lane to characterize the velocity and strain field. In 2010 we installed 11 new campaign monuments, and surveyed (in 2010, 2011, and 2012) several older monuments that were established in the early 1990s. Combined with continuous GPS stations in the area, we have a network of 77 GPS sites yielding velocities. A simple elastic half-space model predicts a far-field slip rate of 10.6 ± 0.5 mm/yr across the Walker Lane. The results of this work are published in Geophysical Research Lettters [pdf].
White Mountain Fault TLS
During the summer of 2012 I collaborated with Dr. Jeffrey Lee, Dr. Anne Egger, and Rex Flake (of Central Washington University) and UNAVCO to scan a segment of the White Mountains fault with a terrestrial laser scanner. Over the course of 7 days we combined 12 scans and 24 unique reflector tie points into a single point cloud. As an interesting side note, this TLS data was collected at the same time as the airborne LiDAR of the same area (in fact our field vehicle is readily visible in the airborne data) and we are exploring ways to merge and compare the data sets.
White Mountains Fault ALSM
With support from an NCALM (National Center for Airborne Laser Mapping) seed grant, I acquired airborne laser swath mapping (ALSM) LiDAR data covering a portion of the White Mountains fault. I used these data to measure features offset by the fault with the LaDiCaoz software developed by Zielke and Arrowsmith . We are preparing a manuscript to be submitted to GSA Bulletin.
The full ALSM dataset is now available via OpenTopography. Below is a hillshade model of the topography for the entire swath. Fault scarps everywhere!
The 1-meter resolution of this DEM was fine enough to pick up our field truck (left image), which was filtered out with the vegetation (right image).
In addition to the GPS and mapping work described above, I also investigated the long-/short-term slip rate discrepancy in the Walker Lane by refining geologic slip rates on the White Mountains fault. I used cosmogenic nuclide exposure dating to constrain the timing of offset of alluvial fans in Owens Valley. Three new soil pits were sampled for 10Be depth profiles. Samples were prepared in Georgia Tech’s cosmogenic nuclide preparation lab, and measured at Lawrence Livermore National Lab’s accelerator mass spectrometer. We presented our latest geochronology results in a poster at AGU 2012 Fall Meeting (abstract #G23B-0925). Slip rates have been calculated using the probabilistic approach of Zechar and Frankel . Final ages, offsets, and slip rates will be presented in a manuscript we are soon submitting to GSA Bulletin.
Lone Mountain fault is a normal fault located in a region of the Walker Lane known as the Silver Peak-Lone Mountain extensional complex (SPLM) that is believed to accommodate extension parallel to the direction of shear. The fault offsets several alluvial fans of different ages, ranging from late Pleistocene to Holocene. Previous work by Hoeft and Frankel  estimated late Pleistocene extension rates. I estimated new Holocene extension rates using 10Be cosmogenic nuclide samples from boulders on the fan surfaces. Hoeft and Frankel’s  rates, combined with my new Holocene extension rates, yield a detailed picture of slip on the Lone Mountain over multiple time scales that suggests the extension rates in the area have increased since the late Pleistocene. These results were published in Tectonics [pdf].
The Clayton Valley fault zone (CVFZ) is a series normal faults located in the Silver Peak-Lone Mountain extensional complex (SPLM) that is believed to accommodate extension parallel to the direction of shear. I assisted fellow graduate student Andy Foy with geomorphologic mapping and geochronologic sampling to determine an extension rate on the CVFZ. Our results suggest that extension rates are low across Clayton Valley, and that deformation is broadly distributed over many structures which are not necessarily preserved in the geologic record. See our publication in Tectonics: [pdf]
I worked on several other side projects as a doctoral student. These projects mostly consisted of GPS surveying in exotic places, as well as some data processing and modeling.
The Solomon Islands are located on the hanging wall of the San Cristobal trench, at the convergence of the Pacific and Australian plates. This convergence zone is highly seismogenic, and has produced large tsunamigenic earthquakes, such as the Mw 8.1 event in 2007. In early 2010 the trench ruptured in a Mw 7.1 event, causing local landsliding and tsunami. I joined a team of researchers from Georgia Tech (Dr. Andrew Newman and Dr. Hermann Fritz) and Technical University of Crete (Nikos Kalligeris) to do a post-seismic campaign GPS survey and tsunami run-up survey. This work was published in 2011 in Geophysical Journal International [pdf].
ARENAL VOLCANO, COSTA RICA
Arenal is an active volcano in north-central Costa Rica. In collaboration with OVSICORI and UNAVCO, Dr. Andrew Newman is working to measure the actively deforming flank of Arenal using both GPS and LiDAR. In March 2011, we traveled to Arenal to occupy GPS monuments and scan the volcano flank with a terrestrial laser scanner. See the UNAVCO science highlight for more info.
SANTORINI CALDERA, GREECE
Santorini caldera is an active volcano in the Aegean sea, which today is manifest as a crescent-shaped group of islands surrounding a submerged caldera. The last catastrophic eruption of Santorini, known as the Minoan eruption, occurred about 3600 years ago and is thought to have devastated the Minoan culture. New dome forming activity is ongoing, creating emergent islands in the caldera. The caldera is now instrumented with continuous GPS, as well as many campaign GPS monuments. In 2011, the caldera began an episode of rapid deformation that continues today. I joined a team of researchers from Georgia Tech and University of Patras to upgrade existing continuous GPS stations and to reoccupy campaign GPS monuments. See the UNAVCO science highlight for more info.