GeoPRISMS Post-Doctoral Fellowship
Released June 30, 2005; Revised March 11, 2011
GeoPRISMS/MARGINS Postdoctoral Fellows: Biographies
Taryn Lopez – NSF Award 1250148 – University of Alaska Fairbanks
Geochemical constraints on the source, flux, migration, and seismic signature of volcanic fluids, Katmai Volcanic Cluster, Alaska
Changes in the chemical composition and flux of volcanic gases released at the surface of volcanoes can provide insight into subsurface volcanic conditions, such as the approximate magma degassing depth, the presence (or absence) of a shallow water system, and/or relative conduit permeability. Additionally, the chemical and isotopic composition of volcanic gases can be used to determine the source of these volatiles at depth. This knowledge is critical for understanding subduction processes, forecasting volcanic eruptions, and estimating the explosivity of impending eruptions.
I obtained my Bachelor of Science degree in Geology at the University of Wisconsin Eau Claire. I then went on to pursue a Masters degree in Volcanology at Michigan Tech University. My advisor at Michigan Tech, Matt Watson, was a spectroscopist whose main area of study was remote sensing of volcanic emissions. He taught me that volcanic gas geochemistry could be used to understand subsurface volcanic processes and this idea has since been the main motivation of my research. My master’s research correlated the sulfur speciation and temperature of volcanic emissions from Cerro Negro Volcano, Nicaragua, where we used a combination of direct sampling and remote sensing techniques. Following completion of my M.S. degree, I went on to pursue my Ph.D. at the University of Alaska Fairbanks, due to its direct involvement with the Alaska Volcano Observatory (AVO) and opportunity for students to participate in daily volcano monitoring and eruption response. My Ph.D. research focused on using repeated volcanic gas measurements throughout varying stages of volcanic unrest to understand both surface activity and subsurface processes at three active volcanoes within the North Pacific: Redoubt (Alaska), Bezymianny (Kamchatka, Russia) and Karymsky (Kamchatka, Russia).
Through regular discussions with my AVO colleagues while pursuing my Ph.D., I gained a strong appreciation for the added value of integrating volcanic gas data with complementary petrologic, geochemical and geophysical datasets to obtain a more complete understanding of volcanic processes. During this time period I was surprised to learn that volcano seismicity is often interpreted to be caused by subsurface fluid movement; however, the actual type of fluid (i.e. magma, gas/volatiles, or hydrothermal waters) is often not well constrained, and these interpretations are often not supported by complementary volcanic gas measurements. This curiosity inspired my current GeoPRISMS postdoctoral project. The aims of this project are to use geochemical measurements of volcanic fluids and complementary seismic data from three historically-active Alaskan volcanoes within the Katmai Volcanic Cluster to: (1) determine the source (i.e. subducted slab, mantle, crust) and flux of volcanic gases, (2) identify proportions of magmatic and hydrothermal fluids within the subsurface, and (3) distinguish trends in gas composition and/or flux that correlate with seismic signatures of fluid movement.
Abhijit Gosh – NSF Award 1144695 – University of California Santa Cruz
Systematic search and characterization of very low frequency earthquakes and offshore tremor in Cascadia using the Amphibious Array
Subduction zones worldwide pose great seismic hazard, as they repeatedly produce large damaging earthquakes and associated tsunamis. Large earthquakes nucleate at the locked zone of the fault, spanning approximately 10 to 40 km in depth. Such fast earthquakes are believed to be the main observable mode of stress release for major plate boundary faults. But recent discovery of slow earthquakes in the transition zones forces earth scientists to rethink this paradigm. Such slow earthquakes are believed to load the up-dip locked zone, taking it closer to the next large megathrust earthquake. I study earthquakes, both fast and slow, using seismology as the main tool to understand the dynamics of earthquakes and faulting.
I did my undergraduate in structural geology. I earned my first Masters Degree in Geology from the University of Calcutta, India. While doing that, I got interested in earthquakes and faults. I got my second Masters Degree in the Earth and Atmospheric Sciences from Georgia Tech, where I studied earthquake statistics to infer variations in plate coupling in the Middle America Trench. In my PhD at the University of Washington, I focused on slow earthquakes and tremor in the Cascadia Subduction Zone, and San Andreas Fault. I developed new array techniques to image slow earthquakes with unprecedented resolution. I used this technique to image slow earthquakes captured by multiple seismic arrays that we designed and installed in Cascadia. I helped to resolve a long-standing scientific debate in Cascadia by showing that the majority of the tremor, the seismic signature of slow quakes, is occurring at the plate interface and likely a result of shear slip on the subduction fault. Furthermore, I showed that the behavior of tremor is complex and varies with distinct, identifiable patterns over timescales of minutes to months. My works suggest that the interaction between the stress field and rheological and/or geometrical asperities on the fault plane may control the evolution of slow quakes.
In the GeoPRISMS Postdoctoral proposal, I plan to integrate land-based and offshore seismic data collected under the Cascadia Initiative to scan the seismicity from the trench offshore to the base of the down-dip transition zone, up to ≈100 km inland from the coast. In the process, I will systematically search for exotic elusive events like, very low frequency earthquakes and offshore tremor. The goal is to take a holistic approach to better understand the full spectrum of fault slip behavior, and how it governs the subduction zone dynamics.
Since fall 2012, Abhijit Gosh is Assistant Professor at University of California Riverside
Hiroko Kitajima – NSF Award 1049591 – Pennsylvania State University
Evolution of Sediment Physical Properties in the Nankai Subduction Zone and Implications for the Updip Limit of Seismogenesis
Both the updip and downdip limits of seismicity are thought to be controlled by temperature. For the updip limit, it has been hypothesized that change in slip behavior from aseismic creep to seismic slip is affected by smectite-illite transition associated with an increase in temperature. However, the updip limit of seismicity may be controlled by an interaction between multiple mechanical and chemical processes including deformation, sedimentation, metamorphism, fluid flow, dissolution, cementation, and solute transport. Along with temperature, stress states and strain rates are important factors that control deformation and slip behaviors.
As a part of my Ph.D. research at Texas A&M University, working with Frederick Chester and Judith Chester, I investigated mechanical and hydraulic properties of marine sediments along different loading paths to simulate the range of stress conditions in accretionary subduction systems. I deformed sediment core samples recovered from relatively shallow portions of the Nankai Trough accretionary prism during the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). The deformation test results revealed that most prism sediment samples are overconsolidated and that consolidation state of sediments is an important factor in determining deformation modes (brittle or ductile deformation) and permeability evolution. I have also conducted high-speed rotary-shear friction experiments on fault materials to understand frictional behaviors of natural faults at coseismic slip rates. At such slip rates, dynamic weakening occurs in association with frictional heating, and I realized the significance of temperature on frictional behaviors.
Now at the Pennsylvania State University, I am working with Demian Saffer and Chris Marone, where I will measure acoustic wave velocities on sediment core samples at different stress states. By incorporating measured data with seismic data, I will estimate the in-situ stress states and pore pressure in subduction systems. The estimation of in-situ stress states can be verified by coring and logging from deeper portions of the accretionary prism in future stages of the NanTroSEIZE. I will also conduct friction experiments on smectite and illite at elevated temperature to document their behaviors and to test the hypothesis for the updip limit of seismicity. I am grateful for the GeoPRISMS/MARGINS postdoctoral fellowship program.
Since Fall 2012, Hiroko Kitajima is Research Scientist at Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan.
John Naliboff – NSF Award 1049660 – UC Davis
3-D numerical models of the dynamics of outer rise faults
The dynamic processes of the lithosphere and convecting mantle are largely governed by buoyancy driven stresses and the solid Earth’s rheological structure. These solid Earth processes operate over a diverse spectrum of spatial and temporal scales, and include frictional sliding along faults, propagation of seismic energy through elastic media and viscous creep in ductile portions of the Earth. In order to correctly link brittle and ductile processes to observations of surface deformation, plate motion and mantle flow it is critical to have independent estimates of the solid Earth’s rheological structure and the buoyancy forces available to drive deformation.
During my PhD at the University of Michigan, I focused on the origins of the lithospheric stress field using numerical simulations of lithospheric deformation and mantle flow. The results of my PhD work suggest that rheology may play a large role in the transmission and distribution of stress through the lithosphere. As a MARGINS postdoctoral fellow I plan to continue examining the role of rheology on lithospheric dynamics with Dr. Magali Billen at UC Davis.
The primary focus of my work will center on the dynamics of normal faulting along the bending-induced topographic bulge seaward of trenches in subduction zones (“outer rise”). Normal faulting in the outer rise regions of subduction zones reflects the extensional stress state generated by bending of the downgoing oceanic lithosphere that may produce new faults in the oceanic lithosphere or reactivate pre-existing faults generated at mid-ocean ridges. A number of recent high-resolution seismic studies have revealed the depth, spacing, dip and offset of these faults at multiple subduction zones, in addition to clear examples of when new faults are formed or pre-existing faults are reactivated. Using high-resolution 2-D and 3-D numerical models, I hope to test how viscous flow laws, brittle yielding parameters, strain-induced weakening and fluid-related weakening affect the formation and evolution of outer rise fault patterns. In addition to providing additional constraints on the rheology of the oceanic lithosphere, these numerical simulations will provide further insight into the large-scale dynamics of subduction zones and the transmission of stress over different wavelengths and timescales in subduction systems.
A post-doctoral appointment is a unique opportunity for a first-rate early-career scientist to solidify research skills, build a track record, establish peer relationships, and acquire professional self-confidence. Accordingly, the NSF-GeoPRISMS Program (formerly known as MARGINS) provides support for post-doctoral researchers to conduct up to two years of multi-disciplinary research at higher education institutions in the United States. The intention is to encourage individuals, typically within five years after award of their Ph.D., to diversify their expertise relative to that used in their thesis research.
The GeoPRISMS Post-Doctoral Fellowship is designed so that recipients can choose the research environment most beneficial for their scientific development and that of the GeoPRISMS Program. To this end, applicants are encouraged to establish a relationship with a proposed advisor well in advance of proposal submission.
Although awards must be held at U.S. institutions, there is no citizenship requirement and nationals of countries involved in the NSF-GeoPRISMS Program are encouraged to apply. It is expected that candidates will write their own materials for submission, except where otherwise required. There is no fixed dollar amount for a post-doctoral proposal; rather, the budget should be for the candidate's direct work only and should be appropriate to the post-doctoral research project, including salary commensurate with the experience of the candidate, institutional standards and local cost of living.
GeoPRISMS Post-Doctoral Fellowship proposals are subject to the same submission and review criteria as other proposals for MARGINS/GeoPRISMS funding. Please refer to the program announcement and NSF grant proposal guidelines for details. Submissions should state that the proposal is for a GeoPRISMS Post-Doctoral Fellowship and must be submitted by the institution to which an award would be made. In addition to the standard NSF proposal requirements, please include: a short abstract of your dissertation research and planned publications (not to exceed one single-spaced page); any fellowships, scholarships, teaching, and other positions relevant to your field held since entering college/university; any academic honors you have received relevant to your major field of study; your native language and fluency in other languages; and a statement of your long-term career goals and (particularly for International fellowship candidates) the ways the GeoPRISMS Fellowship will lead to development of long-term collaborative activities in GeoPRISMS science.
The proposal should be supported by four (4) letters of reference sent directly to the Program Manager who is the NSF Coordinator for the MARGINS/GeoPRISMS Program:
Dr. Bilal Haq
GeoPRISMS Fellowship References, National Science Foundation, National Science Foundation
4201 Wilson Blvd., Arlington, VA 22230
It is anticipated that one of your referees will be your Ph.D. thesis adviser, and another the sponsoring/collaborating scientist at the proposed host institution. The latter reference should state your proposed mentor and institution are willing to host you and can accept the GeoPRISMS Fellowship award. Other referees should be faculty members or researchers with current knowledge of your academic and/or professional experience.