14-13. Understanding mechanical processes driving volcano deformation through geodetic measurements, seismic tomography and numerical modeling
Measuring and modeling transient volcanic deformation is critical in understanding magmatic processes and eruption dynamics, the foundation of the USGS strategy to monitor volcanoes and interpret their precursory unrest. The transient deformation of a volcano in unrest reflects the net effect of several mechanical processes, including magma influx, thermal stress, and degassing within the magma chamber, as well as faulting, viscoelastic relaxation, poroelastic relaxation, and thermal stress outside of the magma chamber. In addition, the surface loads imposed by new lava emplacement can cause transient deformation. Furthermore, erupted materials can undergo thermoelastic contraction for decades after emplacement. To sort out these processes, we consider them in terms of the volcano deformation cycle. In analogy with the earthquake deformation cycle, the time between two eruptions in the volcano deformation cycle can be divided into four successive intervals: syn-eruptive, post-eruptive, inter-eruptive, and pre-eruptive. These four time intervals may be linked together to form a cycle that helps interpret observations. During the syn-eruptive interval, magma moves out of the chamber, changing the stress field and typically causing deflation of the edifice. In the following years or decades of the post-eruptive interval, the stresses continue to change as a result of processes such as viscous relaxation. Eventually, the stress and strain fields may evolve toward a steady state such that little or no deformation is observed during an inter-eruptive interval that may last thousands of years. Then, during the pre-eruptive time interval, the rate of deformation may increase over a period of hours to months or even years.
We seek a postdoctoral fellow to study a fundamental question: what geophysical processes cause volcanoes to deform during a period of unrest that may — or may not — lead to an eruption? To do so, the postdoctoral fellow could analyze the measurements and models for the transient behavior at several volcanoes along the Aleutian arc (Lu et al., 2007). To test competing hypotheses for volcanic processes, the suggested approach is to analyze the transient behavior in terms of “impulse” and “response”. In this experiment, the magma flux during the unrest provides the “impulse” and the subsequent, transient deformation, the “response”. By simulating the impulse, measuring the response, and interpreting the constitutive relations between the two, one can infer the rheology.
The successful Mendenhall postdoctoral fellow will have the opportunity to blend, according to her or his interests, skills, and goals, three components: (1) measuring to explore the spatial and temporal behavior in the available data sets, including: (a) geodetic time series from Interferometric Synthetic Aperture Radar (InSAR) and the Global Positioning System (GPS), (b) earthquake locations; and (c) seismic tomography (Biggs et al., 2010; Fournier et al., 2009; Lu et al., 2007; Masterlark et al., 2010). (2) modeling to develop quantitative models using the Finite Element Method to simulate the timing and location of the observed seismicity and deformation by accounting for: (a) the geometry and loading of the magma chamber and lava flow, (b) the spatial distribution of material properties; and (c) the constitutive (rheological) relations between stress and strain (Lu et al., 2005; Masterlark et al., 2010). (3. interpreting to test hypotheses by iteratively confronting the models with the measurements. Potential targeted volcanoes include Okmok, Akutan, Makushin, Westdahl, and Augustin in the Aleutian. At each of these active volcanoes, the data sets required to complete the proposed research within two years are already available. At each of these volcanoes, the recent periods of unrest present an opportunity to conduct a rheological experiment to unravel the complex processes associated with magma migration, storage, and eruption in an active volcano.
Biggs, J., Z. Lu, T. Fourneir, and J. Freymueller (2010), Magma flux at Okmok Volcano, Alaska from a joint inversion of continuous GPS, campaign GPS and InSAR, J. Geophys. Res., 115, B12401, doi:10.1029/2010JB007577.
Fournier, T., J. Freymueller, and P. Cervelli (2009), Tracking magma volume recovery at Okmok volcano using GPS and an unscented Kalman filter, J. Geophys. Res., 114, B02405, doi:10.1029/2008JB005837.
Lu, Z., T. Masterlark, and D. Dzurisin (2005), Interferometric synthetic aperture radar study of Okmok volcano, Alaska, 1992-2003: Magma supply dynamics and postemplacement lava flow deformation, J. Geophys. Res., 110, 02403.
Lu, Z., D. Dzurisin, C. Wicks, J. Power, O. Kwoun, and R. Rykhus (2007), Diverse deformation patterns of Aleutian volcanoes from satellite interferometric synthetic aperture radar (InSAR), in Volcanism and Subduction: The Kamchatka Region (edited by J. Eichelberger et al.), American Geophysical Union Geophysical Monograph Series 172, 249-261, 2007.
Masterlark, T., M. Haney, H. Dickinson, T. Fournier, and C. Searcy (2010), Rheologic and structural controls on the deformation of Okmok volcano, Alaska: FEMs, InSAR, and ambient noise tomography, J. Geophys. Res., 115, B02409. doi:10.1029/2009JB006324.
Proposed Duty Station: Vancouver, WA; Anchorage, AK
Areas of Ph.D.: Geophysics, volcanology, remote sensing, seismology or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).
Qualifications: Applicants must meet one of the following qualifications - Research Geophysicist, Research Physicist, Research Geologist, Computer Scientist, Research Mathematician.
(This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of theposition will be made by the Human Resources specialist).
Research Advisor(s): Zhong Lu, (360) 993-8911, firstname.lastname@example.org; Kurt Feigl (U Wisconsin), (608) 262-0176, email@example.com.; Timothy Masterlark (South Dakota School of Mines and Technology), (605) 394-5326, Timothy.Masterlark@sdsmt.edu.; Stephanie Prejean, (907) 786-7462, firstname.lastname@example.org
Human Resources Office Contact: Robert Hosinski, (916) 278-9397, email@example.com.
|Summary of Opportunities|