Aloha! I am a postdoctoral research associate in the Planetary Image Research Laboratory, part of the Lunar and Planetary Laboratory at the University of Arizona. I serve as a targeting specialist for the HiRISE camera on-board the Mars Reconnaissance Orbiter.

    My interests in the geological sciences encompass the fields of fault and rock mechanics, planetary geology, volcanology, and remote sensing. Much of my work focuses on developing fresh quantitative approaches in understanding the structural geology and tectonics of Earth and other planets based on field, laboratory and remotely-sensed data. My varied research interests and achievements can be categorized into three broad areas:

MECHANICS OF FAULTING IN POROUS ROCKS
    I am currently working in several field areas in Nevada, Utah and Colorado investigating pre- and syn-fault localization of plastic strain, with emphasis on deformation band growth. Deformation bands are tabular discontinuities of decreased porosity and permeability that form prior to and in response to faulting in porous granular rock, such as sandstone or tuff. Deformation bands provide unique insight into the evolution of fault-related brittle strain because the plastic yielding that is attendant with deformation band strain is not easily erased and is not reversible by changing stress states. Therefore the pattern of strain related to early stages of fault growth is generally not destroyed by subsequent fault growth. Accordingly, changes in causative local stress states are chronologically recorded by each successive population of deformation bands, and cross-cutting relations between each deformation band population provide quantitative and systematic insight into the co-evolution of stresses accompanying fault growth.

PLANETARY TECTONICS
    The ongoing Mars Global Surveyor mission has provided a wealth of topographic data for Mars via the Mars Orbiter Later Altimeter (MOLA) instrument. MOLA data provides topographic characterizations of faults in unprecedented detail, which enables quantitative fault mechanics-based approaches to understanding past tectonic processes on Mars. My work here utilizes numerical methods initially developed for studying coseismic and interseismic deformation around active terrestrial faults, with Earth-based fault mechanics theory. My investigations into faulting on Mars are based in part on numerical model inversion of fault-related topography in order to interpret the subjacent fault geometry, slip distribution and stress state. I have used such findings to demonstrate that previously enigmatic morphologic structures classified as 'wrinkle ridges' in early planetary science research are in fact thrust-fault related folds. Additionally, I have also recognized one of the few populations of strike-slip faults on Mars based on fault-related topography. Previous interpretations of strike-slip faults on Mars based on visible imagery has been controversial although their presence is predicted by numerous geodynamic models. I have used my recognition of wrinkle ridges as thrust-fault related folds, as well as the identification of strike-slip faults to test predicted stress states derived from geodynamic models of lithospheric evolution. I find that geodynamic models that invoke intermittent flexural loading and isostatic support of the lithosphere, under a thick-skin assumption, predict stress states that are most consistent with the stress states required to generate the interpreted styles and distributions of faulting at the surface.

VOLCANO STABILITY
    I am also pursuing research into volcano stability and hazard assessment. For this work, I have employed state-of-the-practice limit equilibrium analyses to evaluate the stability of the Hilina slump, an active ten's of km-scale landslide on the south flank of Kilauea volcano, Hawai'i. The stability analysis is based on field and laboratory estimates of the strength and deformability of the landslide mass, as well as the topography and bathymetry of the slide. I have found that the Hilina slump is currently stable under static gravitational loading and under horizontal ground accelerations up to ~0.45-0.65 g, with failure of the slump predicted at higher accelerations. These numerical models also predict the least stable failure surfaces for the slump (which are not prescribed a priori) that are consistent with interpretations from recent seismic imaging of the submarine portion of the slump. Further, changes in sea-level, appropriate to magnitudes interpreted from the geologic record, as well as further growth of the edifice are predicted to cause in minimal changes to the present-day stability behavior of the slump.

    Detailed information on my research activities, including publications and photographs, is available through the links at the upper left. Thanks for your interest, and please feel free to contact me with any questions or discussions.

Chris H. Okubo
Lunar and Planetary Laboratory
The University of Arizona
Sonett Space Science, Bldg. 63
1541 E. University Blvd.
Tucson, AZ 85721

chriso@lpl.arizona.edu
Office: Sonett Space Science, Room 207
Voice: 1 (520) 626-1458
Fax: 1 (520) 626-8998

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