Samantha E. Hansen

Assistant Professor

Hansen_60below

Contact

E-mail: shansen@geo.ua.edu
Phone: 205-348-7089
Office: 2031 Bevill
Fax: 205-358-0818

Education

B.S., 2000 Geological Engineering, University of Wisconsin, Madison
M.S., 2002  Geology and Geophysics, University of Wisconsin, Madison
Ph.D., 2007 Geology and Geophysics, University of California, Santa Cruz
Postdoctoral Research: Pennsylvania State University

Research Interests

My research is driven by the underlying goal to advance our understanding of fundamental geodynamic processes, such as volcanism, mountain building, continental rifting, and craton formation.  To this end, I employ a wide range of geological and geophysical tools emphasizing earthquake seismology, active tectonics, and the analysis of seismic data to investigate structure and infer associated earth processes.  Past and current research projects have focused on a variety of different geographic locations including Hawaii, Costa Rica, Saudi Arabia, Africa, and Antarctica.

Current Research Interests

Evaluating Tectonic Models for Antarctica

Antarctica is an excellent environment to study large-scale tectonics and related geologic processes shaping our planet; however, the nature of the crust and upper mantle beneath Antarctica is largely unknown.  Since most of Antarctica is covered by large ice sheets, direct geologic observations cannot be made; therefore "remote sensing" methods such as seismology must be used to constrain details about the crustal and upper mantle structure and to infer other geologic properties.

Fieldwork_1

Figure 1
Deploying a seismometer in East Antarctica.

The_Crew

Figure 2
Field crew for the GAMSEIS project, Christmas 2009.

Over the last few years, I have been involved with two seismic deployments in Antarctica: the Gamburtsev Antarctic Mountains Seismic Experiment (GAMSEIS) and the Polar Earth Observing Network (POLENET).  The goals of GAMSEIS are to investigate the Gamburtsev Mountains, a completely subglacial mountain range in East Antarctica whose origin is unknown.  These mountains are of particular interest since they may have served as a nucleation point for the first large-scale ice sheets that covered the continent.  POLENET is focused on the interactions between ice sheets and the underlying bedrock, including rifting and extension in the West Antarctic Rift System.  With new seismic data just becoming available from these deployments (and more on the way!), there is much to investigate.

Refining P-wave Velocity Models for Mantle Structure beneath Africa

A variety of different plume models have been proposed to explain the pattern of uplift, rifting, and volcanism observed throughout East Africa and western Arabia.  Some studies advocate for a single, lower-mantle-originating plume impinging on the lithosphere beneath either southern Ethiopia or Afar.  Other studies support multiple upwellings beneath this region, which may originate in the upper or lower mantle.  A third proposed explanation is that the rifting and volcanism in East Africa and Arabia are connected to the African Superplume, a low-velocity anomaly originating near the core-mantle boundary beneath southern Africa. 

To assess the competing plume models, I have been combining P-wave arrival time data from all regional and temporary seismic networks throughout the study region with reprocessed data from the International Seismological Centre.  These data are then inverted using a global, adaptively parameterized tomography approach that provides improved resolution.  Our results strongly indicate a connection between the lower mantle structure beneath southern Africa and the upper mantle structure beneath East Africa and Arabia.

Africa_Tomo

Figure 3 African Tomography

P-wave tomography model beneath Africa.  (top) Map view at 400 km depth, showing the location of cross-section A-A'.  (bottom) Cross-sectional view showing the connection between the African Superplume beneath southern Africa and the upper mantle low-velocity region beneath eastern Africa and Arabia.

Representative Publications

Hansen, S.E., A.A. Nyblade, D. Heeszel, D.A. Wiens, P. Shore, and M. Kanao, Crustal Structure of the Gamburtsev Mountains, East Antarctica, from S-wave Receiver Functions and Rayleigh Wave Phase Velocities, Earth and Planetary Science Letters, in review.

Hansen, S.E., A.A. Nyblade, and J. Julia, Estimates of Crustal and Lithospheric Thickness in Sub-Saharan Africa from S-wave Receiver Functions, South African Journal of Geology, 112, 89-100, 2009.

Hansen, S.E., J. Julia, A.A. Nyblade, M.L. Pyle, D.A. Wiens, and S. Anandakrishnan, Using S-wave receiver functions to estimate crustal structure beneath ice sheets: An application to the Transantarctic Mountains and East Antarctic craton, G-cubed, 10, Q08014, doi: 10.1029/2009GC002576, 2009.

Hansen, S.E., A.A. Nyblade, J. Julia, P.H.G.M. Dirks, and R.J. Durrheim, Upper Mantle low-velocity zone structure beneath the Kaapvaal Craton from S-wave receiver functions, Geophysical Journal International, 178, 1021-1027, 2009.

Hansen, S.E., J.B. Gaherty, S.Y. Schwartz, A.J. Rodgers, and A.M.S. Al-Amri, Seismic velocity structure and depth-dependence of anisotropy in the Red Sea and Arabian Shield from surface wave analysis, Journal of Geophysical Research, 113, B10307, doi: 10.209/2007JB005335, 2008.

Hansen, S.E., A.J. Rodgers, S.Y. Schwartz, and A. Al-Amri, Imaging Ruptured Lithosphere beneath the Red Sea and Arabian Peninsula, Earth and Planetary Science Letters, 259, 256-265, 2007.

Hansen, S.E., S.Y. Schwartz, A. Al-Amri, and A.J. Rodgers, Combined Plate Motion and Density Driven Flow in the Asthenosphere beneath Saudi Arabia: Evidence from Shear-wave Splitting and Seismic Anisotropy, Geology, 34, 869-872, 2006.

Hansen, S.E., S.Y. Schwartz, H.R. DeShon, and V. Gonzalez, Earthquake Relocation and Focal Mechanism Determination using Waveform Cross-Correlation, Nicoya Peninsula, Costa Rica, Bulletin of the Seismological Society of America, 96, 1003-1011, 2006.

Hansen, S.E., C.H. Thurber, M. Mandernach, F. Haslinger, and C. Doran, Seismic Velocity and Attenuation Structure of the East Rift Zone and South Flank of Kilauea Volcano, Hawaii, Bulletin of the Seismological Society of America, 94, 1430-1440, 2004.

Graduate Student Opportunities

I am seeking graduate students to work on a variety of seismology and tectonic-related projects. Please contact me if you are interested and/or would like more details.

UA Department of Geological Sciences | Box 870338 | Tuscaloosa, AL 35487 | Phone: (205)348-5095 | Fax: (205)348-0818