Samantha E. Hansen

Associate Professor

  • shansen@geo.ua.edu
  • (205) 348-7089
  • 2031 Bevill Bldg.

Education

B.S., Geological Engineering, The University of Wisconsin, 2000

M.S., Geology and Geophysics, The University of Wisconsin, 2002

Ph.D., Geology and Geophysics, The University of California, Santa Cruz, 2007

Postdoc, The Pennsylvania State University

Courses Taught

GEO 101: The Dynamic Earth
GEO 407/507: Seismology
GEO 435/535/635: Honors and Graduate Seminar in Geology
GEO 542: Geodynamics

Curriculum Vitae

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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, Greece, and Antarctica.

Current Research Projects

Transantarctic Mountains Northern Network (TAMNNET)

Current constraints on the crustal thickness and seismic velocity structure beneath the Transantarctic Mountains (TAMs) and the Wilkes Subglacial Basin (WSB) are limited, leading to uncertainties over competing geologic models that have been suggested to explain their formation. To broaden the investigation of this region, I operated a 15-station array across the northern TAMs and the WSB between 2012-2015, which filled a major gap in seismic coverage. Data from TAMNNET is being combined with that from other previous and ongoing seismic initiatives and is being analyzed with a variety of techniques to generate unprecedented images of the subsurface structure beneath this area.  Results from this work are being used to differentiate between competing tectonic models, thereby resolving how the TAMs and WSB originated and how their formation relates to Antarctica’s geologic history.

TAMs SeismicInstall

(left) Transantarctic Mountains.  (right) Installing a TAMNNET seismic station.

(left) Map view image of shear-wave velocity structure at 80 km depth beneath the central and northern TAMs from Graw et al. (2016).  (middle) Cross-sectional image of compressional wave velocity structure along the TAMs front from Brenn et al. (2017).  (right) Shear-wave splitting results from Graw and Hansen (2017).

Antarctic Seismic Investigations of ULVZ Structure

Ultralow velocity zones (ULVZs) are thin, laterally-varying boundary layers seen in some locations just above the Earth’s core-mantle boundary (CMB).  They are associated with dramatic seismic wave velocity reductions and increased density, but their highly variable structure and distributed locations have lead to many questions regarding their origin.  Incomplete sampling of the lowermost mantle has limited our ability to map global ULVZ structure in detail; therefore, investigations that sample the CMB with new geometries are crucial to further our understanding of ULVZs and their possible connection to other deep Earth structures and processes.  The TAMNNET deployment (see above) provides a unique dataset to investigate previously unexplored sections of the CMB.  Working with Dr. Ed Garnero at Arizona State University, we are analyzing core-reflected phases to identify anomalous CMB structure beneath the southern hemisphere.

 Core-reflected phases (ScP, PcP, and ScS) and their principle associated arrivals from a ULVZ at the CMB.  Provided by Ed Garnero (ASU).

Imaging the Mantle Structure along the Western Hellenic Subduction Zone

The Hellenic subduction zone (HSZ) is the most seismically active region in Europe and plays a major role in the active tectonics of the eastern Mediterranean.  This complicated environment has the potential to generate both large magnitude (M > 8) earthquakes and tsunamis, and situated above the western end of the HSZ, Greece faces a high risk from these geologic hazards.  Despite previous investigations, the kinematics of the HSZ are still controversial, and high-resolution images of the HSZ seismic structure are needed to delineate important characteristics influencing the seismic and tsunami potential in this area.  Working with colleagues at the National Observatory of Athens (NOA), I will be developing new tomographic models for the HSZ, which will be used to inform NOA hazard assessment that will ultimately impact the broader Greek community living in this dynamic geologic environment.

 

(left) Map of study area with geographic locations labeled in black and geologic features labeled in red.  Yellow lines mark plate boundaries.  Black dashed line: Central Hellenic Shear Zone.  GC: Gulf of Corinth.  (right) Map highlighting seismic stations throughout Greece that will be used for this study.  HUSN: Hellenic Unified Seismological Network, MEDUSA: Multidisciplinary Experiments for Dynamic Understanding of Subduction under the Aegean Sea.

Research Group Members

Jordan Graw, Ph.D. student

Sarah Carson, M.S. student

Greg Brenn, M.S. student (graduated: December 2016)

Lindsey Kenyon, M.S. student  (graduated: December 2014)

 

Representative Publications

Brenn, G.R., S.E. Hansen, and Y. Park, Variable thermal loading and uplift along the Transantarctic Mountains, Antarctica, Geology, doi: 10.1130/G38784.1, 2017.  Brenn_etal_Geology_2017.pdf (24 downloads)

Graw, J.H., S.E. Hansen, C. Langston, B. Young, A. Mostafanejad, and Y. Park, Assessment of Crustal and Upper Mantle Velocity Structure by Removing the effect of an ice layer on the P-wave response: An application to Antarctic seismic studies, BSSA, 107, doi: 10.1785/0120160262, 2017. Graw_etal_BSSA_2017.pdf (24 downloads)

Graw, J.H. and S.E. Hansen, Upper Mantle Seismic Anisotropy Beneath the Northern Transantarctic Mountains, Antarctica from PKS, SKS, and SKKS Splitting Analysis, Geochem. Geophys. Geosys., 18, doi: 10.1002/2016GC006729, 2017.  Graw_Hansen_G-cubed_2017.pdf (26 downloads)

Graw, J.H., A.N. Adams, S.E. Hansen, D.A. Wiens, L. Hackworth, and Y. Park, Upper mantle shear wave velocity structure beneath northern Victoria Land, Antarctica: Volcanism and uplift in the northern Transantarctic Mountains, Earth Planet. Sci. Lett., 449, 48-60, doi: 10.1016/j.epsl.2016.05.026, 2016.  Graw_etal_2016.pdf (206 downloads)

Hansen, S.E., L.M. Kenyon, J.H. Graw, Y. Park, and A.A. Nyblade, Crustal Structure beneath the Northern Transantarctic Mountains and Wilkes Subglacial Basin: Implications for Tectonic Origins, J. Geophys. Res., 121, 812-825, doi: 10.1002/2015/JB012325, 2016.  SHansen_JGR_2016.pdf (123 downloads)

Ramirez, C., A.A. Nyblade, S.E. Hansen, D.A. Wiens, S. Anandakrishnan, R.C. Aster, A.D. Huerta, P.J. Shore, and T. Wilson, Crustal and Upper Mantle Structure beneath Ice-Covered Regions in Antarctica from S-wave Receiver Functions and Implications for Heat Flow, Geophys. J. Int., 204, 1636-1648, doi: 10.1093/gji/ggv542, 2016. Ramirez_GJI_2016.pdf (142 downloads)

Hansen, S.E., A. Reusch, T. Parker, D. Bloomquist, P. Carpenter, J.H. Graw, and G.R. Brenn, The Transantarctic Mountains Northern Network (TAMNNET): Deployment and Performance of a Seismic Array in Antarctica, Seism. Res. Lett., 86, 1636-1644, doi: 10.1785/0220150117, 2015.  SHansen_SRL_2015.pdf (143 downloads)

Hansen, S.E., J.H. Graw, L.M. Kenyon, A.A. Nyblade, D.A. Wiens, R.C. Aster, A.D. Huerta, S. Anandakrishnan, and T. Wilson, Imaging the Antarctic Mantle using Adaptively Parameterized P-wave Tomography: Evidence for Heterogeneous Structure beneath West Antarctica, Earth Planet. Sci. Lett., 408, 66-78, doi: 10.1016/j.epsl.2014.09.043, 2014.  Hansen_EPSL_2014.pdf (405 downloads)

Hansen, S.E., H.R. DeShon, M.M. Driskell, and A.M.S. Al-Amri, Investigating the P-wave Velocity Structure beneath Harrat Lunayyir, northwestern Saudi Arabia, using Double-Difference Tomography and Earthquakes from the 2009 Seismic Swarm, J. Geophys. Res., 118, 4814-4826, doi: 10.1002/jgrb.50286, , 2013.  Hansen_JGR_2013.pdf (372 downloads)

Hansen, S.E. and A.A. Nyblade, The Deep Seismic Structure of the Ethiopia/Afar Hotspot and the African Superplume, Geol. J. Int., 194, 118-124, doi: 10.1093/gji/ggt116, 2013.  HansenNyblade_GJI_2013.pdf (354 downloads)

Heeszel, D.S., D.A. Wiens, A.A. Nyblade, S.E. Hansen, M. Kanao, M. An, and Y. Zhao, Rayleigh wave constraints on the structure and tectonic history of the Gamburtsev Subglacial Mountains, East Antarctica, J. Geophys. Res., 118, 2138-2153, doi: 10.1002/jgrb.50171, 2013.  Heeszel_JGR_20131.pdf (379 downloads)

Lloyd, A.J., A.A. Nyblade, D.A. Wiens, P.J. Shore, S.E. Hansen, M. Kanao, and D. Zhao, Upper mantle seismic structure beneath central East Antarctica from body wave tomography: Implications for the origin of the Gamburtsev Subglacial Mountains, Geochem. Geophys. Geosys., 14, doi: 10.1002/ggge.20098, 2013.  Lloyd_G-cubed_2013.pdf (328 downloads)

Kanao, M., S.E. Hansen, K. Kamiyama, D. Wiens, T. Higashi, A.A. Nyblade, A. Watanabe, Crustal structure from the Lützow-Holm Bay to the inland plateau of East Antarctica, based on gravity surveys and broadband seismic deployments, Tectonphys., 572-573, 100-110, doi: 10.1016/j.tecto.2012.01.014, 2012.  Kanao_Tectonophysics_2012.pdf (312 downloads)

Hansen, S.E., A.A. Nyblade, and M.H. Benoit, Mantle structure beneath Africa and Arabia from adaptively parameterized P-wave tomography: Implications for the origin of Cenozoic Afro-Arabian tectonism, Earth Planet. Sci. Lett., 319-320, 23-34, doi: 10.1016/j.epsl.2011.12.023, 2012.  Hansen_EPSL_20121.pdf (345 downloads)

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 Planet. Sci. Lett., 300, 395-401, doi: 10.1016/j.epsl.2010.10.022, 2010.  Hansen_EPSL_2010.pdf (328 downloads)

~SEE CV FOR FULL LIST~

 

Graduate Student Opportunities: I am seeking motivated students who are interested in pursuing graduate studies in earthquake seismology.  Prior research experience and computer programming skills are beneficial.  Please contact me for further details.