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Rebekah Lee

About meprofile

I am graduating December 2017 with a  Master of Science degree in geophysics. I have a B.A. in English and International Studies from the University of North Carolina at Greensboro. I taught English as a Second Language for five years after my bachelor’s degree. From 2013 – 2015 I took undergraduate level courses in math, physics and geology at North Carolina State University.

About my Research

The goal of my research is to apply seismic methods to ionospheric signal generated from surface-rupturing earthquakes (magnitude 6.5 and above) and tsunamis. I am using an electromagnetic wave that is created when a pressure wave propagates through the atmosphere and couples with the ionosphere.

2017 AGU oral Presentation and Abstract

Time: Friday, December 15, 9:30am
Session: NH51C: Ionospheric and Atmospheric Responses to Earth’s Surface Disturbances I
Title: Inverting Coseismic TEC Disturbances for Neutral Atmosphere Pressure Wave
Room: 243-244
Research from the past 20 years has shown that we can detect coseismic disturbances in the total electron content (TEC) using global navigation space systems (GNSS). In the near field, TEC disturbances are created by the direct wave from rupture on the surface. This pressure wave travels through the neutral atmosphere to the ionosphere within about 10 minutes. This provides the opportunity to almost immediately characterize the source of the acoustic disturbance on the surface using methods from seismology. In populated areas, this could provide valuable information to first responders. To retrieve the surface motion amplitude information we must account for changes in the waveform caused by the geomagnetic field, motion of the satellites and the geometry of the satellites and receivers. One method is to use a transfer function to invert for the neutral atmosphere pressure wave. Gómez et al (2015) first employed an analytical model to invert for acoustic waves produced by Rayleigh waves propagating along the Earth’s surface. Here, we examine the same model in the near field using the TEC disturbances from the direct wave produced by rupture at the surface. We compare results from the forward model against a numerical model that has been shown to be in good agreement with observations from the 2011 Van (Turkey) earthquake. We show the forward model predictions using both methods for the Van earthquake. We then analyze results for hypothetical events at different latitudes and discuss the reliability of the analytical model in each scenario.

Gõmez, Demián, Robert Smalley, Charles A. Langston, Terry J. Wilson, Michael Bevis, Ian W. D. Dalziel, Eric C. Kendrick, et al. “Virtual Array Beamforming of GPS TEC Observations of Coseismic Ionospheric Disturbances Near the Geomagnetic South Pole Triggered by Teleseismic Megathrusts.” Journal of Geophysical Research A: Space Physics 120, no. 10 (October 2015): 9087–9101. doi:10.1002/2015JA021725.

2016 AGU Presentation

Title: “Imaging earthquake rupture on the surface from backprojection Ionospheric Signals”.

Earthquakes greater than magnitude 6 and tsunamis create vertical displacements at the Earth’s surface which radiate energy into the atmosphere as a pressure wave. The pressure wave couples with the ionosphere to create an electromagnetic wave that disturbs the electron density in the ionosphere. Extensive research from the past 20 years has shown that we can detect these disturbances in the electron density through a variety of methods, including global navigation space systems (GNSS).  This method measures an integrated value of the total electron content (TEC) between a satellite-receiver pair.

While much work has been done to detect and model these ionospheric disturbances, little has been done to image the source. Backprojection is a method in seismology used to image energy released from large earthquakes. Backprojecting directly from the TEC is complicated by polarity changes during the coupling with the ionosphere as well as by the moving satellite. We resolve these obstacles by inverting the TEC to obtain the atmospheric pressure wave. We show results of inversion for synthetic and real data. We then use the ionospheric TEC response associated with the 2011 Van dip-slip event (Mw 7.1) and backproject the pressure wave. We compare these acoustic back projection results to the backprojection of the raw TEC. Finally, we address the effect of the wind on travel times.

Honors and Awards

  • Participant in the SEG/Chevron Student Leadership Symposium, Dallas, Tx, October 2016
  • Allan V. Cox Student Research Award (GSA Geophysics special award), 2016
  • GSA Graduate Student Research Grant Recipient, 2016
  • Invited talk at Rio Grande Valley Geophysical Society, Albuquerque, NM,  August 2016
  • Intern at Sandia National Labs, Albuquerque, NM, summer 2016
  • Participant in SEG/ExxonMobil Student Education Program, New Orleans, 2015
  • Participant: Summer of Applied Geophysical Experience (SAGE), Santa Fe, New Mexico, summer 2015
  • 2nd place award at NC State McCormick Symposium, Raleigh, NC, April 2015
  • American Association for University Women (AAUW) Career Development Grant (2014 – 2015)
  • Intern for Incorporated Research Institutions for Seismology (IRIS), summer 2014
    • Placed at Sandia National Labs, Albuquerque, NM

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