Bridget Smith-Konter
 Research Interests
Lithospheric Deformation and Stress Evolution of the San Andreas Fault System
Tidal Stress &
Faulting of Ganymede, Enceladus & Europa
3-D Elastic & Viscoelastic Crustal Deformation Modeling
GPS & InSAR Applications
SRTM Topography



Lithospheric Deformation & Stress Evolution of the San Andreas Fault System
The primary objective of my research is to improve our understanding of the earthquake cycle through sophisticated computer models of fault system deformation constrained by geologic, geodetic, and seismic data.   Plate boundary interactions, like those characterizing the behavior of the San Andreas Fault System, have been vigorously deforming much of the Earth's crust for over the past several million years.   Recognized as the most widely researched fault system in the world, the San Andreas has become a natural laboratory for investigating the many facets of plate boundary deformation revealed by a synthesis of geologic, geodetic, and seismic observations.

To model lithospheric deformation of the San Andreas Fault System associated with the earthquake cycle, I use a semi-analytical Fourier model that calculates the 3D response of both elastic and viscoelastic mediums to a distribution of body forces. Merging data from the historical & prehistorical earthquake database with geologic and geodetic observations, the model allows for both large-scale and long-term deformation simulations of the earthquake cycle.   To date, I have used this method to investigate 1000-year earthquake scenario models of the San Andreas Fault System. Stress evolution models, simulating interseismic, coseismic, and postseismic changes over the past 200 years, were also constructed based on these findings.

 
Related Publications:

Howell, S., B. Smith-Konter, N. Frazer, X. Tong, and D.T. Sandwell (2015), The vertical fingerprint of earthquake-cycle loading in Southern California, Nature Geosciences, doi: 10.1093/2015-03-04591 (in revision).

Tong, X., D.T. Sandwell, and B. Smith-Konter (2015), An integral method to estimate the moment accumulation rate on the Creeping Section of the San Andreas Fault, Geophysical Journal International, doi: 10.1093/gji/gjis140783.

Smith-Konter, B., G.M. Thornton, and D.T. Sandwell (2014), Vertical crustal displacement due to interseismic deformation along the San Andreas fault: Constraints from tide gauges, Geophysical Research Letters, doi:10.1029/2014GL060091.

Tong,X., B. Smith-Konter, and D.T. Sandwell (2014), Is there a discrepancy between geological and geodetic slip rates along the San Andreas Fault System?, J. Geophys. Res., doi:10.1029/2013JB010765.

Tong, X., D.T. Sandwell, and B. Smith-Konter (2013), High-resolution interseismic velocity data along the San Andreas Fault System, J. Geophys. Res., 118, doi:10.1029/2012JB009442.

Del Pardo, C., B. Smith-Konter, C.Kreemer, G. Blewitt, W. Hammond, and L. Serpa (2012), Interseismic deformation and stress evolution of the Death Valley Fault Zone, J. Geophys. Res., 117, B060404, doi:10.1029/2011JB008552.

Smith-Konter, B., D. Sandwell, and P. Shearer (2011), Locking depths estimated from geodesy and seismology along the San Andreas Fault System:  Implications for seismic moment release, J. Geophys. Res., 116, B06401, doi:10.1029/2010JB008117.

Smith-Konter, B., D. Sandwell, and M. Wei (2010), Integrating GPS and InSAR to resolve stressing rates of the SAF System, EarthScope inSights Newsletter, Summer 2010.

Wei, M., D. Sandwell, and Smith-Konter, B. (2010), Optimal combination of InSAR and GPS for measuring interseismic crustal deformation, J. Adv. in Space Res., doi: 10.1016/j.asr.2010.03.013.

Smith-Konter, B., and D.T. Sandwell (2009), Stress evolution of the San Andreas Fault System: Recurrence interval versus locking depth, Geophys. Res. Lett., 36, doi:10.1029/2009GL037235.

Smith, B.R. and D.T. Sandwell (2006), A Model of the Earthquake Cycle Along the San Andreas Fault System Over the Past 1000 years, J. Geophys. Res., 111, doi:10.1029/2005JB003703.

Smith, B. R. and D. T. Sandwell (2003), Coulomb Stress Along the San Andreas Fault System, J. Geophys. Res., 108, doi:10.1029/2002JB002136.

View  animated models: 

San Andreas 3D deformation (.mov)

San Andreas Coulomb stress accumulation (.mov)

San Andreas stress visualization (.mov)












Tidal Stress & Faulting of Enceladus &  Europa

I recently began applying 3-D crustal deformation models to investigate the tectonic features found on the moons of Enceladus and Europa.  Thus far, this research has been focused on modeling tidally driven stress accumulation and shear failure of fractures on Saturn's moon Enceladus.  Cassini spacecraft observations of the south polar region of Enceladus revealed four large linear fractures, or “tiger stripes,” associated with anomalous heat flow and active plumes.  These features are thought to be sites of tidally induced strike-slip and/or open-close motions, similar to motions inferred for fractures on Jupiter’s moon Europa. These tectonic motions are likely a result of tidally induced stresses that are exerted on a satellite during its daily orbital cycle around its parent body.  I am currently investigating the tidally driven stress conditions at Enceladus’s south polar region for clues about the tiger stripes’ tectonic activity and faulting environment.  I plan to apply similar methods to investigate faulting processes on Jupiter’s moon Europa.

Related publications:

Cameron, M., B. Smith-Konter, A. Nahm, and R. Pappalardo, Modeling tidally driven Coulomb failure at strike-slip lineae on Europa, in preparation.

Olgin, J., B. Smith-Konter, and R.L. Pappalardo (2011), The limits of Enceladus’s ice shell thickness from tidally driven tiger stripe failure, Geophys. Res. Lett.,  38, doi:10.1029/2010GL044950.

Smith-Konter, B. and R.L. Pappalardo (2008), Tidally driven stress accumulation and shear failure of Enceladus's tiger stripes, Icarus, doi:10.1016/j.icarus.2008.07.005.

  View  animated models: 

                                  

(left)  SatStress model: Maximum tensile stress output as a function of orbital position at Enceladus's south pole.

(center)  Tiger stripe modeled fault stress accumulation as a function of orbital position.

(right) Tiger stripe modeled displacement fields (horizontal and vertical) as a function of orbital position.



(Above) False-color Cassini spacecraft image of the south polar region of Saturn’s moon, Enceladus.   The tiger stripes, the four linear gashes on the left side of the image, are thought to be active faults that deform in response to gravitational tidal forces.  (Image courtesy of NASA/JPL/Space Science Institute).






(Above) Looking at the tiger stripes from Enceladus’s south pole, a model of stress accumulation (left) due to fault locking at periapse (Enceladus’s closest orbital position to Saturn) and potential right-lateral fault displacement (right) due to a reduced compressive stresses at apoapse (Enceladus’s orbital position at its farthest distance from Saturn).





3-D Elastic & Viscoelastic Crustal Deformation Modeling

Exploration of earthquake scenarios that span several thousand years, and deform over an equal number of kilometers, requires models that are three-dimensional, time-dependent, and computationally efficient. My Ph.D. thesis research was directed toward the development, verification, & application of a semi-analytical Fourier model describing the 3D response of both elastic and viscoelastic mediums to a distribution of body forces. Using Fourier analysis, the horizontal complexity of a given fault system has no effect on the speed of the computation; likewise, because the solution is analytic in time, no numerical time stepping is required. This approach allows for rapid computer model calculations that are over 20 times faster than previous methods (e.g., finite element methods). A single time-step for a mesh of 2048 by 2048 horizontal grid cells, containing over 400 fault patches, requires only 40 seconds of CPU time on a personal computer. Multiple time steps, including hundreds of years of earthquake history, can be computed in a matter of hours.

Model development involved extensive testing against analytic solutions including: 2-D analytic tests of a homogeneous elastic half-space [Weertman, 1964], a layered elastic half-space [Rybicki, 1971], non-surface observation planes [Savage and Lisowski, 1993], and a layered viscoelastic half-space [Nur and Mavko , 1977]; 2-D analytic Boussinesq tests for the point load solution [Love, 1944] and the thin-plate flexure solution [Le Pichon et al., 1973]; a 3-D elastic half space   [Okada, 1985, 1992].

Related Publications:

Smith, B.R. and D.T. Sandwell, A 3-D Semi-analytic Viscoelastic Model for Time-dependent Analyses of the Earthquake Cycle, J.Geophys. Res., doi:10.1029/2004JB003185, 2004.

Smith, B. R. and D. T. Sandwell, Coulomb Stress Along the San Andreas Fault System, J. Geophys. Res., 108, doi:10.1029/2002JB002136, 2003.

 

 

View animated models:

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                      Example 3D Velocity Model ___________  Example Coulomb Stress Model




GPS & InSAR Applications

Space geodetic techniques, such as GPS and InSAR, provide valuable data that offer a detailed synoptic picture of the strain accumulation along Earth's plate boundaries. However, modeling of these data is critical in order to determine the corresponding tectonic stress and rheologic parameters.   Accurate models must incorporate time-dependent interactions among complex 3-D fault systems. Using the 3D Fourier model described above, along with 1000+ GPS-derived horizontal velocity measurements, calculations of both secular and episodic deformation and stress due to plate boundary forces are feasible.

Likewise, InSAR data can also be efficiently investigated using 3D crustal deformation models. For example, ascending and descending interferograms derived from ERS satellites have been used to estimate surface slip and fault parameters along the Hector Mine earthquake rupture [Sandwell et al., 2002].   Large-scale synthetic interferograms can also be produced for the purpose of integrating GPS and InSAR data to provide both high spatial and high temporal resolution at the plate boundary.

Related Publications:

Tong,X., B. Smith-Konter, and D.T. Sandwell (submitted), Is there a discrepancy between geological and geodetic slip rates along the San Andreas Fault System?, J. Geophys. Res., doi:10.1029/2013JB010765.

Tong, X., D.T. Sandwell, and B. Smith-Konter (2013), High-resolution interseismic velocity data along the San Andreas Fault System, J. Geophys. Res., 118, doi:10.1029/2012JB009442.

Smith-Konter, B., D. Sandwell, and M. Wei (2010), Integrating GPS and InSAR to resolve stressing rates of the SAF System, EarthScope inSights Newsletter, Summer 2010.

Wei, M., D. Sandwell, and Smith-Konter, B., Optimal combination of InSAR and GPS for measuring interseismic crustal deformation, J. Adv. in Space Res., doi: 10.1016/j.asr.2010.03.013, 2010.

Smith, B.R. and D.T. Sandwell, A Model of the Earthquake Cycle Along the San Andreas Fault System Over the Past 1000 years, J. Geophys. Res., 111, doi:10.1029/2005JB003703, 2006.

Smith, B. R. and D. T. Sandwell, Coulomb Stress Along the San Andreas Fault System, J. Geophys. Res., 108, doi:10.1029/2002JB002136, 2003.

Sandwell, D. T., L. Sichiox, and B. R. Smith, The 1999 Hector Mine Earthquake: Vector Near-Field Displacements from ERS InSAR, Bull. Seismo. Soc. Am., 92, 1341-1354, 2002.

 




SRTM Topography

I have also investigated the resolution quality of the Shuttle Radar Topography Mission data. The Shuttle Radar Topography Mission (SRTM) collected radar interferometry data over 80% of Earth's landmass from 60 šN to 56 šS latitude in February of 2000 from the Space Shuttle Endeavour.   Both C-band and X-Band data were acquired simultaneously during the mission and subsequently processed by JPL and DLR, respectively. The completed SRTM Digital Elevation Model (DEM) provides a global topography data set critical for a number of scientific investigations, specifically in areas outside of the U.S. where the quality of data is typically poorer. Many of these applications require high horizontal resolution and vertical accuracy.

The primary objective of my SRTM research was to establish the resolution and accuracy of C-band SRTM-1 topography in order to provide a means of appropriate filter design and scientific application. This work involved cross-spectral analyses of the C-band 30-m SRTM DEM with both the National Elevation Dataset (NED) and Hector Mine Airborne Laser Swath Mapping (ASLM) dataset in order to identify horizontal resolution and any geo-location errors in the SRTM DEM. Spectral comparisons of the NED and SRTM data yield coherent results for wavelengths greater than 200 m.   Two additional spectral comparisons made with the Hector Mine laser topography data suggest that the NED is of poorer quality for wavelengths longer than 350, and that SRTM topography is inferior for wavelengths shorter than 350 m. Additionally, a northeast phase shift of 11.87 m east and 10.58 m north was identified in the NED.   No geo-location errors were identified in the SRTM DEM.   From these results, low-pass filter/decimation algorithms can be designed in order to suppress the short wavelength noise and expedite large-area SRTM processing.

 

Related Publications:

Smith, B. R. and D. T. Sandwell, Accuracy and Resolution of Shuttle Radar Topography Mission Data, Geophys. Res. Lett., 20, doi:10.1029/2002GL016643, 2003.

     


 


                  

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