Time Dependent Estimates of the Velocity Gradient Tensor Field for Transient Detection
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Transcript of Time Dependent Estimates of the Velocity Gradient Tensor Field for Transient Detection
Time Dependent Estimates of the Velocity Gradient Tensor Field for Transient Detection
William Holt, Gina Shcherbenko, Eric Caruso, Yu Chen
Acknowledgements: We thank SCEC for funding support
0.1° x 0.1° Grid
Rigid Pacific Plate
Model magnitude of shear strain rates (pure SS style)(SCEC4.0 Velocity field)
Smoothing or Damping• Maximize signal associated with GPS
• Achieve Reduced Chi-Squared misfit between model displacement and observed displacement of ~1.0 for all epochs
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χ = ( ˙ e ij )ij,kl
∑cells
∑T
Vij,kl−1( ˙ e kl )+ (vi − v i
obs )T Vi, j−1(v j − v j
obs )i, j
∑knots
∑
Haines, Jackson, Holt, Agnew [1998]
Beavan and Haines [2001]
Time Series from SCEC IVc
WNRA – Phase 4c
4th order polynomial fit with annual and semi-annual terms
Annual and semi-annual removed
Red = 15 day moving average filter
Green = 4th order polynomial
Output 2 week epoch solutions of displacement
2 Week Displacements
Subtract out ‘master solution’ to estimate signal only from transients
-For real data we used SCEC4.0 solution as a master solution-For other groups in the SCEC exercise we used time averaged solution (2007 – 2009).5 mm
Output 2 week epoch solutions of displacement
2 Week Displacements
Subtract out ‘master solution’ to estimate signal only from transients
-For real data we used SCEC4.0 solution as a master solution-For other groups in the SCEC exercise we used time averaged solution (2007 – 2009).
Residual Displacements
Phase IVa5 mm 5 mm
What Triggers Selection of Potential Transients?
• Accelerations
• Finite Strain
• Analysis of finite strain tensor and displacement vector fields
• Does signal look tectonic?
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d
dtδE( )
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δE∫
Phase IVa
Residual displacements reference solution subtracted out
Finite Displacements + Strain (principal axes) Phase IVa
Phase IVb
Residual displacements reference solution subtracted out
Phase IVb Finite Displacements + Strain (principal axes)
Phase IVc
Residual displacements reference solution subtracted out
Finite Displacements + Finite Strain (Principal Axes) Phase IVc
Summary of results from Phase IV• The modeling of displacements with
reference field removed captures spatial and temporal magnitudes of transients
• Method can be automated
Analysis of PBO Data from 2010.35 – 2011.25• El Mayor-Cucapah post-seismic
motions and strains– Non-steady state motions with periods of
apparent increasing and decreasing strain
• High frequency strain changes in LA Basin region
Finite Strain (Dilatations) + displacements: PBO Data 2010.35 – 2011.25
See poster B-143
Residual displacements show rapid spatially correlated changes in LA region
2010.35