L4 - Space Geodesy: InSAR and the Earthquake Cycle Flashcards
How does SAR (Synthetic Aperture Radar) work? (3)
The satellite flies over the target area, sending out radar pulses
Time delay and doppler of the radar returns are measured, each location has a unique pairing
Each point measured multiple times as if a larger radar was used
What is the procedure of InSAR (Interferometric Synthetic Aperture Radar)? (2)
Combine two SAR images
Look at the difference in phase between the two images
What affects the phase difference in an interferogram? (3)
The difference in range between the satellite and the ground between the two data acquisitions Atmospheric effects (refractive index changes) Changes in ground scattering characteristics
What are the causes of range differences in InSAR? (3)
Different satellite locations used to collect the two images
Topography
Ground motion
In what kind of area does InSAR work best? (2)
Where the ground rarely changes e.g. a stony desert
No regular change e.g. vegetation, farming, snow
Outline the earthquake cycle (3)
Interseismic strain accumulation: elastic warping as strain builds up
Coseismic slip: strain not supported, rocks break along a fault
Postseismic deformation: stress changes due to EQ relaxed
What are the mechanisms of postseismic deformation? (3)
Continued fault slip
Ductile low below the seismogenic layer
Movement of pore fluids
How can the atmospheric signals be reduced in InSAR? (1)
Stacking numerous individual interferograms
What measurements of interseismic strain accumulation can be obtained from interferograms? (2)
The signal of elastic strain accumulation is focused on the fault, wavelength depends on fault lock depth
The difference in velocity between sides of the fault gives strain accumulation rate
What are important features to think of when interpreting interferograms? (4)
The wavelength of the deformation pattern depends on the maximum depth of slip
The degree of asymmetry between the motions on the two sides depends on the fault dip
The amplitude of the displacements depends on the amount of slip
The sharpness of the surface deformation depends on the shallowest extent of slip
What is poroelastic rebound? (1)
What is the wavelength and why? (1)
What is the timescale and why? (1)
What can it tell us? (1)
Fluid moving around in the crust due to pressure changes from an EQ
Short because shallow
Days to months because of crust permeability
Hydraulic properties of the crust
What is afterslip? (1)
How does it relate to the EQ? (1)
Timescale? (1)
What can it tell us? (1)
Continued slip on the EQ fault plane or extensions beyond the EQ slip patch
Same sense of motion but smaller
Deformation accumulates over years
Rheology of the faults
Ductile flow beneath the upper layer:
Wavelength and why? (1)
Timescale? (1)
What can it tell us? (1)
Long (10s to 100s km) because deep source
Years to decades
Material properties of the ductile lower lithosphere
