Density contrasts in the lower mantle, inferred using seismic tomography, drive viscous flow; thi... more Density contrasts in the lower mantle, inferred using seismic tomography, drive viscous flow; this results in kilometres of dynamically maintained topography at the core-mantle boundary and at the Earth's surface. The total gravity field due to interior density contrasts and ...
We present a crosslink constraint method for numerically modeling dynamic slip on intersecting fa... more We present a crosslink constraint method for numerically modeling dynamic slip on intersecting faults, without prescribing slip (dis-)continuation directions. The fault intersections are constrained by crosslinked split nodes, such that the slip can only be continuous on one of the two intersecting faults at a time and location. The method resolves the episodic intersection offset by examining the dynamic fault traction resulting from two sets of constraint equations, one for each slip direction. To verify this method, we modify two benchmark problems, hosted at Southern California Earthquake Center (SCEC), by allowing a branching fault to step across a main fault. The modified SCEC problem results agree with our expectations that the intersection offset scenarios are dictated by the nucleation patch location and initial fault traction. This new method comes with an open-source finite-element code Defmod.
ABSTRACT We present here L-band radar interferograms derived from ALOS/PALSAR satellite observati... more ABSTRACT We present here L-band radar interferograms derived from ALOS/PALSAR satellite observations over several different Earth surface terrains. These InSAR images are representative of data that would be collected by the proposed DESDynI radar mission. We have examined interferograms over Hawaii, Greenland, Egypt, and California, which present surfaces covered by light vegetation, dense tropical forests, vegetation-free desert, and many ice facies. The interferograms exhibit very high correlation when compared to the C-band radar data commonly available from other existing satellites, yielding improved spatial coverage and reliable temporal sampling. In many cases the acquisitions are fully polarimetric, so that we can compare how the polarization state affects the statistics of the interferometric echoes. Specific results to date show that the use of L-band data rather than C-band permits much more comprehensive deformation modeling of rift events in Hawaii and of creep along faults, with little difference between interferograms formed from co- and cross-polarized returns. Ice from the wet snow, percolation, and dry snow zones in Greenland often correlates well (>50%) even with the PALSAR six-week repeat interval. Observable fringe patterns are seen in the Hawaiian rain forest in many locations over this same orbit interval. Interferograms derived from HH and VV data over ice and vegetation are very similar, and HV InSAR data are similarly correlated when allowance is made for the lower signal to noise ratio, even though considerable volume scatter occurs. Cross-interferograms show that the HH return is rather uncorrelated with the VV return, but that a small shift in the mean phase is present in HH-HV difference interferograms. This could be due to a real several cm shift in the phase center of the echo, but we are currently considering whether this apparent phase shift results from cross-polarized contamination of the radar return. With more frequent repeat observations than are possible with ALOS, but with an otherwise similar instrument, the principal science objectives for an InSAR mission as recommended by the National Research Council can be attained.
Density contrasts in the lower mantle, inferred using seismic tomography, drive viscous flow; thi... more Density contrasts in the lower mantle, inferred using seismic tomography, drive viscous flow; this results in kilometres of dynamically maintained topography at the core-mantle boundary and at the Earth's surface. The total gravity field due to interior density contrasts and ...
We present a crosslink constraint method for numerically modeling dynamic slip on intersecting fa... more We present a crosslink constraint method for numerically modeling dynamic slip on intersecting faults, without prescribing slip (dis-)continuation directions. The fault intersections are constrained by crosslinked split nodes, such that the slip can only be continuous on one of the two intersecting faults at a time and location. The method resolves the episodic intersection offset by examining the dynamic fault traction resulting from two sets of constraint equations, one for each slip direction. To verify this method, we modify two benchmark problems, hosted at Southern California Earthquake Center (SCEC), by allowing a branching fault to step across a main fault. The modified SCEC problem results agree with our expectations that the intersection offset scenarios are dictated by the nucleation patch location and initial fault traction. This new method comes with an open-source finite-element code Defmod.
ABSTRACT We present here L-band radar interferograms derived from ALOS/PALSAR satellite observati... more ABSTRACT We present here L-band radar interferograms derived from ALOS/PALSAR satellite observations over several different Earth surface terrains. These InSAR images are representative of data that would be collected by the proposed DESDynI radar mission. We have examined interferograms over Hawaii, Greenland, Egypt, and California, which present surfaces covered by light vegetation, dense tropical forests, vegetation-free desert, and many ice facies. The interferograms exhibit very high correlation when compared to the C-band radar data commonly available from other existing satellites, yielding improved spatial coverage and reliable temporal sampling. In many cases the acquisitions are fully polarimetric, so that we can compare how the polarization state affects the statistics of the interferometric echoes. Specific results to date show that the use of L-band data rather than C-band permits much more comprehensive deformation modeling of rift events in Hawaii and of creep along faults, with little difference between interferograms formed from co- and cross-polarized returns. Ice from the wet snow, percolation, and dry snow zones in Greenland often correlates well (>50%) even with the PALSAR six-week repeat interval. Observable fringe patterns are seen in the Hawaiian rain forest in many locations over this same orbit interval. Interferograms derived from HH and VV data over ice and vegetation are very similar, and HV InSAR data are similarly correlated when allowance is made for the lower signal to noise ratio, even though considerable volume scatter occurs. Cross-interferograms show that the HH return is rather uncorrelated with the VV return, but that a small shift in the mean phase is present in HH-HV difference interferograms. This could be due to a real several cm shift in the phase center of the echo, but we are currently considering whether this apparent phase shift results from cross-polarized contamination of the radar return. With more frequent repeat observations than are possible with ALOS, but with an otherwise similar instrument, the principal science objectives for an InSAR mission as recommended by the National Research Council can be attained.
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