Geodetic Imaging Using Optical Systems

Three‐Dimensional Surface Deformation in the 2016 MW7.8 Kaikōura, New Zealand, Earthquake From Optical Image Correlation: Implications for Strain Localization and Long‐Term Evolution of the Pacific‐Australian Plate Boundary

“…OIC has shown great utility in previous studies measuring earthquake‐induced surface deformation (e.g., Avouac et al, ; Avouac & Leprince, ; Ayoub et al, ; Barnhart et al, ; Hollingsworth et al, , ; Leprince, Ayoub, et al (); Leprince, Barbot, et al (); Leprince et al, ; Michel & Avouac, , ; Milliner et al, ; Milliner, Dolan, et al, ; Milliner, Sammis, et al, ; Wei et al, ; Zinke et al, ). OIC processing tools, such as COSI‐Corr (Leprince, Ayoub, et al, ), MicMac (Rosu et al, ) and Ames Stereo Pipeline (Shean et al, ), provide fast and cost‐effective means for determining continuous maps of on‐fault and off‐fault 2‐D surface displacement with limited decorrelation near the fault (in stark contrast with InSAR measurements, which typically decorrelate close to fault ruptures if the strain gradient between neighboring pixels exceeds a phase cycle).…”

“…Crucially, the WorldView images were acquired at oblique (off‐nadir) viewing geometries, thus preserving a stereo effect between the two images, which we exploited using a simple ray tracing approach to precisely recover the vertical dimension of ground motion. Following the methods of Avouac and Leprince (), we chose sets of WorldView images such that each ground location was imaged by two preearthquake images and two postearthquake images (each with opposing viewing geometries to exploit the stereo effect). For each set, we coregistered three of the images to a master preearthquake image and orthorectified all four using a relatively coarse‐resolution (8 m) DEM to remove long‐wavelength topographic distortions.…”

“…In much the same way that stereo imagery is used to create topographic maps, we then used a ray tracing approach between the disparity maps and satellite positions, known from the satellite auxiliary information, to invert for the precise horizontal and vertical positions of each point on the ground surface. Finally, we directly solved for the 3‐D vectors by simply differencing the preearthquake and postearthquake locations of each point (see Avouac & Leprince, and supporting information S2). The final result was a map of 3‐D ground displacement measurements every 8 m. Postprocessing was performed to remove noise and linear ramps within the final correlation maps.…”

“…Despite the obvious power of this processing methodology, which has been applied to an earthquake only once previously (in a proof‐of‐concept study documenting the 2010 El Mayor Cucapah earthquake rupture, see Avouac & Leprince, ), the lack of available high‐resolution preearthquake and postearthquake stereo images has thus far severely limited its potential application for recent earthquake studies. The 2016 Kaikōura earthquake therefore represents the first comprehensive application of this technique to an earthquake.…”

Transient Reactivation of a Deep‐Seated Landslide by Undrained Loading Captured With Repeat Airborne and Terrestrial Lidar

“…The location of the peak in C defines the relative displacement between z 1 and z 2 , which has subpixel precision by interpolating C. We implemented equation (1) by modifying the program ImGRAFT (Messerli & Grinsted, 2014; supporting information) and using a 65-m patch size to correlate with the surrounding 97-m wide search region. To extend the horizontal displacement field to 3-D, we subtracted the DEMs, documenting the local vertical elevation change at every grid cell, even where horizontal displacements were undefined (Avouac & Leprince, 2015). To extend the horizontal displacement field to 3-D, we subtracted the DEMs, documenting the local vertical elevation change at every grid cell, even where horizontal displacements were undefined (Avouac & Leprince, 2015).…”