A decade of earthquakes mapped with differential lidar: resolving fault kinematics, off-fault deformation, and rupture anelasticity
Abstract
It is a decade since differential lidar emerged as a new way of mapping earthquake surface deformation, motivating a review of what we can learn from such analyses. By registering point clouds surveyed before and after an earthquake, the Iterative Closest Point (ICP) algorithm can determine the surface displacement field in three dimensions, complementing conventional InSAR and sub-pixel correlation techniques that image only the line-of-sight or horizontal components, respectively. Furthermore, displacements resolved with ICP retain coherence along surface ruptures, allowing for characterization of shallow slip and fault damage zone properties. In the 2010 El Mayor-Cucapah (Mexico) earthquake, we computed slip vectors by profiling the 3-D displacement field at regular intervals along strike. Since slip vectors must lie on the plane of the fault, whose local strike is known, we determined how fault dip changes along the rupture. Within the northern Sierra Cucapah, we interpret that deep-seated rupture of steep faults (resolved by coarse seismogeodetic models) transfers at shallower depths onto low-angle (<30o) structures (as were documented in the field). Slip is pronounced along steep sections of fault and inhibited along low-angle sections, highlighting the control of local structural fabric on the surface slip expression. In the 2011 Fukushima-Hamadori and 2016 Kumamoto (Japan) earthquakes, we document how slip along the primary surface rupture accounts for only a proportion of the total offset, and use ICP to estimate the width of the fault damage zone. In the 2016 Kaikoura (New Zealand) earthquake, we find that the enigmatic Papatea fault exhibits a complex, non planar geometry, twisting from subvertical in the north to shallow-dipping in the south. Multi-meter vertical and left-lateral offsets occurred along the full length of onshore rupture, defying Andersonian mechanics where the fault is steepest and yielding an unusually high slip-to-length ratio. Elastic forward models computed using this known fault geometry and slip distribution are a poor fit to the observed displacement field, implying that the fault ruptured anelastically without releasing stored elastic strain in the way normally assumed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T51B..07N
- Keywords:
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- 8036 Paleoseismology;
- STRUCTURAL GEOLOGY;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS;
- 8123 Dynamics: seismotectonics;
- TECTONOPHYSICS;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS