3-D EARTHQUAKE DEFORMATION FROM 4-D LIDAR TOPOGRAPHY: EXAMPLES FROM MEXICO AND JAPAN

The recent surge in airborne laser scanning along active faults, especially within western North America, provides a topographic baseline against which future, post-earthquake LiDAR datasets can be compared. Here, we showcase a method for differencing pre- and post-earthquake LiDAR point clouds using two recent Mw ~7 earthquakes in Mexico and Japan – the first near-complete ruptures to be captured in this way – as examples. We are able to determine the surface deformation field in 3 dimensions, in contrast with conventional InSAR and pixel-tracking techniques which measure line-of-sight and horizontal displacement components only. A further advantage is that the LiDAR differencing retains coherence in the presence of steep displacement gradients (such as close to surface ruptures) and dense forest cover. Challenges include the reliance on older, "legacy" LiDAR datasets for pre-event coverage; these third party surveys are not optimized for earthquake studies and key metadata may be unavailable.

The two case studies presented here demonstrate some of the potential insights that this new geodetic technique could offer. For the 4 April 2010 El Mayor-Cucapah (Mexico) earthquake, the 3-D displacements are used to explore whether significant slip occurred on low-angle detachment faults, as has been postulated by some field geologists. For the 11 April 2011 Fukushima-Hamadori (Japan) earthquake, LiDAR differencing results are used to investigate the connection between deep slip inferred from far-field InSAR measurements and surface offsets observed along the fault scarp in the field, an important line of evidence for understanding how mechanical fault zone properties vary with depth.