Liquefaction-induced lateral displacements from the Canterbury earthquake sequence in New Zealand measured from remote sensing techniques
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Liquefaction is a significant earthquake hazard that can generate large horizontal displacements associated with lateral spreading and these displacements cause considerable damage. To improve our understanding of liquefaction-induced lateral spreading and the models that can be used to predict the associated displacements, the collection of high quality field data on lateral spreading displacements is essential. Remote sensing techniques, in particular optical image correlation using satellite imagery, can be used for this purpose. This thesis investigates optical image correlation of satellite images as a remote sensing technique for this purpose using images from the 2010-2011 Canterbury earthquake sequence in New Zealand. Optical image correlation uses two optical images – one before and one after the investigated event – to measure displacements that have occurred between the time of the two image acquisitions. The correlation analysis calculates the horizontal displacement at a specified spacing, and the displacements are post-processed and filtered to attain the final displacement field. The displacement results from optical image correlation agreed favorably with qualitative field observations of the severity of liquefaction and lateral spreading, as well as the general crack patterns along the Avon River. A more quantitative comparison was performed using field measured displacements along four linear transects that extended perpendicular from the Avon River. The displacements from optical image correlation also agreed favorably with the field measured displacement profiles, although the optical image correlation displacements somewhat larger than the field measurements. This discrepancy occurs because field measurements are based on discrete measurements of crack width, while the optical image correlation are based on average displacements over larger areas and include displacements associated with ductile movements that may not result in cracking. The results from this research show that optical image correlation of satellite imagery pairs can provide accurate and detailed measurements of horizontal displacements due to liquefaction and lateral spreading. This approach can be used to create more complete and detailed databases of liquefaction-induced movements, which can be used to improve current predictive models for lateral spread displacements. Future post-earthquake investigations and research should make use of optical image correlation to document the displacements associated with liquefaction.