par- 11 octobre 2016
Encadrants : James Hollingsworth , Anne Socket, Cecile Lasserre (ISTerre)
keywords : remote sensing, image processing, dike injection, earthquake cycle
Optical image correlation (OIC) is a modern geodetic technique which measures the relative spatial movement of common features represented by pixels within two or more optical satellite images. Depending on the quality and resolution of the images used in the analysis, pixel shifts as low as 1/10th of the input resolution can be detected. OIC thereby allows for the rapid retrieval of ground deformation over large areas using remotely sensed data. The rich archive of historical optical satellite and aerial photo data available offers the potential for investigating tectonic deformation over the last 60+ years, before GPS or InSAR techniques became available. However, insufficient documentation of the various historical camera systems used, coupled with limited support in modern remote sensing software packages has prevented the widespread use of historical satellite imagery for studying tectonic deformation at the Earth’s surface.
In this study, we will investigate the use of KH-4 Corona satellite imagery with the optical image correlation technique. KH4 satellite images were acquired between 1963-1972 using a dual panoramic camera system, and with a ground resolution between 2-3 m. However, no rigorous camera model has currently been developed for the unique imaging geometry of the KH4 system, while the long, narrow film strips make correcting spatial distortions in the images very challenging. In this study, we will make use of a new methodology developed at the University of Arkansas for processing KH4 panoramic satellite images. This processing chain allows for the precise orthrectification of KH4 images using Rational Polynomial Coefficients (RPCs), despite the absence of detailed camera information needed to develop a specific camera model for the KH4 sensor.
We will test this new processing methodology in two locations : (1) East African Rift - we will use KH4 satellite images to measure any surface deformation associated with the 1969 Serdo and 1989 Dobi earthquake sequences. Both earthquakes occurred in Ethiopia, within an extensional rift setting which experiences episodic earthquake and dike injection events. Both earthquakes occurred between two well-known volcanic dike injection events (1978 Asal rift crisis in Djibouti to the east, and the 2005 Dabbahu rift crisis to the west). KH4 imagery will reveal the magnitude and pattern of extensional slip within this little studied transition zone. (2) Eastern Tibet - we will study a sequence of earthquakes which occurred on the Xianshuihe fault, which contributes to the eastward translation of crustal material in Tibet in response to the northward collision of India relative to Asia. Using optical image correlation, we aim to retrieve the co- and post-seismic surface deformation fields for two large earthquakes (1973 Luhuo, and 1981 Daofu) which broke the Xianshuihe fault. Although these events occurred in the recent historical past, their surface offsets were never mapped in the field and remain poorly understood. A better understanding of the surface deformation associated with these events is important to understand the seismic hazard posed by the Xianshuihe fault, and its role in accommodating regional deformation. Furthermore, our fault slip data will be used to investigate the geological and structural factors which influence the expression (and localization) of fault slip at the surface during large earthquakes.
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