Mining High-Resolution KH-9 Panoramic Imagery to Determine Earthquake Deformation: Methods and Applications

Earthquake deformation is crucial for understanding fault kinematics. Modern earthquakes (moment magnitude $M_{w} >= 6$ ) have been well documented by geodetic techniques, such as radar interferometry and image correlation with unprecedented accuracy. Nonetheless, many large ( $M_{w} >= 7$ ) historical earthquakes remain unexplored due to a lack of preearthquake data. In this article, we provide the first study of using Hexagon KeyHole-9 (KH-9) panoramic imagery to investigate historical earthquakes. We propose patch-based orthorectification and test the method from analog experiments with unmanned aerial vehicle (UAV) photographs. Using the 2013 $M_{w}$ 7.7 Balochistan as a case example, we demonstrate that KH-9 images can be used to retrieve meter-scale horizontal deformation. The displacements, derived from correlating KH-9 (preearthquake) and Sentinel-2 (postearthquake) images, are comparable with published studies. Applying the method to the 1981 $M_{w}$ 7.1 Sirch earthquake, we succeed to measure NS strike-slip motion (up to 5.9 +/- 1.6 m) along the 1981 rupture and find that most of the accumulated strain energy may be released by motion along a 25-km-long segment of the Gowk fault. The southward propagation of the rupture may be prevented by the earlier $M_{w}$ 6.6 Golbaf earthquake that released most of the accumulated strain in the south. The rapid decay of slip in the north seems to be associated with a 3-km-long, 1-km-wide step-over, which may have dissipated a large fraction of seismic energy. The KH-9 panoramic images show great potential for determining horizontal deformation, providing useful information about historical earthquakes that occurred before the era of modern geodesy.