Extracting Surface Displacements of Historical Earthquakes Using KH-9 Satellite Images: A Case Example of 1976 Chaldiran Earthquake, Turkey

Surface ruptures and deformation of large earthquakes are important for investigating earthquake mechanisms, fault activities and continental deformation. With the improvement of satellite techniques, optical and radar images have been widely used in earthquake studies since the 1992 Landers earthquake. However, due to a lack of pre-earthquake images, historical earthquakes prior to the 1990s are rarely studied. Recent declassification of American KeyHole (KH) satellite images opened up new possibilities of investigating old earthquakes back to the 1970s. Researchers have successfully applied KH-9 images to the 1978 Tabas-e-Golshan and 1979 Khuli-Boniabad earthquakes in Iran, and gained some new insights into fault behaviours. We first provided a review of the methodology and progresses of using KH-9 images to measure earthquake deformation, then investigated the 1976 Chaldiran, Turkey earthquake by matching the pre- and post-earthquake KH-9 images, and obtained an E-W displacement of about (3.1±0.7) m (i.e. strike-slip), consistent with the measurements in the field. KH-9 imagery provides a new means of investigating historical earthquakes in detail, but there are some limitations. These limitations are briefly discussed in the end.