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Remote sensing technology has become an important technique of active fault research because of its macro, intuitive and non-contact advantages. With the rapid development of remote sensing technology, the increasement of satellite sensors and the improvement of spatial resolution, a various data of satellite sensors at home and abroad have been widely used in active fault research. Foreign satellite data mainly include ALOS, IKONOS, SPOT, QuickBird, Worldview and so on, among which the spatial resolution of QuickBird is 0.6 m, Worldview up to 0.31 m. Domestic satellite data include GF-1, GF-2 and ZY3, where the spatial resolution of GF-1 multispectral band and panchromatic band is 8 m and 2 m respectively; the spatial resolution of ZY3 multispectral band and panchromatic band is 5.8 m and 2.1 m respectively; the spatial resolution of GF-2 multispectral band and panchromatic band is 4 m and 1 m respectively. In recent decades, the rapid development of urbanization and human activities have seriously destroyed natural landforms. Especially in the eastern part of China, natural landforms have been seriously damaged due to the construction of roads, railways, factories and houses, so that tectonic geomorphology no longer existed, which made a great difficulty for remote sensing interpretation of active tectonics. US Keyhole(KH) satellites began to run in the 1960s, taking a large number of images in China. KH images are characterized by early imaging time, high resolution and better original terrain information, so they can be effective to obtain the characteristics of tectonic geomorphology and determine the geometric distribution and fault behavior. Those are significant for active fault research. In this paper, the basic information and data processing flow of KH satellite is introduced firstly. KH satellite mainly include KH1-12 and other 12 models. KH1-6 is the recoverable reconnaissance satellite of photographic film. The data source of KH1-6 is basically open, which is the main application of the promotion model. The best resolution of KH4A, KH4B and KH6 is 2.7 m, 1.8 m and 0.3 m respectively. Secondly, the application of KH images in active fault is discussed: 1) For the tectonic landform of active fault, with the advantages of early imaging time and high resolution, KH images can obtain the tectonic micro- landform features of active fault such as linear structure, fault scarp, fault cliff, fault groove and channels offset, which can not be identified by current satellite images. They are helpful to complete the precision mapping and quantitative analysis of active fault; 2) For the surface rupture zone of a historical earthquake, the KH images photographed at the nearest time after the earthquake is useful to map the surface rupture of the earthquake and measure the coseismic displacement. KH images visualize the post-earthquake rupture information to reveal the relationship between the rupture and the active fault, which guides us to understand the seismogenic structure, seismogenic mechanism and the process of diastrophism. Finally, this paper take the Jiangsu section of the Tan-Lu Fault Zone(TLFZ) as an example. The Suqian city and surrounding area were selected as the test area, where the remote sensing interpretation of the active fault based on KH-4B satellite image was carried out. The results show that, Malingshan-Chonggangshan Fault(F5) and Xinyi-Xindian Fault (F2) intermittently exposed to the surface. The tectonic micro-landforms of the two faults are very developed. In the Huangchaoguan, Shanxiawu and the south of Xiaodian, F5 exposed to the surface, which formed fault cliff, fault triangular surface, fault scarp and other structural landform. In the west of Huangchaoguan, F2 intermittent exposed to the surface, which formed fault scarp, fault deflection, fault groove and other tectonic micro-landforms. There are no obvious dislocations in the gully of the two faults. The two faults are mainly dip-slip movement with high angle thrust motion. KH satellites have obtained a large number of instantaneous image data from the last century, and recorded the process and evolution of the Earth's surface for a period of time. These images have important application values in the field of active fault research. In order to study and understand the geological structure, tectonic landforms and the latest historical changes, the KH images provide more accurate basic data. How applying KH images to active fault mapping work and seismic hazard assessment is an important development direction in active tectonics research in the future. What is more, It is hoped that, except in the earthquake industry, KH satellite data will be widely used in the fields of forestry, fishery, surveying and mapping, engineering, electric power, and other industries.
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