Using historical aerial images to accurately locate the urban "invisible" active faults: A case study of the Shuiyu fault of the Datong Basin in Shanxi province

Abstract

Active fault is a major risk source of urban earthquake disaster. Accurately identifying the spatial geometry distribution features of active fault is the basis for urban seismic risk migration. However, due to the large-scale and deep urban renewal by human activities and urbanization, the traces of active faults are obscure and invisible on the surface, which makes it hard to identify the surface geometry of this kind of active faults. Though the northern Shuiyu fault in the central part of the Datong Basin is bounded by the eastern edge of the Mapu Mountain and characterized by linear displaced landforms, the southern section of the Shuiyu fault crossing the Yudong District of Datong City is covered by dense buildings and roads, becoming an "invisible" fault. In this study, based on the 1965 historical aerial photos of the Datong region in the 1960's and the 1∶10000 topographic maps, we reconstructed the original DEM and DOM of this region using the aerial photo stereopair and stereoscopic photography. These original data revealed the geometry distribution characteristics of the Shuiyu fault. Our results show that the piedmont fault scarps are marked by prominent linear features along the northern Shuiyu fault. We can accurately locate the fault by the images. Based on the previous Keyhole satellite images, DOM and DEM data, the geometric distribution of the fault in the southern Shuiyu fault can be accurately determined. Topographic profiles extracted from the original DEM show that the vertical offset on terrace T3 along the Shuiyu fault is about 19 meters. On this basis, the fault natural exposures and shallow seismic reflection data demonstrate that it is feasible to accurately locate the "invisible" active fault in the city by using historical aerial photos and stereoscopic photography. This study provides not only an important basis for the seismic hazard assessment in the Datong region but a useful technique for the detection of "invisible" active faults beneath a city.

Keywords

• "invisible" active fault
• historical aerial photo
• dem
• aerial stereoscopic photography
• shuiyu fault